Amphipods are an order of crustaceans of the superorder Peracarida Calman, 1904 characterized by direct development and absence of independent larval stages, with females carrying their embryos on brood pouches between the pereopods. Amphipods are one of the most abundant and diverse groups within Peracarida with over 10.000 described species (Horton et al., 2021). Mostly marine, although some taxa inhabit terrestrial habitats (talitrids) and wide range of freshwater habitats, being especially diverse on subterranean water (Skett, 1999). Amphipods play a vital role on aquatic trophic webs serving as a major component in fish diet, having themselves a wide variety of feeding habits, being herbivores, carnivores, omnivores and detritivores, as well as parasites (Väinölä et al., 2008). Apart from pioneer European Amphipoda systematic works covering some specific areas like Bate & Westwood (1863) and Lincoln (1979) for British Isles, Sars (1895) and Stephensen (1923a, 1923b, 1931) for Norway, Stebbing (1906) compilation or Chevreux & Fage (1925) work on French amphipods, modern and comprehensive monographs based on local fauna are still far from completion and an enormous amount of work is still needed to meet the requirements of modern taxonomy. Portuguese amphipod fauna remains poorly studied with few dedicated surveys (van Maren, 1975; Marques and Bellan-Santini, 1987, 1990, 1991, 1993; Ortiz & Jimeno, 2001; d’Udekem d’Acoz, 2010; Carvalho et al., 2012; Plicanti et al., 2017; Cabezas et al., 2022), despite recent ecological studies (Cunha et al., 1999, 2011; Pereira et al., 2006; Guerra-García & Izquierdo, 2010; Izquierdo & Guerra-García, 2011; Guerra-García et al., 2012; Martins et al., 2013; Sampaio et al., 2016; Dauvin et al., 2021). In this study we provide an overview on Amphipoda fauna collected on the Minho River estuary (with brief diagnosis, ecological notes, global and Portuguese distributions), belonging to 34 species, in which 23 are new records for the Minho River (including one new record for Portugal).

Study Area

The Minho River located at the northwest of the Iberian Peninsula, originates at the Meira mountains (Spain) and has a total extension of around 300 km (APA, 2016). The international section located on the last 70 km represents the Northwest Spanish/Portuguese border, culminating on an estuary flowing into the Northeast Atlantic Ocean. The estuarine area has a length of approximately 40km, with a total area of 23 km² (Sousa et al., 2008), with a mesotidal partially mixed system tending towards a salt wedge estuary during the high floods (Sousa et al., 2005) and is part of the protected areas of the Natura 2000 network as site of ecological importance and a special area of conservation, marked as an Important Bird Area (Dias et al., 2014; BirdLife International, 2021).

Sampling, identification and preservation of specimens

Specimens examined were collected during previous sampling campaigns at the International Minho River, on the estuarine zone (Fig. 1), with following methods: 1) glass eel fishing bycatch, in Caminha, Portugal (41º52’59.00”N / 8º50’14.00”W), during a new moon night on flood tides, using stow net (length of float lines 10 m, bottom anchored lead line of 15 m, height 8 m, mesh size 1-2 mm, covering an area of 50 m²) (Weber, 1986), on April, 2020 and May 2020; 2) glass eel fishing bycatch, in Caminha, Portugal (41º52’44.80”N / 8º50’26.25”W), on March 2021; 3) beam trawl in front of Morraceira das Varandas Island (41°52’04.8”N / 8°51’18.8”W) on June 2021; 4) on sediment sampling with a Van Veen grab sampler in Caminha, Portugal (41º54’36.7”N / 8º49’4.49”W), on September, 2020; 5) on Fucus cf. spiralis Linnaeus 1793 collected by hand in Caminha, Portugal (41°51’58.3’’N / 8°50’55.8’’W), on September 2021.

Species identification was based on specialized literature (i.e., Bate & Westwood 1863; Sars 1895; Stebbing 1906; Chevreux & Fage 1925; Reid 1951; Lincoln 1979; Dauvin & Bellan-Santini 1988; Conlan 1990; Pinkster 1993; Guerra-García & Takeuchi 2002; Guerra-García et al. 2013, 2018) using the family taxonomic classification suggested by (Lowry & Myers, 2013, 2017), and following Hou & Sket (2016) and Sket & Hou (2018) for Gammaridae classification. Synonym’s compilation was performed, mainly according to WoRMS database (WoRMS Editorial Board, 2021) and on species description manuscripts. Type material and locality data were obtained from Global Biodiversity Information Facility (GBIF.org, 2021) or from original descriptions, whenever available. All specimens were photographed with a Nikon Digital Sight D5-L1 camera using a Nikon SMZ800 stereomicroscope and a Nikon ECLIPSE 50i microscope. Specimens were deposited at Arthropod Collection (Crustacean section) from Natural History Museum of the Iberian Peninsula (NatMIP – “Museu de História Natural da Península Ibérica”), sited at Aquamuseu do Rio Minho, Vila Nova de Cerveira, North Portugal.

A total of 100 specimens were examined belonging to 34 species distributed by 18 families and 23 genera (Table 1).

Phylum Arthropoda Siebold, 1848

Subphylum Crustacea Brünnich, 1772

Superclass Multicrustacea Regier, Shultz, Zwick, Hussey, Ball, Wetzer, Martin & Cunningham, 2010

Class Malacostraca Latreille, 1802

Subclass Eumalacostraca Grobben, 1892

Superorder Peracarida Calman, 1904

Order Amphipoda Latreille, 1816

Suborder Amphilochidea Boeck, 1871

Superfamily Amphilochoidea Boeck, 1871

Family Stenothoidae Boeck, 1871

Genus Parametopa Chevreux, 1901

Parametopa kervillei Chevreux, 1901 (Fig. 2)

Parametopa kervillei Chevreux 1901: 233-237, Pl. III. — Chevreux & Fage, 1925: 139-140, figs. 139-140. — Lincoln 1979: 206, figs. 80D-E, 94A-H.

Metopa sarniensis Norman 1907: 365, Pl. XVII figs. 1-5.

Type material: Unknown.

Type locality: Omonville-la-Rogue, France (Chevreux, 1901).

Material examined: 10 adult specimens, size range 3 to 5 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0070.

Diagnosis: Male gnathopod 1 simple with merus rounded distally, merus and carpus setose, propodus long and narrow with 3 robust setae at posterodistal angle (Fig. 2C); male gnathopod 2 merus acute and prolonged distally, propodus broad distally, palm convex, delimited by group of small spines; palmar margin minutely toothed (Fig. 2D); pereopod 7 expanded, merus also expanded with distal angle reaching end of carpus (Fig. 2E); uropod 3 uniramous, peduncle with 4 marginal spines, ramus article 2 shorter than 1; telson entire, elongated, with 2 pairs of dorsolateral spines (Fig. 2F) (Lincoln, 1979).

Geographical distribution: North coast of France and British Isles (Lincoln, 1979), and North Portugal (this study).

Distribution in Portugal: New record.

Ecological notes: Depth range 0 to 50 m, often on holdfasts of Sacchoriza (Lincoln, 1979).

Superfamily Dexaminoidea Leach, 1814

Family Atylidae Lilljeborg, 1865

Genus Nototropis Costa, 1853

Nototropis guttatus (Costa, 1851) (Fig. 3A-B)

Acanthonotus guttatus Costa, 1851: 46. (original description).

Nototropis guttatus Costa, 1853: 194, Tab. 1 fig. 7.— Stebbing, 1906: 331-332. — Chevreux & Fage, 1925: 194-195, figs. 201-203.

Nototropis spinulicauda Costa, 1853: 173.

Atylus spinulicauda – Bate, 1862: 139-140

Paratylus guttatus – Walker, 1901: 304, Pl. 27 figs. 27-28.

Atylus guttatus – Lincoln, 1979: 446, figs. 213A-H.

Type material: Unknown.

Type locality: Naples, Italy (Costa, 1853).

Material examined: 1 adult specimen, size 6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0073.

Diagnosis: Female antenna 1 peduncle article 1 distoventral angle without tooth; pleonites 1-3 with distinct backwardly directed dorsal teeth; pereopod 5 basis with produced triangular posterodistal margin (Fig. 3B); pereopod 6 basis not produced at distal angle (Lincoln, 1979).

Geographical distribution: Mediterranean and Northeast Atlantic from southern North Sea to Senegal (Lincoln, 1979).

Distribution in Portugal: Species recorded at Mira estuary (Marques & Bellan-Santini, 1987) and along the southwestern coast (Marques & Bellan-Santini, 1991; Carvalho et al., 2012), and International Minho River (this study).

Ecological notes: Depth range intertidal to 75 m (Lincoln, 1979).

Nototropis vedlomensis (Bate & Westwood, 1863) (Fig. 3C-D)

Dexamine vedlomensis Bate & Westwood, 1863: 242-243 (original description).

Atylus vedlomensis – Boeck, 1870: 112-113. — Lincoln, 1979: 444, figs. 212A-H.

Paratylus vedlomensis – Sars, 1895: 466-467, Pl. 164 fig. 2.

Nototropis vedlomensis – Stebbing, 1906: 331.

Type material: Holotype collected at Shetland Islands, Scotland in 1861; deposited at Natural History Museum (London), catalogue number 1911.11.8.18078-18081 (GBIF.org, 2021)

Type locality: Shetland Islands, Scotland (Bate & Westwood, 1863).

Material examined: 7 specimens, size range 3 to 6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0072.

Diagnosis: Male with slender tooth on peduncle article 1 of antenna 1; pleonites 1-3 with distinct dorsal teeth; pereopod 5 basis with hook-like process (Fig. 3D); pereopod 6 basis with distal angle produced (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from Norway to Ireland (Lincoln, 1979).

Distribution in Portugal: Species recorded at the International Minho River (this study), at depths <150 m on coastal lines adjacent to the Minho and Douro rivers and Tagus canyon (Marques & Bellan-Santini, 1993), on Ria de Aveiro (Cunha et al., 1997), Mira River estuary (Marques & Bellan-Santini, 1987) and along the southern coast (Carvalho et al., 2012).

Ecological notes: Depth range 10-200 m (Lincoln, 1979).

Family Dexaminidae Leach, 1814

Genus Dexamine Leach, 1814

Dexamine spinosa (Montagu, 1813) (Fig. 3E)

Cancer (Gammarus) spinosus Montagu, 1813: 3-4, Tab. II fig.1 (original description).

Dexamine spinosa – Leach, 1814: 432. — Desmarest, 1825: 263, Pl. 45 fig. 6. — Bate, 1857: 141; 1862: 130-131, Pl. XXIV fig. 1. — Bate & Westwood, 1863: 237-239. — Sars 1895: 475-477, Pl. 166 fig. 2, Pl. 167. — Stebbing, 1906: 515-516. — Chevreux & Fage, 1925: 263, fig. 274. — Lincoln 1979: 450, figs. 214A-H.

Atylus coralinus Risso, 1826: 99.

Amphitoe marionis Milne-Edwards, 1830: 375.

Amphitoe tenuicornis Rathke, 1843: 77-79, Tab. IV fig. 3.

Amphithonotus acanthophthalmus Costa, 1851: 45-46.

Amphithonotus marionis – Costa, 1853: 195.

Amphitoe spinosa – Gosse, 1855: 141.

Dexamine tenuicornis – Bruzelius, 1858: 79-80.

Type material: Deposited at Natural History Museum (London) (Bate & Westwood, 1863).

Type locality: Devonshire, England (Montagu, 1813).

Material examined: 4 specimens, size range 3 to 6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0071.

Diagnosis: Peduncle of antenna 1 article 1 with distoventral tooth; pleon segments 1-4 with a dorsal tooth; pereopods 3-7 merus shorter than carpus and propodus combined; pereopod 7 basis with posterior margin expanded; telson with dorsolateral spines (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from Norway to Senegal, Azores and Canary archipelagos, Mediterranean and Black Seas (Lincoln, 1979).

Distribution in Portugal: International Minho River (this study), species also recorded at Mira estuary (Marques & Bellan-Santini, 1987), on Ria Formosa (Cruz et al., 2003; Carvalho et al., 2007), along the southwest coast (Izquierdo & Guerra-García, 2011; Carvalho et al., 2012; Guerra-García et al., 2012) and on Azores archipelago (Borges et al., 2010).

Ecological notes: Depth range intertidal to 60 m (Lincoln, 1979), collected on Corallina elongata J.Ellis & Solander, 1786 (Izquierdo & Guerra-García, 2011; Guerra-García et al., 2012).

Superfamily Haustorioidea Stebbing, 1906

Family Haustoriidae Stebbing, 1906

Genus Haustorius Müller, 1775

Haustorius arenarius (Slabber, 1778) (Fig. 3F)

Oniscus arenarius Slabber, 1778: 92-96, Pl. IX fig. 4 (original description).

Bellia arenaria – Bate, 1851: 318-320, Pl. XI figs. 1-7.

Sulcator arenarius – Bate & Westwood, 1863: 189-191.

Haustorius arenarius Stebbing, 1906: 125. — Sars, 1895: 135-137, Pl.46. — Chevreux & Fage, 1925: 95-97, figs. 88-89. — Lincoln, 1979: 324, figs. 146A, 152A-E.

Type material: Unknown.

Type locality: Unknown.

Material examined: 9 specimens, size range 2 to 10 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0088.

Diagnosis: Body arched and weakly compressed; head with acute lateral lobes; eyes small and poorly defined, often indistinct in large specimens; antenna 1 densely setose, shorter than 2 with well-developed accessory flagellum; pereopods 3-7 without dactylus; pereopods 6-7 merus and carpus strongly expanded (Lincoln, 1979).

Geographical distribution: North Atlantic Ocean on American and European coasts (Lincoln, 1979).

Distribution in Portugal: Common species along the Portuguese coast (Dexter, 1992), also recorded at the Minho River (Mazé et al., 1993; Sousa et al., 2008), Mondego (Marques et al., 1993) and Mira estuaries (Marques & Bellan-Santini, 1987), Ria de Aveiro (Cunha et al., 1999) and Ria de Alvor (Rodrigues & Dauvin, 1987).

Ecological notes: Intertidal sand burrower usually up to high water mark, numerous in the wet sand at lower levels of the shore (Lincoln, 1979).

Family Urothoidae Bousfield, 1978

Genus Urothoe Dana, 1852

Urothoe brevicornis Bate, 1862 (Fig. 4A-C)

Urothoe brevicornis Bate, 1862: 116-117, Pl. XX fig. 2. — Bate & Westwood, 1863: 198-199. — Stebbing, 1906: 131. — Chevreux & Fage, 1925: 100-101, fig. 94. — Lincoln, 1979: 330, figs. 153F, 155D-F.

Type material: Holotype deposited at Natural History Museum, London catalogue number 1952.5.7.35-37 (GBIF.org, 2021).

Type locality: Tenby, Wales (Bate, 1862).

Material examined: 2 adult specimens, size 7 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0080.

Diagnosis: Antenna 1 flagellum with 7 or 8 segments, accessory flagellum well-developed with 7 segments; antenna 2 peduncle robust and spinose (Fig. 4B); pereopod 5 basis expanded, carpus slightly broader than merus; uropod 1 outer ramus with 3 spines; uropod 2 peduncle short, rami subequal, about equal to length of peduncle, outer ramus with 1-3 spines; uropod 3 rami with subequal length and densely setose (Fig. 4C) (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from the North Sea to France and British Isles (Lincoln, 1979).

Distribution in Portugal: International Minho River (this study), species also recorded at depths <150 m on coastal lines adjacent to the Minho and Douro rivers and Tejo canyon (Marques & Bellan-Santini, 1993) and along the southwestern coast (Marques & Bellan-Santini, 1991).

Ecological notes: Depth range from intertidal to 40 m (Lincoln, 1979).

Superfamily Lysianassoidea Dana, 1849

Family Tryphosidae Lowry & Stoddart, 1997

Genus Lepidepecreum Bate & Westwood, 1868

Lepidepecreum longicorne (Bate, 1862) (Fig. 4D)

Anonyx longicornis Bate, 1862: 72-73, Pl. XI fig. 4 (original description). — Bate & Westwood, 1863: 91-93.

Lepidepecreum carinatum Bate & Westwood, 1866: 509-510. — Sars, 1895: 113-115, Pl. 38 fig. 2, Pl. 39 fig. 1.

Lepidepecreum longicorne – Stebbing, 1906: 80. — Chevreux & Fage, 1925: 63-64, fig. 52. — Ruffo & Schiecke, 1977: 429-435, fig. 1. — Lincoln, 1979: 72, figs. 27A-I.

Type material: Unknown.

Type locality: Shetland, Scotland (Bate & Westwood, 1863).

Material examined: 2 adult females, size range 4.9 to 5.1 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0078 and Caminha, International Minho River (41°52’76.62”N/8°50’41.7”W), 14 March 2021 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0079.

Diagnosis: Body robust and compressed; antenna 1 peduncle article 1 large with compressed anterior margin and prolonged distal angle forming a large lobe, article 2 with small anterodistal lobe, antenna 1 in male little longer than in female, accessory flagellum absent; antenna 2 short and slender on females, flagellum with 4 segments, in male flagellum filiform, as long as body.

Geographical distribution: Northeast Atlantic from Norway to Iberian Peninsula and Mediterranean (Lincoln, 1979).

Distribution in Portugal: International Minho River (this study), species also recorded at depths <150 m on coastal lines adjacent to the Minho and Douro rivers (Marques & Bellan-Santini, 1993) and along the southwestern coast (Marques & Bellan-Santini, 1991; Pereira et al., 2006).

Ecological notes: Depth range 5-60 m (Lincoln, 1979).

Genus Tryphosites Sars, 1891

Tryphosites longipes (Bate, 1862) (Fig. 4E-F)

Anonyx longipes Bate, 1862: 79, Pl. XIII fig. 4 (original description). — Bate & Westwood, 1863: 113-115.

Anonyx ampulla Bate, 1862: 79-80, Pl. XIII fig. 5. — Bate & Westwood, 1863: 116-118.

Tryphosa longipes – Boeck, 1871: 118-119.

Tryphosites longipes – Sars, 1895: 81-82, Pl. 28 fig. 3, Pl. 29 fig. 1. — Stebbing, 1906: 77. — Chevreux & Fage, 1925: 61-62, fig. 49. — Lincoln, 1979: 80, figs. 31A-H.

Type material: Unknown.

Type locality: Shetland, Scotland (Bate & Westwood, 1863).

Material examined: 2 adult females, size 6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0082.

Diagnosis: Antenna 1 peduncle with articles 2-3 compressed segments, flagellum slender with 18 segments in females and up to 30-articulated in males, accessory flagellum with 5 segments; antenna 2 in female equal to length of antenna 1, flagellum with 15 segments and in male exceeding body length; epistome acute produced forward (Fig. 4F); epimeral plate 3 posterodistal angle forming very large tooth (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from Norway to Iberian Peninsula and Canary islands, Mediterranean (Sars, 1895; Lincoln, 1979).

Distribution in Portugal: International Minho River (this study), species also recorded at depths <150 m on coastal lines adjacent to the Minho and Douro rivers (Marques & Bellan-Santini, 1993) and along the southwestern coast (Marques & Bellan-Santini, 1991).

Ecological notes: Depth range 5 to 200 m (Lincoln, 1979).

Family Uristidae Hurley, 1963

Genus Centromedon Sars, 1891

Centromedon sp. (Fig. 5)

Material examined: 1 adult specimen, size 7 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0101.

Description: Lateral view (left): Body compressed; lateral cephalic lobes subtriangular; eyes absent (Fig. 5 B); epimeral plate 3 with large acute tooth produced posteroventrally (Fig. 5E). Antenna 1 reaching beyond peduncle of antenna 2, with stout peduncle, article 1 larger than 2 and 3 combined, article 4 with a group of parallel structures organized perpendicularly to article 4, accessory flagellum 5 articulated, antenna 1 flagellum with 26 articles (Fig. 5B); antenna 2 almost as long as body length (Fig. 5A). Pereopod 5 basis dented on the inferoposterior margin (Fig. 5C); pereopod 7 basis expanded, oval, serrulate on posterior margin (Fig. 5D). Uropods 1 and 2 subequal, uropod 3 reaching beyond uropod 1 and 2; uropod 1 outter ramus armed with 6 spines on dorsal margin, uropod 2 with 5 spines; uropod 3 with 6 spines (Fig. 5F). Telson armed with two pairs of spines on dorsolateral margin and one pair of spines apically.

Remarks: This specimen differs from other Centromedon species described for Europe on antenna 1 and 2 length and on the structures present on article 4 of antenna 1. More specimens (males and females) are required for a complete evaluation, and confirmation of a possible new species.

Superfamily Synopioidea Dana, 1852

Family Ampeliscidae Krøyer, 1842

Genus Ampelisca Krøyer, 1842

Ampelisca aequicornis Bruzelius, 1858 (Fig. 6A)

Ampelisca aequicornis Bruzelius, 1858: 82-84, fig. 15. — Sars, 1895: 177-178, Pl.62 fig. 1. — Stebbing, 1906: 106-107. — Reid, 1951: 216-218, figs. 17A-D, 18A-F. — Lincoln, 1979: 114, figs. 48E-G. — King et al., 2004: 156-158, figs. 1-2.

Type material: Unknown.

Type locality: Gullmarsfjorden, Sweeden (Bruzelius, 1858).

Material examined: 1 specimen, size 4 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0087.

Diagnosis: Head with convex ventral margin; antennae 1 and 2 nearly equal; antenna 1 article 2 with 1.5 times the length of article 1; flagellum longer than peduncle; antenna 2 peduncular articles 4 and 5 subequal in length; flagellum longer than peduncle; urosome 1 with flattened dorsal keel; pereopod 7 merus without posterodistal lobe; uropods 1 and 2 with small marginal spines (Lincoln, 1979; Dauvin & Bellan-Santini, 1988; King et al., 2004).

Geographical distribution: Northwest Atlantic, Northeast Atlantic from Norway to Gulf of Guinea and Canary Islands (Lincoln, 1979; Dauvin & Bellan-Santini, 1988).

Distribution in Portugal: Uncommon species records for the Portuguese coast (Marques & Bellan-Santini, 1990), including International Minho River (this study).

Ecological notes: Depth range 30-835 m (Lincoln, 1979; Dauvin & Bellan-Santini, 1988).

Ampelisca armoricana Bellan-Santini & Dauvin, 1981 (Fig. 6B)

Ampelisca armoricana Bellan-Santini & Dauvin, 1981: 242-247, figs. 1-4.

Type material: Unknown.

Type locality: Pierre Noire, Baie de Morlaix, France (Bellan-Santini & Dauvin, 1981).

Material examined: 1 specimen, size 4.7 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0077.

Diagnosis: Antenna 1 reaching slightly beyond the peduncle of antenna 2; antenna 2 length between one third and half the body size; dactylus of pereopods 3-4 longer than carpus and merus combined; pereopod 7 merus shorter than carpus; epimeral plate 2 with small tooth on inferior-posterior margin; epimeral plate 3 inferior-posterior margin with quadrate angle (Bellan-Santini & Dauvin, 1981).

Geographical distribution: Northeast Atlantic from the English Channel to Senegal (Dauvin & Bellan-Santini, 1988).

Distribution in Portugal: International Minho River (this study), species also recorded at depths <150 m on coastal lines adjacent to the Minho and Douro rivers and Tejo canyon (Marques & Bellan-Santini, 1993).

Ecological notes: Present in intertidal zone on fine sand (Dauvin & Bellan-Santini, 1988).

Ampelisca lusitanica Bellan-Santini & Marques, 1986 (Fig. 6C-D)

Ampelisca lusitanica Bellan-Santini & Marques, 1986: 155-159, figs. 1-4. — Belattmania et al. 2017: 2-3, fig. 2.

Type material: Holotype, 1 female size 4.2 mm deposited at Station Marine d’Endoume, Marseille, France (Bellan-Santini & Marques, 1986).

Type locality: Estoril, Portugal (Bellan-Santini & Marques, 1986).

Material examined: 1 specimen, size 4.7 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0089.

Diagnosis: Antenna 1 shorter than antenna 2, slightly longer than the head and the first 4 pereonites; antenna 2 approximately half the length of the body, article 4 of peduncle slightly shorter than article 5; dactyl long but not exceeding the propodus and carpus length; pereopod 7 with distally rounded basis, the merus without a large posterior lobe, shorter than the carpus and with an anterior peg-like process projecting beyond the proximal end of the carpus but not reaching its distal end (Fig. 6D) (Bellan-Santini & Marques, 1986; Belattmania et al., 2017).

Geographical distribution: Northeast Atlantic from Bay of Biscay to Morocco (Belattmania et al., 2017).

Distribution in Portugal: Species recorded at International Minho River (this study), Viana do Castelo, Peniche, Estoril and Sines (Bellan-Santini & Marques, 1986).

Ecological notes: Depth range intertidal to 37 m (Bellan-Santini & Marques, 1986).

Ampelisca pectenata Reid, 1951 (Fig. 6E-F)

Ampelisca pectenata Reid, 1951: 210, fig. 15.

Ampelisca spooneri Dauvin & Bellan-Santini, 1982: 260-266, figs. 3-4.

Type material: Deposited at Zoological Museum of the University of Copenhagen (Reid, 1951).

Type locality: Gambia (Reid, 1951).

Material examined: 6 specimens, size range 3.9 to 10 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), May 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0076 and NatMIP-CMAm-0091.

Diagnosis: Antenna 1 reaching up to the fourth segment of peduncle of antenna 2; antenna 2 long with almost the body length; pereopod 7 merus with large setose distal lobe overlapping carpus (Fig. 6F), anterodistal margin of carpus produced and spinose; urosome segment 1 with a cockscomb dorsal keel; postero-inferior corner of epimeral plate 3 sinuous with a little tooth (Reid, 1951; Dauvin & Bellan-Santini, 1982, 1988).

Geographical distribution: Northeast Atlantic from the Irish Sea to Sierra Leone (Reid, 1951; Dauvin & Bellan-Santini, 1982).

Distribution in Portugal: International Minho River (this study), species also recorded at depths <150 m on coastal lines adjacent to the Minho and Douro rivers and Tejo canyon (Marques & Bellan-Santini, 1993).

Ecological notes: Depth range 35 to 105 m, among shells (Reid, 1951; Dauvin & Bellan-Santini, 1982).

Ampelisca rubella Costa, 1864 (Fig. 7)

Ampelisca rubella Costa, 1864: 153-155, Pl. II, fig.7. — Valle, 1893: 482-483, Pl. 2 fig. 4, Pl. 37 fig. 21, Pl. 38 figs. 1, 10, 16. — Chevreux, 1900: 44-45. — Stebbing, 1906: 104-105. — Chevreux & Fage, 1925: 79-80, figs 66,70.

Ampelisca serrata Schellenberg, 1925: 123.

Type material: Unknown.

Type locality: Naples, Italy (Costa, 1864).

Material examined: 10 male specimens, size range 4 to 5 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 specimens collected on April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0098; 1 specimen, same data as preceding with pereopods 6 and 7 on mounted blade, deposited as NatMIP-CMAm-0100 and 3 specimens collected on 14 March 2021 on glass eel fishing (41°52’76.62”N/8°50’41.7”W), deposited as NatMIP-CMAm-0099,

Diagnosis: Antenna 1 on female almost as long as antenna 2 with about half the body length; corneal lenses with blots of black pigment behind them (Fig. 7B); epimeral plate 3 posterodistal angle with a tooth (Fig. 7C); pereopod 3-4 with datcylus smaller than propodus and carpus combined (Fig. 7D) pereopod 7 merus without posterodistal lobe (Fig. 7E), basis outer surface without spines; uropod 3 with broad rami; urosome with a small angular carina (Fig. 7F) (Stebbing, 1906; Dauvin & Bellan-Santini, 1988).

Male description: Males similar to female description with the only difference being the length of antenna 2 which is larger than the body length; antenna 1 reaching well beyond the peduncle of antenna 2 (Fig. 7A).

Geographical distribution: Northeast Atlantic on Iberian Peninsula and occidental basin of the Mediterranean sea (Dauvin & Bellan-Santini, 1988).

Distribution in Portugal: International Minho River (this study), species also recorded at depths <150 m on coastal lines adjacent to the Tejo canyon (Marques & Bellan-Santini, 1993).

Ecological notes: Usually among algae (Stebbing, 1906).

Remarks: First description for adult male.

Ampelisca serraticaudata Chevreux, 1888 (Fig. 8A-C)

Ampelisca serraticaudata Chevreux, 1888: 349-350, Pl. VI figs. 3-9. — Stebbing, 1906: 107. — Chevreux & Fage, 1925: 80, fig. 71.

Type material: Holotype deposited at Muséum National d’Histoire Naturelle de Paris, catalogue number AM452 (Bulletin du Museum d’Histoire Naturelle de Paris, 1986).

Type locality: Cherchell, Algeria (Chevreux, 1888).

Material examined: 1 adult specimen, size 8 mm, collected at Caminha, International Minho River (41°52’76.62”N/8°50’41.7”W), 14 March 2021 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0092.

Diagnosis: With 4 corneal lenses; pereopod 7 merus without posterodistal lobe (Fig. 8B), basis outer surface without spines; uropod 3 inner ramus serrulate (Fig. 8C) (Dauvin & Bellan-Santini, 1988).

Geographical distribution: Northeast Atlantic from Iberian Peninsula to Senegal and Mediterranean (Dauvin & Bellan-Santini, 1988).

Distribution in Portugal: Species recorded at International Minho River (this study), and on the southwestern coast (Marques & Bellan-Santini, 1991, 1993; Pereira et al., 2006).

Ecological notes: Depth range 4-52 m (Dauvin & Bellan-Santini, 1988).

Ampelisca spinimana Chevreux, 1887 (Fig. 8D-E)

Ampelisca spinimana Chevreux, 1887: 574-575. — Stebbing, 1906: 109. — Chevreux & Fage, 1925: 81-82, fig. 73.

Type material: Holotype deposited at Museé Oceánographique de Monaco (Bulletin du Museum d’Histoire Naturelle de Paris, 1986).

Type locality: Croisic, France (Chevreux, 1887).

Material examined: 1 female adult, size 8 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0090.

Diagnosis: Antenna 1 on female shorter than antenna 2 slightly longer than antenna 2 peduncle; antenna 2 on female shorter than one third of the body length; gnathopod 1 with large spines on palm (Fig. 8E); pereopod 7 merus not produced (Chevreux, 1887; Stebbing, 1906; Dauvin & Bellan-Santini, 1988).

Geographical distribution: Northeast Atlantic from Brittany to Gulf of Guinea (Dauvin & Bellan-Santini, 1988).

Distribution in Portugal: Species recorded at International Minho River (this study), and on the southwestern coast (Marques & Bellan-Santini, 1991).

Ecological notes: Depth range 15 to 510 m (Stebbing, 1906; Dauvin & Bellan-Santini, 1988).

Suborder Senticaudata Lowry & Myers, 2013

Superfamily Aoroidea Stebbing, 1899

Family Aoridae Stebbing, 1899

Genus Aora Krøyer, 1845

Aora gracilis (Bate, 1857) (Fig. 8F)

Lonchomerus gracilis Bate, 1857: 143 (original description).

Aora gracilis – Bate, 1862: 160-161, Pl. XXIX fig. 7. — Bate & Westwood, 1863: 281-283. — Sars 1895: 545-546, Pl. 191. — Myers & Costello 1984: 281, fig. 1.

Type material: Holotype deposited at Natural History Museum, London, catalogue number 1952.5.7.133 (GBIF.org, 2021).

Type locality: Plymouth, England (Bate, 1857).

Material examined: 3 adult specimens, size 6 mm; 1 male specimen with antenna 1 and 2 missing, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0085; 1 male specimen with pereopods 6 and 7 on mounted blade, same data as preceding, deposited as NatMIP-CMAm-0093; 1 female specimen, antenna 1 missing, same data as preceding, deposited as NatMIP-CMAm-0105.

Diagnosis: Antenna 1 more than half the length, flagellum longer than peduncle; antenna 2 shorter than 1 and more robust, moderately setose, flagellum shorter than peduncle; gnathopod 1 on male extremely large with long and robust basis, merus with enormous pointed process reaching to end of elongate carpus (Fig. 8F) (Bate & Westwood, 1863; Sars, 1895)

Geographical distribution: Northeast Atlantic from Norway to Azores (Sars, 1895).

Distribution in Portugal: Species recorded at International Minho River (this study), Ria de Aveiro (Cunha et al., 1999), Ria Formosa (Cruz et al., 2003) and on Azores archipelago (Borges et al., 2010)

Ecological notes: Present at shallow depths (Sars, 1895).

Superfamily Calliopioidea Sars, 1895

Family Calliopiidae Sars, 1895

Genus Apherusa Walker, 1891

Apherusa jurinei (Milne-Edwards, 1830) (Fig. 9A-B)

Ampithoe jurinei Milne-Edwards, 1830: 376 (original description).

Amphitoe norvegica Rathke, 1843: 83-84, Tab. IV fig. 6.

Paramphithoe norvegica – Bruzelius, 1858: 77.

Calliopius norvegicus – Boeck, 1870: 118.

Apherusa jurinei – Sars, 1895: 445-446, Pl. 157 fig. 1. — Stebbing, 1906: 307-308. — Chevreux & Fage, 1925: 182-183, figs. 187-188. — Lincoln, 1979: 414, figs. 192D, 194A-C, 197A-E.

Type material: Unknown.

Type locality: France (Milne-Edwards, 1830).

Material examined: 1 adult specimen, size 6.8 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0075.

Diagnosis: Antenna 1 approximately half body length, flagellum slender up to 35 segments; antenna 2 longer than 1, peduncle articles 4 and 5 subequal, flagellum long and slender with over 50 segments (Fig. 9A); gnathopods 1 and 2 similar, palm oblique delimited by 3-4 spines (Fig. 9B); telson triangular with rounded apex (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from Norway to Iberian Peninsula (Lincoln, 1979).

Distribution in Portugal: Species recorded at International Minho River (this study), along the western coast (Izquierdo & Guerra-García, 2011), at Peniche (Patrício et al., 2006) and on Azores archipelago (Borges et al., 2010).

Ecological notes: Depth range from intertidal to shallow subtidal, on algae (Lincoln, 1979), collected on Corallina elongata (Izquierdo & Guerra-García, 2011).

Calliopiidae sp. (Fig. 9C-F)

Material examined: 1 adult specimen, size 6 mm, antenna 2 broken, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0102.

Description: Lateral view (left): Pleosome with sinuous dorsal margin (Fig. 9C); epimeral plate 3 with a tooth on inferoposterior margin, followed by a large acute projection on the posterior midline (Fig. 9D). Antenna 1 longer than antenna 2 peduncle, antenna1 peduncle article 1 longer than 2, and longer than 1, flagellum 32 articulated, accessory flagellum absent; antenna 2 longer than 1 with about half the body length, peduncle article 1 and 2 subequal and shorter than article 3 and 4, also subequal, flagellum more than 38 articulated (Fig. 9C). Gnathopod 1 slightly larger than 2, subchelate, propodus oval with stout spine near dactylus (Fig. 9E). Pereopods 3-7 with stout spine on propodus near to hook-like dactylus; pereopod 7 merus and carpus expanded fringed with 4 spines (Fig. 9F). Uropods biramous subequal in length; ramus fringed with spines.

Remarks: The set of morphological features of this specimen don’t fully match with European genera. In this study we prefer to keep family level taxonomic identification. The genus Haliragoides seems to resemble this specimen the most having antenna 2 longer than 1, peduncle articles of antenna 1 progressively shorter, antenna 1 peduncle article 3 not produced, absence of accessory flagellum and epimeral plate 3 toothed shaped, however the fact that gnathopods 1 and 2 carpus is smaller than propodus and lack posterior lobe indicates that we are in the presence of a genus different from Haliragoides. More specimens (males and females) are required for a complete evaluation, and confirmation of a possible new genus/species.

Superfamily Caprelloidea Leach, 1814

Family Caprellidae Leach, 1814

Genus Caprella Lamarck, 1801

Caprella danilevskii Czerniavski, 1868 (Fig. 10A-B)

Caprella danilevskii Czerniavski, 1868: 76-77, Pl. VI figs. 21-34. — Mayer, 1890: 58-60, Pl. 5 fig. 44, Pl. 7 figs. 12-13. — Chevreux & Fage, 1925: 454-455, fig. 432. — Hiro, 1937: 312-313, Pl. 22 fig. 7. — Mccain, 1968: 22-25, figs. 10, 11, 55. — Griffiths, 1974: 205. — Arimoto, 1976: 183-189, figs. 99-101. — Guerra-García & Takeuchi, 2002: 683, fig. 6. — Díaz et al., 2005: 3-4, fig. 3. — Guerra García et al., 2010: 114-115.

Caprella inermis Haswell, 1879: 348, Pl. XXIII fig. 3.

Type material: Unknown.

Type locality: Black Sea (Mccain, 1968).

Material examined: 4 pre-adult males, size range 6 to 8 mm, collected at Caminha, International Minho River (41°52’04.8”N 8°51’18.8”W), June 2021 on beam trawl, deposited as NatMIP-CMAm-0096.

Diagnosis: Gills elliptical parallel to body (Fig. 10A); pereopods 3-5 lacking grasping spines (Fig. 10B); male abdomen with hooked appendages (Mccain, 1968).

Geographical distribution: Widespread, pantropical (Mccain, 1968).

Distribution in Portugal: Species collected at International Minho River (this study), along the western coast (Pereira et al., 2006) and on the southeastern coast (Guerra García et al., 2010, 2012; Guerra-García & Izquierdo, 2010).

Ecological notes: Usually on sea grass, bryozoans, sponges and tunicates (Mccain, 1968; Guerra García et al., 2010), collected on Asparagopsis armata Harvey, 1855 (Guerra-García et al., 2012) and on Corallina elongata (Guerra-García & Izquierdo, 2010).

Remarks: Due to the disparity on the geographical records for this species, the use of DNA barcoding methodologies may provide some insight on the population dynamics and gene flow using a biogeographic approach, although the possibility of the presence of a species complex cannot be ruled out.

Caprella sp. (Fig. 10C-E)

Material examined: 1 adult female, size 6 mm, collected at Caminha, International Minho River (41°52’04.8”N 8°51’18.8”W), June 2021 on beam trawl, deposited as NatMIP-CMAm-0094.

Description: Lateral view (left): Body slender; head without rostrum with well-developed spine on dorsal-posterior zone; pereonite 1 reduced with a single tubercle, pereonites 2-5 sub-equal with 3 well-developed tubercles, pereonites 6-7 sub-equal with 2 tubercles each. Antenna 1 about one third the body length, peduncle with very few setae on inferior surface, flagellum with 8 articles; Antenna 2 about half length of antenna 1, peduncle article 3 with 4 pairs of long setae, article 4 with 7 pairs of long setae, flagellum two-articulated, setose. Gnathopod 1 ischium small, merus and carpus each with marginal row of setae on inferior margin, carpus triangular, propodus inferior margin with small setae; Gnathopod 2 on the proximal end of peronite 2, basis about half the length of pereonite 2, ischium and merus round sub-equal; carpus very short, propodus palm slightly convex with one spine on distal end and two tubercles on mid to proximal end. Oval, length about twice the width. Pereopods 5, 6 and 7 increasing in length; pereopod 7 ischium small, carpus and merus length subequal with a triangular projection on dorsal margin; palm of propodus concave with a hook-like process on inferior proximal margin.

Remarks: This species resembles Caprella erethizon Mayer, 1901 the most except for the absence of spines on pereonite 1 in Caprella sp. as well as pereopod 7 carpus and merus having different shapes comparing these two species. More specimens (mainly males) are needed for a complete evaluation.

Superfamily Corophioidea Leach, 1814

Family Corophiidae Leach, 1814

Genus Corophium Latreille, 1806

Corophium multisetosum Stock, 1952 (Fig. 10F)

Corophium multisetosum Stock, 1952: 3-8, figs. 6-15. — Lincoln, 1979: 526, figs. 252F-I.

Type material: Holotype, adult male, collected at the North Sea Canal, Netherlands, deposited at Naturalis Biodiversity Center, catalogue number ZMA Amph. 100328 (Stock, 1952).

Type locality: North Sea Canal, Netherlands (Stock, 1952).

Material examined: 4 adult specimens, size range 6 to 12.8 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0068.

Diagnosis: Head with triangular rostrum; antenna 1 peduncle article 1 with 3 spines on ventral margin; uropod 1 peduncle with 7-8 spines on outer margin and 2-3 spines on inner margin; uropod 2 peduncle with 3-4 dorsal spines; uropod 3 peduncle with produced distolateral angle (Stock, 1952; Lincoln, 1979).

Geographical distribution: Southern North and Baltic Seas, Northeast Atlantic from Netherlands to France (Lincoln, 1979).

Distribution in Portugal: Species recorded at the Minho River (Mazé et al., 1993; Sousa et al., 2008), Ria de Aveiro (Cunha et al., 1999), Mondego River (Chainho et al., 2006) and Mira River estuary (Marques & Bellan-Santini, 1987).

Ecological notes: Builds mud burrows in clay or sand in fresh brackish waters and occasionally on fixed substrata (Lincoln, 1979).

Genus Leptocheirus Zaddach, 1844

Leptocheirus pilosus Zaddach, 1844 (Fig. 11A)

Leptocheirus pilosus Zaddach, 1844: 8-9. — Stebbing, 1906: 630. — Sexton, 1911: 562. — Chevreux & Fage, 1925: 322-323, fig. 331. — Lincoln, 1979: 484, figs. 231A-F.

Protomedeia pilosa Bate, 1862: 168.

Leptocheirus cornuaurei Sowinsky, 1898: 470.

Leptocheirus subsalsus Norman, 1908: 307-308, Pl. XII figs. 1-6.

Type material: Unknown.

Type locality: Baltic Sea (Zaddach, 1844).

Material examined: 4 specimens, size range 4 to 4.52 mm, collected on sediment at Morraceira das Varandas Island, International Minho River (41°54’36.7”N/8°49’4.49”W) on September 25 2020 with Van Veen grab sampler; on medium sand, deposited as NatMIP-CMAm-0067.

Diagnosis: Antenna 2 flagellum with up to about 10 segments; gnathopod 2 basis anterior margin with dense double row of elongate plumose setae; coxal plate 1 elongated and rounded; urosome segments with a pair of dorsal setae each (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from North Sea to Iberian Peninsula and Mediterranean (Lincoln, 1979).

Distribution in Portugal: Species recorded at Minho River (Picanço et al., 2014), Ria de Aveiro (Cunha et al., 1997), Tejo River (Rodrigues et al., 2006), Mira River (Marques & Bellan-Santini, 1987) and Ria Formosa (Cruz et al., 2003).

Ecological notes: Tube builder, often found in brackish waters (Lincoln, 1979).

Leptocheirus sp. (Fig. 11B-F)

Material examined: 1 specimen, size 6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0104.

Description: Lateral view (left): Coxal plates elongated and overlapping, plate 2 larger than the rest, partially concealing plate 1 (Fig. 11C). Antenna 1 slightly longer than antenna 2, peduncle article 1 smaller than 2, but longer than 3, accessory flagellum absent, flagellum 17 articulated; antenna 2 peduncle article 1 about one third the length of article 2, article 2 and 3 subequal, flagellum 12 articulated (Fig. 11D). Gnathopod 1 subchelate, propodus and carpus subequal in length; gnathopod 2 slender and simple, basis, merus, carpus and propodus with long plumose setae (Fig. 11E). Pereopods 5-7 basis expanded. Uropods 1 to 3 subequal in length; uropod 3 shorter than 1 and 2, peduncle and rami subequal in length (Fig. 11F). Telson broad with one pair of apical setae.

Remarks: More specimens (males and females) are required for a complete evaluation.

Superfamily Gammaroidea Latreille, 1802

Family Bathyporeiidae d’Udekem d’Acoz, 2011

Genus Bathyporeia Lindström, 1855

Bathyporeia robertsoni Sars, 1895 (Fig. 12A-C)

Bathyporeia robertsoni Sars, 1895: 131-132, Pl. 44 fig. 2 (original description). — Stebbing 1906: 121.

Bathyporeia sarsi Watkin, 1938: 231-233, fig. 6. — Lincoln 1979: 320, figs. 150F-J. — d’Udekem d’Acoz, 2004: 68-75, figs. 60-69.

Type material: Holotype, adult male collected in Sorvaer, Finnmark, Norway, deposited at Zoological Museum, Oslo (Watkin, 1938).

Type locality: Sorvaer, Finmark, Norway (Sars, 1895).

Material examined: 4 adult specimens, 2 females and 2 males, size range 5 to 6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0083.

Diagnosis: Antenna 1 apex of peduncle article 1 broadly rounded (Fig. 12B); pleonite 4 dorsally depressed with pair of anteriorly directed setae and without posteriorly directed spines; epimeral plate 3 distal margin with 4-6 spine groups (Fig. 12C) (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from Norway to English Channel (Lincoln, 1979).

Distribution in Portugal: Species recorded at International Minho River (this study), Mondego River estuary (Marques et al., 1993) and at the southwestern Portuguese coast (Marques & Bellan-Santini, 1991).

Ecological notes: Burrower, depth range from intertidal to about 20 m (Lincoln, 1979).

Remarks: After a re-examination of Sars (1895) specimens, Watkin (1938) confirmed that Sars misidentified his specimens as Bathyporeia robertsoni Bate, 1862, and erected Bathyporeia sarsi, based on Sars’ material. Furthermore Barclay (1982) re-examination of Bate’s B. robertsoni, confirmed that it was a junior synonym of Bathyporeia pilosa Lindström, 1855. As Bate’s B. robertsoni was confirmed as a synonym of B. pilosa, Sars’s B. robertsoni has priority over Watkin’s B. sarsi, since Sars provided its original description, so we propose that B. sarsi should be accepted as Bathyporeia robertsoni Sars, 1895.

Family Gammaridae Leach, 1814

Genus Gammarus Fabricius, 1775

Gammarus chevreuxi Sexton, 1913 (Fig. 12D-E)

Gammarus chevreuxi Sexton, 1913: 542-545, figs. 1-5. — Chevreux & Fage 1925: 255-256, fig. 266. — Lincoln, 1979: 256, figs. l18A-I.

Type material: Unknown.

Type locality: Plym River, Devon Meadow, England (Sexton, 1913).

Material examined: 4 adult specimens, size range 5 to 8 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0086.

Diagnosis: Antenna 2 and gnathopods in mature male with long curled setae; mandible palp article 3 ventral setae comb-like (Fig. 12E); pereopods 6-7 basis posterodistal angle not produced; uropod 3 inner ramus between one-half and two-thirds the length of outer ramus (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from north Wales to south Morocco (Lincoln, 1979).

Distribution in Portugal: Species recorded at the Minho (van Maren, 1975; Mazé et al., 1993; Sousa et al., 2008) and Douro estuaries and Esposende (van Maren, 1975), also recorded at Ria de Aveiro (Cunha et al., 1999; Costa et al., 2004) and Figueira da Foz (Stock, 1967) and Mira River (Marques & Bellan-Santini, 1987).

Ecological notes: Brackish water species found in marshy areas and on mud, sand and stones within estuaries (Lincoln, 1979).

Genus Marinogammarus Schellenberg, 1937

Marinogammarus marinus (Leach, 1815) (Figs. 12F, 13A-B)

Gammarus marinus Leach, 1815: 359 (original description). — Bate & Westwood, 1863: 370-375. — Sars, 1895: 497-498, Pl. 175. — Stebbing, 1906: 472-473. — Chevreux & Fage, 1925: 250-251, fig. 261

Marinogammarus marinus – Sexton & Spooner, 1940: 638-644, figs. 1A-I, 2A-J.

Chaetogammarus marinus – Lincoln, 1979: 266, figs. 122A, 123A-J.

Echinogammarus marinus – Pinkster, 1993: 148-150, fig. 63

Type material: Holotype, deposited at Natural History Museum, London, catalogue number White 1 289.a-e (GBIF.org, 2021)

Type locality: Devonshire, Great Britain (Leach, 1815).

Material examined: 2 adult specimens, size range 15 to 17 mm, collected at Caminha, International Minho River (41°51’58.3”N/8°50’55.8”W), September 2021 on Fucus cf. spiralis Linnaeus 1753, deposited as NatMIP-CMAm-0106.

Diagnosis: Antenna 1 peduncle article 1 longer than 2, article 3 about half length of 2, flagellum up to 50 articulated; accessory flagellum 7 to 9 articulated; antenna 2 densely setose; urosome segments 1-3 each with numerous dorsal spines in transverse rows (Fig. 13A); uropod 3 outer ramus densely setose along both margins inner ramus spinose and setose (Fig. 13B); telson with small group of lateral and apical spines and few short setae on each lobe (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from Norway to Portugal (Lincoln, 1979).

Distribution in Portugal: Species recorded at International Minho River (this study), and Mondego estuary (Maranhão et al., 2001).

Ecological notes: Intertidal, upper shore, usually beneath algae on stones, tolerates reduced salinities (Lincoln, 1979).

Genus Relictogammarus Hou & Sket, 2016

Relictogammarus stoerensis (Reid, 1938) (Fig. 13C-D)

Gammarus marinus var. stoerensis Reid, 1938: 287-289, figs. A-E (original description).

Gammarus (Marinogammarus) stoerensis – Stephensen, 1938: 143-146.

Marinogammarus stoerensis – Sexton & Spooner, 1940: 662-667, figs. 8A-O, 11A.

Chaetogammarus stoerensis – Lincoln, 1979: 270, figs. 125A-J.

Echinogammarus stoerensis – Pinkster, 1993: 155-158, fig. 66.

Relictogammarus stoerensis – Hou & Sket, 2016: 330, 336.

Type material: Unknown.

Type locality: Stoer Bay, Scotland (Reid, 1938).

Material examined: 1 specimen, size 4 mm, collected at Caminha, International Minho River (41°52’04.8”N/8°51’18.8”W), June 2021 on beam trawl, deposited as NatMIP-CMAm-0095, uropod 3 on mounted blade.

Diagnosis: Antenna 1 slightly less than half the body length and longer than antenna 2, flagellum 14 to 17 articulated, accessory flagellum 3 to 4 articulated; antenna 2 flagellum 11 to 13 articulated; uropod 3 outer ramus with spinose inner and outer margins and without setae, inner ramus small and scale-like (Fig. 13D) (Lincoln, 1979; Pinkster, 1993).

Geographical distribution: Northeast Atlantic from Norway to Iberian Peninsula (Pinkster, 1993).

Distribution in Portugal: Species recorded at International Minho River (this study), and Mondego River (Pinkster, 1993).

Ecological notes: Intertidal species, vertically distributed from high to low water neaps, usually in areas with freshwater flow, on course gravel beaches (Pinkster, 1993).

Superfamily Hadzioidea Karaman, 1943

Family Maeridae Krapp-Schickel, 2008

Genus Maera Leach, 1814

Maera grossimana (Montagu, 1808) (Fig. 13E-F)

Cancer (Gammarus) grossimanus Montagu, 1808: 97-98, Tab. IV fig. 5 (original description).

Maera grossimana – Leach, 1814: 403. — Bate & Westwood, 1863: 350-352. — Stebbing, 1906: 435. — Chevreux & Fage, 1925: 239-240, figs. 248, 250. — Lincoln, 1979: 282, figs. 131A-F.

Maera grossimanus – Bate, 1862: 188-189, Pl. XXXIV fig. 3.

Type material: Holotype deposited at Natural History Museum, London, catalogue number White 1 287.a-f (GBIF.org, 2021).

Type locality: Devonshire, Scotland (Montagu, 1808).

Material examined: 1 adult specimen, size 6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0103.

Diagnosis: Antenna 1 about half body length, peduncle long and slender, flagellum shorter than peduncle; accessory flagellum elongated 8-articulated; antenna 2 shorter than antenna 1, flagellum short 8 articulated; gnathopod 2 much larger than gnathopod 1, especially in males, propodus broad, palm with double row of small spines and small tooth and 2 long spines on inferior margin (Fig. 13F); epimeral plate 3 with tooth on inferior margin; uropod 3 rami subequal (Lincoln, 1979).

Geographical distribution: Atlantic Ocean from English Channel to southwest Africa, Azores and Canary islands and Mediterranean sea (Lincoln, 1979).

Distribution in Portugal: Species recorded at International Minho River (this study), along the southwestern coast (Marques & Bellan-Santini, 1991, 1993; Carvalho et al., 2012) and on Azores archipelago (Borges et al., 2010).

Ecological notes: Depth range about 0 to 150 m (Lincoln, 1979).

Family Melitidae Bousfield, 1973

Genus Abludomelita Karaman, 1981

Abludomelita gladiosa (Bate, 1862) (Fig. 14A-B)

Melita gladiosa Bate, 1862: 185, Pl. XXXIII fig. 6 (original description). — Bate & Westwood, 1863: 346-347. — Stebbing, 1906: 428. — Chevreux & Fage, 1925: 233-234, fig. 244. — Lincoln, 1979: 302, figs. 137C, 141A-I.

Abludomelita gladiosa – Jarrett & Bousfield, 1995: fig. 2.

Type material: Holotype, specimen deposited at Museum of the Jardin des Plantes (Bate, 1862).

Type locality: Boulogne, France (Bate, 1862).

Material examined: 1 adult female, with antenna 1 missing, size 9.7 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0074.

Diagnosis: Female gnathopod 2 larger than gnathopod 1, propodus subrectangular, palm oblique, weakly sinuous and delimited by small spine; male gnathopod 2 robust, merus distally acute, propodus large and broad distally, palm irregularly toothed, inner surface of propodus with small tooth, dactylus broad and flattened with subacute apex; pleonites 1-5 each with 3 dorsal teeth, pleonite 6 also with small teeth; epimeral plate 3 serrated with distal angle with large upturned tooth (Fig. 14B), distinctly serrate (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from English Channel to Mediterranean and Azores (Lincoln, 1979).

Distribution in Portugal: Species recorded at International Minho River (this study), Sado estuary (Carvalho et al., 2001) and on Azores archipelago (Borges et al., 2010).

Ecological notes: Depth range 10-250 m (Lincoln, 1979).

Genus Melita Leach, 1814

Melita palmata (Montagu, 1804) (Fig. 14C-D)

Cancer palmatus Montagu, 1804: 69, Tab. VI fig. 4 (original description).

Astacus palmatus – Pennant, 1812: 35.

Melita palmata – Leach, 1814. — 403. — Bate, 1857: 144; 1862: 182-183, Pl. XXXIII fig. 2. — Bate & Westwood, 1863: 337-340. — Sars, 1895: 508-509, Pl. 179. — Stebbing, 1906: 425. — Chevreux & Fage, 1925: 230-231, fig. 241. — Lincoln, 1979: 298, figs. 137A, 139A-J.

Gammarus dugesii Milne-Edwards, 1830: 368.

Gammarus inaequimanus Bate, 1857: 145.

Type material: Unknown.

Type locality: Devonshire, England (Montagu, 1808).

Material examined: 3 adult specimens, 1 adult male size 9.7 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0069; 2 adult females, one ovigerous size range 6 to 7 mm, same data as preceding, deposited as NatMIP-CMAm-0081.

Diagnosis: Pleonites without teeth on dorsal margin; first urosome segment with a single dorsal tooth; uropod 3 inner ramus less than half the length of outer ramus, outer ramus longer than peduncle; telson with apical spines (Lincoln, 1979).

Geographical distribution: Northeast Atlantic from Norway to Iberian Peninsula and Macaronesian archipelagos and on the Mediterranean and Black seas (Lincoln, 1979).

Distribution in Portugal: Species recorded at the Minho (Mazé et al., 1993), Mondego (Marques et al., 1993), Tejo (Rodrigues et al., 2006) and Mira (Marques & Bellan-Santini, 1987) estuaries, at Ria de Aveiro (Cunha et al., 1999) and Ria Formosa (Cruz et al., 2003), along the Portuguese coast (van Maren, 1975) and on Azores archipelago (Borges et al., 2010).

Ecological notes: Usually found on sheltered beaches in sediments of sand or mud with stones, depth range from intertidal to 50 m tolerant to a wide range of salinity (Lincoln, 1979).

Superfamily Hyaloidea Bulyčeva, 1957

Family Hyalidae Bulyčeva, 1957

Genus Protohyale Bousfield & Hendrycks, 2002

Protohyale (Protohyale) sp. (Fig. 15A-D)

Material examined: 1 male adult, size 6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0097.

Description: Antenna 1 longer than antenna 2 pedunculum, flagellum with 14 segments; antenna 2 one third the body length, flagellum with 29 segments. Gnathopod 1 propodus oval with group of setae on palm; gnathopod 2 propodus about 3 times the size of gnathopod 1, gnathopod 2 propodus formed by two balloon-like structures with similar size, with a lobed structure rising from propodus midline forming a hook-like structure on the anterior apical margin (Fig. 15B–C). Merus and carpus with small lobes carrying 3 and 4 spines respectively; propodus with 5 spines across the inferior margin; dactylus hook-like, about one third the propodus length. Uropods with 4 apical spines on each ramus; uropod 1 and 2 biramous; uropod 2 reaching uropod 1; uropod 3 uniramous, not reaching uropod 2 (Fig. 15D). Telson not armed with spines or setae.

Remarks: According to Costello et al. (2021) three species of Protohyale (Protohyale) occur on Europe Protohyale (Protohyale) dollfusi (Chevreux, 1911), Protohyale (Protohyale) grimaldii (Chevreux, 1891) and Protohyale (Protohyale) schmidtii (Heller, 1866), nonetheless this species recorded at the Minho river differs from all of them on the shape of gnathopod 2 propodus and number of segments of antenna 2. More specimens (mainly females) are required for a complete evaluation, and confirmation of a possible new species.

Superfamily Photoidea Boeck, 1871

Family Ischyroceridae Stebbing, 1899

Genus Jassa Leach, 1814

Jassa falcata (Montagu, 1808) (Fig. 15E)

Cancer (Gammarus) falcatus Montagu, 1808: 100, Tab. V fig. 2 (original description).

Jassa pulchella Leach, 1814: 433. — Stebbing, 1906: 654-655.

Podocerus calcaratus Rathke, 1843: 91-93, Tab. IV fig. 9.

Podocerus falcatus Bate, 1857: 148. — Bate & Westwood, 1863: 445-446. — Sars, 1895: 594-595, Pl. 212.

Podocerus odontonyx Sars, 1895: 597-598, Pl. 213.

Jassa falcata – Chevreux & Fage, 1925: 344-346, figs. 352-353. — Reid, 1951: 266, fig. 56. — Sexton & Reid, 1951: 30-33. — Lincoln, 1979: 650, figs. 263A-B, 264A-J. — Conlan, 1990: 2069-2071, figs. 1-6, 8-10, 23. — Conlan et al., 2021: 81-87, figs. 42-47.

Type material: Holotype, adult male, length 6.3 mm; collected at Torcross, South Devon, England; deposited at Natural History Museum (London) catalogue number NHM 603a (Conlan et al., 2021).

Type locality: Devonshire, England (Montagu, 1808).

Material examined: 4 adult specimens, size range 6.8 to 7.6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0084.

Diagnosis: Gnathopod 1 basis anterolateral margin with few very short setae; carpus without setae at the anterodistal junction of the propodus; gnathopod 2 basis with few small setae on the anterolateral; propodus of pereopods 5-7 not expanded anteriorly; uropod 1 ventral spinous process with about half of the longest ramus; uropod 3 inner ramus with 1–2 dorsal spines and a single apical spine (Conlan et al., 2021).

Geographical distribution: Cosmopolitan (Lincoln, 1979).

Distribution in Portugal: Species recorded at International Minho River (this study), Ria de Aveiro (Cunha et al., 1999), Mondego River, Figueira da Foz (Dexter, 1992), along the west coast (Izquierdo & Guerra-García, 2011; Guerra-García et al., 2012) and Azores archipelago (Borges et al., 2010).

Ecological notes: Constructs tubes on algae or hydroids, or on solid artificial surfaces such as buoys, rafts or ship hulls (Lincoln, 1979), collected on Corallina elongata (Izquierdo & Guerra-García, 2011; Guerra-García et al., 2012).

Genus Parajassa Stebbing, 1899

Parajassa pelagica (Leach, 1814) (Fig. 15F)

Jassa pelagica Leach, 1814: 433 (original description); 1815: 361

Podocerus capillatus Rathke, 1843: 89-91, Tab. IV fig. 8. — Bate & Westwood, 1863: 442-444.

Jassa capillata – Bruzelius, 1858: 19-20.

Janassa variegata Boeck & Boeck, 1872: 608-611, Pl. XXVIII fig. 1, Pl. XXIX fig. 2.

Janassa capillata – Sars, 1895: 599-600, Pl. 214.

Parajassa pelagica – Stebbing, 1899: 237-240. — Chevreux & Fage, 1925: 349-350, fig. 357. — Lincoln. 1979: 562, figs. 270A-F.

Type material: Unknown.

Type locality: Bell Rock, Scotland (Leach, 1815).

Material examined: 1 adult specimen, size 6 mm, collected at Caminha, International Minho River (41°52’59”N/8°50’14”W), 6 April 2020 on glass eel fishing bycatch, deposited as NatMIP-CMAm-0033.

Diagnosis: Antennae very characteristic, short and robust with dense tuffs of long setae, especially in large male; accessory flagellum rudimentary; pereopod 7 basis with posterodistal angle prolonged and narrowly rounded (Lincoln, 1979).

Geographical distribution: Arctic Ocean and Northeast Atlantic from Norway to Portugal (Lincoln, 1979).

Distribution in Portugal: Species recorded at International Minho River (this study), on the gut content of Lipophrys pholis (Linnaeus, 1758) collected in Aguda (Monteiro et al., 2005) and along the western coast (Izquierdo & Guerra-García, 2011; Guerra-García et al., 2012).

Ecological notes: Among algae and hydroids (Lincoln, 1979), collected on Corallina elongata (Izquierdo & Guerra-García, 2011; Guerra-García et al., 2012).

From the 34 species collected, five were previously recorded on the Minho river estuary, i.e. Haustorius arenarius (Slabber, 1778), Corophium multisetosum Stock, 1952, Leptocheirus pilosus Zaddach, 1844, Melita palmata (Montagu, 1804) and Gammarus chevreuxi Sexton, 1913 (van Maren, 1975; Mazé et al., 1993; Sousa et al., 2008; Picanço et al., 2014). Six species were recorded along the coastal line adjacent (i.e. subtidal zone) to the Minho and Lima rivers mouth: Nototropis vedlomensis (Bate & Westwood, 1863), Lepidepecreum longicorne (Bate, 1862), Urothoe brevicornis Bate, 1862, Tryphosites longipes (Bate, 1862), Ampelisca armoricana Bellan-Santini & Dauvin, 1981 and Ampelisca pectenata Reid, 1951 (Marques & Bellan-Santini, 1993), which could explain their presence on brackish waters (such as in this study) during the high flood tides. Of those 34 species recorded, 23 were new records for the Minho River (Nototropis guttatus (Costa, 1851), Abludomelita gladiosa (Bate, 1862), Ampelisca aequicornis Bruzelius, 1858, Ampelisca lusitanica Bellan-Santini & Marques, 1986, Ampelisca rubella Costa, 1864, Ampelisca serraticaudata Chevreux, 1888, Ampelisca spinimana Chevreux, 1887, Apherusa jurinei (Milne-Edwards, 1830), Aora gracilis (Bate, 1857), Bathyporeia robertsoni Sars, 1895, Caprella danilevskii Czerniavski, 1868, Dexamine spinosa (Montagu, 1813), Marinogammarus marinus (Leach, 1815), Relictogammarus stoerensis (Reid, 1938), Jassa falcata (Montagu, 1808), Maera grossimana (Montagu, 1808), Parajassa pelagica (Leach, 1814) plus the 5 not fully identified species which do not match any of the amphipod species recorded for the Minho River) with the presence of a new record for Portuguese waters, Parametopa kervillei Chevreux, 1901 which was only recorded to date on the north French coast and on the British Isles, extending its southern distribution range to the north of the Iberian Peninsula. The genus Ampelisca was the most represented group with 7 species recorded. For the first time a male specimen of Ampelisca rubella Costa, 1864 was described, complementing the descriptions based on female specimens. Most species are fully marine, with the exception of Haustorius arenarius, Corophium multisetosum, Leptocheirus pilosus, and Gammarus chevreuxi common on the brackish waters of the estuary. High flood tide dynamics seem to bring an unexpected amount of marine adventitious fauna well inside estuary boundaries, since most specimens were collected on the water column with a stationary net capturing organisms transported upstream (e.g. Weber, 1986) (with mostly brackish species during the first hour of continuous sampling, and only marine species on the subsequent hours), providing opportunities on data collection about the populations present on the coastal lines adjacent to the estuary. However, ecological data cannot be collected as those organisms are carried by the water strength. Nonetheless, an in-depth analysis on the lower estuary macroinvertebrate communities may provide insight on shifting population dynamics or on the periods in which those species remain at more brackish areas.

On five of those species a full identification was not possible due to the scarcity or fragmentation of the information on certain amphipod groups however the possibility of being new or exotic species cannot be ruled out.

This represents the first taxonomic study on Amphipoda from the International Minho River, contributing to the knowledge of the Portuguese and Iberian fauna. Apart from a few brackish species which reside permanently on the river estuary, most of the amphipod fauna examined was marine adventitious fauna transported upstream trough high flood tide dynamics.