The paraonids represent a family of elongate, small polychaetes (up to 40 mm long) with numerous segments. They are deposit-feeders and can be found from the littoral zone to abyssal depths (Glasby, 2000), not having been found in fresh water.

Nowadays, this family includes about 156 species distributed in eight genera: Aparaonis Hartman, 1965, Aricidea Webster, 1879, Cirrophorus Ehlers, 1908, Levinsenia Mesnil, 1897, Paradoneis Hartman, 1965, Paraonides Cerruti, 1909, Paraonis Grube, 1873 and Sabidius Strelzov, 1973. The genus Paradoneis was composed of 21 species and 2 subspecies, seven of which have been reported in the Bay of Biscay (North Atlantic): P. lyra (Southern, 1914), P. armata Glémarec, 1966, P. bathyilvana Aguirrezabalaga & Gil, 2009, P. drachi Laubier & Ramos, 1974, P. eliasoni Mackie, 1991, P. ilvana Castelli, 1985 and P. mikeli Aguirrezabalaga & Gil, 2009.

During two sampling campaigns recently carried out on the continental shelf of the Basque coast (SE Bay of Biscay), a new species of Paradoneis is described, illustrated and compared with the currently known species of the genus.

Phylum Annelida

Familia Paraonidae Cerruti, 1909

Genus Paradoneis Hartman, 1965

Paradoneis idoiae n. sp.

urn:lsid:zoobank.org:act:EA821956-368F-4274-857D-4ABDAAC1D88B

Type Material. Holotype (MNCN 16.01/18236), one complete specimen, collected outside of Abra de Bilbao (Bizkaia), station S-50 (43º23.415´N, 03º07.274´W), sand, 51 m depth, 01.05.2018.

Paratypes (MNCN 16.01/18237), three complete specimens, collected at the same time than the holotype. Paratype (MNCN 16.01/18238), one incomplete specimen, collected in Deba (Gipuzkoa), station L-D10 (43º19.594´N, 02º21.147´W), coarse sand, 42 m depth, 24.04.2018).

Additional material. Three complete specimens, collected at the same time than the holotype.

Description. Holotype longest complete specimen, measuring 8.62 mm long, 0.22 mm wide in branchial region for 84 chaetigers. Body relatively small, thin, circular in cross section whit numerous chaetigerous segments (Fig. 2A, 3A). Colour in alcohol white to light tan, with numerous small pigment granules on the dorsal and ventral surfaces (Fig. 2B).

Prostomium elongated, slightly longer than wide (1.2-1.4 times), oval to conical, slightly compressed laterally, lacking median antena. An apical sensorial organ present, in some specimens retracted and not visible. Eyes not visible. A pair of nuchal grooves on postero-lateral part of prostomium. Two dorsal ciliated bands present, one located on anteriormost region of the prostomium, and another posterior, visible at the level of nuchal slits (Fig. 3B). Posterior buccal lip with 3-4 longitudinal folds starting from anterior part of chaetiger 1 (Fig. 2C).

Notopodial postchaetal lobes present in all parapodia throught body; on most anterior three chaetigers short, tuberculate to conical, progressively increasing in length through prebranchial region (Fig. 3C); 2-3 times longer, digitiform, distally rounded in branchial region (Fig. 3D, 3E); becoming short, globular to conical in postbranchial region (Fig. 3F); clearly longer, filiform in posteriormost segments (Fig. 4A). Neuropodial postchaetal lobes absent.

Branchiae beginning from chaetiger 4 in number of 5-6 pairs, elongated, cylindrical, distally rounded whit lateral margins ciliated; each equal or slightly longer than segment width (Fig. 4B).

Simple limbate capillary chaetae in both rami from chaetiger 1, continuing throughout body. 1-2 modified lyriform chaetae in lower part of notopodial chaetal fascicle from chaetiger 2-3 (Fig. 4C). Each has two unequally long tines; both tines similarly thick with inner sides spinous (Fig. 2D).

Pygidial region whit 7 cirri, 2 pairs corresponding to notopodial postchaetal lobes of two reduced segments, and 3 anal cirri, whit the mid-ventral one more robust and thicker than de two lateral ones, all long, filiform, similar in lenght (Fig. 4D).

Remarks. Paradoneis idoiae n. sp. is most closely related to P. perdidoensis (McLelland & Gaston, 1994), a meiofaunal species from the coast of the Northern Gulf of Mexico, in having a reduced number of branchiae, three prebranchial chaetigers, modified notochaetae exclusively lyriform and a pygidial region with some pre-anal segments whitout chaetae. However, according to McLelland & Gaston (1994), adults of both species can be differentiated by the number of branchiae [3 (rarely 4) pairs in P. perdidoensis, vs. 5-6 pairs in P. idoiae n. sp.]; presence of eyespots on prostomium (present in P. perdidoensis, vs. absent in P. idoiae n. sp.); size of notopodial postchaetal lobes [prominent and uniform in length in all branchial chaetigers and first ones of the postbranchial region in P. perdidoensis, vs. unequal, relatively long and digitiform in all branchial chaetigers (except in the last, clearly shorter) and shorter in the adjacent postbranchial region in P. idoiae n. sp.]; shape of three anal cirri (all similar in P. perdidoensis, vs. one mid-ventral more robust and thicker than the two lateral ones in P. idoiae n. sp.); number of pre-anal segments (3 in P. perdidoensis, vs. 2 in P. idoiae n. sp.); and bathymetry [P. perdidoensis found in shallow waters (1-7 m depth), vs. P. idoiae n. sp. has been collected in circalittotal botoms (42-51 m depth)].

Paradoneis idoiae n. sp. is also similar to P. lyra, which was originally described from the coast of Ireland (N Atlantic Ocean). However, both species differ by the number of branchiae (5-6 pairs in P. idoiae n. sp., vs. up to 16 pairs in P. lyra); the morphology of branchiae (proportionally thin with same width throughout in P. idoiae n. sp., vs. proportionally more robust, basally wider in P. lyra); the size of branchiae (equal or slightly longer than segment width in P. idoiae n. sp., vs. shorter, equal to distance between branchial bases in P. lyra); and the size of anal cirri (long in P. idoiae n. sp., vs. relatively short in P. lyra).

Habitat. In the Basque Contry, P. idoiae n. sp. found in sand and coarse sand sediment with moderate to low percentage of organic matter content, between 42 and 51 m depth. The biocenosis where this species was collected is characterized by the abundance of the polychaetes Pisione remota (Southern, 1914), Hesionura elongata Southern, 1914, Sphaerosyllis bulbosa Southern, 1914, Glycera lapidum Quatrefages, 1866, and Polygordius appendiculatus Fraipont, 1887, the oligochaeta Grania sp, the molluscs Limatula subauriculata (Montagu, 1808) and Asbjornsenia pygmaea (Lovén, 1846), the sea cucumber Leptosynapta minuta (Becher, 1906), nemertean and nematoda indeterminate.

Distribution. Basque Country (NE Iberian Peninsula, SE Bay of Biscay), between 42 and 51 m depth.

Etymology. This species is dedicated to Idoia Adarraga Marrodán, wife of the author.

The following dichotomous key has been elaborated based on the information included in Southern (1914), Day (1955), Hartman (1965), Glémarec (1966), Storch (1967), Hobson (1972), Imajima (1973), Strelzov (1973), Hartmann-Schröder (1974), Laubier & Ramos (1974), Amoureux (1985), Castelli (1985), Hartmann-Schröder & Rosenfeldt (1988), Mackie (1991), McLelland & Gaston (1994), De León-González et al. (2006), Aguirrezabalaga & Gil (2009), Sardá et al. (2009), Arriaga-Hernández et al. (2013) and López & Sikorski (2017).

Note: Some authors like López-Jamar et al. (1987) and Lowell (2002) consider Paradoneis harpagonea as a junior synonym of Paradoneis armata.

This discovery confirms the high presence of the Paraonidae family in the NE Iberian Peninsula. Around 40 species of this family have been reported on the Iberian coasts, of which 80% inhabit the Basque coast and adjacent areas. This percentage is even higher in the case of the Paradoneis genus. Including P. idoiae n. sp., eight of the nine Iberian Paradoneis species have been collected in this geographical area.

The identification of this new paraonid species on a common and relatively well studied sediment type on the Basque coast could be explained by possible misidentifications in the past. The foreign introduction via ballast water, although possible, seems less likely. The two stations where the specimens have been collected (S-50 and L-D10) are separated by 63 km, and more than 3 km away from the coast.

Among all species of the genus Paradoneis described to date in the SE Bay of Biscay, P. lyra is the best represented species. Their records range from shallow waters to 1772 m depth, showing preference for muddy and fine sands (Aguirrezabalaga, 2012). For many years, in the Bay of Biscay all those specimens of the genus Paradoneis without prostomial median antenna and having lyriform chaetae have been assigned to this species; however recent studies carried out by Aguirrezabalaga & Gil (2009) and Aguirrezabalaga (2012) suggest that other different species have also been included, such as P. ilvana, P. bathyilvana and P. mikeli. The same could have happened with P. idoiae n. sp.. It is possible that previous identifications of P. lyra in circalittoral samples from medium and coarse sands (Aguirrezabalaga, 1984; Martínez & Adarraga, 2001; Martínez et al., 2007), correspond actually to the new species.