MORPHOLOGY OF THE FIRST ZOEA OF THE SHAMEFACED CRAB CALAPPA GRANULATA (LINNAEUS, 1758) (BRACHYURA, CALAPPIDAE) OBTAINED IN THE LABORATORY

The first zoeal stage of the calappid crab Calappa granulata is described and illustrated from laboratory-reared material obtained from an ovigerous female captured in the western Mediterranean. The morphology of this larval stage is clearly different from previous description from plankton-collected specimens attributed to this species. The present stage is compared with those previously described from other species of the genus Calappa.


Introduction
Knowledge on the larval stages of calappid crabs is limited and fragmentary (Rice, 1980;Stevcic, 1983).There are only a few papers concerning the larval development of calappid crabs and most of them deal only with the zoeal or prezoeal stages (Lebour, 1944;Raja Bai, 1959;Motoh, 1977;Terada, 1987;Seridji, 1993;González-Gordillo, 1994;Taishaku & Konishi, 1995).Most of the authors which have tried to rear larvae of crabs of this family have found serious difficulties in rearing them, probably related with feeding (Taishaku & Konishi, 1995).
The prezoeal stage of Calappa granulata was obtained in the laboratory and described by González-Gordillo (1994).Seridji (1993) described and figured a first stage zoea from Mediterranean plankton samples collected off the Algerian coast, which was attributed the family Calappidae and, with some doubts, to the species C. granulata.Guerao et al. (1998) described the megalopa and first juvenile stage of C. granulata obtained from a megalopa collected in a plankton sample and subsequently reared in the laboratory.
The present paper aims to describe the morphology of the first zoeal stage of Calappa granulata and to compare its larval features with those known for other species of the genus.

Material and methods
An ovigerous female Calappa granulata, 65.9 mm carapace width, with eggs in an early stage of development, was collected by trawling on muddy bottoms off Cartagena (37º30.65 N, 1º09.49W, western Mediterranean) from a depth of 184-187 m on the 19th May 1997.Sampling was performed within the frame of the EU demersal fisheries research program "MEDITS" on board B/O "Cornide de Saavedra".
The crab was placed in an aquarium (60 x 35 x 30 cm) on board the ship containing well-aerated sea water at a salinity of approx.37.5 and kept at 17 ± 1ºC.The crab was transported to the laboratory and kept at 15 ± 1ºC.Hatching took place on the 23rd June 1997.The first zoeae were placed in both mass culture and compartmented boxes and freshly hatched Artemia nauplii were provided.Specimens zoeae were preserved in 7% buffered formalin.A high mortality followed and no larvae reached the second zoeal stage.
An Olympus phase contrast microscope was used in the dissection and observation of the setal formula of the appendages.Measurements were taken with a M5 Wild binocular microscope equipped with an ocular micrometer, and are based on measurements of 5 individuals.All drawings were made with the aid of a camera lucida.The following measurements were taken: distance from base to tip of dorsal spine (DS); distance between tips of dorsal and rostral spines (TL); carapace length, from between eyes to the posterio-lateral margin of the carapace (CL); total width, distance between the tips of lateral spines (TW).Larval description followed the basic malacostracan body pattern (Clark et al., 1998).
The adult female crab of the present study was deposited in the Biological Collections of Reference of the Institut de Ciències del Mar (CSIC) in Barcelona (Registration Number: ICMD 086/1998).
Antenna (Fig. 1H).Exopod less than half (1/6) the length of the spinous process, with one long and one short setae; spinous process with small spinules on the surface of the distal half.
Mandible.Incisor and molar processes well developed; mandibular palp absent.
Abdomen (Fig. 1A, E).Five somites; somites 2 and 3 with 1 pair of lateral processes, those on the     Telson (Fig. 1E, F).Each telson fork with a well developed dorsal and lateral spine, and a very minute and vestigial lateral spine observed in most, not all, the zoeae studied; inner margin with 3 pairs of plumodenticulate setae, separated by a shallow median notch; setules of plumodenticulate setae smaller on the distal part.

Discussion
The morphology of the first zoea of Calappa granulata is very similar to that of other described species of the genus (see Table 1), but differs widely from the larva described by Seridji (1993).Thus, the zoea I described in the present paper does not bear denticles nor spicules on the dorsal spine or on the carapace.Also, the second lateral spine of the telson is vestigial, very minute, in C. granulata.The present zoeae are also smaller (TL: 1.70-1.78mm vs 2.20 mm).Other important differences affect the setation of the appendages (Table 1), such as the basal segment of the endopod of the maxillule, which lacks the seta figured by Seridji and is also lacking in all the rest of first zoeae of the genus Calappa described to date.The larva described by Seridji also differs widely in the setation of the maxillipeds and of the coxa of the maxilla (Table 1).All these differences lead us to conclude that Seridji's larva most probably does not belong to the genus Calappa.