Parastenocaris salvadorensis

Corgosinho, Paulo H. C., Arbizu, Pedro Martínez & Dos Santos-Silva, Edinaldo N., 2010, Revision of Brasilibathynellocaris Jakobi, 1972 (Copepoda: Harpacticoida: Parastenocarididae) with redefinition of the genus, Zoological Journal of the Linnean Society 159 (3), pp. 527-566 : 558

B. SALVADORENSIS

Considering the aberrant morphology of the neotenic male of B. salvadorensis , it might be considered a juvenile rather than a sexually mature male. Even Noodt, when labelling the slide containing this specimen, supposed that it was a juvenile, probably because of the two-segmented condition of the exopod of leg 3 and the antennule morphology. However, some indirect as well as direct evidence, derived from comparison of the neotenic male with a copepodid V of B. salvadorensis , strengthens support for an hypothesis of neoteny. First, the neotenic male has a five-segmented urosomite before the telson. In the copepodid V of B. salvadorensis as well as in other species within the family (see, e.g. Glatzel, 1991: 390, fig. 12E on Parastenocaris phyllura Kiefer, 1938 ), parastenocaridid males have only four urosomites before the telson. The presence of a five-segmented urosomite before the telson is a clear adult character, present in the groundpattern of Harpacticoida . Copepodid V males of Parastenocaris phyllura and Parastenocaris hispanica Martínez Arbizu (1997) have a two-segmented leg 3 with two setae on exp-2 and a one-segmented short endopod ( Glatzel, 1991; Martínez Arbizu, 1997). In the case of Parastenocaris hispanica , the moult from copepodid V to adult involves the loss of one seta of exp-2 and the endopod, whereas two setae are retained in Parastenocaris phyllura . An alternative condition can be seen in the copepodid V of B. salvadorensis . In this species, leg 3 has a lamelliform short endopod, whereas its exp-2 has only one strong spine. In the neotenic male, the endopod (arrowed in Fig. 19C ) is lost. Additionally, in the copepodid V of B. salvadorensis there is no trace of the strong curved spinule on the inner margin of the basis of leg 3, and the exp-1 has no inner cushion. In fact, these characters can be observed inside the limb, both appearing after the moult between copepodid V and adult. An additional character supporting our hypothesis concerns the structure of leg 4. In both Parastenocaris phyllura and Parastenocaris hispanica , copepodid V still has an endopod that does not differ significantly from the female endopod, whereas the most apparent sexual dimorphism appears after the moult between copepodid V and adult. The condition present in the copepodid V of B. salvadorensis is somehow modified, already showing a lamelliform triangular morphology. However, it still retains a medial transverse row of spinules as in the female, and the distal hyaline margin present in the adults is absent. Additionally, it does not have the outer serrated margin, although the latter can be seen inside the endopod as a developing adult character. The neotenic male of B. salvadorensis has a leg 4 endopod quite similar to in the one of the typical male, with an outer row of spinules and the distal hyaline margin. It is worth mentioning here that, similar to the copepodid V, the neotenic male also does not have the modified spinules on the anterior margin of the basis of leg 4. Completely developed adults males of Brasilibathynellocaris share the loss of the proximal outer setae of the leg 5 exopod. This character is also present in the neotenic male of B. salvadorensis , and in copepodid V a very reduced seta appears near the insertion of the outer basal seta. Finally, we can mention the presence of a weakly geniculate eightsegmented antennule without the normal development of the fifth segment in the neotenic male of B. salvadorensis . In accordance with Glatzel (1991), male antennules of the copepodid V are sixsegmented (or probably seven-segmented, considering that the third segment illustrated below the proximal aesthetasc-bearing segment was not counted). In B. salvadorensis a seven-segmented antennule occurs in the copepodid V instar.

Figures

Figure 19. Brasilibathynellocaris salvadorensis, male of copepodid V. A, furca. B, antennule. C, leg 3. D, leg 4. E, leg 5. Solid arrows point to structures of the adult developing inside the copepodid; open arrows point to structures of the copepodid that will be reduced or absent in the adult. Scale bars (upper for A–D, lower for E) = 20 Mm.