Hexapleomera robusta (Moore, 1894) sensu Sieg 1980

Hexapleomera robusta (Moore, 1894) sensu Sieg, 1980

Tanais robustus Moore, 1894: 90 –93, pl. 5.?

Hexapleomera robusta Sieg, 1980: 122 –129, figs 33–34, 39. (Literature and synonymy)

Diagnosis: Adult uropod with four segments; pleopod endopod with one subdistal inner marginal seta, pleopod 3 basis without inner seta; coxa of pereopod 1 without apophysis; maxillule palp with eight distal setae; maxilliped basis with two unequal distal setae, coxa with two setae, endite with no distal spines; cheliped fixed finger with five ventral setae; dactylus of male cheliped with spinulation along cutting edge; fixed finger with large triangular proximal tooth-like apophysis on cutting edge (?).

Remarks: While the number of aesthetascs on the male antennule is relatively consistent across al the taxa discussed herein, Sieg (1980) describes eight on the female antennule, significantly more than any other of these taxa; this may also be a species-diagnostic character

The original description and figuring by Moore (1894) was limited, while Richardson (1900) merely repeated the text and figures of Moore (1894). Moore’s type-material is lost (Sieg 1980). Sieg (1980) gave a more complete description and figuring based on material either from Brazil or from the Galapagos (he did not specify). The limited features shown by Moore (1984), notably the male cheliped morphology (with the notable exception of the tooth-like apophysis on the fixed finger), the number of uropod segments and the number of maxillule palp setae, agree with their equivalents in Sieg’s description but, until material from off northeastern North America is analyzed in detail, we cannot be sure that the remaining features are consistent. Until then, this taxon is defined as that described by Sieg, although it is unlikely that the same species occurs in Atlantic Brazil and Pacific Galapagos. Sieg (1980) examined type-material of both Tanais testudinicola and Hexapleomera schmidti and, while finding the two taxa indistinguishable, stated “Unfortunately it was not possible to prove the actual identity of these two species with robustus [sensu stricto], because the type material of robustus is no longer available”. He could, however, find no distinction of these type-specimens from his H. robusta. Dollfus’ (1898) description of T. testudinicola (also collected from the carapace of Caretta caretta) interestingly does highlight the proximal tooth-like apophysis on the fixed finger of the male chela, while Dudich (1931) states “The most striking feature of the H. Schmidti is the strong tooth on the inner corner of the immovable finger of the male chela. H. robusta shows at this point only a slight elevation, but in H. testudinicola it is present as a tooth, and it reaches an excessive development in H. schmidti. The three species form a morphological series, so to speak.” On this feature these taxa are only similar to H. robusta sensu Sieg, and on this feature alone they may all be distinct from H. robusta sensu stricto.

Mediterranean Hexapleomera commensal with turtles thus all appear to be H. robusta sensu Sieg, the distribution of which also includes the Northwest Atlantic, possibly the Caribbean (Heard et al., 2004), and probably Atlantic Brazil (but probably not the Galapagos). Whether the material recorded as commensal with manatees by Morales-Vela et al. (2008) is actually H. robusta must await re-examination in the light of the present study—i.e. without the presumption of a single cosmopolitan taxon.