The female reproductive organ in podocopid ostracods is homologous to five appendages: histological evidence from Liocypris grandis (Crustacea, Ostracoda)

Abstract

The giant ostracod, Liocypris grandis, found in South African temporary pools, has five pairs of additional appendage-like structures, seemingly associated with the Female Reproductive Organ (FRO). Original investigations of these structures by light and scanning electron microscopy could not unequivocally determine whether or not these structures are homologous to genuine appendages and if so, to how many. The present paper investigates morphology and attachment of these structures by frontal and transversal micro-sectioning (thickness=1 μm) of the caudal soft parts of mature females of L. grandis. It is found that all five appendages (R1–R5) have one individual attachment point where they enter into the FRO. Also R3(I) and R3(II) have a single attachment only, these two parts thus represent one single appendage. Whereas R1–R4 have clear lateral insertions, R5 is caudally positioned. The fusion of this latter appendage with the FRO occurs internally, at the posterior edge of the bulge of the FRO and is not externally visible. It is herewith thus accepted that R1–R5 are genuinely endogenous structures (and not, for example, exogenous parasites), that the five structures are homologous to five appendages, and not for example to parts of biramous appendages. It follows from this that the female reproductive organ is homologous to at least five, not to one segment. This would bring the number of (original) thoracic segments in podocopid ostracods to at least 8. An additional pair of triangular structures, inserted in between the two FRO is here described as structures ‘X’. Their homology and function remain unknown.