The ontogeny of the entocytherid ostracod Uncinocythere occidentalis (Kozloff & Whitman, 1954) Hart, 1962 (Crustacea)

The Entocytheridae is a cytheroidean family that is known for its commensal mode of life on other crustaceans. However, due to their small size and large sexual dimorphism in the sizes of the carapace, the ontogeny of the entocytherids is poorly understood. This paper documents the basic body plans and pore systems of the entocytherid Uncinocythere occidentalis (Kozloff & Whitman, 1954) Hart, 1962 through ontogeny and compares them with other podocope groups. U. occidentalis has seven juvenile stages, one less than other cytheroidean groups. The general appearance of the limbs during the ontogeny of U. occidentalis is similar to that of other podocope ostracods, such as Limnocythere inopinata (Cytheroidea) Loxoconcha japonica (Cytheroidea),Eucypris virens (Cypridoidea), and Neonesidea oligodentata (Bairdioidea) with the exception of the maxillula. The adult maxillula of U. occidentalis is reduced to just a palp and third masticatory lobe (endite), and the third masticatory lobe and branchial plate of this appendage form later in the ontogeny compared with other podocope species (i.e., these features show post displacemental ontogenetic development). The number of the pore systems of the earliest juvenile (A-7) of U. occidentalis is 10, and is different from that of the corresponding stage of other cytheroidean groups which have 9. This fact, together with the different mode of development of the maxillula, indicates that the entocytherids are not only highly specialized to their commensal mode of life but that they are also phylogenetically distant from most other cytheroidean families, possibly differentiating from the others during the early evolution of the cytherids.