Order LEPTOSTRACA Claus, 1880

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Order LEPTOSTRACA Claus, 1880

Compiler and date details

P.J.F. Davie

Introduction

This is a small, poorly known group of crustaceans including only three extant families, Nebaliidae Samouelle, 1819, Nebaliopsididae Hessler, 1984, and Paranebaliidae Walker-Smith & Poore, 2001. These families together encompass only seven genera and 38 species. Walker-Smith & Poore (2001) have provided a key to families and genera, and a listing of known species.

There is an extensive fossil record for Leptostraca with more than 50 fossil genera (Glaessner 1969). Schram (1986) considered the Phyllocarida to be a separate lineage from the Malacostraca, a view strongly contested by Dahl (1987). Recent work by Spears & Abele (1999), using 18S rDNA, provided very strong evidence that phyllocarids are true malacostracans, albeit a lineage that diverged very early.

Diagnosis

Malacostracans with separate head, thorax and abdomen; head consisting of five somites, thorax with eight, and abdomen with seven excluding telson. Carapace bivalved, laterally compressed, with adductor muscle, but lacking hinge or hinge line; enclosing thorax but not cephalon; rostrum articulated. Eyes stalked, compound (not functional in some genera), ocular scales sometimes present. Antennules usually biramous, exopod scale or plate-like, occasionally markedly reduced or absent; antennae uniramous, well developed, may be sexually dimorphic. Mandibles with palp, molar and incisor processes usually well developed, occasionally reduced; maxillulae with paired endites and flagelliform palp, latter occasionally reduced; maxillae protopod usually with four endites, endopod and exopod usually well developed, sometimes endopod reduced and exopod vestigial. Maxillipeds absent. Eight pairs of biramous, foliaceous, thoracic appendages (thoracopods), usually well developed, but sometimes reduced, with or without epipods. Six pairs of abdominal appendages, first four pairs large and biramous, last two pairs uniramous and reduced; telson bearing pair of broad, oval, setose caudal rami. Gonopores on coxae of sixth thoracopods of female, and on eighth coxae of males. (After McLaughlin 1980; Schram 1986).