Suborder PLEOCYEMATA Burkenroad, 1963

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Introduction

This group contains the greatest diversity of forms, and includes seven infraorders: Anomura (hermit-crabs, squat lobsters, mole-crabs, stone-crabs, porcelain-crabs and allies), Astacidea (marine and freshwater clawed lobsters, scampi, etc.), Brachyura (crabs), Caridea (shrimps), Palinura (true lobsters), Stenopodidea (cleaner shrimp), and Thalassinidea (burrowing lobsters). An older systematic approach was to divide pleocyemates into two groups, those that walk on the bottom (Reptantia), and those that swim (Natantia). This is a simplification of the evolutionary history of the Pleocyemata, but it is still commonplace to refer to natant and reptant decapods.

Diagnosis

Carapace variable in shape; fused or not fused to epistome. Eyes stalked, compound; generally well developed but occasionally reduced or absent. Antennules with peduncle 3-segmented; biramous (occasionally triramous), but flagella may be reduced or vestigial; stylocerite present or absent. Antennal peduncles with one to six segments; exopod present, reduced to acicle, or absent; flagellum variable in length, sometimes absent; with or without scaphocerite. Mandibles with or without palp; molar and incisor processes usually not distinct. Maxillulae usually with endopodal palp. Maxillae biramous; usually with two bilobed endites. Maxillipeds with flagella usually present, but may be reduced or absent; third maxilliped with ischium and merus pediform or operculate. Endopod of first maxillipeds with two or fewer segments; with or without crista dentata. Pereiopods with first pair usually chelate, subsequent pairs variously chelate, subchelate or simple; one pair often forming more robust chelipeds. Abdomen with pleopods well developed, reduced, or present only on one side; uni- or biramous; both sexes may have copulatory structures; male first and/or second pairs of pleopods may be developed as gonopods; otherwise male first pleopods often with appendix masculina, with or without appendix interna; telson often forming tailfan with uropods; uropods present, reduced, modified, or absent; telson occasionally reduced or absent. Segmentation: head with 5 + 3 thoracic (maxillipeds); thorax with five; abdomen with six or fewer, excluding telson (some frequently coalesced). Gills phyllobranchiate or trichobranchiate (without secondary rami of branchiae). Sexes separate; female with or without a thelycum; gonopores on coxae or sternite of third pereiopods of female, on fifth of male; eggs attached to pleopods of female, female sometimes with abdominal brood pouch; eggs hatch as zoea; protandry and protogyny may sometimes occur.

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