Infraorder Stenopodidea Claus, 18721)
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CHAPTER 65 INFRAORDER STENOPODIDEA CLAUS, 18721) BY JOSEPH W. GOY Contents. – Introduction – General – Diagnosis – Number of species and size. External morphol- ogy – Cephalothorax – Pleomeres – Appendages. Internal morphology – Digestive system – Ner- vous system – Reproductive system. Embryology and larval development. Ecology and ethology – Symbiosis. Fossil record. Systematics. Appendix: checklist of species. Bibliography. INTRODUCTION General The infraorder Stenopodidea can be divided into three distinct ecological groups: littoral/sublittoral forms, which frequent rocky bottoms or coral reefs; deepwater forms on muddy substrates or mostly as commensals in hexactinellid sponges; and stygobitic in anchialine caves on an island. This chapter summarizes our present knowledge of the crustacean decapod infraorder Stenopodidea. This infraorder is rather small in numbers of species compared to the remaining sub- and infraorders of decapod crustaceans but presents some unique characteristics that makes it hard to place in the taxonomic hierarchy of Decapoda. One of its members, Stenopus hispidus has become a widely recognized symbol of tropical marine biodiversity. The main characteristics of the infraorder are presented and a complete examination of the external anatomy is given. The few studies of the internal anatomy, embryology, larval development, reproduction, and behavior are listed and discussed. Also, the results of recent ecological, genetic, taxonomic, paleontological, and phylogenetic studies are reviewed. Stenopodidea represent a unique group of shrimp-like crustaceans that bear an interest- ing blend of “natant” and “reptant” characters that make them difficult to exactly place in 1) Manuscript concluded April 2009. © Koninklijke Brill NV, Leiden, 2010 Crustacea 9A (65): 215-265 216 J. W. GOY the family tree of Decapoda. However, they are a relatively homogenous group found in a variety of both shallow warm water and deep-sea benthic marine habitats. Diagnosis Body shrimp-like. Carapace more or less cylindrical, fused to thorax; eyes stalked, compound; antennules biramous; antennae with 5-segmented peduncle and scaphocerite. Epistome consisting of narrow anterior portion between antennae and posterior portion usually heavily armed with spines on perimeter of a circular margin to which the labrum is attached. Pleura of anterior pleomeres usually not expanded, when expanded, enlarged so that first overlaps second; only 3 posterior somites hinged together by definite locking joints; males have strong ventral medial spines on pleomeres 1-5, lacking in females. Mandibles with incisor and molar processes fused, but separated by groove; palp incurved, usually 3-segmented. Maxillule with slender, undivided endopodal palp; maxilla biramous, with 2 bilobed endites. First maxilliped with endopod usually 2- segmented, without crista dentata; scaphognathite long, narrow, with numerous plumose marginal setae. Second maxilliped 7-segmented; ischium and coxa fused; dactylus suboval; propodus at inner margin, near the base, often with a hooked spine. Third maxilliped long, pediform, with 7 segments. Pereiopods uniramous; first 3 pairs chelate, third enlarged, rarely second longer than third. First pleopods uniramous in both sexes; all pleopods lacking petasma, appendices internae, and appendices masculinae. Uropods biramous, lacking diaeresis; telson together with broad uropods forming tail fan. Gills trichobranciate; gill axis bearing numerous simple filaments arranged in irregular row; rarely gills simple, completely lacking lamellae or filaments. Female gonopores on coxae of third pereiopods; on fifth in males; eggs attached to ovipositing setae on female pleopods, hatch as zoeae (or decapodids) with four pairs of natatory appendages; fifth pereiopods appear later in development; pleurobranchs appear before arthrobranchs in development. The combination of uniramous first pleopods, reduced first pleomere pleuron, posterior three pleomeres with locking joints, first three pereiopods chelate with the third the largest, no pereiopodal exopods, and trichobranch gills, are reliable characters to distinguish stenopodideans from other decapod crustaceans. Number of species and size Up to 1986, Stenopodidea consisted of a single family, Stenopodidae Claus, 1872 with about 40 described species, when Schram (1986) separated the mostly deep-water glass sponge commensals into Spongicolidae. In 2006, Alvarez et al. erected a new family, Macromaxillocarididae, for the monotypic cave shrimp, Macromaxillocaris bahamaensis. The three families currently contain 70 species in 12 genera. Members of the genus Stenopus have the largest recorded specimens: Stenopus hispidus (Olivier, 1811) at 80 mm total length, Stenopus spinosus Risso, 1826 at 77 mm, and Stenopus pyrsonotus Goy & Devaney, 1980 at 74.3 mm; the smallest stenopodids are Stenopus earlei Goy & Randall,.