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Cephalocarid and mystacocarid crustaceans are not closely related. Both groups contain relatively few species, all of which are very small and somewhat vermiform, and they are treated together here only for that reason. The crustacean class Cephalocarida includes 5 genera and 10 species (Hessler and Elofsson 1996, Hessler and Wakabara 2000). Most reports are based on very few specimens (see Martin, Cadien, and Zimmerman 2002). For example, the original description of the genus Hutchinsoniella was based on only 8 specimens from Long Island Sound, New York (Sanders 1955); the genus Sandersiella was originally erected on the basis of only one specimen from Japan (Shiino 1965); the genusChiltoniella was based on 2 specimens from New Zealand (Knox and Fenwick 1977), and the genus Lightiella was based on 7 specimens from San Francisco Bay (Jones 1961). Lightiella moniotae was described for a single individual from New Caledonia (Cals and Delamare-Deboutteville 1970); Sandersiella calmani for 2 specimens from Peru (Hessler and Sanders 1973); and Sandersiella bathyalis for 2 specimens from the deep ocean off southwest Africa (Hessler and Sanders 1973). The single eastern Caribbean record (Barbados) of a cephalocarid also was based on 2 specimens (Gooding 1963), although Gooding also discussed 2 specimens from Puerto Rico in that account and more have been discovered since then (see Martin, Cadien, and Zimmerman 2002). Cephalocarids are of such interest morphologically and phylogenetically, and are found so infrequently, that their presence anywhere is noteworthy. Hessler and Sanders (1973: 195) noted that “the single common feature of all cephalocarid habitats is the flocculent nature of the superficial sediment to which these animals are intimately bound by their basic mode of life.” Schiemer and Ott (2001) recently shed additional light on the microhabitat of Lightiella incisa, documenting its occurrence only below the redox potential discontinuity layer and with a maximum density at 12–15 cm below the surface at a shallow sand bar on Carrie Bow Cay, Belize. Schiemer and Ott (2001) suggested that L. incisa inhabits “oxygen-rich microzones” in deeper sediments (see also Ott and Novak 1989). This was also suggested by 821 44 Cephalocarida and Mystacocarida (Crustacea) of the Gulf of Mexico Joel W. Martin  Cephalocarida. After Martin, Cadien, and Zimmerman 2002. 822 ~ Cephalocarida and Mystacocarida (Crustacea) Mystacocarids (only distantly related to cephalocarids) are even smaller crustaceans than are cephalocarids. Currently there are 13 described species in 2 genera: Dereocheilocaris (with 8 known species) and Ctenocheilocaris (with 5 species) (Boxshall and Defaye 1996, Olesen 2001). All species of mystacocarids described to date live interstitially among sand grains. There has been only one report of a mystacocarid from the Gulf of Mexico: Friauf and Bennett (1974) described Derocheilocaris hessleri from Ship and Horn Islands, Mississippi (see checklist). However, both D. typica Pennak and Zinn, 1943, and D. ingens Hessler, 1969, have been found along the east coast of the United States (see map, fig. 154, in Boxshall and Defaye 1996), and it is likely that more records will be found from the Gulf with additional collecting efforts aimed at the right habitats and using the specialized collecting techniques needed for these crustaceans. Other species of that genus are known from temperate Africa (D. katesae Noodt, 1954; D. delamarei Hessler, 1972; and D. angolensis Hessler, 1972) and the far eastern Mediterranean (D. tehiyae Masry and Por, 1970), with the relatively more widespread D. remanei Delamare-Deboutteville and Chappuis, 1951, known from the Mediterranean and tropical west Africa. Records of the genus Ctenocheilocaris exist only for western Australia (C. enochra Bartsch, 1993) and temperate South America (C. galvarini Dahl, 1952); C. claudiae Renaud-Mornant, 1976; C. armata Renaud-Mornant, 1978; and C. minor Renaud-Mornant, 1978). The absence of the group in such broad geographical regions as the Indo-West Pacific, northeastern South America, western North America, and eastern Australia almost certainly reflects a lack of intense sampling for this taxon. Abbreviations Abbreviations used in the checklist are: ben = benthic; bns = bay and nearshore; bsl = beach and shoreline; end = endemic to Gulf of Mexico; inf = infaunal; ins = interstitial ; ne = northeast. Acknowledgments This work was supported in part by the U.S. National Science Foundation via grants DEB 9972100 (Biotic Surveys and Inventories), DEB 9978193 (Systematic Biology PEET initiative), DEB 0120635 (Genomes and EnvironDe Troch, Friauf, and Bennett (2000) in their study of L. incisa from the Yucatan Peninsula. De Troch, Fiauf, and Bennett (2000) concluded that L. incisa was “an endobenthic species occupying anoxic sediments oxygenated by bioturbation (e.g., Polychaeta) rather than being an animal living...

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