Engystenopus Alcock & Anderson, 1894

Goy, Joseph W., 2010, A review of the genus Engystenopus (Crustacea: Decapoda: Stenopodidea) Juxtastenopus, gen. nov., a new combination for E. spinulatus Holthuis, 1946, and transfer of E. palmipes Alcock & Anderson, 1894 to the family Spongicolidae Schram, 1986 *, Zootaxa 2372, pp. 263-277 : 273-274

Engystenopus Alcock & Anderson, 1894

Engystenopus Alcock & Anderson, 1894: 141 , 149. — Alcock 1901: 143. — A. Milne-Edwards & Bouvier 1909: 264. — Holthuis 1946: 5, 43; 1955: 143,144. — Burukovsky 1974: 91. — de Saint Laurent & Cleva 1981: 161. — Burukovsky 1983: 128, 131. — Holthuis 1993: 313. — Poore et al. 2008: 12.

Diagnosis. Small stenopodidean shrimp with cephalothorax slightly depressed dorsoventrally. Rostrum laterally compressed with dorsal and ventral teeth, laterally with few spinules. Carapace and dorsal pleon smooth, polished; only large supraorbital spines, few small pterygostomian spines on carapace. Cervical groove distinct, unarmed. Pleon smooth, somewhat depressed dorsoventrally, rounded dorsally; posterior border of fourth and fifth pleura of female with denticles, narrower, all finely denticulate in males; sternites smooth in female, armed with median spine in male. Telson subtriangular to lance-shaped, strong spine near middle of lateral border, posterior margin with 3 teeth; two dorsal longitudinal carinae with 4 or 5 spines. Eye well developed, with small cornea, reduced pigmentation; ophthalmic peduncle smooth. Antennular peduncle with 3 short segments, strong stylocerite and anterodorsal lamellar projection on first, few spinules on second. Antennal basicerite with strong ventromesial spine, second segment with ventral oblique spinulose crest, few spinules at outer external angle; scaphocerite subsemicircular, lateral margin slightly concave, serrate; dorsal surface with 2 longitudinal carinae. Mandible with fused molar and incisor processes; palp 3-segmented. Maxillule with broad coxal endite, rounded basal endite, simple endopod. Maxilla with slender endopod, bilobed basal and coxal endites, scaphognathite narrow, well developed. First maxilliped with 3-segmented endopod, distal segment short, less than one third as wide as second segment; basal endite broad, coxal endite bilobed; exopod well developed; epipod large, bilobed. Second maxilliped endopod with 5 segments; coxa and basis with small rounded tubercle laterally; ischium distinctly separated from basis; exopod well developed; one arthrobranch, podobranch, and epipod present. Third maxilliped strongly developed, with slender endopod; propodus with rudimentary setiferous organ; ischium with row of fine spinules on mesial border; merus with row of spinules ventrally; strong, anteromesial projection on carpus; exopod well developed; pleurobranch, 2 arthrobranchs, small epipod present. First 3 pereiopods chelate; first 2 very slender, all segments glabrous, cutting edges of chelae lacking teeth. First pereiopods with weak carpopropodal setiferous organ. Third pereiopod largest thoracic appendage; outer distal edge of ischium with spine; outer and inner edges of merus and carpus strongly spinate, carpus distally inflated; palm very large, broad, compressed, distally spinulate; dactylus thin, compressed, proximally serrate; cutting edges of chelae consisting of scalloped chitinous ridge. Fourth and fifth pereiopods long, slender; carpus and propodus indistinctly segmented; propodus with movable ventral spines; dactylus long, uniunguiculate. Pleopods without appendices internae, biramous except first uniramous pair; basipodites glabrous. Uropods as long as telson; exopod quadrangular, outer margin serrate, dorsal surface with 2 longitudinal carinae; endopod elongate triangular, outer margin smooth; dorsal surface with 2 carinae, median one strong, other at inner half starting from basal part of inner margin curving to median one and distally runs parallel with it.

Type species Engystenopus palmipes Alcock & Anderson, 1894 by monotypy.

Remarks. The family Spongicolidae is characterized by depressed body; long or short telson, but broad, triangular, subtriangular, or subquadrangular, and ending in three to five subequal spines. Uropodal endopod usually with single longitudinal dorsal ridge. Propodus of second maxilliped with rounded, unarmed ventral margin. Third maxilliped with exopod well developed, rudimentary or absent. Second or third pereiopod longest; propodus of third pereiopod broad, if long, robust not slender. Chelate appendages with chitinous ridges distally on cutting edges, rarely with few small sharp teeth. Branchial formula always composed of 12– 19 branchial endites ( Holthuis 1993; Alvarez et al. 2006). The genus Engystenopus shares these characteristics and is transferred from the family Stenopodidae to the Spongicolidae .

Systematic position. Engystenopus is morphologically closely similar to Spongicola with respect to spination on the carapace, smooth pleomeres, spination of thoracic sternites, and overall shape and spination of the fingers of the 3rd pereiopod. Engystenopus is readily distinguishable from Spongicola by the welldeveloped exopod of the third maxilliped; dactyli of the fourth and fifth pereiopods being long, slender and uniunguiculate; uropodal endopod dorsal surface bearing 2 carinae, and the elongate merus and carpus of the third pereiopod.