Juxtastenopus, Goy, 2010

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 : 264-265

Juxtastenopus gen. nov.

Diagnosis. Small stenopodidean shrimp with slender, laterally compressed body. Carapace densely covered with scattered spines arranged in longitudinal rows. Cervical groove distinct, very deep at dorsum of carapace. Rostrum long, compressed, dorsally and ventrally dentate. Antennal spine strong; hepatic spine, supraorbital spine, branchiostegal spine and pterygostomial spine present. Pleon feebly spinose; first 3 pleomeres dorsally with transverse ridges provided with small spinules, last three pleomeres with few oblique rows of small spinules. Telson narrow, lance-shaped with median groove flanked by 2 longitudinal spined carinae; lateral margin with medial spine; posterior margin ending in 2 distinct posterolateral teeth between which, margin somewhat rounded with small median denticle. Eyes well developed with globular, pigmented cornea. Dorsal surface of eyestalk with few spines near base of cornea; submarginal spines partially overlap cornea. Antennular peduncle with strong, acute stylocerite on outer margin; inner margin with broad, subrectangular process and setose scale-like projection distodorsally. Antenna with well developed, narrow scaphocerite with serrate outer margin, 2 dorsal longitudinal carinae. Mandible with fused molar and incisor processes; palp 3- segmented. Maxillule with broad proximal endite, rounded distal endite and simple setose endopod. Maxilla with slender endopod, bilobed basal and coxal endites, scaphognathite slender, well developed. First maxilliped with 3-segmented endopod; basal endite broad, coxal endite feeble, bilobed; exopod well developed; epipod well developed, bilobed; arthrobranchs absent. Second maxilliped with distal segments of endopod distinct; coxa and basis reduced to rounded lobes; propodus with prominent ventral hook proximally; exopod well developed. Third maxilliped with strongly developed, slender endopod; propodus with weak setiferous organ; carpus, merus and ischium spinulate; exopod well developed. First 3 pereiopods slender, chelate. First pereiopods with weakly developed carpo-propodal setiferous organ; pincers of chela long, slender, palm slightly swollen. Third pereiopods larger than first and second, with slender chelae and spinulate meri, carpi, propodi and dactyli. Fourth and fifth pereiopods long, slender; carpus and propodus distinctly segmented; propodus with movable ventral spines, lacking on carpus; dactylus long, uniunguiculate. Pleopods without appendices internae, biramous except first pair; basipodites ventrally with spines. Uropods normal, exopod and endopod laterally serrated; dorsal surfaces each with 2 carinae, 0–1 spinules on exopod, row of 3– 7 spinules on endopod.

Type species. Engystenopus spinulatus Holthuis, 1946 by present designation and monotypy.

Etymology. The genus name is derived from a combination of the Latin word “ juxta ” meaning "close to" and the genus Stenopus Latreille, 1819 , to which the new genus is closely related. The gender is masculine.

Remarks. The family Stenopodidae is characterized by compressed body; elongate, lance-shaped telson ending in two strong spines, sometimes with a third spine in between; endopod of uropod with two longitudinal dorsal ridges; propodus of second maxilliped with cristate ventral margin; third maxilliped with distinct exopod; third pereiopod longest; chela long, slender; chelate appendages with cutting edges bearing series of peg-like teeth separated by chitinous lamellae distally; branchial formula always composed of 19 branchial endites ( Holthuis 1993; Alvarez et al. 2006). Based on these characters, the present new genus clearly falls into those characteristics of the family Stenopodidae .

Systematic position. The new genus is morphologically closely similar to Stenopus , from which it is readily distinguishable by dactyli of fourth and fifth pereiopods being long, slender and uniunguiculate, and lacking ventral carpal movable spines; telson ending in two posterolateral teeth, and median denticle; pleon with transverse spined grooves and dorsal spinules on first to third pleomeres; oblique rows of spines on the last three pleomeres; and anterolateral angle of antennular peduncle lacking spiny scale. Species of Stenopus have biunguiculate dactyli (rarely uniunguiculate) on fourth and fifth pereiopods, and ventral carpal movable spines; telson ending in two posterolateral teeth; pleon with numerous erect spines, curved forward on first three pleomeres; last three pleomeres with straight posteriorly directed spines, pressed against body; anterolateral angle of antennular peduncle with spiny scale.