Cheramus ohuranus, Komai, Tomoyuki, Maenosono, Tadafumi & Fujita, Yoshihisa, 2014

Komai, Tomoyuki, Maenosono, Tadafumi & Fujita, Yoshihisa, 2014, Two new species of ghost shrimp assigned to the genus Cheramus Spence Bate, 1888 (Crustacea: Decapoda: Axiidea: Callianassidae) from the Ryukyu Islands, Japan, Zootaxa 3895 (4), pp. 503-524 : 513-521

Cheramus ohuranus n. sp.

New Japanese name: Ohura-sunamoguri ( Figs. 9–15 )

Material examined. Holotype: ovigerous female (cl 4.6 mm), Ohura Bay, Okinawa Island, stn D5, 3 m, 20 June 2009, SCUBA diving with yabby pump, CBM-ZC 12568.

Paratypes: 1 female (cl 5.7 mm), same locality, 18 m, 17 November 2013, SCUBA diving with yabby pump, coll. Y. Fujita, RUMF-ZC 02657; 1 female (cl 5.5 mm), same locality, 5–10 m, 20 October 2013, SCUBA diving with yabby pump, coll. Y. Fujita, RUMF-ZC 0 2730.

Description. Rostrum ( Figs. 10 A–C; 12A) flattened dorsoventrally, spiniform, directed forward, reaching distal margins of eyestalks. Carapace ( Figs. 9 ; 10A–C) about 0.3 length of pleon; orbital margins sloping; anterolateral projections triangular with blunt tip; excavation inferior to anterolateral projections deep, V-shaped; cervical groove deep, across 0.8 length of carapace, extending to postrostral region but not reaching to midline, thus dorsal oval incomplete; linea thalassinica extending nearly to posterolateral margin of carapace.

Thoracic shield (plate on thoracic sternite 7) ( Fig. 12 B) subpentagonal with slightly produced anterior margin; anterolateral margins concave; ventral surface with shallow median groove over entire length.

Length ratio of first pleomere to telson measured along midline 1.0: 1.3: 1.1: 0.9: 1.0: 1.2: 1.0 ( Fig. 10 D–G). First pleomere ( Figs. 9 ; 10D) narrowing anteriorly in dorsal view; pleuron with poorly defined ventral margin. Second pleomere ( Figs. 9 ; 10D) nearly as long as wide; posterior margin of pleuron slightly expanded, bearing tuft of long setae directed laterally adjacent to posterolateral margin. Third to fifth pleura ( Figs. 9 ; 10E, F) each with patch of soft plumose setae and tuft or short longitudinal row of short setae; posterolateral margins slightly expanded. Sixth pleomere ( Figs. 9 ; 10F) approximately as long as wide, subquadrate, slightly narrowing posteriorly, lacking ventrolateral projection; lateral margin with shallow notch at about posterior 0.3.

Telson ( Figs. 10 G; 11A) trapezoidal, as wide as long, slightly narrowing posteriorly, broadest at anterior 0.3. Dorsal surface slightly convex transversely, with 3 or 4 small movable spines (noticeably becoming shorter laterally) arranged in transverse row on either side of median tuft of long setae at about anterior 0.3, and lateral pair of 2 closely set movable spinules at posterior 0.3. Lateral margins each with 1 minute spinule adjacent to posterolateral angle. Posterior margin ( Fig. 11 B) faintly concave medially, with 2 widely separated short rows of short spiniform setae on either side of minute median tooth; prominent tuft of long setae between short rows of spinules or spiniform setae; setae fringing posterior margin plumose, longest laterally, distinctly longer than spinules or spiniform setae.

Eyestalks ( Figs. 10 C; 12A) flattened distally, tapering to bluntly pointed distal projection, contiguous, slightly reaching distal margin of first segment of antennular peduncle; dorsal surface separated from rostrum, sloping anteriorly; lateral margin sinuous. Cornea subterminal and lateral, darkly pigmented, its width slightly less than half of greatest width of eyestalk.

Antennular peduncle ( Fig. 10 B, C) subequal in length to antennal peduncle; first segment short, hardly visible in dorsal and lateral views; second segment subequal in length to first segment; third segment about 1.8 times longer than second segment; second and third segments with longitudinal row of numerous long setae ventrally; antennular flagella subequal in length to peduncle; dorsal flagellum thicker than ventral flagellum.

Antennal peduncle ( Fig. 10 B, C) with distal two segments subcylindrical; fourth segment about 1.3 times longer than fifth segment; scaphocerite ( Fig. 12 C) tiny, subovate, terminating in sharp spine strongly curved mesially.

Small process on either side of epistome bearing tuft of long setae ( Fig. 10 C).

First maxilliped ( Fig. 12 D) with exopod moderately broad. Second maxilliped ( Fig. 12 E) with exopod slightly overreaching midlength of ischium-merus fused segment. Third maxilliped ( Fig. 12 F, G) without exopod; ischiummerus suboval, operculiform, 1.3 times longer than wide; articulation between ischium and merus slightly oblique; ischium 1.3 times wider than long, mesial face with crista dentata consisting of row of 13 small spines (these spines moderately spaced); merus about 0.5 times as long as ischium measured along dorsal margin, about 1.5 times wider than long, distolateral margin slightly produced, reaching beyond dorsodistal margin, broadly rounded, unarmed; distomesial margin also unarmed; carpus cup-shaped; propodus narrowing distally, 1.9 times longer than high, slightly longer than carpus; dactylus moderately slender, digitiform, about 0.7 times as long as propodus.

First pereopods (chelipeds) slightly unequal and slightly dissimilar ( Fig. 13 A, C). Major (left) cheliped ( Fig. 13 A, B) stout, carpus-chela combined length about 1.1 times longer than carapace. Ischium becoming slightly wider distally in general contour, dorsal margin sinuous, unarmed; lateral surface gently convex; ventral margin with row of 4–6 small spines. Merus subequal in length to ischium; dorsal margin convex, unarmed; lateral surface forming shallow concavity ventrally to accommodate proximoventral margin of carpus; mesial surface generally flat; ventral margin convex, faintly denticulate, with small spine located at proximal 0.2. Carpus subsemicircular, about 1.2 times wider than long; dorsal and proximoventral margins sharply carinate, smooth, proximoventral margin broadly rounded; lateral surface smooth, convex; mesial surface nearly flat. Palm square, 1.1 times wider than long; dorsal margin sharply carinate, with row of short setae; lateral surface smooth, convex, distolateral margin at base of dactylus forming broadly rounded convexity; mesial surface slightly convex generally, but with shallow depression at base of fixed finger; ventral margin sharply carinate, with row of short to moderately long setae extending onto fixed finger. Fixed finger about 0.6 times as long as palm, almost straight, terminating in acute tip; cutting edge with 1 differentiated tooth arising distal to midlength; lateral surface convex, with 2 rows of tufts of long setae adjacent to cutting edge; mesial surface depressed along cutting edge, with tufts of setae adjacent to cutting edge. Dactylus subequal in length to palm, slightly hooked distally, crossing fixed finger distal to midlength of latter, terminating in acute tip; dorsal surface rounded, with numerous stiff setae; lateral surface with rows of tufts of long setae along dorsal margin and cutting edge; cutting edge with low, obtuse tooth at midlength; mesial surface convex, with tufts of setae adjacent to cutting edge.

Minor cheliped ( Fig. 13 C, D) stout, carpus-chela combined length equal to carapace length. Ischium with dorsal margin sinuous, unarmed; ventral margin with row of 4 small spines or spinules. Merus subequal in length to ischium; dorsal margin convex, unarmed; ventral margin slightly convex, with small spine located at proximal 0.2. Carpus subtrapezoidal, subequal in length to merus, about 1.2 times wider than long; dorsal margin straight, sharply carinate; proximoventral margin arcuate, sharply carinate. Palm square, 1.3 times wider than long; dorsal margin nearly straight, sharply carinate, with sparse setae; ventral margin sharply carinate, with row of short setae extending onto fixed finger; lateral and mesial surfaces slightly convex, smooth, former with distinct concavity at base of fixed finger; distolateral margin forming convexity. Fixed finger 1.1 times longer than palm, slightly curving, terminating in acute tip; cutting edge minutely denticulate; lateral surface with row of tufts of setae adjacent to cutting edge, extending onto distolateral margin of palm; mesial surface depressed along cutting edge, with row of numerous setae adjacent to cutting edge, extending onto distomesial margin of palm. Dactylus 1.4 times longer than palm, crossing fixed finger distal to midlength of latter; dorsal margin rounded, with covered with numerous setae; lateral surface with rows of tufts of setae adjacent to dorsal margin and cutting edge; cutting edge with faint convexity at midlength, but without conspicuous spines or teeth.

Second pereopod ( Fig. 14 A) with ischium short, ventrodistal angle produced in small spine. Merus with slightly sinuous ventral margin; dorsal margin slightly convex. Carpus cup-shaped, about 2.0 times longer than wide. Chela subtriangular; palm much wider than long; cutting edges of fingers bordered by thin corneous edge; dactylus about 2.0 times longer than palm.

Third pereopod ( Fig. 14 B, C) with carpus cup-shaped, about 2.0 times longer than wide. Propodus suboval; proximoventral angle (heel) not markedly produced; lateral face bluntly carinate medially; ventral margin convex, faintly undulate, with slender spinule subdistally. Dactylus nearly straight with convex dorsal margin, slightly shorter than propodus.

Fourth pereopod ( Fig. 14 D, E) with coxa somewhat flattened ventrally, immovable ( Fig. 12 B). Merus longer than ischium. Carpus slightly widened distally. Propodus strongly compressed laterally, slightly longer than carpus, with dense grooming setae on distal half of ventral margin. Dactylus nearly straight with convex dorsal margin, about half-length of propodus.

Fifth pereopod ( Fig. 14 F) moderately slender. Chela subequal in length to carpus, widened distally, fixed finger deflexed; dactylus about 0.3 times as long as palm.

Female first pleopod ( Figs. 9 ; 12H, I) consisting of protopod and single ramus; protopod dorsally curved in lateral view, ramus subequal in length to protopod, slightly curved ventrally in lateral view, with shallow convexity at midlength on mesial margin. Female second pleopod ( Figs. 9 ; 12J) biramous; endopod divided in 2 subequal articles, without appendix interna; exopod not divided, gently curved mesially, slightly longer than endopod. Third to fifth pleopods ( Fig. 12 K) biramous, moderately broad; each appendix interna ( Fig. 12 L) moderately stout, not tapering distally, about twice longer than basal width, bearing coupling hooks on obliquely truncate terminal margin.

Uropod ( Figs. 10 G; 11C) slightly overreaching posterior margin of telson. Endopod subovate, about 1.3 times longer than wide and subequal in length to telson; outer margin nearly straight, inner margin broadly convex; distal margin with cluster of 4 movable spinules; fringe of thin setae on posterior to inner margin; dorsal surface with row of 4 movable spinules adjacent to outer margin and 4 similar spinules along midline. Exopod subsemicircular in general outline, about 1.1 times longer than wide and 1.2 times longer than telson, exceeding beyond endopod by 0.2 length; lateral margin faintly sinuous, distal margin roundly truncate, inner margin rounded; dorsal surface bluntly ridged along midline, with 1 minute movable spinule laterally at midlength; dorsal plate well delineated, with distal row of spiniform setae and stiff setae distinctly separated from setal row of posterior margin; setal row on posterior to inner margin consisting of stout to thin setae.

Coloration in life. Body generally translucent, with tint of yellow; female gonad (extending from cephalothorax to anterior part of fifth abdominal somite) and eggs red. Cornea black. Chelipeds with ischia and meri white, carpi and chelae pale pink. Pereopods and pleopods white. Uropod with tint of yellow on endopod and exopod. See Fig. 15 .

Distribution. Presently known only from Ohura Bay, Okinawa Island, shallow subtidal to 18 m. Etymology. Named after the type locality, Ohura Bay, Okinawa Island.

Figures

FIGURE 9. Cheramus ohuranus n. sp., holotype, ovigerous female (cl 4.6 mm), CBM-ZC 12568, habitus, lateral view. Scale bar: 2 mm.

FIGURE 10. Cheramus ohuranus n. sp., holotype, ovigerous female (cl 4.6 mm), CBM-ZC 12568. A, carapace, lateral view; B, carapace and cephalic appendages, dorsal view; C, anterior part of carapace and cephalic appendages, lateral view; D, first and second pleomeres, dorsal view; E, third and fourth pleomeres, dorsal view; F, fifth and sixth pleomeres, dorsal view; G, telson and left uropod, dorsal view (setae on uropod omitted). Scale bars: 2 mm for B, D – G; 1 mm for A, C.

FIGURE 11. Cheramus ohuranus n. sp., holotype, ovigerous female (cl 4.6 mm), CBM-ZC 12568. A, telson, dorsal view (setae on posterior margin omitted); B, posterior margin of telson, dorsal view (setae on left half shown, long submarginal setae omitted); C, left uropod, dorsal view (perpendicular; most marginal setae omitted). Scale bars: 1 mm for A, C; 0.5 mm for B.

FIGURE 12. Cheramus ohuranus n. sp., holotype, ovigerous female (cl 4.6 mm), CBM-ZC 12568. A, rostrum and eyes, dorsal view; B, shield on seventh thoracic sternite and coxa of right fourth pereopod; C, left scaphocerite, dorsal view; D, left first maxilliped, outer view (setae omitted); E, left second maxilliped, inner view (setae omitted); F, left third maxilliped, lateral view; G, same, mesial view (setae omitted); H, left first pleopod, lateral view; I, same, endopod, ventral view (setae omitted); J, left second pleopod, dorsal view (setae omitted); K, right third pleopod, dorsal view; L, same, appendix interna, ventral view. Scale bars: 1 mm for A, D – G, K: 0.5 mm for B, H – J, L; 0.25 mm for C.

FIGURE 13. Cheramus ohuranus n. sp., holotype, ovigerous female (cl 4.6 mm), CBM-ZC 12568. A, major (left) cheliped, lateral view; B, same, carpus and chela, mesial view; C, minor (right) cheliped, lateral view; D, same, carpus and chela, mesial view. Scale bar: 1 mm.

FIGURE 14. Cheramus ohuranus n. sp., holotype, ovigerous female (cl 4.6 mm), CBM-ZC 12568. A, left second pereopod, lateral view; B, left third pereopod, lateral view; C, same, propodus and dactylus, mesial view; D, left fourth pereopod, lateral view; E, same, propodus and dactylus, mesial view (setae partially omitted); F, right fifth pereopod, lateral view. Scale bars: 1 mm for A, B, D – F; 0.5 mm for C.

FIGURE 15. Cheramus ohuranus n. sp., holotype, ovigerous female (cl 4.6 mm), CBM-ZC 12568. showing coloration in life. A, entire animal, dorsal view; B, same, lateral view.