Cheramus spinicauda, 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 : 505-512

Cheramus spinicauda n. sp.

New Japanese name: Togeo-sunamoguri ( Figs. 1–8 )

Material examined. Holotype. Ohmine, Naha, Okinawa Island, 0–1 m, sand flat near seagrass bed, 11 November 2011, yabby pump, coll. T. Maenosono, female (cl 7.1 mm), CBM-ZC 12561.

Paratypes. Okinawa Island: Ohura Bay, Nago, subtidal, soft sediments, 24 June 2009, yabby pump, coll. Y. Fujita et al., 1 female (cl 5.4 mm), RUMF-ZC-02654; same locality, 5–20 m, 20 October 2013, SCUBA diving with yabby pump, coll. Y. Fujita, 1 female (cl 6.2 mm), RUMF-ZC-02655. Ohmine, Naha, 0–1 m, sand flat near grass beds, 14 October 2011, coll. T. Maenosono, 2 females (cl 6.4, 7.4 mm), CBM-ZC 12562; same data as holotype, 4 females (cl 6.1–6.8 mm), CBM-ZC 12563; same locality, 25 December 2011, yabby pump, coll. T. Maenosono, 1 female (cl 6.3 mm), NHMW 25648; same locality, 25 April 2013, yabby pump, coll. T. Komai, 1 female (cl 4.6 mm), CBM-ZC 12564; same locality, 27 April 2013, yabby pump, coll. T. Maenosono, 2 females (cl 6.8, 7.0 mm), RUMF-ZC-02656; same locality, 25 May 2013, yabby pump, coll. T. Maenosono, 1 female (cl 5.1 mm), 1 ovigerous female (cl 7.3 mm), CBM-ZC 12565. Kita-nashiro Beach, Itoman, sea grass bed, 21 April 2012, yabby pump, coll. T. Maenosono, 2 females (cl 4.7, 5.1 mm), CBM-ZC 12566. Minatogawa, Urasoe, seagrass beds, 28 March 2013, yabby pump, 1 female (cl 4.5 mm), CBM-ZC 12567. Yaeyama Islands: Hori, Kuroshima Island, lower intertidal, sand, 11 April 1998, hand, coll. K. Nomura, 1 ovigerous female (cl 7.6 mm), CBM-ZC 8241.

Description. Rostrum ( Figs. 2 A–C; 4A) flattened dorsoventrally, spiniform, directed slightly downward, overreaching midlength of eyestalks. Carapace ( Figs. 1 ; 2A–C) about 0.4 length of pleon; orbital margins slightly convex; anterolateral projections triangular with subacute tip; excavation inferior to anterolateral projections deep, U-shaped; cervical groove deep, across 0.8 length of carapace, extending anteriorly as shallow sulcus, but not reaching to midline, thus dorsal oval incomplete; linea thalassinica reaching nearly to posterior margin of carapace.

Thoracic shield (plate on thoracic sternite 7) ( Fig. 4 B) pentagonal with strongly produced anteromedian margin; ventral surface with shallow groove posteriorly.

Length ratio of first pleomere to telson measured along midline 1.0: 1.7: 1.2: 0.9: 1.2: 1.4: 0.9 ( Fig. 2 D–G). First pleomere ( Figs. 1 ; 2D) narrowing anteriorly in dorsal view; pleuron with poorly defined ventral margin. Second pleomere ( Figs. 1 ; 2D) approximately as long as wide; pleuron having posterolateral margin slightly expanded, without tuft of setae. Third to fifth pleura ( Figs. 1 ; 2E, F) each with patch of soft plumose setae and posterior tuft of long setae; posterolateral margins slightly expanded. Sixth pleomere ( Figs. 1 ; 2F) about 1.3 times wider than long, subtrapezoidal, slightly narrowing posteriorly, lacking ventrolateral projection; lateral margin with faint notch at about posterior 0.2.

Telson ( Figs. 2 G; 3A) trapezoidal, narrowing posteriorly, 1.2–1.3 times wider than long, broadest at anterior 0.2. Dorsal surface slightly convex, bearing 1 or 2 movable spines just lateral to prominent median tuft of long setae located at about anterior 0.3 and 1 pair of lateral movable spinules slightly posterior to midlength. Lateral margins unarmed. Posterior margin very slightly convex or faintly bilobed, with 1–8 slender movable spines on each side of tiny median tooth (usually with hiatus between lateral set and mesial set of movable spines), and with 2 microscopic movable spinules at each lateral angle ( Fig. 3 B–E); prominent tuft of long submarginal setae laterally, between 2 sets of movable spines ( Fig. 3 A); setae fringing posterior margin short (subequal to shorter than movable spines) and sparse.

Eyestalks ( Figs. 2 C; 4A) flattened distally, tapering to short, rounded distal projection, contiguous, slightly overreaching distal margin of first segment of antennular peduncle; dorsal surface narrowly 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. 2 B, C) slightly longer than or subequal in length to antennal peduncle; first segment short, hardly visible in dorsal and lateral views; second segment shorter than first segment; third segment about 2.8 times longer than second segment; second and third segments with longitudinal row of sparse long setae ventrally; antennular flagella both slightly shorter than peduncle; dorsal flagellum thicker and slightly shorter than or subequal to ventral flagellum.

Antennal peduncle ( Fig. 2 B, C) with distal two segments subcylindrical; fourth segment 1.2–1.3 times longer than fifth segment; scaphocerite ( Fig. 4 C) tiny, subovate, terminating in sharp spine curved mesially.

Small process of cephalothorax lateral to epistome bearing tuft of long setae.

First maxilliped ( Fig. 4 D) with exopod relatively narrow. Second maxilliped ( Fig. 4 E) with exopod overreaching midlength of merus-ischium fused segment. Third maxilliped ( Fig. 4 F, G) without exopod; ischiummerus roundly subrectangular, operculiform, 1.7–1.8 times longer than wide; ischium 1.2–1.3 times wider than long, mesial face with crista dentata consisting of row of 12 small spines; merus about 0.5 times as long as ischium measured along dorsal margin, about 1.3–1.4 times wider than long, slightly wider than merus, distolateral margin rounded, exceeding as far as dorsodistal margin, unarmed; distomesial margin also unarmed; carpus cup-shaped, slightly shorter than merus measured along dorsal margin; propodus narrowing distally, 2.0 times longer than high and distinctly longer than carpus; dactylus slender, digitiform, about 0.7 times as long as propodus.

First pereopods (chelipeds) varying from slightly unequal and dissimilar to subequal and similar. Major cheliped ( Figs. 5 A, B; 6A, B) varying from stout to moderately slender; carpus-chela combined length 0.9–1.2 of carapace length. Ischium slightly widened distally, dorsal margin nearly straight, unarmed; lateral surface gently convex; ventral margin serrated with row of 7–10 spines slightly increasing in size distally. Merus subequal in length to ischium; dorsal margin convex, unarmed; lateral surface with small concavity ventrodistally to accommodate proximoventral margin of carpus; mesial surface generally flat; ventral margin with small spine located at proximal 0.3 and faintly denticulate in distal 0.7. Carpus approximately as long as wide; dorsal and ventral margins sharply carinate, smooth, proximoventral margin broadly rounded; lateral surface smooth, convex; mesial surface nearly flat. Palm square, 1.1–1.2 times as long as wide; dorsal margin sharply carinate, with sparse row of short setae; lateral surface smooth, convex; mesial surface slightly convex generally, but with small shallow depression at base of fixed finger; ventral margin sharply carinate, with row of tufts of setae extending onto fixed finger, increasing in length distally; distolateral margin with broad convexity superior to base of fixed finger. Fixed finger 0.5–0.6 times as long as palm, gently curving, terminating in acute tip; cutting edge smooth; lateral surface convex, usually with blunt ridge on midline (rarely sharply carinate; Fig. 6 A), with tufts of long setae along cutting edge; mesial surface depressed along cutting edge, with tufts of setae in proximal half. Dactylus 0.8–0.9 times as long as palm, slightly curved distally, tip crossing fixed finger, terminating in acute or subacute tip; dorsal surface rounded, with tufts of long setae; lateral surface with longitudinal row of tufts of long setae along cutting edge; cutting edge with broad obtuse tooth proximal to midlength, nearly smooth in distal half; mesial surface rounded, also with tufts of setae adjacent to cutting edge.

Minor cheliped ( Fig. 5 C, D) moderately stout; carpus-chela combined length subequal to carapace length. Ischium and merus generally similar to those of major cheliped in general shape and armature; ventral margin of merus with 1 small spine located at proximal 0.4. Carpus widened distally, about 1.1 times as long as merus and about 1.5 times as long as wide; dorsal margin nearly straight, sharply carinate; proximal to ventral margin convex, sharply carinate. Palm square, almost as long as wide; dorsal margin nearly straight, sharply carinate, with row of setae; ventral margin sharply carinate, with row of tufts of long setae extending onto fixed finger; lateral and mesial surfaces slightly convex, smooth; distolateral margin with distinct convexity superior to base of fixed finger. Fixed finger 1.1–1.2 times as long as palm, slightly curving, terminating in acute tip; cutting edge minutely denticulate in proximal 0.8; lateral surface with sharp median carina delimiting concavity along cutting edge and longitudinal row of stiff setae. Dactylus 1.4–1.6 times as long as palm, slightly curving, tip crossing fixed finger; dorsal margin rounded, with numerous long setae; lateral and mesial surfaces with longitudinal row of tufts of long stiff setae; cutting edge unarmed.

When chelipeds subequal, either showing form of minor cheliped as described above.

Second pereopod ( Fig. 7 A) with ischium short, ventrodistal angle slightly produced; merus with sinuous ventral margin, dorsal margin faintly convex; carpus cup-shaped, about 2.1 times longer than wide; chela subtriangular; palm distinctly wider than long; dactylus about 2.0 times longer than palm.

Third pereopod ( Fig. 7 B, C) with carpus cup-shaped, 2.1 times longer than wide. Propodus suboval in general; proximoventral angle (heel) not markedly produced; lateral face covered with dense setae except for obtuse median ridge; ventral margin convex, smooth, with tiny spiniform seta subdistally. Dactylus nearly straight, about 0.8 times as long as propodus measured along dorsal margin.

Fourth pereopod ( Fig. 7 D, E) with coxa somewhat flattened ventrally, immovable ( Fig. 4 B); merus longer than ischium; carpus slightly widened distally; propodus strongly compressed laterally, slightly longer than carpus, with dense grooming setae on ventral margin and tufts of stiff setae on outer surface; dactylus slightly curving, about 0.3 times as long as propodus.

Fifth pereopod ( Fig. 7 F) moderately slender, chelate; chela slightly longer than carpus; dactylus about 0.3 times as long as palm.

Female first pleopod ( Fig. 4 H) consisting of protopod and single ramus, ramus simple or divided in two articles (distal article slightly shorter than proximal article). Female second pleopod ( Fig. 4 I) biramous; endopod divided in two subequal articles, lacking appendix interna; exopod distinctly longer than endopod, incompletely divided in 4 articles. Third to fifth pleopods ( Fig. 4 J) biramous, rami moderately broad; appendix interna ( Fig. 4 K, L) slightly tapering distally, more than twice as long as basal width; subtruncate terminal margin with cluster of coupling hooks.

Uropod ( Figs. 2 G; 3F) distinctly overreaching posterior margin of telson when directed posteriorly. Endopod subsemicircular, with distinctly convex inner margin and nearly straight outer margin, gradually tapering toward rounded distal margin, about 1.3 times as long as wide; lateral margin unarmed; mesial margin with 1 or 2 movable spinules posterior to midlength, distal margin with cluster of 4 or 5 movable spinules; dorsal surface with obtuse median ridge, armed with 2–4 movable spinules adjacent to lateral margin and 2 or 3 movable spinules along midline. Exopod 1.2–1.3 times as wider than long and 1.1 times as long as telson, subsemicircular, slightly exceeding beyond endopod; lateral margin faintly sinuous, unarmed; inner margin broadly rounded; dorsal surface slightly elevated in midline, armed with 1 movable spinule laterally at about midlength; dorsal plate with distal row of stiff or spiniform setae distinctly separated from setal row of posterior margin; posterior margin with stiff setae of various lengths and stoutness.

Color in life. Body translucent, pale pinkish dorsally. Inside of gastric region light brown. Chelipeds pale pink or light brown. Second to fifth pereopods translucent. See Fig. 8 .

Variation. Chelipeds are variable from distinctly unequal and dissimilar to slightly unequal and slightly dissimilar, although available specimens were all females. The proportion of the major cheliped varies as illustrated ( Figs. 5 A; 6A, B). The number of prominent slender spines on the posterior margin of the telson is also considerably variable from two to eight on each side of the median spine ( Fig. 3 B–E).

Distribution. Known from Okinawa Island and Kuroshima Island in Yaeyama Islands; lower intertidal to shallow subtidal.

Etymology. From the combination of the Latin, spinosus (= spinous) and cauda (tail), in reference to the posterior margin of the telson armed with movable spines. Used as a noun in apposition.

Figures

FIGURE 1. Cheramus spinicauda n. sp., holotype, female (cl 7.1 mm), CBM-ZC 12561, habitus, lateral view. Scale bar: 2 mm.

FIGURE 2. Cheramus spinicauda n. sp., holotype, female (cl 7.1 mm), CBM-ZC 12561. 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 and armature omitted). Scale bars: 2 mm for A, B, D – G; 1 mm for C.

FIGURE 3. Cheramus spinicauda n. sp., A, B, F, holotype, female (cl 7.1 mm), CBM-ZC 12561; C, paratype, female (cl 6.8 mm), Ohmine, RUMF-ZC- 2656; D, paratype, female (cl 6.6 mm), Ohmine, CBM-ZC 12563; E, paratype, female (cl 6.4 mm), Ohmine, CBM-ZC 12562. A, telson, dorsal view; B – E, posterior margin of telson, dorsal view, showing variation in armature (setae omitted); F, left uropod, dorsal view (perpendicular; setae omitted except for stiff marginal setae on dorsal plate). Scale bars: 1 mm for A, F; 0.5 mm for B – E.

FIGURE 4. Cheramus spinicauda n. sp., holotype, female (cl 7.1 mm), CBM-ZC 12561. A, rostrum and eyes, dorsal view; B, shield on seventh thoracic sternite and right coxa of fourth pereopod, ventral view; C, left scaphocerite, dorsal view; D, left first maxilliped, outer view (setae omitted; epipod missing); E, left second maxilliped, inner view (setae omitted); F, left third maxilliped, lateral view; G, same, mesial view (setae omitted); H, left first pleopod, ventral view (setae omitted); I, left second pleopod, ventral view (setae omitted); J, left third pleopod, dorsal view (setae omitted); K same, appendix interna, ventral view; L, same, dorsal view. Scale bars: 1 mm for A, D – G, J; 0.5 mm for B, H, I, K, L; 0.25 mm for C.

FIGURE 5. Cheramus spinicauda n. sp., holotype, female (cl 7.1 mm), CBM-ZC 12561. A, major (left) cheliped, lateral view; B, same, chela, mesial view (setae partially omitted); C, minor (right) cheliped, lateral view; E, same, chela, mesial view (setae partially omitted). Scale bar: 1 mm.

FIGURE 6. Cheramus spinicauda n. sp. A, paratype, female (cl 6.4 mm), Ohmine, CBM-ZC 12562; B, paratype, female (cl 6.3 mm), Ohmine, NHMW 25648. A, carpus and chela of major (left) cheliped, lateral view (setae omitted); B, carpus and chela of major (right) cheliped, lateral view (setae omitted). Scale bars: 2 mm.

FIGURE 7. Cheramus spinicauda n. sp., holotype, female (cl 7.1 mm), CBM-ZC 12561. 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, left fifth pereopod. Scale bars: 1 mm.

FIGURE 8. Cheramus spinicauda n. sp., paratype, female (cl 6.2 mm), RUMF-ZC 2655, showing coloration in life. A, entire animal, lateral view; B, same, dorsal view.