Chirostylus stellaris, Osawa, Masayuki, 2007

Osawa, Masayuki, 2007, A new species of Chirostylus Ortmann, 1892 (Crustacea: Decapoda: Anomura: Chirostylidae) from the Ryukyu Islands, southwestern Japan, with a supplemental description of Chirostylus ortmanni Miyake & Baba, 1968, Zootaxa 1450, pp. 31-43 : 36-42

Chirostylus stellaris n.sp.

( Figs. 3 , 4 , 5 C–F)

[New Japanese name: Hoshizora-waraebi]

Chirostylus sp.— Minemizu, 2000: 164, unnumbered fig.; 2002: 164, unnumbered fig. — Kawamoto & Okuno, 2003: 97, unnumbered fig.

Material examined. Holotype: CMNH-ZC 2127, male (cl 3.5 mm), off Shimoji Islet, Miyako-jima Island, Ryukyu Islands, 21 m, 15 April 2003, coll. R. Minemizu.

Paratypes: CMNH-ZC 0 0 539, 1 female (cl 2.6 mm), Maeda-misaki, Okinawa Island, Ryukyu Islands, 20 m, 10 August 2001, coll. T. Yanagisawa; CMNH-ZC 0 0 616, 1 female (cl 2.5 mm), Shichu-gama, Kume-jima Island, Ryukyu Islands, 15 m, 25 July 2001, coll. T. Kawamoto; CMNH-ZC 0 1018, 1 male (cl 3.8 mm), 1 ovigerous female (cl 3.5 mm), Umagai, Kume-jima Island, Ryukyu Islands, 25 m, 12 November 2002, coll. J. Okuno; CMNH-ZC 0 1115, 1 male (cl 4.1 mm), Umagai, Kume-jima Island, Ryukyu Islands, 25 m, 12 November 2002, coll. T. Kawamoto; CMNH-ZC 2128, 1 ovigerous female (cl 4.4 mm), off Shimoji Islet, Miyako-jima Island, Ryukyu Islands, 21 m, 15 April 2003, coll. R. Minemizu; CMNH-ZC 2129, 1 female (cl 2.6 mm), Zanpa-misaki, Okinawa Island, Ryukyu Islands, 30 m, 26 May 2001, coll. Y. Fujita; CMNH-ZC 2130, 1 female (cl 3.3 mm), Zanpa-misaki, Okinawa Island, Ryukyu Islands, 30 m, 26 May 2001, coll. Y. Fujita; CMNH-ZC 2131, 1 female (cl 3.6 mm), Maeda-misaki, Okinawa Island, Ryukyu Islands, 15.4 m, 31 July 2004, coll. Y. Fujita; CMNH-ZC 2132, 1 female (cl 3.5 mm), Maeda-misaki, Okinawa Island, Ryukyu Islands, 19 m, 21 June 2003, coll. Y. Fujita; CMNH-ZC 2133, 1 female (cl 3.8 mm), Maeda-misaki, Okinawa Island, Ryukyu Islands, 14.9 m, 22 June 2003, coll. Y. Fujita; CMNH-ZC 2134, 1 female (cl 4.2 mm), Maedamisaki, Okinawa Island, Ryukyu Islands, 22 m, 21 June 2003, coll. Y. Fujita; CMNH-ZC 2135, 1 female (cl 3.3 mm), Maeda-misaki, Okinawa Island, Ryukyu Islands, 18.4 m, 13 August 2003, coll. Y. Fujita; CMNH- ZC 2136, 1 female (cl 3.8 mm), Maeda-misaki, Okinawa Island, Ryukyu Islands, 16 m, 30 September 2004, coll. Y. Fujita; CMNH-ZC 2137, 1 male (cl, 3.7 mm), Sesoko, Okinawa Island, Ryukyu Islands, 23 m, 18 July 2003, coll. Y. Fujita.

Size. Male cl 3.5–4.1 mm, female cl 2.5–4.2 mm, ovigerous female cl 3.5–4.4 mm.

Description. Carapace ( Fig. 3 A, B) 1.2–1.3 times longer than greatest width, glabrous. Lateral margins diverging posteriorly to point approximately one third from posterior end, converging behind it with strong concavity. Posterior margin strongly concave. Rostrum low, rounded, with spine clearly smaller than epigastric spines and directed anterodorsally. Anterolateral (first) spine prominent, preceded by smaller spine at lateral limit of orbit. Pair of epigastric spines situated behind eyes, directed anterodorsally. Gastric region weakly convex, unarmed, distinctly separated from cardiac region by narrow depression (cervical groove), and indistinctly from anterior branchial region. Cardiac region more strongly convex than gastric region, with 1 or 2 spines anteriorly (if 2 spines present, posterior spine minute). Branchial region unarmed or with 1–4 spines mesiad and parallel to lateral margin.

Pterygostomial flaps ( Fig. 3 B) anteriorly ending in small spine, surface with several small spines.

Excavated sternum ( Fig. 3 C) anteriorly produced, subtriangular, ending in subacute or acute tip, surface with weak ridge in midline on anterior half. Sternite 3 ( Fig. 3 D) somewhat convex on surface; anterior margin nearly transverse, usually with 4 small spines (3 spines in CMNH-ZC 2134, 1 spine subdivided distally in CMNH-ZC 00539). Sternite 4 ( Fig. 3 D) with acute or blunt spine on each proximal lateral margin.

Abdomen ( Fig. 3 A, B) unarmed, but with few short setae on dorsal surface; pleura of second to fourth segments subtriangular, those of fifth and sixth segments each ending in rounded margin. Telson ( Fig. 3 E) divided into 2 lobes by transverse suture; anterior lobe with strongly convex lateral margins; posterior lobe narrower but distinctly longer than anterior, semi-elliptical.

Eyestalk ( Fig. 3 A, B, F) elongate, 0.4–0.5 length of postorbital carapace, subcylindrical, slightly broadened proximally; cornea slightly dilated, about 0.4 length of remaining ocular peduncle.

Antennular peduncle ( Fig. 3 F), when fully extended, overreaching distal margin of cornea by distal one third to half length of ultimate article; basal article with 2 spines on distolateral elongate projection, distolateral spine much larger than distomesial; distal 2 articles unarmed, ultimate article distinctly longer than penultimate.

Antennal peduncle ( Fig. 3 F) short but slender, reaching or not reaching proximal margin of cornea, consisting of 5 articles, lacking antennal scale; proximal 4 articles unarmed; article 5 much longer than article 4, with ventromesial distal spine; flagellum consisting of 4 or 5 articles.

Third maxilliped ( Fig. 3 C, G) slender; ischium with well developed crista dentata of 16–20 acute teeth; merus and carpus each with distolateral spine; propodus unarmed; exopod reaching to 0.6–0.8 length of merus.

P1 ( Fig. 4 A–D) subcylindrical, slender, 10.6–16.1 times as long as postorbital carapace; surfaces with sparse short setae except for setose fingers. Ischium with several spines. Merus longer than carpus and propodus, with 4 rows of sparse spines (1 dorsolateral, 1 dorsomesial, 1 mesial, and 1 ventral); in males, proximal half of ventral row composed of strong, closely-set spines; distal margin with 4 or 5 spines (1 or 2 dorsolateral, 1 dorsomesial, 1 ventrolateral, and 1 ventromesial). Carpus with 4 rows of sparse spines (1 dorsolateral, 1 dorsomesial, 1 mesial, and 1 ventral); distal margin with usually 6 spines (1 dorsolateral, 1 ventrolateral, 1 lateral, 1 dorsomesial, 1 ventromesial, and 1 mesial), lateral and mesial spines sometimes obsolete. Palm 2.6– 2.9 times longer than dactylus (movable finger), with 6 rows of sparse spines (1 dorsolateral, 1 ventrolateral, 1 lateral, 1 dorsomesial, 1 ventromesial, and 1 mesial). Fingers narrow; opposable margins each with prominent tooth proximally and subtriangular, moderately large tooth on distal 0.3; median margin gaping, and bearing small teeth; distal margin with row of minute sharply pointed, corneous teeth interspaced by small calcareous teeth; distal end usually with 2 unequal corneous spines.

P2–4 ( Fig. 4 E, F) long and slender, subcylindrical, somewhat depressed lateromesially; P2 reaching or slightly overreaching distal margin of P1 carpus; entire length of P3 slightly shorter than P2 and P4, meri successively diminishing in size posteriorly, length of carpi subequal in P2–4, P4 propodus longer than P2 and P3. Each ischium unarmed or with few, very small spines. Each merus longer than carpus and propodus; extensor margin with row of spines and few short setae; lateral surface with few spines; flexor margin with row of sparse spines; mesial surface unarmed or few spines. Each carpus with extensor margin bearing row of closely-spaced spines in proximal part with few scattered spines beyond; lateral and mesial surfaces unarmed; flexor margin with few spines. Each propodus narrower than merus and carpus in lateral view, 1.2–1.3 (mean, 1.2, on P2) and 1.2–1.4 (mean, 1.3, on P3 and P4) times as long as carpus, 7.0–10.4 (mean, 7.8, on P2), 6.4– 8.4 (mean, 7.7, on P3), and 7.4–9.9 (mean, 8.2, on P4) length of dactylus, 16.0–20.2 (mean, 18.6, on P2), 16.3–21.3 (mean, 19.0, on P3), and 17.7–22.6 (mean, 20.3, on P4) times longer than proximal height; extensor margin with row of sparse spines and setae; lateral surface unarmed; mesial face unarmed or with few small spines; flexor margin with row of 13–20 (P2), 14–18 (P3), and 13–17 (P4) slender, corneous spines, distal spines closely arranged. Each dactylus with moderately curved extensor margin; flexor margin nearly straight, with 7 or 8 corneous spines (including terminal spine) gradually decreasing in size toward base of segment, distal 2 spines subequal in length, ultimate spine slightly or somewhat narrower than penultimate.

Coloration ( Fig. 5 C–E). Body and pereopods with ground color of reddish brown. Carapace with moderately narrow, white or pale blue line in large triangle bordered by dark brown, narrow lines; white line present along lateral margin; part between white and yellow lines and gastric and cardiac regions occasionally with irregular-sized, white marks. Abdominal tergites with dark brown and white or pale blue, narrow lines along anterior and posterior margins and with moderately broad, dark brown line bordered by white or pale blue, narrow lines along midline. Pterygostomial flaps with 2 narrow, longitudinal white stripes. P1 merus, carpus, and chela with longitudinal rows of small white spots of moderate intervals; carpus and chela also occasionally with longitudinal narrow, white or pale blue stripes. P2–4 meri and carpi each bearing longitudinal rows of small white spots on extensor margin (bases of spines) and lateral surface; propodi with scattered small white spots, distal part dark brown and yellow tinge; dactyli yellow.

Distribution. At the present, only known from the Ryukyu Islands, southwestern Japan; at depths of 14.9– 30 m.

Habitat and ecology. Like C. ortmannni , C. stellaris , n. sp. is also found on soft and black corals (Alcyonacea and Antipatharia) ( Minemizu 2000, 2002; Kawamoto & Okuno 2003; as Chirostylus sp). This species is observed more frequently at night than during the day ( Minemizu 2000, 2002).

Etymology. The specific name is derived from the Latin stellaris (speckled), referring to its spotted coloration.

Remarks. Chirostylus stellaris n. sp. closely resembles C. ortmanni in sharing the following characters: carapace with a small number of spines; posterior gastric region unarmed; anterior cardiac region with at least one spine; no spine near anterior extremity of branchial margin; rostrum rounded, with or without a median spine being shorter than epigastric spines; sternite 3 usually with four spines on the anterior margin; weakly dilated cornea; and P2–4 dactyli each armed with ultimate spine being subequal with penultimate. However, when the male specimens of the two species are compared, C. stellaris is distinguished from C. ortmanni by having a row of strong, closely-set spines on the proximal half of the ventral surface of the P1 merus ( Fig. 4 C). Chirostylus ortmanni possesses only sparse spines on the ventral surface ( Fig. 2 A). In both sexes, the P2– 4 propodi are generally more slender in C. stellaris than C. ortmanni , although the ranges of the length relative to the height do partially overlap. In C. stellaris , the propodi are 16.0–20.2 (mean, 18.6, on P2), 16.3–21.3 (mean, 19.0, on P3), and 17.7–22.6 (mean, 20.3, on P4) times longer than high; whereas in C. ortmanni , they are 12.3–15.3 (mean, 13.7, on P2), 12.3–16.8 (mean, 14.5, on P3), and 14.3–18.5 (mean, 16.1, on P4) times longer ( Figs. 2 C, 4E). Chirostylus stellaris appears to reach a much smaller size than C. ortmanni based on the specimens examined. The maximum postorbital carapace lengths of the largest male and female are 4.1 and 4.4 (ovigerous) mm, respectively, in C. stellaris ; and 7.0 and 6.8 mm, respectively, in C. ortmanni . The sizes of the smallest ovigerous females are also different between these species. Their postorbital carapace length is 3.5 mm in C. stellaris and 4.9 mm in C. ortmanni .

As shown in the photographs and pointed out under the name Chirostylus sp. by Minemizu (2000: 164, unnumbered fig., 2002: 164, unnumbered fig.) and Kawamoto & Okuno (2003: 97, unnumbered fig.), C. stellaris is clearly different from C. ortmanni in live coloration. The pereopods of C. stellaris have numerous, white or pale blue spots, whereas those of C. ortmanni possess comparatively less numerous and smaller, yellow spots ( Fig. 5 B, D). Chirostylus ortmanni also has a short, white or pale blue blotch or band caught between dark brown bands on the distal part of each of the P2–4 meri, which is not found in C. stellaris ( Fig. 5 A, C).

Figures

FIGURE 2. Chirostylus ortmanni Miyake & Baba, 1968. NSMT-Cr 8037, male (cl 6.5 mm), Zyogasaki, Shizuoka Prefecture (A, B); NSMT-Cr 11678, female (cl 6.1 mm), Miyake-jima Island, Izu Islands (C, D); CMNH-ZC 531, male (cl 4.1 mm), Kamogawa, Chiba Prefecture (E); NSMT-Cr 7787, female (cl 6.7 mm), Manazuru, Kanagawa Prefecture (F). A, ischium and merus of left P 1, mesial view; B, chela of left P 1, dorsal view; C, carpus, propodus, and dactylus of right P 2, lateral view; D – F, dactylus and distal part of propodus of right P 2, lateral view. Scales equal 1.0 mm.

FIGURE 3. Chirostylus stellaris, n. sp. CMNH-ZC 2127, holotype male (cl 3.5 mm), Miyako-jima Island, Ryukyu Islands. A, carapace, abdomen, ocular peduncles, and left antennular and antennal peduncles, dorsal view; B, same, lateral view; C, anterior part of sternal plastron, including proximal parts of maxillipeds, ventral view; D, sternites 3 and 4, ventral view; E, telson, extensor view; F, left ocular, antennular, and antennal peduncles, ventral view; G, merus and carpus of left third maxilliped, lateral view. Scales equal 1.0 mm.

FIGURE 4. Chirostylus stellaris, n. sp. CMNH-ZC 2127, holotype male (cl 3.5 mm), Miyako-jima Island, Ryukyu Islands. A, left P 1, ischium, merus, and carpus, dorsal view; B, same, chela, dorsal view; C, same, ischium and merus, mesial view; D, same, fingers, dorsal view; E, left P 2, lateral view; F, same, dactylus and distal part of propodus, lateral view. Scales equal 1.0 mm.

FIGURE 5. Fresh specimens. Chirostylus ortmanni Miyake & Baba, 1968, CMNH-ZC 531, male (cl 4.1 mm), Kamogawa, Chiba Prefecture (A, B); Chirostylus stellaris, n. sp., CMNH-ZC 0 1115, paratype male (cl 4.1 mm), Kumejima Island, Ryukyu Islands (C, D); CMNH-ZC 2130, paratype female (cl 3.3 mm), Zanpa-misaki, Okinawa Island, Ryukyu Islands (E, F). A, C, entire specimen, dorsal view; B, D, carapace, abdomen, and meri of pereopods, dorsal view; E, F, live specimen in aquarium. Photographed by J. Okuno (A – D) and Y. Fujita (E, F).