Calastacus formosus, Lin, Tomoyuki Komai Feng-Jiau & Chan, Tin-Yam, 2010

Lin, Tomoyuki Komai Feng-Jiau & Chan, Tin-Yam, 2010, Five new species of Axiidae (Crustacea: Decapoda: Axiidea) from deep-water off Taiwan, with description of a new genus, Zootaxa 2352, pp. 1-28 : 13-18

Calastacus formosus n. sp.

( Figs. 6–8 , 13 D)

Type material. Holotype: hermaphrodite (cl 7.1 mm), TAIWAN 2001, stn CP 104, 24°48.86’N, 122°05.31’E, 365–447 m, 19 May 2001 ( NTOU A00083 ).

Paratypes: 2 hermaphrodites (cl 6.0, 6.5 mm), 1 ovigerous hermaphrodite (cl 9.0 mm), TAIWAN 2001, stn CP 102, 24°48.38’N, 122°07.97’E, 326–331 m, 19 May 2001 ( NTOU A00110).

Description of holotype. Rostrum ( Fig. 6 A–D) 0.2 times as long as carapace and about 0.4 times of distance between rostral base and cervical groove, spike-like with acute tip, unarmed anterior to supraocular spine, not continuous with lateral gastric carinae on carapace. Carapace ( Fig. 6 A–D) smooth; gastric region convex, higher than rostral base; supraocular spines prominent; lateral and submedian gastric carinae absent; median gastric carina unarmed, extending over midway between rostral base and cervical groove; cervical groove distinct, extending nearly to pterygostomial part of carapace; no postcervical carina; pterygostomial margin with small spine.

Thoracic sternum ( Fig. 7 A) with poorly delimited shield on seventh somite, medially separated by deep groove; sixth somite with spade-shaped prominence.

First abdominal pleuron ( Fig. 6 E) short, produced ventrally as acute projection; second pleuron broad, anteroventrally rounded; third to fifth pleura rounded; sixth pleura also rounded. Telson ( Fig. 6 F) 1.6 times longer than wide, widest proximally, then approximately parallel-sided, lateral margin unarmed, posterior margin strongly convex without posteromedian spine, posterolateral region with 1 minute spiniform seta; dorsal face without spines on obsolete oblique ridges.

Eyestalks ( Fig. 6 C, D) subglobose, 0.4 length of rostrum, immovably attached to cephalothorax, not contiguous; cornea unpigmented, unfaceted, division between cornea and eyestalk unclear. Antennular peduncle ( Fig. 6 C) reaching distal margin of fourth segment of antennal peduncle; first segment with small submarginal spine on statocyst lobe dorsodistally; flagella missing. Antennal peduncle ( Fig. 6 C, D) with first segment bearing 2 spines on ventrodistal margin (lateral spine longer than mesial spine); second segment with dorsolateral distal spine slender, slightly curved inward in dorsal view, slightly directed dorsally in lateral view, reaching to midlength of fourth segment; scaphocerite slender, directed slightly upwards, slightly falling short of distal margin of fourth segment; third segment with sharp spine on distomesial angle; fourth segment slightly longer than second segment (excluding dorsolateral distal spine); fifth segment about half length of fourth segment; flagellum missing.

Third maxilliped ( Fig. 8 A) moderately slender; coxa with 1 small ventromesial spine; basis also with small ventromesial spine; ischium unarmed on ventral margin; crista dentata with about 20 corneous-tipped teeth; merus with 2 long subdistal spines on ventral margin; carpus unarmed.

Chelipeds ( Fig. 7 B–E) subequal, similar, fairly elongate. Right cheliped ( Fig. 7 D, E) with coxa bearing spine on ventrodistal margin. Basis also with small spine ventrodistally. Ischium with row of 3 slender spines on ventral margin. Merus with 1 subdistal spine (slightly hooked) and row of 5 slender spines increasing in size distally on ventral margin. Carpus unarmed. Chela 0.9 times as long as carapace and 3.6 times longer than high, ventral margin slightly curving. Palm slightly becoming higher distally, 1.8 times longer than high, with 1 subdistal spine on faintly carinate dorsal margin and 1 spine on lateral surface adjacent to base of fixed finger; lateral surface slightly convex, with few tufts of long setae and row of low tubercles bearing tufts of setae adjacent to ventral margin, extending onto fixed finger; mesial face also with spine adjacent to base of fixed finger. Fixed finger with row of small tubercles and tufts of long setae on mesial face along ventral margin, latter extending onto palm; cutting edge with row of rounded teeth. Dactylus with 3 longitudinal rows of long stiff setae on lateral surface; mesial face medially carinate, also with rows of long stiff setae; cutting edge with broad concavity proximally, forming narrow hiatus when closed, tip closing with tip of fixed finger.

Left cheliped ( Fig. 7 A, B) only slightly shorter than major cheliped, otherwise generally similar. Ischium with 4 spines on ventral margin. Merus with 1 subdistal spine on dorsal margin and 7 spines on ventral margin. Armament and setation of other segments identical with those on major cheliped.

Second pereopod ( Fig. 8 B) slender, unarmed on ischium to carpus; carpus about 0.6 length of chela; chela with tufts of long setae on margins, fingers slightly shorter than palm, each with row of minute corneous spinules on cutting edge. Ambulatory legs (third to fifth pereopods) somewhat elongate. Third pereopod ( Fig. 8 C) unarmed on ischium to carpus; propodus with row of spiniform setae on lateral surface distally ( Fig. 8 D); dactylus ( Fig. 8 D, E) subconical, slender, about 0.3 times as long as propodus, slightly twisted, setose. Fourth pereopod ( Fig. 8 F) unarmed on ischium to carpus; propodus distally with cluster consisting of stiff setae and longer, stout setulose setae, possibly representing grooming apparatus, and with sets of 1 or 2 spiniform setae and longer stiff setae on lateral surface distally ( Fig. 8 G); dactylus ( Fig. 8 G, H) subconical, setose, slightly twisted (tip broken, thus proportion against propodus unknown). Fifth pereopod ( Fig. 8 I) not subchelate, unarmed on ischium to carpus; propodus distally with grooming apparatus consisting of cluster of short to long setae, extending onto lateral and mesial faces ( Fig. 8 J, K); dactylus ( Fig. 8 J, K) very slender, elongate, about 0.4 times as long as propodus, flexor surface excavated near base, proximomesial margin expanded, dorsal surface with row of tufts of stiff setae.

Gonopores present on coxae of third and fifth pereopods ( Fig. 7 A).

Pleurobranchs absent; podobranchs and arthrobranchs present on second maxilliped through fourth pereopods, podobranchs bearing papillae representing rudimentary gill filaments; epipods present on first maxilliped through fourth pereopod.

First pleopod ( Fig. 7 F) with first segment (protopod) strongly flattened; second segment (ramus) 0.7 length of first segment, leaf-like, deeply concave on mesial margin proximally, proximomesial protrusion representing appendix interna conspicuous on broad triangular anterior fold, lateral fold forming definite shoulder on lateral margin. Second pleopod ( Fig. 7 G, H) with inner ramus consisting of 2-segmented endopod plus distally articulated appendix masculina, all components more or less in line with peduncle, with thumblike appendix interna at base of second segment of endopod; second segment of endopod with slightly concave dorsal (or anterior) margin bearing numerous stiff, curving setae; appendix masculina tapering distally with row of sparse stiff setae laterally and mesially, and with terminal tuft of stiff setae; exopod very slender, half length of endopod. Third to fifth pleopods very slender, without appendices internae.

Uropodal endopod ( Fig. 6 G) about 2.0 times as long as wide, without lateral spines, dorsal ridge unarmed, distal margin subtruncate; exopod ( Fig. 6 G) without lateral serration, posterolateral angle with 1 spine, but no spiniform setae apparent; transverse suture with about 10 slender spiniform setae ( Fig. 6 H).

Note on paratypes. One paratype lacks right first and fifth pereopods; other two missing first chelipeds and several pereopods. Antennal peduncle with first segment bearing 2 spines on ventrodistal margin (lateral spine longer than mesial spine, and mesial spine small to distinct). First chela 0.7 times as long as carapace and 3.3 times longer than high, ventral margin slightly curving; palm slightly becoming higher distally, 1.8 times longer than high, with 1 subdistal spine on dorsal margin and 1 spine on lateral surface near base of fixed finger; carpus unarmed; merus with 1 subdistal spine on dorsal margin and 7 spines on ventral margin; ischium with 3 spines on ventral margin. Uropodal endopod about 2.0 times as long as wide, without lateral spines, dorsal ridge unarmed, distal margin subtruncate; exopod without lateral serration, posterolateral angle with 1 spine and 1 small spiniform seta; transverse suture with 10 or more slender spiniform setae.

Coloration. Body and appendages entirely pale yellowish to pale yellowish pink; cornea of eye opaque. Inner margins of fingers of second chelae dark purplish.

Distribution. Known only from northeastern Taiwan; at depths of 326– 447 m.

Remarks. The present new species agrees well with the diagnosis of Calastacus , provided by de Saint Laurent (1972), Kensley (1989), Poore (1994) and Poore & Collins (2009). The genus is currently represented by seven species worldwide, C. stilirostris Faxon, 1893 (type species) from the eastern Pacific off Mexico to Peru, C. laevis de Saint Laurent, 1972 from the eastern Atlantic and Mediterranean, C. colpos Kensley, 1996 from the northwestern Gulf of Mexico, C. mexicanus Kensley, 1996 from the Gulf of Mexico, C. crosnieri Kensley & Chan, 1998 from Taiwan, C. inflatus Komai, Lin & Chan, 2009 from the South China Sea off the Pratas Islands, and C. myalup Poore & Collins, 2009 from south Western Australia ( Kensley 1996a; Kensley & Chan 1998; Ngoc-Ho 2003; Komai et al. 2009; Poore & Collins 2009). The new species appears closest to C. myalup in the presence of a pterygostomial spine on the carapace and the suture of the uropodal exopod, which bears 10 or more slender spiniform setae. Nevertheless, C. formosus n. sp. differs from C. myalup in the shape of the uropodal endopod. In C. formosus , the posterior margin of the uropodal endopod is subtruncate, but it is rounded in C. myalup . Furthermore, the supraorbital spine on the carapace only just exceeds the orbital margin of the carapace in C. formosus n. sp., rather than overreaching the middle of the eye in C. myalup . The ornamentation of the appendix masculina of the second pleopod consists only of stiff setae in C. formosus , but it includes spiniform setae in C. myalup .

This is the second species of Calastacus known from Taiwan. The other species is C. crosnieri , which is golden yellow in color and very different from the pale yellowish body of C. formosus . Considering the general scarcity of species of the genus around the world, the presence of two species from the same region is rather remarkable.

Etymology. The species is named after its type locality Taiwan derived from a former name, “ Formosa ”.

Figures

FIGURE 6. Calastacus formosus n. sp., holotype, hermaphrodite (cl 7.6 mm), NTOU A 00083. A, carapace and cephalic appendages, dorsal view; B, same, lateral view; C, anterior part of carapace and cephalic appendages, dorsal view; D, same, lateral view; E, posterior part of thorax, abdomen and telson, lateral view; F, telson, dorsal view (setae partially omitted); G, left uropod, dorsal view (perpendicular to horizontal plane of uropod; setae partially omitted; lateral margin of exopod damaged proximally); H. close up of distal part of uropodal exopod (setae partially omitted). Scale bars: A, B, E = 2 mm; C, D, F, G = 1 mm; H = 0.5 mm.

FIGURE 7. Calastacus formosus n. sp., holotype, hermaphrodite (cl 7.6 mm), NTOU A 00083. A, sixth to eighth thoracic sternites and coxae of third to fifth pereopods, ventral view (setae omitted); B, chela and carpus of left cheliped, lateral view; C, merus and ischium of left cheliped, lateral view; D, chela and carpus of right cheliped, lateral view; E, merus and ischium of right cheliped, lateral view; F, left first pleopod, lateral view; G, left second pleopod, lateral view; H, distal segments of right second pleopod, mesial view. Scale bars: 1 mm.

FIGURE 8. Calastacus formosus n. sp., holotype, hermaphrodite (cl 7.6 mm), NTOU A 00083. A, left third maxilliped, lateral view; B, left second pereopod, lateral view; C, right third pereopod, lateral view; D, same, distal part of propodus and dactylus, lateral view; E, same, mesial view; F, left fourth pereopod, lateral view (distal part of dactylus damaged); G, same, distal part of propodus and dactylus, lateral view; H, same, mesial view; I, right fifth pereopod, lateral view; J, same, distal part of propodus and dactylus, lateral view; K, same, mesial view. Scale bars: 1 mm.

FIGURE 13. A, Formosaxius dorsum n. gen., n. sp., holotype, female (cl about 12.0 mm), NTOU A 01087; B, Formosaxius dorsum n. gen., n. sp., paratype, female (cl 12.6 mm), NTOU A 00023; C, Ambiaxius propinquus n. sp., holotype, hermaphrodite (cl 11.8 mm), NTOU A 00110; D, Calastacus formosus n. sp., holotype, hermaphrodite (cl 7.6 mm), NTOU A 00083; E, Eiconaxius rubrirostris n. sp., holotype, male (cl 5.4 mm), NTOU A 00114; F, Eiconaxius kensleyi n. sp., holotype, male (cl 3.1 mm), NTOU A 00111.