Calastacus inflatus, Komai, Tomoyuki, Lin, Feng-Jiau & Chan, Tin-Yam, 2009

Komai, Tomoyuki, Lin, Feng-Jiau & Chan, Tin-Yam, 2009, A new mud shrimp species of Calastacus (Crustacea: Decapoda: Thalassinidea) from the South China Sea, Zootaxa 2088, pp. 24-30 : 25-30

publication ID	https://doi.org/ 10.5281/zenodo.187424
DOI	https://doi.org/10.5281/zenodo.6213348
persistent identifier	https://treatment.plazi.org/id/03A28783-FFE3-FFED-5EF8-FF5446E88810
treatment provided by	Plazi
scientific name	Calastacus inflatus
status	sp. nov.

Treatment

Calastacus inflatus n. sp.

( Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Material examined. Holotype: hermaphrodite (cl 21.5 mm), off Pratas (Dongsha), South China Sea, 19˚49’S, 116˚18’E, 1400 m, R/V Ocean Researcher 1, 3 June 2008, NTOU A00895 View Materials .

Description. Body ( Fig. 1 View FIGURE 1 ) stout; integument fragile, naked.

Rostrum ( Fig. 2 View FIGURE 2 A, C, D) spiniform, unarmed, supposed to reach distal margin of second segment of antennular peduncle (tip broken off); dorsal surface faintly sulcate in proximal half. Carapace ( Fig. 2 View FIGURE 2 A–D) somewhat compressed laterally, faintly rugose on branchiostegites, otherwise nearly smooth; dorsal surface strongly convex, gastric region much higher than base of rostrum; supraorbital spines small, directed anterodorsally; median carina on gastric region obsolete, far falling short of cervical groove; cervical groove very shallow; suprabranchial groove faint; orbital margin nearly straight in lateral view, suborbital angle delimited; pterygostomial margin with some minute denticles dorsally ( Fig. 2 View FIGURE 2 E).

Abdomen ( Fig. 2 View FIGURE 2 F) dorsoventrally flattened. First pleuron shortest, posteroventrally narrowed; second to sixth pleura rounded ventrally (fourth pleuron damaged on left side). Telson ( Fig. 2 View FIGURE 2 G) roughly rectangular in shape, 1.8 times longer than wide; posterior margin gently convex, unarmed; no posterolateral spines present; dorsolateral carinae faint; lateral margin with faint convexity proximally.

Eyes ( Fig. 2 View FIGURE 2 A, C, D) slightly flattened dorsoventrallly, hardly mobile, contiguous along midline, no division between cornea and eyestalk apparent, lacking pigment. Antennular peduncle moderately stout; first segment subequal in length to distal two segments combined, bearing minute spine on anterolateral margin of statocyst lobe; flagella broken off. Antennal peduncle moderately stout, longer than antennular peduncle; second segment with weakly produced, rounded dorsolateral distal angle; third segment with small spine at ventromesial distal angle; fourth segment longest; antennal acicle slender, spiniform, reaching midlength of fourth segment; flagellum missing.

Epistome ( Fig. 2 View FIGURE 2 C) produced in rounded lobe, naked.

Thoracic shield on seventh somite poorly delimited, concave, anteriorly fused with sixth thoracic sternite.

Mouthparts not dissected. Third maxilliped ( Fig. 3 View FIGURE 3 A) moderately stout; carpus with blunt dorsodistal projection; merus with 1 small subdistal spine on ventral margin; ischium unarmed on ventral margin, crista dentata (not illustrated) with row of about 20 small acute teeth; exopod overreaching distal margin of merus.

First pereopods (chelipeds) ( Figs. 1 View FIGURE 1 , 3 View FIGURE 3 B) slightly unequal (right larger than left), but similar in shape. Right chela shorter than carapace; dactylus subequal in length to palm, terminating in slender, curved tip, lateral surface with weak longitudinal carina adjacent to dorsal margin, cutting edge with row of blunt or subacute teeth; fixed finger also terminating in slender, curved tip crossing tip of dactylus, cutting edge with row of small, triangular teeth; scattered tufts of stiff setae on surfaces of both fingers; palm slightly widened distally, about 2.0 times as long as wide, with 1 small subdistal spine dorsally and with sparse tufts of short setae on lateral surface; dorsal and ventral surfaces rounded, both with row of long stiff setae, row of minute denticles also present on ventral surface; carpus about half length of palm; merus slightly widened distally, dorsal and ventral margins each with 1 moderately small subterminal spine, ventral margin also with 2 tiny denticles mesially; ischium with some minute denticles on ventral margin mesially; coxa with minute denticle on ventrodistal margin. Left cheliped broken, chela missing after preservation; merus without subterminal spines on dorsal and ventral margins.

Second pereopod ( Fig. 3 View FIGURE 3 C) chelate, moderately slender, reaching anterolateral margin of carapace by tip of merus; dactylus ( Fig. 3 View FIGURE 3 D) about half length of palm, with row of stiff setae on sharply carinate dorsal surface and with row of minute corneous spinules on cutting edge; fixed finger ( Fig. 3 View FIGURE 3 D) also with row of minute spinules on cutting edge; palm about 2.7 times as long as wide, with row of long setae on sharply carinate dorsal and ventral margins; carpus slightly shorter than palm, with row of long setae on dorsal surface and few setae on ventral surface; merus with few setae subdistally on dorsal margin and with row of long setae on ventral margin, without spination; ischium very short, unarmed. Third pereopod ( Fig. 3 View FIGURE 3 E, F) long, slightly overreaching anterolateral margin of carapace by tip of merus; dactylus 0.3 times as long as propodus, slightly depressed dorsoventrally; propodus with tufts of stiff setae on dorsal and ventral margins, bearing slender terminal spine at ventrodistal margin; carpus about half length of propodus; merus and ischium unarmed. Fourth and fifth pereopods damaged ( Fig. 3 View FIGURE 3 G, H); meri and ischia unarmed; fifth pereopod slenderer than fourth pereopod; coxal lateral plate of fifth pereopod suboval. Large gonopores on coxae of both third and fifth pereopods.

Gill formula summarized in Table 1. Epipods on third maxilliped to fourth pereopods (cf. Fig. 3 View FIGURE 3 I) foliaceus, with tiny marginal hooks; no podobranch on epipod of second maxilliped, podobranchs on third maxilliped to third pereopod all simple, rudimentary, distinctly shorter than epipods; rudimentary arthrobranch above base of second maxilliped, paired arthrobranchs above bases of third maxilliped to fourth pereopod.

Maxillipeds Pereopods

1 2 3 1 2 3 4 5 Exopods 1 1 1 0 0 0 0 0 Epipods 1 1 1 1 1 1 1 0 Podobranchs 0 0 r r r r 0 0 Arthrobranchs 0 r 2 2 2 2 2 0 Pleurobranchs 0 0 0 0 0 0 0 0 Setobranchs 0 0 0 1 1 1 1 0 First pleopod ( Fig. 4 View FIGURE 4 A, B) with distal segment basally broadened, terminating in triangular lobe, with longitudinal fold ending distally at shallow emargination; bud-like appendix interna at proximomesial angle, bearing cluster of hooks; proximal segment (protopod) longer than distal segment, narrowed distally, slightly twisted. Second pleopod ( Fig. 4 View FIGURE 4 C) with flagelliform, multiarticulated exopod bearing sparse setae; endopod bearing appendix masculina consisting of 2 slender articles; distal article longer than proximal article, tapering distally, with row of spiniform setae on mesial margin and with single row of similar setae on midline of ventral surface; proximal article with multiple longitudinal row of spiniform setae mesially, articulation to distal article strongly oblique; appendix interna bud-like, fused basally with proximal article of appendix masculina. Third to fifth pleopods each with well-developed appendix interna; both rami slender, multiarticulated, endopods slightly longer than exopods. Uropodal exopod ( Fig. 2 View FIGURE 2 H) without spination along suture or on margins, lateral margin slightly convex; endopod broadened posteriorly, without marginal spination; dorsal carinae faint.

Coloration. Entirely white to yellowish-white, without conspicuous patterns or markings ( Fig. 1 View FIGURE 1 ).

Remarks. The holotype possesses both male and female gonopores and with the anterior two pairs of pleopods modified into gonopod-like appendages. Therefore, as in other calocaridid species, this new species is hermaphroditic. Although the left chela of the first pereopod was still present during photography ( Fig. 1 View FIGURE 1 ), it could not be found later when the specimen was examined.

In spite of the presence of some apparently unique features, this new species is clearly assignable to Calastacus because of the following characters: rostrum simple, spiniform; no middorsal carina on the carapace posterior to the cervical groove; antennal acicle well-developed, spiniform; and appendix interna of second pleopod fused to the base of the appendix masculina. Unique features for the new species include: the cervical groove on the carapace is faint; the second segment of the antennal peduncle lacks an elongate spiniform projection at the dorsolateral distal angle; the merus of the third maxilliped bears only one subdistal spine on the ventral margin; the merus of the cheliped bears only one subterminal spine on the ventral margin; and the suture on the uropodal exopod is entire. In all of the five known Calastacus species, the cervical groove is distinct dorsally; the dorsolateral distal angle of the second segment of the antennal peduncle bears a long, spiniform projection; the merus of the third maxilliped is armed with at least two subdistal spines; the merus of the cheliped bears four or more spines on the ventral margin; the suture on the uropodal exopod has a row of small spines ( Faxon 1893; de Saint Laurent 1972; Kensley 1996; Kensley & Chan 1998; Ngoc-Ho 2003). Furthermore, the absence of a posterolateral spine on the uropodal endopod distinguishes C. inflatus from all but C. mexicanus .

This is the sixth species of Calastacus known, and the second from the West Pacific. It is the first thalassinidean known from the lower bathyal zone in the South China Sea. Thalassinidean shrimps are cryptic burrowers, and therefore difficult to catch. There is no doubt that many more species, probably including unknown forms, await discovery in this region.

Etymology. Named in reference to the considerably inflated carapace.