Cheiroplatea rotundioculus, Komai, Tomoyuki & Chan, Tin-Yam, 2016

Komai, Tomoyuki & Chan, Tin-Yam, 2016, “ Symmetrical ” hermit crabs of the family Pylochelidae (Crustacea: Decapoda: Anomura) collected by the “ BIOPAPUA ” and “ PAPUA NIUGINI ” expeditions in the Papua New Guinea, with descriptions of two new species, Zootaxa 4088 (3), pp. 301-328 : 312-317

Cheiroplatea rotundioculus n. sp.

( Figs. 2–4 )

Material examined. Holotype: BIOPAPUA, stn DW 3696, NE of Manus Island, 01°54’S, 147°12’E, 326–355 m, 30 September 2010, female (sl 2.2 mm), MNHN-IU-2011-2620.

Description. Shield ( Fig. 2 A) broader than long and longer than posterior carapace, with very shallow transverse sulcus subrostrally; cervical groove delineated laterally by moderately wide groove; lateral parts somewhat inflated. Rostrum ( Fig. 2 A, B) rounded, reaching slightly beyond level of lateral projections, with 5 apical spinules; lateral projections obtusely triangular, each with 1 (left) or 2 (right) marginal spinules; margins between rostrum and lateral projections deeply concave. Carapace with hepatic region bearing cluster of spinules; anterior margins of branchiostegites moderately produced, each with few minute spinules distally. Epistome unarmed.

Ocular peduncle ( Fig. 2 A, B) about 0.5 length of shield, noticeably swollen basally and tapering to rounded, slightly laterally directed cornea, with several short setae proximal to base of cornea. Ocular acicle not apparent.

Antennular peduncle ( Fig. 2 A, C) overreaching distal corneal margin by 0.3 length of basal segment. Ultimate segment short, about 0.6 length of penultimate segment, widened distally in lateral view, armed with 2 small, unequal spines on dorsal surface distal to midlength. Penultimate segment elongate, unarmed. Basal segment with prominent spine on dorsolateral margin of statocyst lobe and also prominent ventrodistal spine; statocyst lobe moderately inflated. Upper flagellum about twice length of ultimate peduncular segment. Lower flagellum slender, much shorter than upper flagellum, consisting of 5 articles.

Antennal peduncle ( Fig. 2 A–C) overreaching ocular peduncle by 0.6 length of fifth segment. Fifth segment subcylindrical, somewhat elongate, slightly widened distally, unarmed. Fourth and third segments also unarmed. Second segment with dorsolateral distal angle elongate, terminating in small spine and with 2 or 3 accessory spines on lateral surface; dorsomesial distal angle unarmed. First segment with 4 small spines on produced ventrolateral margin (2 spines prominent, one upturned, and another one curved downward). Antennal acicle overreaching distal corneal margin and reaching midlength of fifth segment, terminating in small spine; mesial margin with 1 or 2 tiny spines distal to prominent proximal spine (proximal spine bifid in left, simple in right); lateral margin with 2 small spines distal to midlength. Antennal flagellum subequal in length to carapace, each article distinctly longer than wide, bearing 2–6 short to long setae (longest setae approximately 2 articles length).

Third maxilliped ( Fig. 2 D) weakly chelate. Ischium with prominent spine at ventrodistal angle; crista dentata well-developed, but no accessory tooth. Merus with 1 tiny dorsodistal spine and 3 moderate spines on ventral margin. Carpus subequal in length to merus, cup-shaped. Propodus widened distally; fixed finger short, broadly rounded distally. Dactylus short, terminally rounded. Exopod slender, elongate, overreaching distal margin of merus by about half length; flagellum well developed, divided into 2 articles.

Chelipeds symmetrical, operculate ( Fig. 3 ). Chela subtriangular in dorsal view, fairly flattened dorsoventrally, with narrow hiatus between dactylus and fixed finger. Dactylus about 0.8 times as long as palm measured along mesial margin; dorsal surface with scattered small conical spines or tubercles, and with moderately long, sparse plumose setae; dorsomesial margin sharply delimited by row of small spines or tubercles becoming blunt and smaller distally; mesial face with few tiny tubercles adjacent to dorsal margin and 4 short, oblique ridges each bearing setal row along ventral margin; ventral surface unarmed, with longitudinal row of tufts of moderately long setae; cutting edge with row of rounded calcareous teeth, terminating in strong, curved calcareous claw crossing tip of fixed finger. Palm with dorsal surface generally flat, bearing numerous scattered spines or tubercles; shape of dorsal armature quite variable ( Fig. 3 E), those few on midline somewhat elongate, spiniform, others tear-dropshaped to rounded, vast majority of these spines or tubercles having striate surface and basally constricted; dorsolateral and dorsomesial margins each with row of small, erect spines accompanied by tufts of moderately long setae, former extending onto fixed finger (spines on dorsolateral row longer than those on dorsomesial row); lateral and mesial faces sloping to ventral surface, lateral face with scattered granules (often paired) and short setae, extending to lateral half of ventral surface, while mesial surface nearly smooth, glabrous. Fixed finger triangular, slightly upturned, with few tiny rounded tubercles on dorsal surface; ventral surface with blunt subterminal process to accommodate claw of dactylus; cutting edge with row of small, rounded calcareous tooth, terminating in large calcareous claw. Carpus with dorsodistal facet prominently elevated, nearly perpendicular against horizontal plane of palm when palm fully extended, armed marginally with row of moderately large to very large, acute spines; anterior surface of facet with scattered small, rounded, basally constricted tubercles; remainder of dorsal carpal surface with few small but prominent spines and tiny tubercles proximomesially, and scattered tiny tubercles or granules and short setae on distolateral part; mesial and ventral surfaces almost glabrous. Merus with tiny spine at dorsodistal margin, dorsal surface with row of tiny, forwardly directed spines and sparse short setae; lateral face microscopically granulate, ventrolateral margin with row of tiny spines increasing in size distally; mesial face glabrous, ventromesial margin with widely spaced tiny spines or spinules, including one at distal angle; ventral surface flat. Ischium with 1 small but prominent spine at ventrolateral distal angle; ventromesial margin smooth, unarmed.

Second and third pereopods ( Fig. 4 A, D) generally similar in shape and setation, slender. Dactyli about 1.1 times as long as propodi; dorsal surfaces with sparse moderately long setae; lateral faces with few tufts of setae distally; mesial faces with 2 rows of widely spaced tufts of stiff setae; ventral margins each with 3 small corneous spines in distal half ( Fig. 4 B, E). Propodi each with sparse setae on dorsal and ventral surfaces, lateral and mesial faces almost glabrous; ventrodistal margins each with 1 minute spinule (second) or with small corneous spine (third). Carpi each with row of 9 small spines decreasing in size proximally (second; Fig. 4 C) on dorsal surface or unarmed, both with sparse setae; lateral faces glabrous; ventral surfaces with few setae. Meri each with sparse setae and 1 (third) or 2 (second) tiny spines on dorsal surface proximal to midlength; lateral and mesial faces glabrous; ventral margin nearly straight (second) or slightly sinuous (third), each with sparse setae. Ischium armed with 1 small dorsal subdistal and 3 small spines (second) or unarmed (third).

Fourth pereopod ( Fig. 4 F) semichelate, each with propodal rasp consisting of 1 row of scales (these scales calcified basally and corneous distally). Dactylus terminating in small corneous claw. Merus widened basally. Ischium with 3 small tubercles on ventral margin.

Fifth pereopods weakly chelate; propodal rasp well developed.

Pleon with first to fifth pleomeres weakly calcified. Sixth pleomere ( Fig. 2 E) subpentagonal with broadly convex anterior margin, distinctly wider than long; dorsal surface gently convex, with few tufts of setae on either side of midline; dorsal midline with faint groove posteriorly; lateral margin forming obtuse angle at junction of anterior and posterolateral margins; posterolateral margins each with low convexity; posterolateral angle blunt but clearly delimited; posterior margin with few minute denticles medially. Protopods of uropods each with horizontal posterior margin drawn-out at inner angle into prominent spine.

Telson ( Fig. 2 F) 1.1 times as long as wide, with transverse suture crossing at about posterior 0.6. Anterior lobe slightly widened posteriorly, about 1.8 times as long as wide; dorsal surface with scattered moderately long setae; posterolateral angle rounded, well delimited; posterior margin shallowly concave. Posterior lobe slightly narrower than anterior lobe; terminal margin broadly rounded, entire; margins with fringe of fine long setae.

Coloration. In preservative, entirely whitish.

Distribution. Known only from the type locality, NE of Manus Island, Bismarck Sea, 326–355 m.

Habitat. Not known.

Remarks. Cheiroplatea rotundioculus n. sp. appears closest to C. scutata , represented only by the holotype from an unknown locality in the Gulf of Mexico (Ortmann 1892; Forest 1987a; McLaughlin & Lemaitre 2009). Shared characters include: rostrum with five marginal spinules; and ocular peduncle noticeably swollen at base and tapering to rounded cornea (Forest 1987a). Nevertheless, the new species is unique within the genus in having spines on the dorsal surface of the ultimate segment of the antennular peduncle. In other congeneric species, this segment is unarmed. Furthermore, C. rotundioculus n. sp. differs from C. scutata in the different armature on the palms of chelipeds and the lack of a dorsal row of spinules on the second pereopod propodi. The armature of the palms of the chelipeds consists of some sharp prominent spines on the midline and scattered small, tear-dropshaped or rounded tubercles in C. rotundioculus n. sp., rather than numerous scattered sharp, elongate spines in C. scutata .

Cheiroplatea stenurus , known only from the holotype from off Mayotte Island in the western Indian Ocean, is also similar to the present new species, particularly in the rounded shape of the cornea (Forest 1987a). The unarmed ultimate segment of the antennular peduncle, elongate spines on the median area of the cheliped palm and the presence of a dorsal row of spinules on each second pereopod propodus immediately distinguish C. stenurus from C. rotundioculus n. sp.

Etymology. The specific epithet is a combination of the Latin, rotundus (= rounded) and oculus (eye), in reference to the rounded cornea of the present new species; used as a noun in apposition.

Figures

FIGURE 2. Cheiroplatea rotundioculus n. sp., holotype, female (sl 2.2 mm), MNHN-IU- 2011 - 2620. A, carapace and cephalic appendages, dorsal view (right antennule in process of regeneration); B, anterior margin of carapace, ocular peduncles and left antennal peduncle, dorsal view; C, left antennule and antennal peduncle, lateral view; D, left third maxilliped, lateral view; E, sixth pleomere, dorsal view; F, telson and protopod of right uropod, dorsal view. Scale bars: A, E, F = 1 mm; B – D = 0.5 mm.

FIGURE 3. Cheiroplatea rotundioculus n. sp., holotype, female (sl 2.2 mm), MNHN-IU- 2011 - 2620. A, left cheliped, chela and carpus, dorsal view; B, left cheliped, mesial view; C, same, lateral view; D, same, carpus, posterodorsal view; E, details of spines on median part of palm, dorsolateral view. Scale bars: A – D = 1 mm; E = 0.5 mm.

FIGURE 4. Cheiroplatea rotundioculus n. sp., holotype, female (sl 2.2 mm), MNHN-IU- 2011 - 2620. A, left second pereopod, lateral view; B, same, dactylus, mesial view; C, same, carpus, mesial view; D, left third pereopod, lateral view; E, same, dactylus, mesial view; left fourth pereopod, lateral view. Scale bars: A – E = 1 mm; F = 0.5 mm.