Catapaguroides kasei, Osawa & Takeda, 2004

Osawa, M. & Takeda, M., 2004, Hermit crabs (Crustacea: Decapoda: Anomura: Paguroidea) from submarine caves in the Ryukyu Islands, south-western Japan, Journal of Natural History 38, pp. 1097-1132 : 1121-1128

Catapaguroides kasei sp. nov.

(figures 8–10)

Material examined. H  : NSMT-Cr 14375; male (SL 2.3 mm); Ie Island ; ‘ Shodokutsu’ (=small cave); 26°42.9∞N, 127°50.1∞E; 20 m; 13 October 1990 . P    : NSMT-Cr 14376; one male (SL 1.9 mm); same data as holotype. NSMT-Cr 14377; one male (SL 2.1 mm), one female (SL 1.5 mm); Ie Island ; ‘ Shodokutsu’; 20 m; 27 May 1993 .

Catapaguroides foresti McLaughlin, 2002a . McLaughlin’s personal collection; two males (SL 1.3, 1.5 mm), two females (SL 1.5, 1.6 mm), two ovigerous females (SL 1.4, 1.5 mm); Agat Bay, north of Aluton Island, Guam; fore-reef, 3–8 m; June to July 2000; coll. H. T. Conley.

Description. Ten pairs of biserial phyllobranchiate gills; arthrobranchs on third maxilliped apparently reduced to very small, poorly developed lamellate rudiments; arthrobranchs on cheliped to fourth pereopods moderately developed; no pleurobranch on seventh thoracic somite (above arthrobranchs of fourth pereopod).

Shield (figure 8A) slightly broader than long to slightly longer than broad; anterior margin between rostrum and lateral projections concave; anterolateral margins terraced, slightly concave; posterior margin roundly truncate, with shallow median concavity; dorsal surface weakly convex, with few tufts of short setae laterally; posterior gastric region weakly calcified. Rostrum broadly subtriangular with rounded apex, extending as far as or slightly over-reaching lateral projections. Lateral projections well developed, narrowly subtriangular, each with small submarginal spine. Accessory portions of carapace narrow, weakly calcified; each with strongly calcified plate bearing a row of short setae along linea transversalis. Posterior carapace (figure 8A) membranous; posteromedian plate weakly calcified, with moderately calcified anterior part along posterior margin of shield (in paratypes, calcified part indistinct); cardiac sulci weakly marked, divergent posteriorly, not extending to posterior margin; sulci cardiobranchialis extending posteriorly along posterior margin of branchiostegite. Branchiostegites membranous, with few scattered short setae; anterior and dorsal margins unarmed.

Ocular peduncles (figure 8A, B) stout, subcylindrical, tapering, 0.7–0.8 times as long as shield; dorsal surface with row of sparse tufts of long setae mesially and single tuft laterally at base of cornea; basal portion slightly or distinctly broader than base of cornea; lateral face straight or slightly concave; cornea occupying 0.3 length of peduncle, reduced, cone-shaped, terminating bluntly, pigmented. Ocular acicles subtriangular, terminating in small, sharply or bluntly pointed spine, separated basally by entire basal width of one acicle; dorsal surface moderately convex; lateral margin oblique; mesial margin bearing moderately long setae.

Antennular peduncles (figure 8A) long; when fully extended, slightly exceeding ocular peduncles by distal margin of penultimate segment. Ultimate segment elongate, 0.7–0.8 times longer than shield, 1.6–1.7 times longer than penultimate segment, somewhat deeper distally, with one or two long, distally plumose setae on dorsodistal margin; ventral surface with few minute or short setae. Penultimate segment glabrous. Basal segment elongate; statocyst lobe produced laterally, with spine on distolateral margin; ventrodistal margin with short setae and stout spine laterally. Upper flagellum elongate, 0.7–1.1 times longer than ultimate peduncular segment; lower flagellum 0.5–0.7 length of upper flagellum.

Antennal peduncles (figure 8A, B) when fully extended, over-reaching distal margins of corneas of ocular peduncles by 0.3–0.5 length of fifth segment; with supernumerary segmentation. Fifth segment with scattered tufts of long setae. Fourth segment with few long setae. Third segment with few moderately long setae on ventrodistal and ventrolateral margins and spine at ventromesial distal angle. Second segment with dorsolateral distal angle strongly produced, slightly over-reaching proximal margin of fourth segment, terminating in small spine; dorsomesial distal angle with small spine and few short setae; mesial margin with short setae. First segment unarmed on ventrolateral and ventrodistal margins. Antennal acicles (distal part of right acicle of holotype broken) slender, weakly arcuate, slightly overreaching, or reaching nearly to, distal margin of fifth peduncular segment and distinctly over-reaching distal margin of corneas, terminating in rounded apex or small spine, with tufts of long setae marginally. Antennal flagella 4.8–5.5 times longer than shield, with two to six long, simple setae on every article.

Mandible (figure 8G) with one small tooth on posterior mesial margin of incisor process, distal segment of palp with several short and moderately long setae on distal margin. Maxillule (figure 8H) with subquadrate proximal endite; endopod with moderately produced, subtriangular external lobe bearing two bristles, internal lobe with one bristle. Maxilla (figure 8I) with endopod over-reaching anterior margin of scaphognathite. First maxilliped (figure 8J) with endopod 0.4 length of exopod, exopod noticeably inflated proximally. Second maxilliped (figure 8K) with incomplete basis–ischium fusion, coxa strongly inflated mesially, exopod elongate. Third maxilliped (figure 8L) slender; carpus unarmed on dorsodistal margin, merus with strong spine at dorsodistal angle; ischium with crista dentata composed of row of six or seven small, subequal-sized corneous teeth, no accessory tooth; basis–ischium fusion incomplete, coxa with bifid strong spine at mid-length and small spine at distal angle of mesial margin; exopod slender, over-reaching distal margin of merus.

Chelipeds (figures 9A–E, 10A–D) unequal, right appreciably stronger than left. Right cheliped (figure 9A–E) with dactylus articulating obliquely with palm, propodal–carpal articulation rotated clockwise approximately 30° from perpendicular. Chela subovate in dorsal view, 1.9–2.1 times as long as broad; fingers subequal in length, fixed finger moderately curved ventrally; dactylus strongly curved ventrolaterally; with very narrow hiatus, each terminating in small corneous claw. Dactylus 0.7–1.0 length of palm, overlapped by fixed finger distally; cutting edge with two or three large, rounded or subtriangular calcareous teeth; dorsal surface convex, with moderately well-developed, longitudinal roundly crested ridge proximally and numerous tufts of moderately long setae distally; dorsomesial margin generally rounded, with subacute ridge armed with prominent spine or spinulose protuberance in proximal part; mesial surface nearly naked, shallowly concave in proximal part; ventral surface with moderately well-developed longitudinal ridge along mesial margin and few tufts of short setae along cutting region. Palm 1.0–1.2 times as long as carpus; dorsomesial margin weakly delimited, unarmed except for distal small spine or spinule; dorsoproximal margin unarmed; dorsal surface of palm and fixed finger convex, unarmed, fixed finger and distal part of palm with scattered tufts of setae, setae of fixed finger becoming longer and more densely distributed; dorsolateral margin not clearly delimited; mesial surface with short transverse scales each bearing tuft of moderately long setae anteriorly; lateral and ventral surfaces of palm almost naked but those of fixed finger with tufts of short setae becoming fewer along cutting region; cutting edge of fixed finger with three widely separated, rounded or subtriangular calcareous teeth, proximal spine small or indistinct, size of teeth smaller than those of dactylus. Carpus broad, subtriangular in dorsal view, 1.1–1.3 times longer than merus; dorsomesial, distal angle with small or moderately large, slender spine, margin not clearly delimited, unarmed but with irregular row of short transverse scales each bearing tuft of moderately long setae anteriorly; mesial face with few short transverse scales each bearing tuft of moderately long setae; dorsal surface with distinct ridge bearing small spines along midline, one to three on distal 0.8 of ridge and one on distal margin; dorsolateral surface strongly sloping ventrally; dorsolateral margin not clearly delimited; lateral surface naked; ventral surface strongly convex, with few moderately long setae; ventrolateral distal angle with small spine. Merus subtriangular; dorsal surface with rounded ridge along midline; dorsodistal margin with small spine mesially; ventromesial and ventrolateral margins nearly smooth, each with two to four and one or two spines distally; ventral surface smooth, with moderately long setae. Ischium with unarmed dorsal surface; other surfaces with few tufts of short setae. Coxa with spine at ventrolateral distal angle.

Left cheliped (figure 10A–D) slender, reaching beyond proximal margin of dactylus of right cheliped; propodal–carpal articulation twisted approximately 30–45° counterclockwise from perpendicular. Chela 3.0–3.3 times as long as broad, nearly straight laterally; fingers equal in length, weakly curved ventrally, with very narrow hiatus, each terminating in small corneous claw. Dactylus 0.9–1.1 length of palm, overlapped by fixed finger distally; surfaces each with longitudinal rows of tufts of moderately long setae; dorsomesial margin not delimited, unarmed; dorsal surface convex; cutting edge with row of sharply pointed, small corneous teeth. Palm 0.5–0.6 times as long as carpus; surfaces each with regular or irregular rows of tufts of long or moderately long setae, setae becoming fewer in dorsal and lateral faces of palm and arising from short transverse scales on mesial surface; dorsomesial and dorsolateral margins not delimited, unarmed; dorsal surface of palm and fixed finger convex; cutting edge of fixed finger with row of sharply pointed, small corneous teeth. Carpus 1.2–1.4 times longer than merus; dorsomesial and dorsolateral angles each with spine, mesial larger than lateral, margins each with row of short transverse scales and low protuberances, proximalmost scales usually each replaced by small spine or spinule, bearing tuft of short or long setae anteriorly; ventrolateral distal angle with strong or small spine; mesial surface smooth except for row of short transverse scales each bearing tuft of short or moderately long setae anteriorly; lateral surface naked; ventral surface with tufts of short and long setae. Merus subtriangular; dorsal surface roundly ridged along midline, naked; dorsodistal margin unarmed but with few short setae; ventromesial margin with small tubercle (holotype) or small spine (paratypes) at distal angle; ventrolateral margin with two small spines distally; mesial and lateral surfaces naked; ventral surface with few short setae. Ischium unarmed on dorsal surface, with few short setae dorsally and ventrally. Coxa with spine at ventrolateral distal angle.

Second and third pereopods (figure 10E–G) generally similar from left to right, right dactyli and propodi longer than left; elongate; over-reaching tip of right cheliped by entire length of dactyli. Dactyli (right third of holotype broken distally) of second 1.3–1.5 times as long as propodi, third 1.4–1.8 times as long, slender, moderately strongly curved ventrally in lateral view, slightly twisted in dorsal view, terminating in long, slender corneous claws; lateral surfaces each with irregular rows of short setae along dorsal margin; mesial surfaces with sparse tufts of short and long setae along dorsal and ventral margins; dorsal margins each with row of long setae, distal setae stiff; ventromesial margins each with row of four to eight small, slender corneous spines and sparse long setae. Propodi 1.1–1.4 length of carpi, each with one or two elongate corneous spines and few short and long setae at mesial ventrodistal angle; lateral and mesial surfaces with few short setae; dorsal and ventral surfaces each with row of sparse tufts of short and long setae, more numerous on dorsal face. Carpi 0.6–0.9 length of meri, with spinule near dorsodistal angle, spinule of second larger than third (in paratypes, spinule of third very small or absent); lateral and mesial surfaces with few short setae; dorsal surface with irregular row of sparse tufts of long setae; ventral surface with few tufts of short and long setae. Meri with tufts of short and long setae marginally; lateral and mesial surfaces with few scattered short setae; ventrolateral margin unarmed or with very small subdistal spine in second pereopods but always unarmed in third pereopods. Ischia unarmed but with tufts of short and long setae marginally. Coxa unarmed, left third pereopod of female with gonopore.

Fourth pereopods (figure 10H) semi-chelate, with scattered tufts of short and long setae marginally. Dactylus weakly curved, with row of tiny corneous teeth on ventral margin, no preungual process at base of terminal claw. Propodus distinctly overlapping dactylus dorsally, with moderately convex ventral margin; propodal rasp composed of single row of small ovate corneous scales present on distal half of ventral margin. Carpus unarmed on dorsal surface.

Fifth pereopods chelate. Right coxa of male (figure 9F) with long sexual tube, directed from right to left under thorax, reaching slightly (holotype) or distinctly (paratypes) beyond left coxa, recurved posteriorly, terminating in narrow but bluntly pointed apex and bearing short setae distally; distal part of paratypes more slender than that of holotype. Left coxa with short sexual tube directed anteriorly from left to right, partially obscured by setae arising from surface of eighth thoracic sternite, and bearing few short setae distally.

Third thoracic sternite unarmed on anterior margin. Sixth thoracic sternite (figure 8D) with broadly subsemicircular anterior lobe slightly skewed to left and bearing short or long setae on anterior margin. Eighth thoracic sternite (figure 9F) developed anteriorly as two somewhat flattened subovate lobes separated by shallow median depression, with dense long setae on surface.

Abdomen well developed, coiled. Male with three unpaired, unequally biramous, left pleopods on third to fifth abdominal somites; all pleopods subequal in size; each endopod approximately 0.7 length of exopod. Female with unpaired biramous, left pleopods on fourth and fifth abdominal somites, existence of second and third pleopods uncertain because of damaged abdomen of single female specimen (NSMT-Cr 14377); fourth pleopod well developed, with endopod approximately half length of exopod; fifth pleopod smaller than fourth, with endopod 0.4 length of exopod. Uropods distinctly asymmetrical.

Telson (figure 8E, F) with weakly marked transverse identations on lateral margins; slightly or strongly asymmetrical posterior lobes separated by deep or moderately deep median cleft; terminal margins oblique, each with small spine and moderately (holotype) or acutely (paratypes) pointed lateral angle; dorsal surface with scattered short setae; lateral margins each delimited by chitinous plate.

Colour. The remaining colour pattern in preservative appears as follows: shield, ocular peduncles, antennal peduncles, third maxillipeds, chelipeds, ambulatory legs with pale reddish brown markings on creamy white ground colour, most numerous on chelipeds.

Habitat. No detailed data.

Etymology. The species is named in honour of Dr T. Kase of the National Science Museum, Tokyo, in recognition of his extensive contributions to mollusc faunas of submarine caves. He kindly offered us the present interesting material of hermit crabs.

Remarks. The arthrobranchs on the third maxilliped of Catapaguroides kasei are apparently reduced to very small, poorly developed lamellate rudiments. The vestigial condition of the arthrobranchs with complete loss of pleurobranch on the seventh thoracic somite has been observed in Decaphyllus barunajaya McLaughlin, 1997 . This similarity seems to be an example of convergence. These two species are clearly distinct in many characters including diagnostic or supplemental differences between the two genera, such as the degree of development of the rostrum, shape of the ocular acicles, chelipeds, fourth pereopod and telson, and the number of pleopods in males.

In having reduced and cone-shaped corneas, C. kasei resembles C. microps A. Milne-Edwards and Bouvier, 1892 from the north-east Atlantic and Indonesian deep waters of 835–2220 m, C. hooveri and C. foresti . However, C. microps is immediately distinguished from the other three species by having considerably shorter ocular peduncles with more distinctly reduced corneas, and more elongate and completely unarmed chela and carpus of the right cheliped. Both C. kasei and C. foresti differ from C. hooveri by the appreciably longer, antennular ultimate segment and antennal acicles, and completely unarmed left chela. Catapaguroides kasei very closely resembles C. foresti , but is distinguished from the latter by the longer carpus of the left cheliped. Comparison of specimens of the two species (see ‘Material examined’) reveals that the carpus of the left cheliped is 1.7–2.0 times as long as the palm in C. kasei , whereas it is 1.5–1.6 length of the palm in C. foresti .

The tapering ocular peduncles with cone-shaped corneas may link C. kasei as well as the three allied species mentioned above to species of two other genera, Pygmaeopagurus hadrochirus McLaughlin, 1986 from the Hawaiian Islands, and Scopaeopagurus megalochirus McLaughlin and Hogarth, 1998 from the Seychelles. However, this structure is thought to be an example of convergence, as discussed by McLaughlin and Hogarth (1998: 37, 38). Catapaguroides kasei is readily distinguished from these two species by the possession of a well-developed right sexual tube in males and the structure of the right cheliped.

The subovate right chela, unarmed except for a small tubercle or spine at the dorsomesial distal angle, is also seen in two other congeners, Cartapaguroides inermis de Saint Laurent, 1968 and C. mortenseni de Saint Laurent, 1968 , both recorded from Indonesia. However, C. kasei is distinguished from C. inermis and C. mortenseni by having a prominent, spine or spinulose protuberance on the dorsomesial proximal margin of the dactylus of the right cheliped (in C. inermis and C. mortenseni , unarmed) and a pair of small spines on the terminal margin of the telson (in C. inermis , two pairs of spines; in C. mortenseni , three pairs of spines), in addition to the cone-shaped corneas of the ocular peduncles and the broad subtriangular carpus of the right cheliped in dorsal view. Catapaguroides inermis and C. mortenseni have very weakly or moderately dilated corneas, and an elongate and subrectangular carpus of the right cheliped (see de Saint Laurent, 1968: 943, 947, figures 19, 20, 27, 28).

The very long antennular peduncles and antennal flagella of C. kasei bearing numerous long, simple setae are presumably suitable for detecting and gathering sparse biological particles as food. These structures, as well as the shape of the ocular peduncles, suggest possible adaptation to the dark and oligotrophic environment of submarine caves.