Catapaguroides bythos, Komai, 2017

Komai, Tomoyuki, 2017, Redescription of the pagurid hermit crab Catapaguroides fragilis (Melin, 1939) and descriptions of two new species from deep-sea off the Ryukyu Islands, Japan (Crustacea: Decapoda: Anomura), Zootaxa 4273 (2), pp. 235-257 : 251-256

Catapaguroides bythos n. sp.

[New Japanese name: Soko-hime-yadokari] ( Figs 10–13 )

Material examined. Holotype: TRV “ Toyoshio-maru ”, 2013-4 cruise, stn 6, Nago Bay, Okinawa Island, Ryukyu Islands, 26°32.04’N 127°43.64’E, 412–428 m, mud bottom, 24 May 2013, sledge, coll. T. Komai, male (sl 0.98 mm), CBM-ZC 11920.

Paratypes: TRV “ Toyoshio-maru ”, 2010 cruise, stn 9, Nago Bay, Okinawa Island, 26°32.59’N 127°44.54’E to 26°33.06’N 127°44.85’E, 395– 386 m, mud bottom, 23 May 2010, sledge net, coll. H. Komatsu, 6 males (sl 0.79– 0.91 mm), 1 female (sl 1.03 mm), 4 ovigerous females (sl 0.86–1.04 mm), NSMT-Cr 25554; same data as holotype, 1 male (sl 1.03 mm), 1 ovigerous female (sl 1.1 mm), CBM-ZC 12705.

Description. Eight pairs of biserial phyllobranchiate gills (2 arthrobranchs on each pereopods 1–4; no arthrobranchs on maxilliped 3; no pleurobranch.

Shield ( Fig. 10 A) approximately as long as wide; anterior margins between rostral lobe and lateral projections shallowly concave; anterolateral margins sloping; posterior margin rounded; dorsal surface almost glabrous, anteriorly with few tufts of short setae on either side of midline. Rostrum broadly rounded. Lateral projections broadly triangular, exceeding as far as rostral lobe, each with minute submarginal spine.

Ocular peduncle ( Fig. 10 A) 0.8–0.9 length of shield, stout, widened distally; dorsal surface with rows of few setae dorsally and dorsomesially; cornea dilated, corneal width about 0.5 of peduncular length. Ocular acicle small, triangular, with submarginal spinule terminally, separated to each other basally by basal width of 1 acicle. Interocular lobe with nearly flat anterior surface.

Antennular peduncle ( Fig. 10 A), when fully extended, overreaching distal corneal margin by full length of ultimate article. Basal article with spinule on convex lateral surface of statocyst lobe. Ultimate article approximately as long as shield, slightly broadened distally in lateral view, with 2 long plumose setae at dorsolateral distal portion; dorsal surface with row of widely spaced thin setae increasing in length distally; mesial face also with row of thin setae. Dorsal flagellum with distal portion distinctly longer than proximal aesthetascbearing portion, consisting of 6 articles; ventral flagellum short, consisting of 5 articles.

Antennal peduncle ( Fig. 10 A, B) overreaching distal corneal margin by 0.2–0.3 length of article 5. Articles 5 and 4 with few short setae. Article 3 unarmed at ventromesial distal angle. Article 2 with dorsolateral distal angle produced in simple or bifid spine nearly reaching midlength of fourth segment; dorsomesial distal angle with minute spine. First segment unarmed. Antennal acicle slender, slightly sinuous, slightly falling short of distal corneal margin, terminating in slender spine, with row of short to long setae along mesial margin. Antennal flagellum exceeding 4.0 times of shield length; articles each with several short to long setae on distal margin (long setae present every 2 or 3 articles).

Maxilliped 3 ( Fig. 10 C) slender, with crista dentata on ischium consisting of 1 triangular tooth located at midlength or slightly proximal to midlength of ischium ( Fig. 10 D). Carpus and merus each without dorsodistal spine. Exopod long, reaching nearly distal margin of endopodal propodus.

Chelipeds distinctly unequal and dissimilar, left reaching midlength of right chela in males. Right cheliped ( Figs 11 A–C, male holotype; 12A–C, female paratype) not particularly elongate; no conspicuous rotation of propodal-carpal articulation. Chela elongate subovate in dorsal view, about 2.2 times longer than wide, widest at base of dactylus (males) or at midlength of palm (females). Dactylus 0.7 length of palm, slightly curved ventrally (males) or nearly straight (females); dorsal surface slightly convex transversely, unarmed, dorsomesial margin not delimited; surfaces with scattered tufts of short to moderately long setae; cutting edge with 3 triangular calcareous teeth and short distal row of corneous teeth (females), terminating in minute corneous claw. Palm approximately as long as carpus (males) or slightly shorter (females); dorsal surface gently convex, armed with 2 or 3 tiny spines mesially, situated all in distal half, and 1 similarly tiny spine proximal to base of fixed finger, and with scattered tufts of short to moderately long setae; dorsolateral and dorsomesial margins not delimited; lateral and mesial faces almost glabrous or with few short setae; ventral surface gently convex, with few short to long setae. Fixed finger with 2 or 3 triangular calcareous teeth on cutting edge, terminating in minute corneous claw. Carpus subequal in length to merus, widened distally, about 2.0 times (male) or 1.7 times (female) as long as distal width; dorsal surface with 2 small spines on midline and occasionally with 1 subdistal mesial spine; few tufts of short to long stiff setae dorsomesially; lateral face almost glabrous, ventrodistal angle with 1 tiny spine; mesial face with some tufts of long setae, distomesial angle unarmed or armed with 1 tiny spine; ventral surface gently convex, with few long setae (males) or almost glabrous (females). Merus with dorsal margin almost glabrous, dorsodistal margin unarmed or armed with 1 minute spine; lateral surface glabrous, ventrolateral distal margin slightly concave, with 2 small spines and tufts of setae; mesial surface also glabrous, ventromesial margin with 2 moderately strong spines at distal angle and 1 subdistal spine, and few tufts of long setae; ventral surface with few long setae. Ischium unarmed, with prominent tuft long setae on ventromesial margin (males) or with few setae (females). Coxa with small ventrolateral distal spine.

Left cheliped ( Fig. 11 D–F) moderately slender; propodal-carpal articulation without noticeable rotation. Chela slightly arched, about 2.6 times longer than wide; distinct hiatus between fingers in distal half. Dactylus 1.1–1.2 length of palm, unarmed, curved in distal half, terminating in small corneous claw, having sparse tufts of short to long setae; dorsomesial margin not delimited; cutting edge with row of minute corneous teeth in distal half. Palm 0.6–0.7 length of carpus; dorsal surface gently convex, with 1 or 2 tiny spines mesially, otherwise unarmed; surfaces with scattered tufts of short to long setae. Fixed finger terminating in small corneous claw; cutting edge sinuous, concave distal half with row of minute corneous teeth. Carpus widened distally, 2.3 times longer than distal width; dorsal surface with 1 tiny mesial subdistal spine and 1 middorsal spine slightly proximal to midlength, and with some tufts of short to long setae; lateral face almost glabrous, with tiny spine at ventrolateral distal angle; mesial face with some tufts of long setae dorsally and subdistally, distomesial angle with tiny spine; ventral surface gently convex, with few tufts of long setae. Merus with dorsal margin glabrous; dorsodistal margin unarmed; ventrolateral margin, with 2 small spines subdistally; ventromesial margin with 2 small spines distally; ventral surface gently convex, with several long setae. Ischium unarmed. Coxa with small ventrolateral distal spine.

Ambulatory legs ( Fig. 12 D, E) moderately long and slender, right second reaching tip of right cheliped. Dactyli 1.2–1.3 (second) or 1.5 times as long as propodi, 14–15 times longer than wide, straight in dorsal view, gently curved ventrally in lateral view, terminating in long, slender corneous claws; dorsal margins each with row of sparse stiff setae increasing in length distally; mesial faces ( Fig. 12 F, G) each with row of stiff setae on midline; ventral margins unarmed. Propodi each with 1 long spiniform setae flanked by 3 much shorter bristle-like setae (second in males) or single short spiniform seta (third in males and second and third in females); dorsal and ventral margins with few setae. Carpi each with minute dorsodistal spine and with few setae on dorsal margin. Merus armed with 1 minute subdistal spine on ventrolateral margin (second) or unarmed (third); dorsal and ventral margins each with few stiff setae; ventral margins unarmed, with row of tufts of long setae. Ischia with subterminal tuft of long setae followed by shorter setae (second) or row of short setae on ventral margins (third). Second pereopods with deep notch on ventral margin at articulation between merus and ischium. Female with unpaired left gonopore.

Pereopod 4 ( Fig. 10 E) slightly semichelate; dactylus with several minute corneous teeth on ventral margin; propodal rasp consisting of single row of corneous scales. Pereopod 5 semichelate.

Anterior lobe of thoracic sternite 6 ( Fig. 10 F) subsemicircular, with moderately long setae on anterior margin.

Male sexual tube of medium length (about 4 times of coxal length) extending from coxa of right pereopod 5 ( Fig. 10 G), directed from right to left across ventral body surface and far overreaching lateral margin of left coxa, terminating in rounded tip; left coxa with gonopore, but no sexual tube. Median lobe on thoracic sternite 8 ( Fig. 10 G) partially obscured by numerous long setae.

Telson ( Fig. 10 H) approximately as long as wide, narrowed posteriorly in posterior half; no lateral indentations; posterior lobes strongly asymmetrical; terminal margins oblique, each with 2 minute spinules, both outer angles subacute.

Eggs about 0.60 × 0.55 mm, few in number (about 8).

Coloration in life. Body and appendages entirely semitransparent, without conspicuous markings. See Fig. 13 .

Variation. Fourteen specimens, including eight males and six females, were available for study. They are generally very similar in the morphology except for characters relating to the sex. Like in other congeneric species, the propodus of the pereopod 2 bears a set of spiniform setae on the ventrodistal margin in males. Thirteen of the 14 specimens have a small spine on the dorsal surface of the palm of the right cheliped, located proximal to the base of the fixed finger, but in the smallest specimen, such a spine is wanting.

Distribution and habitat. Presently known only from Nago Bay, Okinawa Island, Ryukyu Islands, at depths of 386–428 m; mud bottom. Found to use gastropod shells for housing; no association with other invertebrates was observed.

Remarks. Catapaguroides bythos n. sp. appears closest to C. pectinipes , known only from the Dahlak Archipelago in the Red Sea. The latter species was originally assigned to Cestopagurus Bouvier, 1899 ( Lewinsohn 1969) , but was subsequently transferred to Catapaguroides by de Saint Laurent (1970). Shared characters include: (1) ocular peduncle stout, cornea distinctly dilated; (2) article 5 of antennal peduncle distinctly overreaching distal corneal margin; (3) sinuous cutting edge of fixed finger of left cheliped, forming distinct hiatus distally between fingers when closed. In particular, the third character is not known for the other congeneric species, suggesting the close relationship between the two species. The new species can be distinguished from C. pectinipes by the following particulars: (1) the antennal acicle is much longer in C. bythos n. sp. than in C. pectinipes , reaching about the midlength of article 5 of the antennal peduncle (only reaching to the distal margin of article 4 in C. pectinipes ; cf. Lewinsohn 1969: Fig. 14a); (2) the palm of the right cheliped bears a small spine on the dorsal surface proximal to the base of the fixed finger in C. bythos n. sp. ( Figs. 11 C; 12C), whereas such a spine is absent in C. pectinipes (cf. Lewinsohn 1969: fig. 14b); (3) the left palm is armed with one or two tiny dorsomesial spines in C. bythos n. sp. ( Fig. 11 D, F), rather than being unarmed in C. pectinipes (cf. Lewinsohn 1969: fig. 14c); (4) the carpus of the left cheliped is armed with a tiny dorsomesial spine subdistally in C. bythos n. sp. ( Fig. 11 E, F), whereas no dorsomesial spine is present on the left cheliped carpus in C. pectinipes (cf. Lewinsohn 1969: fig. 14c).

Catapaguroides mortenseni , known from Indonesia, is also substantially similar to C. bythos n. sp. However, the new species is easily separated from C. mortenseni by the possession of two or three dorsomesial spines and one dorsal spine proximal to the base of the fixed finger on the right palm (unarmed on the dorsal surface of the right palm, except for a minute spine at the distomesial angle in C. mortenseni ; cf. de Saint Laurent 1968: fig. 28). The left palm is armed with one or two dorsomesial spines and the carpus is also armed with one dorsomesial and one or two middorsal spines in C. bythos n. sp., whereas the left palm and carpus are unarmed in C. mortenseni (cf. de Saint Laurent 1968: 945). Furthermore, de Saint Laurent (1968: 945) specifically mentioned that the crista dentata on the ischium of maxilliped 3 is composed of three or four teeth in C. mortenseni , but in the new species, there is consistently only one tooth on the mesial margin of the ischium of maxilliped 3, representing the crista dentata.

Etymology. The specific name is the Greek meaning “from the deep”, referring to the bathyal habitat of this new species.

Figures

FIGURE 10. Catapaguroides bythos n. sp., holotype, male (sl 0.98 mm), CBM-ZC 11920. A, shield (including carapace lateral lobes) and cephalic appendages, dorsal view; B, left antennal peduncle, ventral view; C, left maxilliped 3, lateral view; D, same, ischium, ventral view; E, left pereopod 4, lateral view; F, thoracic sternite 6, ventral view; G, coxae of pereopods 5 and thoracic sternite 8, ventral view; H, telson, outer view.

FIGURE 11. Catapaguroides bythos n. sp., holotype, male (sl 0.98 mm), CBM-ZC 11920. A, right cheliped, mesial view; B, same, lateral view, setae partially omitted; C, same, chela and carpus, dorsal view; D, left cheliped, lateral view, setae omitted; E, same, chela and carpus, dorsal view.

FIGURE 12. Catapaguroides bythos n. sp. A – C, paratype, ovigerous female (sl 1.1 mm), CBM-ZC 12705; D – G. holotype, male (sl 0.98 mm), CBM-ZC 11920. A, right cheliped, lateral view; B, same, mesial view; C, same, chela and carpus, dorsal view; D, right pereopod 2, lateral view; E, left pereopod 3, lateral view; F, G, dactyli of right pereopod 2 and left pereopod 3, mesial view.

FIGURE 13. Catapaguroides bythos n. sp., holotype, male (sl 0.98 mm), CBM-ZC 11920, showing colouration in life.