Catapaguroides fragilis ( Melin, 1939 )

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 : 236-243

Catapaguroides fragilis ( Melin, 1939)

[Japanese name: Madara-hime-yadokari] ( Figs 1–4 )

Eupagurus (Catapagurus) fragilis Melin, 1939: 45 , figs 23–26 (type locality: Takinoura, Ani-jima Island, Ogasawara Islands). Catapaguroides fragilis .—De Saint Laurent 1968: 940 (in part).— Miyake 1978: 134 (in part), text-fig. 53.— McLaughlin & Pittman 2002: 43, fig. 1E.—McLaughlin 2002: 499 (key).— Okuno & Arima 2006: 35, fig. 3B.—Komai et al. 2010: (key).— Komai & Rahayu 2013: 144 (Table 1), 151, 187 (key).— Arima 2014: 155, unnumbered figs.

Material examined. Holotype (digital image provided by SMNH): Dr. Sixten Bock Expedition to the Bonin Islands 1914, Takinoura, Ani-jima Island, Ogasawara (Bonin) Islands, subtidal, 29 July 1914, male (cl 2.4 mm) , SMNH Type-2291 (entire body with ocular peduncles and left cheliped).

Other material: TRV “Toyoshio-maru”, 1996-6 cruise, stn 7, SE of Tanegashima Island, Ohsumi Islands, 30°15’N, 130°45’E, 75 m, sand, 2 June 1996, dredge, coll. T. Komai, 1 female (sl 1.18 mm), CBM-ZC 9018; 1997- 5 cruise, stn 8, S of Mage-jima Island, Ohsumi Islands, 30°38.50’N, 130°49.00’E, 39 m, 29 May 1997, dredge, coll. T. Komai, 4 males (sl 1.25–2.16 mm), CBM-ZC 13594; Kashiwa-jima Islet, Ohtsuki, Kochi Prefecture, subtidal, July 2008, SCUBA diving, coll. Y. Hirai, 1 female (sl 1.04 mm), CBM-ZC 13595.

Description. Ten pairs of biserial phyllobranchiate gills; 2 very small, but lamellate arthrobranchs on maxilliped 3; no pleurobranch on either wall of thoracomere 7 (above base of pereopod 4).

Shield ( Fig. 1 A) approximately as long as wide; anterior margins between rostral lobe and lateral projections concave; anterolateral margins slightly terraced or sloping, posterior margin roundly truncate; dorsal surface almost glabrous, with few tufts of short setae laterally. Rostrum rounded. Lateral projections triangular, produced to level of rostrum, each with small marginal or submarginal spine. Carapace lateral lobes moderately wide, well calcified.

Ocular peduncle ( Fig. 1 A) long, slender, 0.8–0.9 times as long as shield, subcylindrical, with basal part slightly inflated; dorsal surface mesially with row of 4 tufts of stiff setae; cornea small, rounded, very slightly dilated, corneal width approximately 0.2 of peduncular length. Ocular acicle triangular, terminating in small marginal spine, bearing few short setae subdistally, separated to each other basally by basal width of 1 acicle. Interocular lobe with slightly convex anterior surface.

Antennular peduncle ( Fig. 1 A), when fully extended, overreaching distal corneal margin by 0.8 length of ultimate article. Basal article with spinule on lateral face of statocyst lobe. Ultimate article 0.6–0.7 length of shield, slightly broadened distally, with 2 long plumose setae at dorsolateral distal portion; dorsal surface with row of some widely spaced setae. Dorsal flagellum longer than ultimate peduncular segment; distal portion more than 3 times as long as proximal aesthetasc-bearing portion, consisting of 6 or 7 articles; ventral flagellum consisting of 6 articles.

Antennal peduncle ( Fig. 1 A, B) not reaching distal corneal margin. Articles 5 and 4 with few setae. Article 3 with 1 prominent spine at ventromesial distal angle, extending as far as dorsolateral distal angle of article 2. Article 2 with dorsolateral distal angle produced into simple spine far falling short of midlength of article 4, occasionally with 1 subterminal spinule on mesial margin; dorsomesial distal angle with small spine. Article 1 unarmed. Antennal acicle moderately slender, gently arcuate, overreaching corneal base, occasionally reaching distal corneal margin, terminating in small spine, with row of short to long stiff setae mesially. Antennal flagellum exceeding 6 times of shield length, reaching to tip of extended right cheliped in males; articles each principally with 2 or 3 setae on distal margin, those in proximal half of flagellum each with setae of 2 or more length of 1 article.

Maxilliped 3 ( Fig. 1 C) moderately stout, with crista dentata on ischium consisting of 3–5 acute, triangular teeth ( Fig. 1 D); no accessory tooth. Carpus without dorsodistal spine. Merus also unarmed. Exopod reaching midlength of carpus.

Chelipeds greatly unequal in length, dissimilar. Male right cheliped ( Fig. 2 A–D) somewhat elongate; propodalcarpal articulation with slight clockwise rotation. Chela about 2.5 times as long as wide, widest at base of dactylus. Dactylus articulating moderately obliquely with palm, about 0.6 length of palm, gently curved ventrally; dorsal surface convex, unarmed, dorsomesial margin not delimited, armed with 1 small spine proximally; cutting edge with 3 blunt, triangular calcareous teeth, terminating in calcareous claw; scattered tufts of short to long setae on surfaces. Palm 1.8 times as long as wide, subequal in length to carpus, with scattered tufts of short to long setae on surfaces (ventral setae longest); dorsal surface gently convex transversely, with dorsomesial row of 8 or 9 small spines and 1 dorsoproximal spine or tubercle, otherwise unarmed; dorsolateral and dorsomesial margins not delimited; ventral surface slightly convex. Fixed finger with 2 blunt calcareous teeth on cutting edge, terminating in calcareous claw. Carpus subcylindrical, about 1.2 length of merus, slightly broadened distally, about 2 times longer than distal width; surfaces with scattered tufts of long setae; dorsal surface with row of 7–9 small spines or tubercles on midline (often in double row) and 1 small mesial spine proximal to midlength; ventrolateral distal angle and distomesial angle each with tiny spine. Merus with transverse rows of stiff setae on dorsal surface; dorsodistal margin with small spine mesially, partially obscured by stiff setae; lateral surface with several tufts of setae adjacent to ventrolateral margin, ventrolateral margin with 2 or 3 small spines distally; mesial surface mostly glabrous, ventromesial margin with 2 small spines at distal angle and 1 subdistal spine; ventral surface with scattered tufts of long setae. Ischium unarmed, but bearing long bristle-like setae on dorsal margin and mesial face.

Female right cheliped ( Fig. 3 A–C) not particularly elongate; setation less developed. Chela about 2.4 times as long as wide, ovate in general outlines. Dactylus 0.8 length of palm, gently curved ventrally; dorsal surface unarmed, dorsomesial margin not delimited, with 1 small spine proximally; cutting edge with 3 blunt, triangular calcareous teeth, terminating in tiny calcareous claw. Palm 1.4 times as long as wide, subequal in length to carpus; dorsal surface gently convex, with dorsomesial row of 5 or 6 small spines and 1 small but conspicuous dorsoproximal spine; dorsolateral and dorsomesial margins not delimited; ventral surface convex. Fixed finger with 2 blunt calcareous teeth on cutting edge, terminating in calcareous claw. Carpus slightly longer than merus, slightly broadened distally, about 1.7 times longer than distal width; dorsal surface with row of 4 small spines on midline and 1 mesial spine at about midlength; ventrolateral distal distomesial angles each with small spine. Merus with 3 spines on ventrolateral margin distally; ventromesial margin somewhat expanded, with 2 spines at distal angle and 1 subdistal spine; ventral surface concave, with scattered tufts of long setae. Ischium as in male cheliped.

Left cheliped ( Fig. 3 D–F) moderately slender, reaching midlength of right chela in males; propodal-carpal articulation without noticeable rotation. Chela not arched, 3.2 times longer than wide. Dactylus 0.9–1.0 times as long as palm, unarmed, with numerous tufts of short to long setae on surfaces; dorsomesial margin not delimited, unarmed; cutting edge with row of minute corneous teeth, terminating in small corneous claw. Palm 0.8 length of carpus, with scattered tufts of long setae on surfaces; dorsal surface slightly convex, with 2 or 3 small dorsomesial spines (second spine sometimes larger than others), otherwise spineless. Fixed finger with row of minute corneous teeth at least on distal half of cutting edge, terminating in small corneous claw. Carpus slightly widened distally, about 2.6 times longer than distal width, with small spine at dorsomesial distal angle; dorsal surface with 2–5 small spines on midline, and with numerous tufts of long stiff setae; lateral, mesial and ventral surfaces also with scattered tufts of long setae, ventrolateral distal angle with tiny spine; ventral surface slightly convex. Merus with some tufts of short to long stiff setae on dorsal surface, dorsodistal margin unarmed; ventrolateral margin generally convex, with 2 small spines distally; ventromesial margin also convex, with 2 small spines subdistally; ventral surface with scattered long setae. Ischium with tufts of long bristle-like setae on dorsal surface and distomesial margin.

Ambulatory legs (pereopods 2 and 3) ( Fig. 4 A, B) long and slender, right second reaching extended right cheliped in males. Dactyli 1.1–1.2 (second) or 1.4–1.5 (third) times as long as propodi, about 13–14 times as long as wide, straight in dorsal view, weakly curved ventrally in lateral view, terminating in long, slender corneous claws; dorsal margins each with row of moderately long bristle-like setae; mesial faces each with row of stiff setae on midline and row of 2–4 (second) or 4–7 slender spiniform setae adjacent to ventral margin ( Fig. 4 C, D); ventral margin unarmed. Propodi each with long, slender spiniform setae flanked by 2–4 shorter spiniform or bristle-like setae (male second) or 1 small spiniform setae (female second and third in both sexes) on ventrodistal margin mesially; dorsal margins each with tufts of moderately long stiff setae; ventral surface with sparse long setae. Carpi usually with tiny dorsodistal spine; sparse tufts moderately long setae on dorsal margins. Meri each with 1 tiny distal spine on ventrolateral margin (second) or unarmed (third); dorsal margins each with row of tufts of moderately long setae; ventral margins with tufts of long setae. Ischia each with sparse setae on dorsal and ventral margins. Second pereopods with conspicuous notch on ventral margin at articulation between merus and ischium. Female with unpaired left gonopore.

Pereopod 4 ( Fig. 1 E) weakly semichelate; dactylus terminating in large corneous claw; propodal rasp consisting of single row of several corneous scales. Pereopod 5 semichelate.

Anterior lobe of thoracic sternite 6 ( Fig. 1 F) subsemicircular, no conspicuous armature, slightly skewed to left, bearing short setae on anterior margin.

Male with sexual tube of medium length (3–4 times of coxal length) extending from coxa of right pereopod 5 ( Fig. 1 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 very short, papilla-like sexual tube. Median lobe on thoracic sternite 8 ( Fig. 1 G) partially obscured by numerous, often curled, long setae.

Telson ( Fig. 1 H) slightly longer than wide, narrowed posteriorly; no trace of lateral indentations; posterior lobes strongly asymmetrical, separated by deep median cleft; left terminal margin with 2 or 3 minute spines and laterally directed, acute outer angle; right terminal margin strongly oblique, with 1–3 or 2 minute spines and acute or subacute outer angle.

Colouration in life. Carapace reddish. Ocular peduncles with red and white longitudinal stripes on light orange background. Antennular peduncle translucent yellowish or orangish. Antennal peduncle translucent. Chelipeds generally whitish or translucent, with scattered small red spots on chelae, carpi and meri. Ambulatory legs generally translucent, each with row of small red spots along dorsal and ventral margins of dactylus to merus.

Variation. Other than the holotype, six specimens, four males and two females, were available for examination. They are generally very similar except for sexual differences. Like vast majority of the other species in Catapaguroides , the propodus of the pereopod 2 of males is provided with a set of spiniform setae, consisting of one long spiniform setae flanked by two to four shorter spiniform or bristle-like setae, on the ventrodistal margin. In females, there is only one small spiniform seta on the ventrodistal margin of the pereopod 2 propodus. The right cheliped is much more elongate in males than in females; spines on the palm and carpus are more numerous and smaller in males than in females (for example, dorsomesial spines on the palm are seven to nine in males, five or six in females).

Distribution and habitat. Southwestern part of Japan, from Sagami Bay to Ohsumi Islands, and Izu Islands to Ogasawara Islands; and possibly from Mururoa, French Polynesia; subtidal to 75 m; sand bottoms. Found to use gastropod shells for housing.

Remarks. Catapaguroides fragilis was originally described on the basis of a single male specimen by Melin (1939) collected from the Ogasawara (= Bonin) Islands [as Eupagurus (Catapagurus) ]. The holotype lacked the right cheliped. In her revision of Catapaguroides and Cestopagurus Bouvier, 1891 , de Saint Laurent (1968) transferred the Melin’s taxon to Catapaguroides and placed the Hawaiian Cestopagurus setosus Edmondson, 1951 in the synonymy of C. fragilis . De Saint Laurent (1968) compared Edmondson’s (1951) male holotype with the “mutilated” male holotype of Melin’s taxon and a small additional female from Mururoa, French Polynesia, at depth of 40 m. Although de Saint Laurent noted certain differences among the three specimens, she provisionally considered that all three specimens represent a single species. Only the right cheliped of the Mururoan specimen was illustrated by de Saint Laurent (1968). Miyake (1978) reported on C. fragilis on the basis of numerous specimens from the Japanese main islands ( Sagami Bay and Amakusa, Kumamoto Prefecture). McLaughlin & Pittman (2002) clarified that Edmondson’s (1951) Catapaguroides setosus is distinct from C. fragilis on the basis of examination of respective holotype . They illustrated the chela and carpus of the left cheliped of the holotype of C. fragilis to show morphological differences in this appendage in discriminating C. setosus from C. fragilis . Komai & Takeda (2006) has clarified that the specimens from Sagami Bay , Miyake (1978) identified with C. fragilis , actually represent C. japonicus de Saint Laurent, 1968 ; they assumed that only the material from Amakusa might actually represent C. fragilis , because the illustrations of C. fragilis given by Miyake (1978: text-fig. 53) did not agree with C. japonicus , particularly in the non-inflated corneas and the lack of scattered small spines on the dorsal surface of the right palm. Okuno & Arima (2006) and Arima (2014) published color photographs of C. fragilis , but neither provided detailed morphological description. Komai & Rahayu (2013) examined one female specimen identified with C. fragilis from Ohsumi Islands , Japan, in comparison with their new species C. crassimanus Komai & Rahayu, 2013 . Identification keys to species of Catapaguroides ( McLaughlin 2002; Komai et al. 2010; Komai & Rahayu 2013) included C. fragilis .

As noted by McLaughlin (2002) and McLaughlin & Pittman (2002), the holotype of Catapaguroides fragilis is represented in the collections of the Museum of Evolutionary Zoology (MEZ), Uppsala, Sweden, by a series of 11 slides (MEZ 439 a–k) of the antennules, antennae, maxillipeds 1–3, right pereopod 2 and right pereopod 5. The body and detached left cheliped is housed in the collection of the Swedish Museum of Natural History , Stockholm ( SMNH Type-291), corresponding to the “mutilated” specimen examined by de Saint Laurent (1968). During this study, I examined a color image of the body and left cheliped of the holotype kindly provided by E. D. Akerman of SMNH. I confirmed that the additional specimens examined in this study agree well with the holotype in many diagnostic aspects seen in the holotype in the present condition, including the small, non-inflated corneas, the presence of multiple mid-dorsal spines on the left cheliped carpus and the relatively short right sexual tube without an elongate, anteriorly directed distal portion. McLaughlin & Pittman (2002) stated that the dactylus of the left cheliped was appreciably shorter in relation to the palm in the holotype of C. fragilis ; the given illustration ( McLaughlin & Pittman 2002: Figure 1 E) shows the dactylus of the left cheliped being about half-length of the palm. However, this is not accurate. The dactylus is actually subequal in the length to the palm in the holotype. As pointed out by de Saint Laurent (1968), a discrepancy is seen in the length of the dactylus of pereopod 2 between Melin’s (1939) original description and the present specimens. Melin (1939) specifically noted that the dactylus of the pereopod 2 is equal in the length to the propodus, but in the additional Japanese specimens, the dactylus is always longer than the propodus (1.1 times as long as propodus). As far as I aware, there is no other congeneric species having the dactylus of the pereopod 2 being subequal in the length to the propodus, and thus the observation by Melin (1939) is questionable. De Saint Laurent (1968) remarked that it is possible that Melin did not take account of the terminal claw of the dactylus.

Differentiating characters between C. fragilis and C. setosus are now assessed more precisely. The structure of the right chela is quite different between the two species. For example, the palm is non-operculiform with dorsomesial margin of the dactylus and dorsolateral margin of the palm being all rounded in C. fragilis ( Fig. 2 A– C); the dorsomesial margin of the dactylus bears a small proximal spine. In contrast, the right chela in C. setosus is suboperculiform and entirely arched; the dorsomesial margin of the dactylus has a prominent thin ridge, but spineless; the dorsolateral margin is bordered with a slightly elevated ridge extending to the tip of the fixed finger ( McLaughlin & Pittman 2002: 42, fig. 1A). The carpus of the right cheliped is armed with a longitudinal row of four to nine spines or tubercles on the dorsal surface in C. fragilis ( Fig. 2 A, B, D), whereas there are only three very small, blunt tubercles in C. setosus (cf. McLaughlin & Pittman 2002: 42). As shown by McLaughlin & Pittman (2002: 42, fig. 1C), the left chela is entirely arched in C. setosus , but only the fingers are slightly curved ventrally in C. fragilis ( Fig. 3 D). Other potentially specific differences are discussed below. The rostral lobe extends as far as the lateral projections in C. fragilis ( Fig. 1 A), rather than extending beyond them in C. setosus ( McLaughlin & Pittman 2002: 42, fig. 1A). The antennular peduncle overreaches the distal corneal margin by the approximately 0.8 length of the ultimate segment in C. fragilis ( Fig. 1 A), while 0.35 in C. setosus ( McLaughlin & Pittman 2002: 42, fig. 1A). The dactyli of the pereopods 3 bear four to six spiniform setae on the mesial face adjacent to the ventral margin in C. fragilis ( Fig. 4 C, D), whereas apparently unarmed in C. setosus ( McLaughlin & Pittman 2002: 42) .

The right cheliped of the Mururoa female specimen, depicted by de Saint Laurent (1968: fig. 26), agrees well with those of the present Japanese female specimens of C. fragilis in the general shape and armature. De Saint Laurent specifically noted the number of spines on the chela and carpus of the left cheliped (one spine on the palm and two spines on the carpus), which could be within range of intraspecific variation. I concur de Saint Laurent’s (1968) identification of the Mururoa specimen with C. fragilis .

Figures

FIGURE 1. Catapaguroides fragilis (Melin, 1939), male (sl 1.54 mm), CBM-ZC 13594. 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 2. Catapaguroides fragilis (Melin, 1939), male (sl 1.54 mm), CBM-ZC 13594. A, right cheliped, mesial view; B, same, lateral view, setae omitted; C, same, chela, dorsal view; D, same, carpus, dorsal view.

FIGURE 3. Catapaguroides fragilis (Melin, 1939), A – C, female (sl 1.18 mm), CBM-ZC 9018; C – E, male (sl 1.54 mm), CBM-ZC 13594. A, right cheliped, mesial view; B, same, lateral view, setae omitted; C, same, chela and carpus, dorsal view; D, left cheliped, mesial view; E, same, lateral view, setae omitted; F, same, chela and carpus, dorsal view, setae omitted.

FIGURE 4. Catapaguroides fragilis (Melin, 1939), male (sl 1.54 mm), CBM-ZC 13594. A, right pereopod 2, lateral view; B, left pereopod 3, lateral view; C, D, dactyli of right pereopod 2 and left pereopod 3, mesial view.