Pagurixus boninensis ( Melin, 1939 )

Komai, Tomoyuki & Osawa, Masayuki, 2006, A review of the Pagurixus boninensis species group, with descriptions of six new species (Crustacea: Decapoda: Anomura: Paguridae), Zootaxa 1214 (1), pp. 1-107 : 48-58

Pagurixus boninensis ( Melin, 1939)

( Figs. 19–22 , 45A , 48 )

Eupagurus (Pagurixus) boninensis Melin, 1939: 38 , figs. 16–19 [type locality: Takinoura , Bonin (Ogasawara) Islands].

Pagurus (Pagurixus) boninensis .— Gordan, 1956: 327.

Pagurus boninensis .— Miyake, 1978: 79 (key, in part); 1982: 198, 225 (key, in part); 1998: 198, 225 (key, in part).

Pagurixus boninensis .— Okuno & Arima, 2004: 60, Fig. 3C .

? Pagurixus boninensis .— Asakura et al., 1994: 280.— Asakura, 1995: 356, fig. 21–278.— Komai & Asakura, 1995: 341.

Pagurixus nomurai .—Asakura, 2002: 452, fig. 4, left. Not Pagurixus nomurai Komai & Asakura, 1995 .

Not Pagurus boninensis .— Lewinsohn, 1969: 64, fig. 11; 1982: 58. [= Pagurixus anceps ( Forest, 1954) ].

Not Pagurixus boninensis .— Ooishi, 1970: 90, pl. 12: fig. 13. [= Pagurixus brachydactylus n. sp.].

Not Pagurixus boninensis .— McLaughlin & Haig, 1984: 124, fig. 1 [in part, = Pagurixus ruber n. sp.].— Paulay et al., 2003: 490 [= Pagurixus ruber n. sp.].

Not Pagurixus cf. boninensis .— Morgan, 1990: 22; 1992: 171, 1993: 169, fig. 4A. Not Pagurixus boninensis ( Melin, 1939) . See ’Remarks.’

Type material

SYNTYPE: SMNH Type­2289, male (SL 2.1 mm), Takinoura ( Ani­jima Island ), Bonin (Ogasawara) Islands, coral, coll. S. Bocks Expedition to Japan and Bonin Islands 1914 .

Other material. Japan. Ogasawara Islands . CBM­ZC 8472, 1 male (SL 2.2 mm), Miyano­hama, Chichi­jima Island, 0.5 m, under dead coral, coll. M. Osawa , 24 September 2000; CBM­ZC 8473, 2 males (SL 1.7, 2.6 mm), 1 ovigerous female (SL 1.7 mm), same data as CBM­ZC 8472; CBM­ZC 8474, 2 males (SL 2.3, 2.5 mm), Tsurihama , Chichi­jima Island, 2 m, among accumulated dead corals, coll. M. Osawa , 24 September 2000; CBM­ ZC 8475 , 1 male (SL 2.0 mm), Tsurihama , Chichi­jima Island, 2–3 m, among accumulated dead corals, coll. M. Osawa , 26 September 2000; CBM­ZC 8476, 2 females (SL 1.5, 1.6 mm), Miyanohama , Chichi­jima Island, 1–2 m, among dead coral branches, coll. M. Osawa , 20 October 1999; CBM­ZC 8477, 1 male (SL 1.7 mm), 3 females (SL 1.6–1.7 mm), Tsurihama , Chichi­jima Island, subtidal, dead coral, coll. M. Osawa , 3 March 1998. Izu Islands . CMNH­ZC 1688 , 1 ovigerous female (SL 2.7 mm), Sokodo , Hachijo Island, Izu Islands, 15 m , 8 July 2002, SCUBA diving, coll. J. Okuno.

Redescription

Shield ( Fig. 19A ) 1.1–1.2 times longer than broad; anterior margin between rostrum and lateral projections slightly concave; anterolateral margins sloping; dorsal surface with few tufts of short setae laterally. Rostrum triangular, distinctly overreaching lateral projections, moderately broad, terminating in spinule. Lateral projections obtusely triangular, slightly produced, with submarginal spinule.

Ocular peduncle ( Fig. 19A ) moderately long and stout, 0.6–0.7 length of shield, each with row of tufts of short setae on dorsal surface; corneas weakly dilated, corneal width about 0.4 of peduncular length; basal part somewhat inflated, as broad as corneal width. Ocular acicles suboval or subtriangular, with small submarginal spine.

Antennular peduncle ( Fig. 19A ) overreaching distal margin of cornea by 0.5–0.6 length of ultimate segment. Ultimate segment with tufts of short to long setae at dorsolateral distal angle; ventral surface with 2 rows of equidistantly spaced tufts of short setae ( Fig. 19B, C ). Basal segment with small spine on lateral face of statocyst lobe. Ventral flagellum with numerous long setae on lateral and mesial margins.

Antennal peduncle ( Fig. 19A ) overreaching distal margin of cornea by 0.4–0.7 length of fifth segment. Second segment with very small spine at dorsomesial distal angle; laterodistal projection moderately short, not reaching midlength of fourth segment, terminating in simple or bifid spine. First segment with minute laterodistal spine; ventromesial distal margin produced, unarmed or with spinule just lateral to antennal gland opening. Antennal acicle relatively long, arcuate, nearly reaching to slightly overreaching distal margin of cornea; mesial margin with row of tufts of moderately long setae.

Right cheliped of males ( Fig. 20A–D ) not particularly elongate, moderately stout. Chela subovate in dorsal view, 2.0–2.2 times longer than broad. Dactylus 0.7–0.9 length of palm; dorsomesial margin not clearly delimited; surfaces granular; cutting edge with row of low, unequal calcareous teeth in middle part and row of small corneous teeth in distal 0.3, terminating in small corneous claw. Palm 0.9–1.2 times as long as carpus; convex dorsal surface granular, dorsolateral margin moderately delimited, dorsomesial margin not delimited; lateral, mesial and ventral surfaces also granular, occasionally with few tufts of short setae on ventral surface. Cutting edge of fixed finger with low calcareous teeth (middle one largest) on proximal 0.7 and smaller calcareous teeth on distal 0.3, terminating in small corneous claw. Carpus 1.0–1.1 length of merus; dorsolateral margin not delimited, dorsomesial margin faintly delimited by row of small spines; all surfaces granular, lateral surface lacking median ridge; mesial surface with small spinulose tubercles and moderately long, stiff setae adjacent to dorsomesial margin; ventral surface strongly convex. Meral­carpal articulation lacking any pronounced clockwise rotation; dorsal surface of merus with row of low transverse ridges, dorsodistal margin unarmed or armed with few small spines and row of moderately long stiff setae; lateral face nearly smooth, ventrolateral margin with 2–5 spines in distal half; mesial face smooth, with few stiff setae, ventromesial margin with row of small denticles or tubercles; ventral surface with granules and few moderately long setae. Ischium with faintly denticulate ventromesial margin; surfaces unarmed.

Right cheliped of females ( Figs. 20E, F , 21A, B ) moderately stout for genus, generally similar to that of male. Chela 2.1–2.2 times longer than broad. Dactylus 1.1–1.3 length of palm; dorsal surface weakly granular, with weak median ridge; dorsomesial margin delimited by row of granules; mesial and ventral faces microscopically granular, with few tufts of short setae; cutting edge with small, blunt calcareous teeth in proximal 0.4–0.5 and row of small corneous teeth in distal 0.5–0.6, terminating in small corneous claw. Palm 0.5–0.6 length of carpus; dorsolateral margin delimited by faintly tuberculate or crenulate ridge, dorsomesial margin at most faintly delimited; mesial surface granular. Cutting edge of fixed finger with small, blunt calcareous teeth in proximal 0.7–0.8 (distal teeth subacute and interspersed by row of small corneous teeth), terminating in small corneous claw. Carpus subequal in length to merus; dorsolateral margin weakly delimited by row of small spines and protuberances; dorsomesial margin weakly delimited by row of small spines and protuberances; surfaces granular, granules on lateral and mesial faces larger, sometimes forming short denticulate ridges; lateral face nearly perpendicular, devoid of median longitudinal ridge. Meral­carpal articulation lacking any pronounced clockwise rotation; dorsal surface of merus with row of transverse ridges; lateral face microscopically granular, ventrolateral margin with 2 or 3 subdistal spines and small protuberances; mesial face nearly smooth, ventromesial margin with row of small tubercles or low protuberances. Ischium entirely unarmed.

Left cheliped ( Fig. 21C–F ) moderately stout, similar between males and females. Chela 2.5–3.0 times longer than broad. Dactylus 1.2–1.4 times as long as palm, with sparse tufts of setae on surfaces; dorsal surface unarmed, dorsomesial margin not delimited; cutting edge with row of small corneous teeth, terminating in small corneous claw. Palm about half length of carpus; dorsal surface slightly elevated in midline and bearing scattered granules, dorsolateral margin not delimited, dorsomesial margin faintly delimited by row of small tubercles and protuberances (proximalmost tubercle acute or subacute); lateral, mesial and ventral surfaces with granules or low protuberances; scattered tufts of moderately long setae present on mesial and ventral surfaces. Cutting edge of fixed finger with row of small calcareous teeth interspersed by corneous teeth, terminating in small corneous claw. Carpus moderately slender, 0.8–0.9 length of chela and 0.9–1.1 length of merus; length 2.5–2.9 of distal width and 2.2–2.9 of greatest height; dorsal surface with spines at dorsolateral distal and dorsomesial distal angles, dorsolateral and dorsomesial margins each delimited by row of small spines (spines of dorsomesial row stronger than those of dorsolateral row); lateral face granular, lacking median longitudinal ridge, thus nearly perpendicular; mesial face with sparse granules or low protuberances and setae. Merus with row of faint, low transverse ridges on dorsal surface, dorsodistal margin unarmed; lateral surface with small, flattened tubercles ventrally, ventrolateral distal margin with row of small spines; mesial faces nearly smooth, ventromesial margin with row of small tubercles; ventral surface with granules and scattered long stiff setae. Ischium with row of tiny denticles on ventromesial margin, otherwise unarmed.

Ambulatory legs ( Fig. 22A, C ) moderately long and slender, generally similar from right to left. Dactyli ( Fig. 22B, D ) 0.8–0.9 length of propodi, 4.8–7.1 times longer than high, terminating in large corneous claws; dorsal surfaces each with row of sparse short and moderately long setae; lateral and mesial faces shallowly sulcate in midline, each with row of short setae along dorsal margin, mesial faces unarmed (second) or armed with row of corneous spinules adjacent to dorsal margin (third); ventral margins each with 6–9 long corneous spines notably increasing in size distally. Propodi slightly tapering distally, 4.7–5.6 times longer than high; dorsal surfaces slightly protuberant, with short and moderately long stiff setae, some setae plumose; lateral faces nearly smooth; ventral margins each with row of 4–6 small corneous spinules, ventrodistal margins each with paired corneous spines. Carpi distinctly shorter than propodi; dorsal surfaces each with small dorsodistal spine and row of sparse short and moderately long setae; lateral and mesial faces nearly smooth. Meri with short ridges on dorsal surfaces and sparse, short and moderately long setae; lateral surfaces nearly smooth, ventrolateral distal margins each with small subdistal spine (second) or unarmed (third), ventral surfaces slightly serrated (second) or slightly protuberant (third), all with few short setae.

Fourth pereopods ( Fig. 19G–I ) subequal or slightly unequal (left larger) and similar from right to left in both male and female. Dactyli moderately broad, terminating in small corneous claws; dorsal margins with short to long setae. Propodi with several long setae on dorsal margins; mesial faces slightly convex, each with row of short setae ventrally. Carpi with sparse long setae on mesial faces near ventrodistal margins.

Anterior lobe of sixth thoracic sternite ( Fig. 19D ) subrectangular or transversely oblong, anterolateral angles rounded; anterior margin with row of moderately long setae. Eighth thoracic sternite ( Fig. 19E ) composed of two unequal (right larger), closely set, rounded lobes.

Males with coxae of fifth pereopods somewhat unequal ( Fig. 19E ). Right with tuft of long, stiff setae directed toward left and passing left coxa; posteromesial protrusion short, clearly demarcated; papilla­like very short sexual tube apparent. Left coxa also with papilla­like sexual tube or protrusion of vas deferens partially masked by tuft of setae directed ventrally. Female with paired, unequal gonopores (left distinctly larger than right) or only unpaired left gonopore.

Telson ( Fig. 19F ) with posterior lobes rounded, oblique terminal margins each with 4–7 small spines.

Colour in life. ( Fig. 45A ) Shield pale red. Ocular peduncles generally white, with tinge of red at base of corneas. Antennular peduncles pale red. Antennal peduncles pale red with white spots, flagella banded with red (4–6 articles) and white (1 or 2 articles). Chelipeds generally reddish brown, dactyli and fixed fingers white distally, meri each with white band near dorsodistal margin and 2 white spots on median dorsal surface. Ambulatory legs semitransparent white; dactylus to meri red on dorsal surfaces and with continuous, longitudinal, red stripe each on lateral and mesial surface; median and proximal parts of propodus, distal part of carpus, and median part of merus each with transverse red markings.

Distribution

Known with certainty from the Ogasawara Islands (Chichi­jima Island) and Izu Islands (Hachijo­jima and Izu­oshima Islands) ( Fig. 48 ); 0.5–3.0 m.

Remarks

The syntype lot of Pagurixus boninensis ( SMNH Type­2289) contains only the body with all pereopods removed. Appendages of the syntype, including right antennular and antennal peduncles and second and third pereopods, are separately deposited in the Zoological Museum of the Uppsala University (K. Sindemark, personal communications), although they were not available for study. The present material from the Ogasawara Islands has made possible to fully assess the specific diagnosis of this species .

Pagurixus boninensis is most similar to P. ruber n. sp. Differences between the two species are summarized in Table 2. The living coloration of P. boninensis is diagnostic ( Fig. 45A ), and therefore, if the color pattern is preserved, recognition of this species is easy.

Lewinsohn (1969) reported what he believed to be P. boninensis from the Red Sea, but noted certain differences between his material and Melin (1939) ’s original description. Most significant of these differences was the absence of rows of tufts of setae on the ventral surface of the ultimate segment of the antennular peduncle. Subsequently, he ( Lewinsohn, 1982) recognized the similarity between his Red Sea and Somalia specimens and P. anceps , and remarked that P. anceps might prove to be a junior synonym of P. boninensis . McLaughlin & Haig (1984) placed the records of Lewinsohn (1969, 1982) in the synonymy of P. anceps , because their extensive material of P. anceps , including specimens from the Red Sea, agreed with the description of P. boninensis of Lewinsohn (1969). We concur with McLaughlin & Haig’s (1984) interpretation, as the specimens of P. anceps personally examined also agree well with Lewinsohn’s (1969) description of P. boninensis .

Ooishi (1970) reported P. boninensis based on material collected during the Bonin (Ogasawara) Islands expedition of 1968. Our examination has revealed that Ooishi’s (1970) specimens do not represent P. boninensis s. s., but P. brachydactylus n. sp.

Miyake (1978) extended the range of P. boninensis to three islands of the Ryukyu Islands, but gave no further information. McLaughlin & Haig (1984) suggested the possibility that Miyake actually was reporting P. anceps from Okinawa, Amami­oshima, and Meshima Islands. Our study shows that several congeneric species exist in the Ryukyu Islands, but there is no evidence to document the occurrence of P. boninensis in the Ryukyu Islands. It is impossible to determine which species Miyake (1978) was reporting.

McLaughlin & Haig (1984) diagnosed what they believed to be P. boninensis from the Maldives and Marshall Islands. They noted that the structure of the setal row(s) on the ventral surface of the ultimate segment of the antennular peduncle was different between males and females; in males, there were two rows of equidistantly spaced tufts of setae, whereas in females, there was a ventromesial row of closely­spaced, fine short setae. However, examination of the present extensive material has shown that the structure of the setal rows is constant within a single species. There is little doubt that two species were included in McLaughlin & Haig’s (1984) material referred to P. boninensis . The male specimens agree better with P. ruber n. sp. than with P. boninensis . In particular, their description and figures clearly indicate that there are no conspicuous spines on the dorsomesial margin of the carpus of the right cheliped. Even in large specimens, P. boninensis has dorsomesial spines on the carpus of the right cheliped. Furthermore, the available data suggests that P. boninensis is limited to the Izu and Ogasawara Islands in Japan, whereas P. ruber n. sp. is widespread in the Indo­West Pacific. The occurrence of P. ruber n. sp. in the Maldives is confirmed in this study. The female specimens used by McLaughlin & Haig (1984) cannot be assigned to any species known at present, as we have not encountered a species characterized by the possession of a single setal row on the ultimate segment of the antennular peduncle. Furthermore, McLaughlin & Haig’s female specimens are characteristic in having relatively long, slender spines on the terminal margins of the telson. Paulay et al. (2003) listed Pagurixus boninensis as a representative of the fauna of Mariana Islands based on a voucher material ( UF 490) identified by Dr. P. A. McLaughlin. During this study, we have examined numerous specimens from Guam, including those identified by Dr. McLaughlin as P. boninensis , although the voucher material used by Paulay et al. (2003) was not reexamined. They all represent P. ruber n. sp., instead of P. boninensis s.s.

Morgan (1990) referred a specimen from the Long Reef, Kimberly region of Western Australia, to Pagurixus cf. boninensis . In the description of the coloration in life, he clearly noted the presence of transverse bands on the ambulatory legs, and therefore, Morgan’s specimen cannot be assigned to P. boninensis s. s. or the closely related P. ruber n. sp. Morgan (1992) also recorded P. cf. boninensis from the Cocos­Keeling Islands in the eastern Indian Ocean. He noted that the dactyli of the second and third pereopods were very elongate, nearly as long as the propodi, and with 9–11 ventral spines. These characters clearly suggest that Morgan’s specimens do not represent P. boninensis s. s. The identities of Morgan’s (1990, 1992) specimens remain unclear.

As mentioned before, one of the two color pictures taken in situ, referred to P. nomurai by Asakura (2001), actually represents P. boninensis . The single specimen from Pagan Island in the northern Mariana Islands, used by Asakura et al. (1994), Komai & Asakura (1995) and Asakura (1995), has not been available for study. Therefore, these references are only questionably included in the synonymy. Okuno & Arima (2004) correctly identified specimens from Izu­oshima Island as P. boninensis with a help of one of us (MO).

Figures

FIGURE 3. Pagurixus laevimanus (Ortmann, 1892). Holotype male (SL 3.7 mm) from Tahiti (MZS 464, in spirit). A, right second pereopod, lateral view; B, left third pereopod, lateral view; C, right second pereopod, dactylus and distal part of propodus, mesial view; D, left third pereopod, dactylus and distal part of propodus, mesial view. Scale bars: 2 mm for A, B; 2 mm for C, D.

FIGURE 19. Pagurixus boninensis (Melin, 1939). A–F, male (SL 2.2 mm) from Chichi­jima Island, Ogasawara Islands (CBM­ZC 8472); G–I, male (SL 2.3 mm) from Chichi­jima Island, Ogasawara Islands (CBM­ZC 8474). A, shield and cephalic appendages, dorsal view (setae omitted from right side); B, ultimate segment of left antennular peduncle, lateral view; C, same, ventral view; D, sixth thoracic sternite, ventral view; E, coxae of fifth pereopods and eighth thoracic sternite, ventral view; F, telson, dorsal view; G, left fourth pereopod, dactylus and propodus, lateral view; H, same, mesial view; I, right fourth pereopod, dactylus and propodus, lateral view. Scales bars: 1.0 mm.

FIGURE 20. Pagurixus boninensis (Melin, 1939). Right cheliped. A–D, male (SL 2.2 mm) from Chichi­jima Island, Ogasawara Islands (CBM­ZC 8472); E, F, female (SL 1.6 mm) from Chichijima Island, Ogasawara Islands (CBM­ZC 8476). A, entire cheliped, mesial view; B, same, lateral view (setae and surface structure partially omitted); C, E, chela, dorsal view (setae omitted); D, F, carpus dorsal view (setae omitted). Scales bars: 1.0 mm.

FIGURE 21. Pagurixus boninensis (Melin, 1939). A, B, female (SL 1.6 mm) from Chichi­jima Island, Ogasawara Islands (CBM­ZC 8476); C–F, male (SL 2.2 mm) from Chichi­jima Island, Ogasawara Islands (CBM­ZC 8472). A, entire right cheliped, lateral view; B, same, mesial view; C, entire left cheliped, mesial view; D, same, lateral view; E, same, chela (setae omitted); F, same, carpus (setae omitted). Scale bars: 1.0 mm.

FIGURE 22. Pagurixus boninensis (Melin, 1939). Male (SL 2.2 mm) from Chichi­jima Island, Ogasawara Islands (CBM­ZC 8472). A, right second pereopod, lateral view; B, same, dactylus, mesial view; A, left third pereopod, lateral view; B, same, dactylus, mesial view. Scale bars: 1.0 mm.

FIGURE 45. A, Pagurixus boninensis (Melin, 1939), ovigerous female (SL 2.7 mm) from Hachijo Island, Izu Islands, Japan (CMNH­ZC 1688), photo taken by J. Okuno; B, Pagurixus carinimanus n. sp., paratype female (SL 1.6 mm) from Okinawa Island, Ryukyu Islands (CBM­ZC 8481), photo taken by Y. Fujita; C, D, Pagurixus brachydactylus n. sp., male (SL 2.6 mm) from Chichi­jima Island, Ogasawara Islands, photo taken by M. Osawa.

FIGURE 48. Geographic distribution of Pagurixus boninensis (), P. festinus (), P. brachydactylus n. sp. (), P. carinimanus n. sp. (), P. paulayi n. sp. (Π), P. pseliophorus n. sp ()., and P. ruber n. sp. ().