Pagurixus tweediei ( Forest, 1956 )

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 : 25-32

Pagurixus tweediei ( Forest, 1956)

( Figs. 8–11 , 44B , 47 )

Eupagurus (Pagurixus) tweediei Forest, 1956: 50 , pl. 4 [type locality: Cocos­Keeling Islands ].

Pagurus (Pagurixus) tweediei .— Dechancé, 1964: 38.— Ball & Haig, 1972: 103.— Lewinsohn, 1982: 58.

? Pagurixus tweediei .— Morgan, 1992: 171.

? Pagurixus cf. tweediei .— Gherardi & McLaughlin, 1994: 644.

Pagurixus tweediei .— Davie, 2002: 82 (in part).

Type material

SYNTYPES: MNHN­Pg 584, 2 males (SL 2.8, 3.2 mm), Cocos (Keeling) Islands .

Other material. Japan. CBM­ZC 7424, 1 ovigerous female (SL 3.1 mm), Miyanohama , Chichi­jima Island, Ogasawara Islands, intertidal, coll . T. Komai , October 1997; CBM­ZC 7785, 2 males (SL 2.4, 3.2 mm), 3 females (SL 2.3–3.5 mm), same locality, subtidal, coll. M. Osawa, 3 May 1998; CBM­ZC 8257, 1 male (SL 2.8 mm), same data . Mariana Islands. Guam. UF 7077 , 1 male (SL 2.6 mm), 1 female (SL 1.6 mm), 3 ovigerous females (SL 2.3–2.6 mm), Ipan fore reef, 2–7 m in surge channels, coll. G. Paulay, 14 May 2000 . French Polynesia. UF 1731 , 3 males (SL 3.0– 3.9 mm), 3 ovigerous females (SL 1.9–3.1 mm), Trou de Souffleur , Tahiti, Society Islands, 1–6 m, reef slope, coll. G. Paulay, 19 October 2001 .

Redescription

Shield 1.0–1.1 times ( Fig. 8A ) as long as broad; anterior margin between rostrum and lateral projections concave; anterolateral margins sloping or slightly terraced. Rostrum triangular, distinctly overreaching lateral projections. Lateral projections triangular, somewhat produced, with large submarginal spine.

Ocular peduncle ( Fig. 8A ) relatively short and stout, 0.5–0.6 length of shield, with row of tufts of short setae on dorsal surfaces; cornea slightly dilated, corneal width 0.4–0.5 of peduncular length; basal part weakly inflated, as broad as corneal width. Ocular acicles subovate or subtriangular, each with small submarginal spine.

Antennular peduncle ( Fig. 8A ) overreaching distal margin of cornea by 0.2–0.3 length of ultimate segment. Ultimate segment with tufts of long setae at dorsolateral and dorsomesial angles; 2 longitudinal rows of setae, each consisting of numerous short, obliquely transverse rows of very short setae ( Fig. 8B, C ). Basal segment with small lateral spine on statocyst lobe. Ventral flagellum with numerous long setae on lateral and mesial margins.

Antennal peduncle ( Fig. 8A ) overreaching distal margin of cornea by 0.3–0.5 length of fifth segment. Second segment with long spine at dorsomesial distal angle; laterodistal projection reaching midlength of fourth segment, terminating in simple or bifid spine. Antennal acicles moderately long, overreaching base, but not reaching distal margin of cornea; mesial margin with row of tufts of short, stiff setae. Antennal flagellum long, exceeding 7.0 times of shield length.

Right cheliped of males elongate ( Fig. 9A–C ). Chela subovate in dorsal view, 2.1–2.3 times longer than wide. Dactylus 0.6–0.7 length of palm; dorsomesial margin not delimited; surfaces minutely granular; cutting edge with 1 or 2 prominent calcareous teeth and row of long corneous teeth in distal 0.2–0.3, terminating in very small corneous claw. Palm slightly longer than carpus; convex dorsal surface minutely granular, dorsolateral margin delimited by granular ridge becoming obsolete proximally, dorsomesial margin not delimited; lateral, mesial and ventral surfaces granular, with tufts of short to long setae. Cutting edges of fixed finger with 1 or 2 low calcareous teeth in proximal 0.6, remaining distal 0.4 crenulate, terminating in very small corneous claw or small calcareous claw. Carpus slightly shorter than or subequal to merus; dorsomesial margin faintly delimited by row of spines increasing in size distally, dorsolateral margin also faintly delimited by row of small, low, simple or bifid tubercles; all surfaces granular, lateral surface divided in oblique dorsal and perpendicular ventral sections by weak, granular or tuberculate ridge on midline. Meral­carpal articulation lacking any pronounced clockwise rotation; dorsal surface of merus with row of low transverse ridges, dorsodistal margin with 2 or 3 spines; lateral and ventral faces with small tubercles or coarse granules; ventrolateral margin with row of small spines in distal half and row of tiny tubercles in proximal half; ventromesial margin with row of small spines or spinulose tubercles; ventral surface slightly concave, covered with coarse granules and with scattered long setae. Ischium with row of minute denticles on ventromesial margin; posterolateral angle with few tiny tubercles.

Right cheliped of females ( Fig. 10A–C ) relatively elongate for genus. Chela subovate in dorsal view, 1.9–2.1 times longer than broad. Dactylus subequal in length to palm; dorsomesial margin not clearly delimited but with short row of granules proximally; surfaces minutely granular; cutting edge with 1 or 2 low calcareous teeth proximally and row of long corneous teeth in distal half, terminating in small corneous claw. Palm shorter than carpus; convex dorsal surface minutely granular, dorsolateral margin delimited by granular ridge, dorsomesial margin not delimited; lateral, mesial and ventral surfaces granular, with few tufts of short to long setae. Carpus 1.3–1.5 times longer than distal width, slightly shorter than or subequal to merus; dorsolateral margin weakly delimited by row of small spines, dorsomesial margin weakly indicated by row of small, low, tubercles; all surfaces granular, lateral surface divided into two sections (oblique dorsal and perpendicular ventral sections) by distinct, granular or tuberculate ridge. Merus with row of low transverse ridges on dorsal surface, dorsodistal margin unarmed or with 1 small spine; lateral face granular; ventrolateral margin with small acute spine at distal angle followed by row of small tubercles; ventromesial margin with row of small, low tubercles becoming obsolete proximally. Ischium with row of minute denticles on ventromesial margin; posterolateral angle smooth.

Left cheliped ( Fig. 9D–F ) elongate, slender, similar between male and female. Chela 2.4–2.5 times longer than broad. Dactylus slightly longer than palm, with sparse tufts of setae on surfaces (setae on ventral surface longest); dorsal surface with few tiny tubercles; cutting edge with fine row of long corneous teeth, terminating in small corneous claw. Palm about half length of carpus; dorsal surface weakly elevated in midline and armed with row of tiny tubercles extending onto fixed finger, sloping mesial part with some tiny tubercles; dorsomesial margin faintly delimited by row of tiny tubercles; lateral part of dorsal surface also sloping, dorsolateral margin faintly delimited by row of small tubercles; lateral, mesial, ventral surfaces each with few small, low tubercles and tufts of short to long setae. Carpus elongate, subcylindrical, 1.1–1.2 length of chela and subequal in length to merus; length 2.3–2.8 of distal width and 2.9–3.0 of greatest height; surfaces microscopically granular; dorsolateral and dorsomesial margins each with row of moderately small spines and long stiff setae; lateral surface divided into oblique dorsal and perpendicular ventral sections; mesial surface with several tufts of long setae; ventral surface smooth, with few long setae. Merus with row of short transverse ridges and tufts of short setae or bristles on dorsal surface, dorsodistal margin unarmed, but with several long bristles; lateral surface with several tiny tubercles or spinules adjacent to ventrolateral margin, otherwise microscopically granular, ventrolateral margin with few small tubercles; mesial face with tiny tubercles adjacent to ventromesial margin, otherwise nearly smooth, ventromesial margin nearly smooth or with row of small tubercles proximally. Ischium with row of small, low denticles on ventromesial margin, otherwise unarmed.

Ambulatory legs ( Fig. 11A, B ) comparatively long and slender, similar from right to left. Dactyli ( Fig. 11C, D ) 0.7–0.8 length of propodi, 5.0–7.0 times longer than high, terminating in large corneous claws; dorsal surfaces each with row of short setae (setae broken off in syntypes); lateral and mesial faces each with few tufts of short setae, mesial faces unarmed (second) or armed with row of corneous spinules adjacent to dorsal margins (third); ventral margins each with 6–8 long corneous spines notably increasing in size distally. Propodi tapering distally, 4.5–4.9 times longer than high; dorsal surfaces with row of low protuberances and moderately short stiff setae; lateral faces with sparse granules; ventral margins each with row of 4–6 corneous spinules, ventrodistal margins with paired corneous spines. Carpi each with small dorsodistal spine; each dorsal surface with row of low protuberances and tufts of short setae; lateral faces with sparse granules and short setae dorsally. Meri each with row of low protuberances and short stiff setae on dorsal surface; lateral surfaces with scattered granules and tufts of short setae (granules fewer on third than second); ventrolateral distal margins each with small subdistal spine, ventral surfaces each with row of spinules or small spinulose tubercles (second) or smooth (third), and with tufts of short setae.

Fourth pereopods ( Fig. 8D–F ) similar from right to left in both males and females. Dactyli terminating in small corneous claws, each with row of moderately long setae on dorsal margin. Propodi each with longitudinal row of tufts of short setae on nearly flat mesial face.

Anterior lobe of sixth thoracic sternite ( Fig. 8G ) transversely oblong, anterolateral angles distinctly produced laterally, each angle usually bearing 1 or 2 small tubercles; anterior margin concave, with row of moderately short setae. Eighth thoracic sternite ( Fig. 8H ) composed of 2 subequal, closely set, rounded lobes.

Males with coxae of fifth pereopods somewhat unequal ( Fig. 8H ). Right coxa with tuft of long stiff setae directed toward left and reaching to left coxa; posteromesial protrusion absent, but short, papilla­like sexual tube apparent. Left coxa also with papilla­like sexual tube partially masked by tuft of setae directed ventrally. Female with paired gonopores.

Telson ( Fig. 8I ) with terminal margins slightly oblique, each bearing 4–7 very small spines.

Colour in life. ( Fig. 44B ) Shield generally mottled brown and white. Ocular peduncles, chelipeds and ambulatory legs generally brown. Chelae with fingers pale brown, carpi and meri without distinct markings. Ambulatory dactyli white, each with brown band in proximal 0.2; propodi each with white marking in proximal and distal part; carpi each with pale brown tint in dorsodistal part; meri each with 2 broad, pale brown bands medially and subdistally.

Distribution

Previously known with certainty from Cocos (Keeling) Islands in the Indian Ocean ; here newly recorded from Ogasawara Islands , Guam, Society Islands in the western Pacific Ocean (Fig. 50); intertidal to 7 m. This species appears to be widely distributed in the Indo­West Pacific .

Remarks

As discussed before, P. tweediei is most similar to P. laevimanus . Further, P. tweediei differs from two other similar species, P. maorus and P. nomurai , in the comparatively broad carpus of the left cheliped, and the comparatively short and stout dactyli of the ambulatory legs (Table 1). The transversely oblong anterior lobe of the sixth thoracic sternite and the structure of the ventral setal series of the ultimate segment of the antennular peduncle also distinguish P. tweediei from P. maorus and P. concolor n. sp. (Table 1).

Although Forest’s (1956) description of P. tweediei was relatively detailed, there has been confusion in subsequent literature. McLaughlin & Haig (1984) described what they assigned to P. cf. tweediei from the Philippines, but noted some differences between their specimen and Forest’s description, which they interpreted to fall within a range of variation of a single species. Our reexamination of the syntypes of P. tweediei has revealed that this species has a lateral longitudinal ridge on the carpus of the left cheliped, which is absent in the specimen of P. cf. tweediei of McLaughlin & Haig (1984). Although the specimen examined by McLaughlin & Haig (1984) was not available for study, their description agrees closely with P. carinimanus n. sp. Morgan (1992) referred specimens from Christmas and Cocos (Keeling) Islands to P. tweediei , but remarked that his females had only a single left gonopore. Davie (2002) listed P. tweediei in the Zoological Catalogue of Australia on the basis the records of the species by Forest (1956) and Morgan (1992). In the present specimens of P. tweediei , the females exclusively have paired gonopores. The material examined by Morgan (1992) was not available for study, and therefore certain identification is difficult. Nevertheless, there is little doubt that Morgan’s (1992) material represents a species other than P. tweediei .

Gherardi & McLaughlin (1996) tentatively identified a single male specimen from Mauritius with P. cf. tweediei . They noted that their specimen agreed better with Forest’s (1956) original description and figures than with the diagnosis presented by McLaughlin & Haig (1984). The left cheliped was missing in the Mauritius specimen (Gherardi & McLaughlin 1996), and it is difficult to make certain identification without examination of the specimen. Therefore, the record of Gherardi & McLaughlin (1996) is included questionably in the synonymy. The identity of P. cf. tweediei reported by Asakura et al. (1994) from the northern Mariana Islands remains unclear, because the material has not been available for reexamination. Nevertheless, their identification was based on McLaughlin & Haig’s (1984) interpretation, and therefore there is little doubt that their specimens do not represent P.tweediei s.s.

Figures

FIGURE 8. Pagurixus tweediei (Forest, 1956). A–C, G–I, Syntype male (SL 2.8 mm) from Cocos (Keeling) Islands (MNHN­Pg 584); D–F, male (SL 2.8 mm) from Chichi­jima Island, Ogasawara Islands (CBM­ZC 8257). A, shield and cephalic appendages, dorsal view; B, ultimate segment of right antennular peduncle, lateral view; C, same, ventral view (setae partially omitted); D, dactylus and propodus of left fourth pereopod, lateral view; E, same, mesial view (setae partially omitted); G, dactylus and propodus of right fourth pereopod, lateral view; G, sixth thoracic sternite, ventral view, slightly damaged; H, coxae of fifth pereopods and eighth thoracic sternite, ventral view; I, telson, dorsal view. Scale bars: 1 mm for A, H; 0.5 mm for B–G.

FIGURE 9. Pagurixus tweediei (Forest, 1956). Syntype male (SL 2.8 mm) from Cocos (Keeling) Islands (MNHN­Pg 584). A, right cheliped, chela and carpus, dorsal view; B, entire right cheliped, mesial view; C, same, mesial view; D, left cheliped, chela and carpus, dorsal view; E, entire left cheliped, mesial view; G, same, lateral view. Scale bar: 1 mm.

FIGURE 10. Pagurixus tweediei (Forest, 1956). Female from Chichi­jima Island, Ogasawara Islands (CBM­ZC 7785). Right cheliped. A, chela and carpus, dorsal view (setae omitted); B, entire right cheliped, mesial view; C, same, lateral view. Scale bar: 1 mm.

FIGURE 11. Pagurixus tweediei (Forest, 1956). Syntype male (SL 2.8 mm) from Cocos (Keeling) Islands (MNHN­Pg 584). A, left second pereopod, lateral view; B, left third pereopod, lateral view; C, left second pereopod, dactylus and distal part of propodus, mesial view; D, left third pereopod, dactylus and distal part of propodus, mesial view. Scale bars: 1 mm.

FIGURE 44. A, Pagurixus maorus (Nobili, 1906), male (SL 3.9 mm) from Kume­jima Island, Ryukyu Islands, photo taken by M. Osawa; B, Pagurixus tweediei (Forest, 1956), male (SL 3.9 mm) from Tahiti, Society Islands, French Polynesia (UF 1731), photo taken by G. Paulay; C, Pagurixus nomurai Komai & Asakura, 1995, ovigerous female from Guam, Mariana Islands (UF), photo taken by G. Paulay; D, Pagurixus concolor n. sp., paratype female (SL 3.2 mm) from Tokashiki Island, Kerama Islands (CBM­ZC 8484), photo taken by M. Osawa.

FIGURE 47. Geographic distribution of Pagurixus laevimanus (), P. maorus (), P. tweediei (), P.nomurai (), P. pulcher () and P. concolor n. sp. ().