Oncopagurus indicus

Oncopagurus indicus (Alcock, 1905)

Figs 17, 18

Sympagurus bicristatus var. indicus Alcock, 1905: 105, p1.10, fig. 4.- Gordan, 1956: 341 (type locality: Andaman Sea).

Parapagurus bicristatus.- Balss, 1912: 98, figs 6, 7. (Not Parapagurus bicristatus [A. Milne Edwards, 1880]).

? Parapagurus minutus.- Thompson, 1943: 417. (? Not Parapagurus minutus Henderson, 1896). (See remarks).

Sympagurus bicristatus.- Thompson, 1943: 418.

Parapagurus bicristatus indicus.-De Saint Laurent, 1972: 112.

Sympagurus indicus.- Lemaitre, 1989: 37.- Lemaitre, 1994: 412.

Type Material. Syntypes from Andaman Sea, Indian Ocean, probably in Indian Museum, Calcutta (not seen).

Material examined. WESTERN AUSTRALIA: 1 male (SL 2.7 mm), 1 female ovig. (SL 2.1 mm), WSW of Lancelin, WAM 1746-86.

QUEENSLAND: 1 male (SL 2.3 mm), off Tully, CIDARIS I, sta. 43-2, 17°35'S, 146°53'E, epibenthic sledge, ORV Franklin, 458-500 m, 15 May 1986, colI. ICU, QM W16590. 2 females ovig. (SL 3.0, 3.3 mm), off Tully, CIDARIS I, sta. 49-2, 17°51'S, 147°10'E, epibenthic sledge, ORV Franklin, 904-916 m, 17 May 1986, colI. ICU, QM W16599. 17 males (SL 2.7- 4.2 mm), offTully, CIDARIS I, sta. 47 -2, 17°51.8'S, 147°07.9'E, epibenthic sledge, ORV Franklin, 503- 497 m, 16 May 1986, coli. ICU, QM W16600.

NEW SOUTH WALES: 1 male (SL 2.4 mm), 1 female ovig. (SL 2.7 mm), off Newcastle, NZOI Tangaroa, cruise U207, 34°11.1'S, 151°26'E, 1998 m, 5 Oct 1982, AM P44032. 1 female (SL 3.2 mm), NZOI Tangaroa, cruise U222, off Newcastle, 1075 - 1040 m, 9 Oct 1982, AM.

Other material (all from Albatross). PHILIPPINES: 1 female (SL3.0 mm), sta. 5342, 10056'55''N, 119°17'24"E, 26- 46 m, 23 Dec 1908, USNM 168969.

INDONESIA: 1 male (SL 3.0 mm), sta. 5586, 04°06'50"N, 118°47'20"E, 635 m, 28 Sep 1909, USNM 168970. 3 males (SL 1.8-4.2 mm), sta. 5619, 00035'N, 12TI4'40"E, 796 m, 27 Nov 1909, USNM 168971. 2 males (SL 3.6, 4.2 mm), sta. 5631, 00057' S, 127°56'E, 1480 m, 2 Feb 1909, USNM 168972.

HAWAIIAN ISLANDS: 1 male (SL 4.2 mm), sta. 3979, Oahu, SW of Bird Island, 406 -708 m, 3 lun 1902, USNM 168959. sta. 4134, Oahu, Kauai Channel, 22°03'35"N, l 59°19'40"W, 593- 412 m, 1 Aug 1902, USNM 168968. 2 males (SL 1.6, 2.2 mm), 1 female (SL 1.8 mm), sta. 4133, Oahu, Kauai Channel, 22°02'40"N, 159°19'55"W, 302 m, 1 Aug 1902, USNM 168967. 1 male (SL 2.7 mm), sta. 4132, Oahu, Kauai Channel, 22°01'30"N, 159°21'10"W, 470-571 m, 1 Aug 1902, USNM 168966. 2 females (SL 2.1, 2.2 mm), sta. 4131, 21°59'35"N, 159°20'40"W, 565- 470 m, 1 Aug 1902, USNM 168965. 1 male (SL 3.0 mm), 1 female (SL 2.5 mm), sta. 4122, Oahu, SW of Barbers Point Light, 351-644 m, 26 lul 1902, USNM 168964. 1 male (SL 2.8 mm), sta. 3917, Oahu, SW of Diamond Head, 604- 538 m, 6 May 1902, USNM 168857. 1 female (SL 2.5 mm), sta. 3815, Oahu, SE of Diamond Head, 571 - 417 m, 28 Mar 1902, USNM 168952. 2 males (SL 2.7, 3.1 mm), sta. 3909, Oahu, SW of Diamond Head, 563-589 m, 5 May 1902, USNM 168956. 1 male (SL 1.6 mm), sta. 3918, Oahu, SW of Diamond Head, 538- 470 m, 6 May 1902, USNM 168958. 1 male (SL 1.5 mm), 1 female (SL 1.6 mm), sta. 4095, Pailolo Channel, off Mokuhooniki Is., 21°14'30"N, 156°29'45"W, 530- 523 m, 22 lul 1902, USNM 168962. 3 males (SL 1.9- 2.2 mm), sta. 3866, 21°10'40"N, 156°34'50"W, 518- 519 m, 10 Apr 1902, USNM 168955. 2 males (SL 1.6, 2.8 mm), 4 females (SL 1.6- 2.1 mm), sta. 4084, Maui, W of Puniawa Point, 21°06'40"N, 156°20'15"W, 463-488 m, 21 lul 1902, USNM 168960. 1 female (SL 3.1 mm), sta. 4102, between Maui and Moloka Is., Pailolo Channel, 21°03'10"N, 156°45'20"W, 223- 241 m, 23 lul 1902, USNM 168963. 1 male (2.2 mm), 2 females (SL 1.8, 1.8 mm), sta. 4085, Maui, W of Puniawa Point, 488- 518 m, 21 lul 1902, USNM 168961. 12 males (SL 1.5-3.0 mm), 8 females (SL 1.5-2.8 mm), sta. 3839, south coast of Molokai Is., 21°02'N, 157°09'40"W, 474-487 m, 4 Apr 1902, USNM 168954. 3 males (SL 2.5-3.0 mm), 5 females (SL 1.9- 2.4 mm), sta. 3836, 21°00'05"N, 157°08'20"W, 435- 466 m, 3 Apr 1902, USNM 168953.

Diagnosis. Shield (Fig. l7a) as long as broad; rostrum broadly rounded, with low dorsal ridge; anterior margins weakly concave; lateral projections subtriangular, usually terminating in small spine; ventrolateral margin with small spine (not always visible in dorsal view); posterior margin broadly rounded. Ocular peduncles more than half length of shield; ocular acicles subtriangular, terminating in strong spine; corneae slightly dilated. Maxillule with internal lobe of endopod with long seta. Sternite of 3rd maxillipeds with small spine on each side of midline. Antennular peduncle exceeding distal margin of corneae by full length of ultimate segment. Antennal peduncle (Fig. 17b) at most reaching distal margin of cornea; 2nd segment with dorsolateral distal angle produced, terminating in strong simple or multifid spine; acicles reaching distal margin of corneae, mesial margin with 8 to 11 spines; flagellum with few setae about 1 flagellar article in length. Chelipeds markedly dissimilar, both with moderately dense setae. Right cheliped (Fig. 17d, 18 a-d) exhibiting sexual dimorphism. Males with right palm varying from as long as broad to slightly longer than broad; dorsomesial margin always well delimited by row of spines, ventromesial margin varying from weakly to well delimited by row of tubercles or spines; mesial face occasionally weakly expanded distally. Females with right palm broader than long, mesial face concave and expanded distally (more so in large females SL> 3.0 mm). Left cheliped (Fig. 17c) usually weakly calcified on lateral face of carpus; dorsal margin of carpus with irregular row of small spines, or few small tubercles, or unarmed; carpus with dorsodistal spine. Ambulatory legs (Fig. l7 f-h) with dactyl with row of about 4 corneous spines on ventromesial margin, and dorsal and dorsomesial rows of long setae; carpus with small dorsodistal spine; merus of 3rd pereopods (Fig. 18e,t) each with row of 2 to 8 small spines (occasionally with 1 spine). Anterior lobe of sternite of 3rd pereopods setose, armed with marginal spine. Fourth pereopod (Fig. 17i) with propodal rasp consisting of ovate scales. Uropods and telson (Fig. 17j) markedly asymmetrical, lacking transverse suture separating anterior and posterior lobes; posterior lobes separated by shallow U-shaped median cleft, terminal margins armed with often strongly curved corneous spines. Male 1st gonopods (Fig. 18g) each with weakly concave distal lobe; 2nd gonopods (Fig. 18h) each with distal segment nearly flat. Females with vestigial right 2nd pleopod.

Habitat and symbiotic associations. Inhabits gastropod shells; occasionally with one or more anthozoan polyps attached to the shell.

Distribution. Indo Pacific: Zanzibar; Maldives; Indonesia; Australia; Philippines; and Hawaiian Islands. Depth: 183 to 1480 m.

Affinities. Among the Indo Pacific speCIes of Oncopagurus n.gen., O. indicus is most similar to 0. monstrosus (Alcock, 1894), from which it is often difficult to separate, particularly if only male specimens are available. Females of the two species can immediately be separated by differences in the mesial face of the palm of the right cheliped. In 0. indicus, the mesial face of the palm is expanded distally, and has a well delimited ventromesial margin that consists of a row of spines (Fig. 18a,c). The mesial face of the palm of 0. monstrosus is not expanded distally; the ventromesial face is rounded and lacks spines (Fig. 1 ge,c).

In males, the mesial face of the right palm is only of limited help in separating the two species. The mesial face of O. indicus is at most weakly expanded distally (Fig. 17d,e); the mesial face of 0. monstrosus is not expanded (Fig. 19c,e). The ventromesial margin of 0. indicus exhibits a well developed row of spines, or occasionally a row of weak spines or small tubercles distally (Fig. 17e), whereas in 0. monstrosus the ventromesial margin is unarmed (Fig. 1 ge). Males of both 0. indicus and 0. monstrosus have a dorsomesial row of spines.

Males of the two species can best be separated by using differences in the development of the ocular peduncles and corneae, and armature of the merus of the 3rd pereopod. In both males and females of O. indicus, the peduncles are nearly subequal in width throughout the peduncle, and the width of the corneae is subequal to the distal width of the peduncles (Fig. 17a); in 0. monstrosus, the peduncles increase in width distally, are slightly constricted medially, and the width of the corneae is distinctly greater than that of the peduncles (Fig. 19a). Additionally, the merus of the right 3rd pereopod is armed with spines in 0. indicus (Fig. 18e,t), whereas it is usually unarmed in 0. monstrosus (Fig. 19f,h).

Supplemental characters that can help to differentiate the two species of either sex are the armature of the ventral surface of the right chela, and size of the individuals. The ventral surface of the right chela in 0. indicus is usually smooth or at most is armed with scattered small tubercles (Fig. 18d); the ventral surface in 0. monstrosus frequently has strong spines or tubercles (Fig. 20c,d). Individuals of O. indicus do not grow as large as those of 0. monstrosus, the former rarely exceeding a SL of 3 mm (largest specimen measured is 4.0 mm), whereas the latter can reach a SL of 6.0 mm.

Oncopagurus indicus also resembles two Atlantic species, 0. bicristatus (A. Milne Edwards, 1880), and O. gracilis (Henderson, 1888). In the absence of distributional data, 0. indicus can be separated from the two Atlantic species by differences in the shape and armature of the right chela, antennal acicles, and 1st gonopods in males (see Lemaitre, 1989). It is of interest to note the sexually dimorphic differences of the right chela between 0. indicus and O. bicristatus. In 0. indicus, the distal expansion of the mesial face of the chela is more distinctly developed in females than in males, whereas the reverse is true in O. bicristatus.

Remarks. The high degree ofvariability in proportions and armature of the right cheliped, and especially the marked differences frequently seen in this cheliped between males and females, has caused problems in defining this species. Particularly problematic has been the interpretation of the usefulness of the dorsomesial and ventromesial rows of spines (often described in the literature as "crests") on the palm of the right chela. Only after examining a large number of specimens of 0. indicus and related forms during this study, has it been possible to elucidate the limits of morphological variations of the right cheliped, and to define useful diagnostic characters for this and other structures. To fully understand how this variation has hampered proper definition of this taxon, it is useful to summarise how carcinologists have used or interpreted characters derived from the right cheliped.

A1cock (1905) initially proposed the "variety" indicus for the Atlantic Sympagurus bicristatus (A. Milne Edwards, 1880), in order to accommodate specimens from the Indian Ocean that differed slightly from the Atlantic form. A1cock noted that in his "variety" the carpus and chela of the right cheliped were longer, the right chela less oval in shape, and the antennal acicle longer, than in the typical Atlantic form. Balss (1912), who considered Sympagurus Smith a synonym of Parapagurus Smith, subsequently reported specimens of Parapagurus bicristatus from the Indian Ocean, and indicated that his material contained specimens assignable to both the typical form and "variety" indicus; the former were characterised by a short right cheliped, the latter by a long one. Balss did observe substantial variability in the shape of the right cheliped, and in particular the development of the "upper crest" (=dorsomesial row) of spines on the chela. For example, he found both short and long types of chelipeds in males of the "variety" indicus, and observed that in contrast to the distinct "upper crest" of spines on the chela found in the typical form, some of his specimens had only a rudimentary "upper crest". Thompson (1943) again reported specimens of Sympagurus bicristatus from the Indian Ocean, and made observations similar to those of Balss (1912). Thompson (1943) was unable to assign his specimens to either the typical form or the "variety" indicus, because of the great variability and overlap of characters he encountered. Although Thompson suggested the possibility that A. Milne Edwards's S. bicristatus could be divided into as many as three species, he did not formally take that action. It was De Saint Laurent (1972) who divided, although only provisionally, this taxon into three subspecies which she placed in Parapagurus Smith: P bicristatus bicristatus, P b. gracilis Henderson, 1888, and P b. indicus. Lemaitre (1989) reevaluated the characters used to define these subspecies and returned them to their original specific status. In so doing, he placed all three species in Sympagurus, and showed that S. bicristatus and S. gracilis occurred only in the Atlantic, whereas S. indicus is broadly distributed in the Indo Pacific. These three species are herein placed in the new genus Oncopagurus.

De Saint Laurent (1972) synonymised, without comment, the taxon that Thompson (1943) reported as Parapagurus minutus Henderson, 1896, with P bicristatus indicus. It has not been possible to examine Thompson's material, and he did not supply sufficient information in order to confirm the assignment of his specimens to Oncopagurus indicus.