Sargassocarcinus cristatus ( Balss, 1924 )

Ng, Peter K. L., Lin, Chia-Wei & Naruse, Tohru, 2016, Revision of the spider crab genus Sargassocarcinus Ward, 1936 (Crustacea: Brachyura: Epialtidae), Zootaxa 4162 (2), pp. 313-330 : 321-327

Sargassocarcinus cristatus ( Balss, 1924)

( Figs 1 ; 2; 3E, F; 5F, G; 6I –N; 7H, J, K; 8C–H; 9J–R; 10)

Mimulus cristatus Balss, 1924: 28 , pl. 1 figs 4, 5.

Mimulus cristatipes (sic) Ward 1936: 9.

Mimulus cristatus Sakai 1938: 262 .

Sargassocarcinus sublimis Sakai 1965: 77 , text-figs 11a, b, pl. 34 fig. 3; Serène 1968: 53; Sakai 1976: 205, pl. 71 fig. 3; Miyake 1983: 206 (list); Griffin & Tranter 1986: 97 (part), fig. 18e, f; Miyake 1998: 206 (list); Ng et al. 2008: 101 (part) (not Peltinia sublimis Rathbun, 1916 ).

Material examined. 1 male (8.2 × 7.4 mm) ( USNM 48248 ), station 3730, off Omaezaki , Honshu Island, Shizuoka Prefecture, Suruga Bay , Japan, 34°35’N 138°15’E, 62–68 m, on mud, gravel and rock, coll. RV Albatross, 16 May 1900 ; 1 ovigerous female (14.3 × 11.1 mm) (RUMF-ZC-3912), off Taketomi Island, Ryukyus, Japan, coll. Y. Akutsu & K. Okuda, 23 November 2014 ; 1 male (14.4 × 11.7 mm) ( ZRC 2015.288 ), Hejie, Pingtung, southern Taiwan, coll. C.- W. Lin by SCUBA, 8 July 2013 ; 1 male (12.5 × 10.1 mm), 1 female (10.8 × 8.9 mm) (NMMBCD 4065), 1 ovigerous female (16.2 × 12.1 mm) ( ZRC 2015.289 ), Hejie, Pingtung, southern Taiwan, coll. C.- W. Lin by SCUBA, 4 April 2015 .

Diagnosis. Carapace with distinct median tubercle on protogastric region; sub-branchial regions not raised ( Figs 2 E, F; 3E, F; 5F, G; 10A); pararostral teeth distinctly deflexed, slightly visible from dorsal view ( Figs 3 E, F; 7J; 10A); postorbital lobe distinct, separated from margin by distinct cleft, outer part of margin with additional low but distinct lobe ( Figs 3 E, F; 10A); eye relatively long ( Figs 7 K; 10B, C); wing-like lateral expansion lamelliform, with asymmetrical, relatively shallow, wide concavity separating 2 subequal, low lateral lobes, anterior lobe larger, posterior lobe sharply tapering to acute point, posterior margin of posterior lobe confluent with posterolateral margin of carapace; ambulatory legs (notably merus) relatively longer ( Fig. 6 I–M); G1 proportionately longer, more slender, with bent distal part longer, relatively stouter, gently curving downwards ( Fig. 9 M, O–Q).

Variation. The variation in the structure of the lamelliform lateral expansion is not substantial, even between specimens of different sexes or sizes. The expansions are relatively less broad in smaller specimens ( Fig. 3 E), progressively wider in larger specimens ( Figs 3 F; 10A). In small specimen, these lateral expansions are relatively less broad ( Fig. 3 E), whereas in larger ones, they are progressively wider ( Figs 3 F; 10A). The preorbital lobe in smaller specimens is triangular and directly obliquely laterally ( Fig. 3 E), becoming more acute and curved more anteriorly in larger specimens ( Figs 3 E, 10A).

Male and female specimens do not differ substantially in non-sexual characters, their carapaces being very similar ( Figs 1 A–D; 2E, F; 3E, F; 10A). The adult female abdomen is strongly convex, with somites 1–3 and telson free, and somites 4–6 completely fused ( Figs 8 E–G; 10C). The female abdominal somite 1 is mostly hidden under the posterior margin of the carapace in life ( Fig. 8 G). In subadult females, the abdomen is not prominently swollen or laterally expanded, and while somites 4–6 remain fused, the sutures are just visible as shallow grooves ( Fig. 10 B). The female vulva is similar to that of S. foliatus ; it has an operculum and is positioned on a raised mount on sternite 6, with the structure produced obliquely forwards, pushing the suture between sternites 5 and 6 anteriorly ( Figs 8 H; 10D). As a result, the posterior margin of the vulva is at the same level as the lateral and mesial portions of the suture between sternites 5 and 6.

Colour. In life ( Fig. 1 ), the carapace varies from red to orange or dull pink, with a characteristic heart-shaped white patch in the cardiac region, with the lateral margins white. The chelipeds are greenish with most of the fingers white. The last two pairs of ambulatory legs are white with the distal half of the dactylus green or orange. The first two pairs of ambulatory legs are greenish with the distal half of the dactylus dark green or orange. These generally agree with the colour of the female specimens figured by Sakai (1965: pl. 34 fig. 3; 1976: pl. 71 fig. 3).

Remarks. Balss (1924) described this species (under Mimulus ) on the basis of one male (9.5 × 9.0 mm) and an unmeasured female from a depth of 130 m, Zushi, Sagami Bay, Japan. The depository is not known. Balss’ description and figure ( Balss 1924: pl. 1 figs 4, 5) nevertheless leave no doubt to its identity. The present specimens from Japan and Taiwan agree in almost all aspects. They also agree very well with the figures of this species by Sakai (1965: text-fig. 11a, b, pl. 34 fig. 3; 1976: pl. 71 fig. 3). Mimulus Stimpson, 1860 (type species Mimulus foliatus Stimpson, 1860 ) is now regarded as a junior subjective synonym of Pugettia Dana, 1851 (see Wicksten & Stachowicz 2013).

In his discussion of the genus, Sakai (1965) believed that S. cristatus was synonymous with S. foliatus , and used only Ward’s (1936: pl. 3 fig. 4–6) figures for comparisons because he did not have specimens of the latter species. The differences observed between these two species (carapace details and leg proportions) are not easily discernible from Ward’s figures.

Biology. Sakai (1965: 75, 1976: 205) records the habitat of specimens he received from Akiya and Kii Nagashima, Japan as “weedy rock bottoms 15–30 m deep”. The present Japanese specimen from the Ryukyus (RUMF-ZC-3912) was collected from under dead coral rubble. The Taiwan specimens were found climbing around coral rubble encrusted with red and brown algae on mud and sand. There was no Sargassum or other macrophytic seaweeds in the area. The form of the carapace, colour, and encrusting organisms on it (notably bryozoans) are a very effective camouflage on the preferred habitat. It would appear that Ward’s (1936) choice of the genus name “ Sargassocarcinus ” is unfortunate as the species was not associated with these seaweeds. Ward (1936) did not state that he had obtained the species from seaweeds, and he may have made the association from the general appearance of the type species ( S. foliatus ), which he said resembled Huenia , a known associate of Sargassum . Noteworthy is that the two recent specimens of S. foliatus (QM W14482 ) were found on a piece of subtidal coral and not associated with any macroalgae. The habitat of Sargassocarcinus therefore appears to be dead coral, being a rubble mimic, like many species of leucosiids (see Tan & Richer de Forges 1993; Tan & Ng 1995; Naruse & Ng 2006; Komai & Ng 2012). This would make sense as specimens of S. cristatus have been obtained from waters as deep as 64 m, where there are few, if any, macroalgae.

Distribution. Known from Japan: Sagami Bay (type locality), Akiya (Sagami Bay), Kii-Nagashima (Mie Prefecture), Omaezaki (Suruga Bay, Shizuoka Prefecture) and off Taketomi Island (Ryukyus); and Taiwan (Pingtung) ( Balss 1924; Sakai 1965, 1976; Griffin & Tranter 1986; present record).

Figures

FIGURE 1. Sargassocarcinus cristatus, colour in life. A – D, overall habitus; E, frontal view of cephalothorax; F, ventral view of cephalothorax. A, male (14.4 × 11.7 mm) (ZRC 2015.288), Taiwan; B, ovigerous female (16.2 × 12.1 mm) (ZRC 2015.289), Taiwan; C, male (12.5 × 10.1 mm) (NMMBCD 4065), Taiwan; D – F, ovigerous female (14.3 × 11.1 mm) (RUMF-ZC- 3912), Ryukyus, Japan.

FIGURE 2. Overall habitus. A, Sargassocarcinus foliatus, holotype female (7.8 × 6.8 mm) (QM W 739), Queensland, Australia; B, S. foliatus, male (6.4 × 6.0 mm) (QM W 14482), Queensland, Australia; C, S. foliatus, male (5.7 × 5.4 mm) (QM W 14482), Queensland, Australia; D, S. sublimis, holotype male (13.3 × 10.8 mm) (USNM 48247), Philippines; E, S. cristatus, male (14.4 × 11.7 mm) (ZRC 2015.288), Taiwan; F, S. cristatus, male (12.5 × 10.1 mm) (NMMBCD 4065), Taiwan.

FIGURE 3. Dorsal view of carapace. A, Sargassocarcinus foliatus, holotype female (7.8 × 6.8 mm) (QM W 739), Queensland, Australia; B, S. foliatus, male (6.4 × 6.0 mm) (QM W 14482), Queensland, Australia; C, S. foliatus, male (5.7 × 5.4 mm) (QM W 14482), Queensland, Australia; D, S. sublimis, holotype male (13.3 × 10.8 mm) (USNM 48247), Philippines; E, S. cristatus, male (8.2 × 7.4 mm) (USNM 48248), Japan; F, S. cristatus, male (14.4 × 11.7 mm) (ZRC 2015.288), Taiwan.

FIGURE 6. Ambulatory legs and cheliped. A – H, Sargassocarcinus sublimis, holotype male (13.3 × 10.8 mm) (USNM 48247), Philippines [all same scale]; I – N, S. cristatus, male (8.2 × 7.4 mm) (USNM 48248), Japan [all same scale]. A, left first ambulatory leg; B, right first ambulatory leg (denuded); C, J, left second ambulatory leg; D, right second ambulatory leg; E, K, left third ambulatory leg; F, L, right third ambulatory leg; G, left fourth ambulatory leg; H, M, right fourth ambulatory leg; I, right first ambulatory leg; N, left cheliped. Scales = 1.0 mm.

FIGURE 9. Gonopods. A – E, Sargassocarcinus foliatus, male (6.4 × 6.0 mm) (QM W 14482), Queensland, Australia; F – I, S. sublimis, holotype male (13.3 × 10.8 mm) (USNM 48247), Philippines; J – N, S. cristatus, male (8.2 × 7.4 mm) (USNM 48248), Japan; O – R, S. cristatus, male (14.4 × 11.7 mm) (ZRC 2015.288), Taiwan. A, F, J, O, left G 1 (ventral view); B, G, K, P, left G 1 (dorsal view); C, H, L, Q, distal view of left G 1 (ventral view); D, distal part of left G 1 (dorsal view); E, I, N, R, left G 2; M, distal half of right G 1 (ventral view). Scales: A, B, F, G, I, J, K, M, N, O, P, R = 0.5 mm; C – E, H, L, Q = 0.1 mm.

FIGURE 10. Sargassocarcinus cristatus. A, B, female (10.8 × 8.9 mm) (NMMBCD 4065), Taiwan; C, D, ovigerous female (16.2 × 12.1 mm) (ZRC 2015.289), Taiwan. A, overall habitus; B, ventral view of cephalothorax showing buccal cavity, epistome, eyes and abdomen; D, sterno-abdominal cavity showing vulvae. Abbreviation: v, vulvae.

FIGURE 7. A, B, D – F, Sargassocarcinus foliatus, holotype female (7.8 × 6.8 mm) (QM W 739), Queensland, Australia; C, S. foliatus, male (6.4 × 6.0 mm) (QM W 14482), Queensland, Australia; G, I, S. sublimis, holotype male (13.3 × 10.8 mm) (USNM 48247), Philippines; H, S. cristatus, male (8.2 × 7.4 mm) (USNM 48248), Japan; J, S. cristatus, male (14.4 × 11.7 mm) (ZRC 2015.288), Taiwan; K, S. cristatus, ovigerous female (16.2 × 12.1 mm) (ZRC 2015.289). A, I, J, frontal margin and orbits; B, frontal margin, orbits, epistome, antennules and antennae; C, thoracic sternum and sternoabdominal cavity; D, inner view of left third maxilliped; E, outer view of left third maxilliped; F, G, dactylus of first ambulatory leg (denuded); K, ventral view of left eye. Scales: A – C, F – J = 1.0 mm; D, E = 0.5 mm.

FIGURE 8. A, Sargassocarcinus foliatus, male (6.4 × 6.0 mm) (QM W 14482), Queensland, Australia; B, S. sublimis, holotype male (13.3 × 10.8 mm) (USNM 48247), Philippines; C, S. cristatus, male (8.2 × 7.4 mm) (USNM 48248), Japan; D, S. cristatus, male (14.4 × 11.7 mm) (ZRC 2015.288), Taiwan; E – H, S. cristatus, ovigerous female (16.2 × 12.1 mm) (ZRC 2015.289), Taiwan. A – D, male abdomen (somites 3 – 6 and telson); E, female fused abdominal somites 4 – 6 and telson; F, female abdominal somites 2 – 4; G, female abdominal somite 1; H, female vulvae (arrow points to buccal cavity). Scales = 1.0 mm.