Parasesarma carolinense ( Rathbun, 1907 )

Ng, Peter K. L., Davie, Peter J. F. & Li, Jheng-Jhang, 2016, On the identities of Parasesarma carolinense (Rathbun, 1907) and Parasesarma sigillatum (Tweedie, 1950), with description of a new species from Taiwan (Crustacea: Brachyura: Sesarmidae), Raffles Bulletin of Zoology 64, pp. 257-268 : 259-261

Parasesarma carolinense ( Rathbun, 1907)

( Figs. 2 ; 5A–C ; 6A–F )

Sesarma (Parasesarma) carolinensis Rathbun, 1907: 34 , pl. 5 fig.

2, 2a; pl. 9 fig. 1; Tesch, 1917: 141; Serène, 1968: 108. Parasesarma carolinense – Ng et al., 2008: 222 (list, part).

Material examined. Holotype: male (9.2 × 7.0 mm) ( USNM 32861 ), Kusaie, Carolines, coll. 9 February 1900.

Diagnosis. Carapace 1.31 times broader than long; lobes of frontal margin separated by broad, very shallow concavity ( Fig. 2A–C ); upper surface of cheliped palm with 2 transverse pectinate crests, primary (distalmost) consisting of row of 14 or 15 tall pectinate teeth, tip of each tooth gently curved, secondary crest with 16 or 17 relatively lower pectinate teeth ( Fig. 2F, I ); inner surface of palm with short obliquely transverse granulated ridge on upper half ( Fig. 2G ); dorsal surface of dactylus with 15 or 16 triangular tubercles, each dactylar tubercle with distinct transverse ridge ( Fig. 2F, G, I ); inner distal margin of lamelliform process of merus lined with sharp triangular teeth ( Fig. 2F, G ); ambulatory legs short, stout; merus of third leg 2.0 times as long as wide; upper margin of merus with subdistal spine; propodus of third leg 2.7 times as long as wide; dactylus of third and fourth legs 0.7 and 0.8 times length of propodus, respectively ( Figs. 2A ; 5A–C ); male telson triangular with strongly convex lateral margins, ca. 1.5 times length of pleonal somite 6 ( Fig. 6B ); G1 relatively slender, straight; apical process bent to form an angle of about 80º from the vertical, chitinous distal part long ( Fig. 6C–F ).

Description. Carapace trapezoidal, 1.31 times broader than long; dorsal surfaces relatively smooth, glabrous; regions poorly defined, separated by shallow grooves except for deeper H-shaped median gastric groove; lateral parts of dorsal carapace surface with distinct oblique striae; posterior surface with short transverse striae; lateral margins with numerous tufts of short setae ( Fig. 2A, B ). Postfrontal region distinct, low, rounded, not cristate, separated into 4 lobes by narrow, distinct longitudinal grooves; median lobes approximately same width as lateral lobes ( Fig. 2A–C ). Front truncate, distinctly deflexed downwards, margin weakly bilobed from dorsal view with lobes separated by broad, very shallow median concavity; confluent with supraorbital margin ( Fig. 2A–C ). Supraorbital margin entire, posteriorly oblique, convex along anterior half, posterior half gently sinuous ( Fig. 2A, B ). External orbital tooth triangular, directed obliquely outwards, representing point of greatest carapace width; antero- and posterolateral margins not demarcated, without trace of tooth or indentation, lateral margins straight, converging to meet weakly convex posterior carapace margin ( Fig. 2A, B ). Eyes with large cornea, not reaching to external orbital tooth ( Fig. 2A, B ). Antennal and antennular basal segments adjacent, not separated by septum; basal antennular segment large; antennal flagellum relatively long, entering orbit.

Third maxilliped with ischium relatively short, subrectangular in shape, with shallow median sulcus, left one relatively shorter than right one (see Remarks) ( Figs. 2E ; 6A ); merus subovate, with distinct submedian ridge; inner margin of merus-ischium with stiff setae; exopod slender, tip reaching about half length of outer margin of merus, flagellum long ( Figs. 2D, E ; 6A ).

Chelipeds relatively stout in adult male, symmetrical ( Fig. 2A ). Merus short, inner distal part prominently carinate, forming large lamelliform structure; distal margin of lamelliform structure appears serrated, with short sharp teeth, inner margin with denticles; outer margin uneven or with low granules; outer surface with dorsal striation; inner surface gently concave, smooth, with 2 rows of setae ( Fig. 2A, F, G ). Carpus with inner angle not produced, rounded; outer margin and surface striated ( Fig. 2F, G ). Upper surface of palm with 2 obliquely transverse pectinate crests, primary (distalmost) crest with row of 14 or 15 tall pectinate teeth, tip of each tooth gently curved, secondary crest with 16 or 17 relatively lower pectinate teeth ( Fig. 2F, I ). Outer surface of palm with striations and punctations; inner surface of palm with short oblique granulated crest on upper part ( Fig. 2H ). Fingers short, subequal to length of palm; cutting edge of pollex with large, rounded teeth on distal half, teeth on proximal part relatively lower, tip excavated, spatulate; dactylus with rounded tooth on subproximal part of cutting margin, rest of margin with small teeth, tip excavated, spatulate; dorsal surface of dactylus with 15 or 16 triangular tubercles, gradually sloping distally, becoming lower, each tubercle with a strong proximal transverse ridge ( Fig. 2F–I ).

Ambulatory legs short, stout, laterally flattened; second and third pairs longest ( Fig. 2A ). Merus with low transverse striae on upper surface, meri of second and third legs 2.2 and 2.0 times as long as wide, respectively; upper margin of merus with subdistal spine ( Figs. 2A ; 5A–C ). Carpus with 2 accessory carinae on outer surface. Propodus of third leg ca. 2.7 times as long as wide with low carina on inferior proximal portion of outer surface, dorsal and ventral margins with short stiff setae ( Figs. 2A ; 5A–C ). Dactylus of third and fourth legs 0.7 and 0.8 times length of propodus, respectively, tip gently curved distally, terminating in acute calcareous tip, dorsal and ventral margins with short stiff setae ( Figs. 2A ; 5B, C ).

Surface of thoracic sternites 1–4 smooth; sternites 1–3 completely fused, without trace of sutures; separated from sternite 4 by deep suture ( Fig. 2D ). Male sternopleonal cavity reaching suture between sternites 3, 4. Male pleon relatively broad, all somites free; telson triangular with strongly convex lateral margins, ca. 1.5 times length of pleonal somite 6; somite 6 almost twice as wide as long, lateral margins strongly convex; somites 3–5 progressively more trapezoidal; somites 1, 2 very narrow longitudinally; reaching coxa of fourth ambulatory leg, sternite 8 completely covered ( Fig. 6B ).

G1 relatively slender, straight; apical process bent to form an angle of about 80° from the vertical, chitinous distal part long, aperture terminal ( Fig. 6C–F ). G2 short, about a third length of G1.

Colour in life. Not known.

Habitat. Not known.

Remarks. The left third maxilliped ( Fig. 6A ) appears to be abberant, with the ischium relatively short. On the right third maxilliped, the ischium is proportionately longer ( Fig. 2E ). The right third maxilliped structure of P. carolinense agrees well with those of P. sigillatum and P. corallicum ( Fig. 6G, N ), respectively.

The species is known only from the holotype specimen. Comparisons with P. sigillatum and P. corallicum n. sp. are provided in the Discussion.

Figures

Fig. 2. Parasesarma carolinense (Rathbun, 1914), holotype male (9.2 × 7.0 mm) (USNM 32861), Caroline Islands. A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, anterior thoracic sternum and pleon; E, third maxillipeds; F, dorsal view of left cheliped; G, dorsal view of right cheliped; H, outer view of left chela; I, dactylar tubercles of left chela.

Fig. 5. Left ambulatory legs. A–C, Parasesarma carolinense (Rathbun, 1914), holotype male (9.2 × 7.0 mm) (USNM 32861), Caroline Islands; D–G, Parasesarma sigillatum (Tweedie, 1950), male (9.5 × 6.8 mm) (ZRC 1965.8.2.269), Cocos-Keeling Island; H–K, Parasesarma corallicum n. sp., holotype male (9.5 × 7.0 mm) (NMMBCD 4697), Taiwan. A, D, H, first ambulatory leg; B, E, I, second ambulatory leg; C, F, J, third ambulatory leg; G, K, fourth ambulatory leg. Legs of all species to scale.

Fig. 6. A–F, Parasesarma carolinense (Rathbun, 1914), holotype male (9.2 × 7.0 mm) (USNM 32861), Caroline Islands; G–M, Parasesarma sigillatum (Tweedie, 1950), male (9.5 × 6.8 mm) (ZRC 1965.8.2.269), Cocos-Keeling Island; N–T, Parasesarma corallicum n. sp., holotype male (9.5 × 7.0 mm) (NMMBCD 4697), Taiwan. A, G, N, left third maxilliped; B, H, male pleon; O, male pleon (somites 1 and 3 broken); C, P, ventral view of left G1; D, Q, dorsal view of left G1; E, ventral view of right G1; F, distal chitinous part of right G1 (ventral view); I, ventral view of right G1; J, dorsal view of right G1; K, distal chitinous part of right G1 (ventral view); L, distal chitinous part of right G1 (dorsal view); M, right G2; R, distal chitinous part of left G1 (ventral view); S, distal chitinous part of left G1 (dorsal view); T, left G2. Setae for all structures denuded. Scale bars = 0.5 mm [A–E, G–J, M–Q, T]; 0.1 mm [F, K, L, R, S].