Parasesarma cognatum, Rahayu & Li, 2013

Rahayu, Dwi Listyo & Li, Jheng-Jhang, 2013, A New Species Of The Genus Parasesarma (Crustacea: Brachyura: Sesarmidae) From Taiwan And The Philippines, And Redescription Of P. Jamelense (Rathbun, 1914), Raffles Bulletin of Zoology 61 (2), pp. 633-639 : 636-639

Parasesarma cognatum , new species

( Figs. 4–7 )

crests (one crest with 14 corneous teeth, the other with 10); outer surface of palm striated proximally, granular distally, inner surface with numerous tubercles; dorsal surface of dactylus with 11–12 symmetrical, obliquely elongate tubercles, first three tubercles small, fourth to tenth tubercles large but becoming smaller distally, last two tubercles indistinct. Ambulatory legs relatively stout; P4 merus 2.8 times as long as broad; P4 propodus 3.6 times as long as broad; P4 dactylus 0.8 times length of propodus. Male telson semicircular, evenly rounded, slightly shorter than somite 6; G1 straight; apical process corneous, slightly bent at angle of 60°, long, stout, ending in rounded tip.

Description. — Carapace 1.1 times broader than long ( Figs. 4 , 5 ); regions well defined, separated by well marked grooves; lateral surface lined with strong oblique striae; dorsal surface with numerous tufts of short setae, lateral margins with row of short setae. Postfrontal region distinct ( Fig. 6B ), separated into four lobes by narrow, deep grooves; median lobes approximately same width as lateral lobes. Front deflexed downwards, margin bilobed from dorsal view, each lobe broadly convex, separated by broad median concavity. Supraorbital margin gently convex, entire. Exorbital tooth triangular, directed obliquely forward, representing point of greatest width; contiguous with entire lateral carapace margin; antero-, posterolateral margins not demarcated, without trace of tooth or indentation, lateral margin gently sinuous, subparallel along most of length before curving to join almost straight posterior carapace margin. Eyes not extending beyond edge of exorbital tooth. Basal segments of antenna, antennule adjacent, not separated by septum; basal antennular segment swollen. Antennal flagellum relatively long, entering orbit. Third maxilliped with shallow median sulcus on surface of ischium, surface of merus with distinct Material examined. — Holotype, male (14.3 × 13.1 mm) (NMMBCD 3975), mouth of Kankou stream, Manchow, Pintung County, south eastern Taiwan, 1 Sep.2012. Paratypes: 1 male (13.9 × 12.2 mm (ZRC 2013.722), 1 male (11.8 × 10.3 mm) (USNM), 1 ovigerous female (11.52 × 10.5 mm) (NMMBCD 3976), male (14.1 × 12.9 mm), (NMMBCD 3506), 8 Jun.2012, 2 females (11.5 × 10.3 mm; 14.4 × 12.6 mm) (NMMBCD 3505), 7 Jun.2012, 7 males (9.9 × 9.0 mm – 12.3 × 10.6 mm), 6 females (9.7 × 8.3 mm – 13.0 × 11.8 mm) (NMMBCD 3507), 1 Jun.2012; same locality as holotype.

Other material. — 1 male (10.2 × 10.1mm), 1 female (10.2 × 10.1mm) ( NMMBCD3980 ) , Houwan , Pintung County, south western Taiwan, 20 May 2013.6 males (7.2 × 6.5 mm – 11.5 × 10.4 mm) ( NMMBCD3508 ) , 27 Jun.2012, mouth of Kanzai stream, Manchow, Pintung County, south eastern Taiwan ; 2 males (12.9 × 11.3 mm; 12.0 × 10.7 mm), 28 Jul.2012, mouth of Meilun stream, Hualian city, eastern Taiwan. ( NMMBCD3509 ) ; 3 males (14.6 × 12.7 mm; 13.9 × 12.4 mm; 13.3 × 11.4 mm) ( ZRC.2008.1017) , 1 male (13.9 × 12.4 mm) ( ZRC.2008.0901), Kawasan Falls , southern Cebu, Philippines, coll. P. K. L. Ng et al., 4 Dec.2001 .

Diagnosis. — Carapace 1.1 times broader than long; regions well defined; postfrontal region separated into four lobes by narrow, deep grooves; frontal margin bilobed from dorsal view, each lobe broadly convex; exorbital tooth directed forward; eyes not extending beyond tip of exorbital tooth. Upper surface of cheliped palm with two transverse pectinated submedian ridge; exopod slender, tip overreaching half length of outer margin of merus, flagellum long; inner margin of merus, ischium with long setae, proximal outer margin of ischium, base of exopod with long, densely packed setae.

Chelipeds subequal, large, robust ( Figs. 4 , 5A , 6C ). Merus outer margin tuberculate, with large subdistal spine; inner margin tuberculate ending in large subdistal spine; outer surface striated, inner surface with longitudinal row of setae, scattered setae near upper margin. Carpus inner angle not produced, outer margin, across dorsal surface tuberculate. Upper surface of palm with two transverse pectinated crests ( Fig. 6D ). Primary (distalmost) crest composed of 14 high corneous teeth; proximal crest well developed, shorter than primary crest, with 8–10 lower, more widely spaced corneous teeth; crests not followed by row of tubercles. Outer surface of palm striated proximally, granular distally, glabrous; inner surface of palm with numerous tubercles. Fixed finger smooth on outer, inner surfaces. Cutting edge of fixed finger, dactylus with small, large rounded teeth. Dorsal surface of dactylus with 11–12 obliquely elongate tubercles ( Fig. 6D ), first three proximal tubercles small, fourth to sixth tubercles larger, seventh to tenth tubercles rounded, smaller, last two tubercles indistinct. Several low tubercles on proximal third of upper surface of dactylus; scattered low tubercles also on proximal third of inner edge of dorsal surface of dactylus. Fingers with chitinous tips, proximal gap distinct when fingers closed.

Ambulatory legs long, robust, laterally flattened ( Figs. 4A , 5A ); P3, P4 subequal, longer than others, about 1.9 times carapace width. P4 merus 2.8 times as long as broad; propodus 3.6 times as long as broad; dactylus 0.8 times length of propodus. In P2 to P5 upper margin of meri with an acute subdistal spine, carpi with two accessory carinae on outer surface, propodi with accessory carina on inferior proximal portion of outer surface, dorsal, ventral margins with short stiff setae; tip of dactyli slightly recurved, terminating in acute, corneous tip; dorsal, ventral margins with short stiff setae.

Male abdomen relatively broad ( Figs. 6A , 7E ). Telson semicircular, evenly rounded, about same length as somite 6; somite 6 about 2 times as long as wide, lateral margins slightly convex. Somites 3–5 progressively more trapezoidal, lateral margins of somites 4, 5 straight, lateral margins of somite 3 slightly convex, somites 1, 2 very narrow longitudinally.

G1 slender ( Figs. 7A–D ), apical process corneous long, bent at an angle of 60°, tip rounded. Setae long, simple, originating at base of apical process. G2 very short.

Female with smaller chelipeds, pectinated crests on palm replaced by two transverse rows of tubercles, dactylar tubercles indistinct. Vulvae on anterior edge of sternite 5.

Ecological note. — Parasesarma cognatum was usually found under rocks or stones in river/stream bank, about 50–200 m upstream from mouth.

Colour. — Specimen from Taiwan: carapace light brown with black and dark brown blotches, chelipeds yellow to brownish yellow ( Fig. 4 ). Specimen from Philippines (preserved in alcohol for 12 years): carapace light brown mottled with dark brown, chelipeds cream or whitish.

Distribution. — Southern and Eastern Taiwan and Cebu, Philippines.

Etymology. — From the Latin cognatus, related to, for the close resemblance to P. jamelense .

Remarks. — Rahayu & Ng (2009) recognised two major groups of species in Parasesarma : one group with relatively short and broad walking legs in which the meri and propodi of the second and third legs are less than three times as long as broad, and a second group which has relatively long and slender walking legs, with the meri and propodi of the second and third legs more than three times as long as wide. Parasesarma cognatum , new species, belongs to the first species-group. It most resembles P. jamelense in having the carapace almost as long as broad, and having the same number of dactylar tubercles on the chelipeds (11 to 12 tubercles vs 10 to11 tubercles in P. jamelense ), and with the distal corneous part of G1 long and stout. In P. jamelense , however, the ambulatory legs are relatively shorter and stouter, with the length of the P4 1.4 times the carapace width, and the merus 2.3 times longer than broad ( Fig.1A). In P. cognatum , the length of the P4 is 1.9 times the carapace width, with the merus slightly less than three times as long as broad ( Fig. 4A , 5A ). The shape of each male dactylar tubercle is also quite different. Parasesarma jamelense has oblique, narrow, closely-spaced tubercles ( Fig. 2D ), while in P. cognatum only the first three tubercles are narrow and oblique, with the following three wide, oblique, and the seventh to twelfth tubercles are rounded and widely spaced ( Fig. 5D ).

Among the species of Parasesarma with broad and short ambulatory legs, P. cognatum is also closely related to P. dumacense ( Rathbun, 1914) in having the first three tubercles small, obliquely elongate (Rahayu & Ng, 2010: fig. 13D), and the stout, broad-tipped of G1 (Rahayu & Ng, 2010: fig. 14A–D). However, the number of dactylar tubercles in P. dumacense is eight, each with fine transverse lines, while in P. cognatum it is 11 or 12 tubercles, without transverse lines ( Fig. 5D ). Their G1 structures are very different. The apical process of the G1 of P. dumacense is wide distally (Rahayu & Ng, 2010, fig. 14A–D), but in P. cognatum , it is slightly narrowed at the tip ( Figs. 6A–D ).

Parasesarma liho Koller et al., 2010 , a recently described species from eastern Taiwan, shares some characters with P. cognatum , such as relatively slender G1 and long ambulatory legs. In P. cognatum , however, the ambulatory propodi are longer (3.6 as long as broad vs 2.8 as long as broad in P. liho ), the apical process of the G1 is relatively broader and longer ( Fig. 6A–D ) (vs slightly tapered tip in P. liho ; cf. Koller et al., 2010: fig. 2d, e). The two species can also be easily separated by the number and shape of the dactylar tubercles of the male chela (10–13 dactylar tubercles which are oblique and perpendicular to the orientation of dactylus in P. liho vs 11–12 obliquely elongate and rounded dactylar tubercles in P. cognatum ). Moreover their coloration is very different, P. liho has a grey-beige carapace with violet blotches and light grey-violet chelae with fingers fading into cream or yellow ventrally ( Koller et al., 2010: fig. 3) while P. cognatum has a light brown carapace with black and dark brown blotches, and yellow to brownish yellow chelipeds ( Fig. 4 ).

Figures

Fig. 4. Parasesarma cognatum, new species, live colouration. A, paratype, male (14.1 × 12.9 mm); B, male (13.9 × 12.4 mm).

Fig. 5. Parasesarma cognatum, new species, holotype, male (14.3 × 13.1 mm),A, whole animal, dorsal view; B, dorsal view of carapace.

Fig. 6. Parasesarma cognatum, new species, holotype, male (14.3 × 13.1 mm). A, ventral view showing anterior part of thoracic sternum, abdomen; B, frontal view of carapace; C, cheliped; D, dactylus of cheliped, showing dactylar tubercles.

Fig. 7. Parasesarma cognatum, new species, holotype, male (14.3 × 13.1 mm). A–D, left G1; E, abdomen. Scale bars = 1 mm (A, B, E), 0.5 mm (C, D).Setae omitted.

Fig. 2. Parasesarma jamelense (Rathbun, 1914), holotype, male (11.5 × 10.0 mm).A, ventral view showing anterior part of thoracic sternum, abdomen; B, frontal view of carapace; C, cheliped; D, dactylus of cheliped, showing dactylar tubercles.