Geosesarma batak, Manuel-Santos & Ng & Freitag, 2016

Manuel-Santos, Marivene, Ng, Peter K. L. & Freitag, Hendrik, 2016, Two new species of Geosesarma De Man, 1892 (Crustacea: Brachyura: Sesarmidae) from Palawan, the Philippines, Raffles Bulletin of Zoology 64, pp. 335-342 : 336-340

Geosesarma batak , new species

( Figs. 1A–C , 4A–F , 5A, B )

Material examined. Holotype: male (22.8 × 22.4 mm) (NMCR-40105), Puerto Princesa, Concepcion, near Cleopatra Needle , c. 8.5 km upstream of highway, primary forest, phytothelmata, c. 600 m asl, 10°06’N 119°00’E, coll. H. Freitag, 31 January 2015 . Paratypes: 1 female (20.6 × 20.1 mm), 2 juveniles (larger 9.1 × 8.5 mm) (NMCR-40106), same data as holotype ; 1 male (11.7 × 11.4 mm) ( PCSD), Puerto Princesa, Tagpaya, Camp Aga, Taranaban River , c. 7 km upstream of highway, disturbed primary forest, hygropetric rocks, c. 350 m asl, 10°05’08”N 119°00’33”E, coll. H. Freitag, 2 February 2015 ; 1 female (21.9 × 21.4 mm) ( ZRC 2015.290 ) , 1 male (14.5 × 14.1 mm), 7 juveniles (largest 9.6 × 9.4 mm) ( CFM-ADMU), Puerto Princesa, Concepcion, Taranaban River , c. 4 km upstream highway, tree phytothelmata, c. 100 m asl, 10°02’00”N 119°01’00”E, coll. H. Freitag, 20 January 1994 ; 1 male (18.9 × 18.5 mm) ( ZRC 2015.291 ), Puerto Princesa, 2 km SE Laptay / Napsan, Kalalagbong forest, Tagbanua rainforestation, 9°41’20”N, 118°27’15”E, coll. H. Freitag, 22 August 2008 ; 2 females (18.0 × 17.6 mm, 15.7 × 15.6 mm) ( SMTD-S170 , SMTD-S171 ) , 2 females (18.3 × 18.0 mm, ovigerous), 1 male (20.2 × 19.8 mm, dried) ( CFM-ADMU), Puerto Princesa, Langogan, side of small temporary tributary near National Highway km 83.9, c. 600 m asl, degraded primary forest, c. 10°01’50”N 119°08’31”E, coll. H. Freitag, 22 August 1994 . All locations in Palawan Island, Philippines .

Diagnosis Carapace almost squarish, slightly wider than long; dorsal surfaces rough, gastric and branchial regions slightly swollen, frontal margin strongly deflexed at 90° from horizontal view; postfrontal crest separated into 4 unevenly shaped, dentiform granulated lobes; posterolateral regions with fine granular striae. Outer surface of chela covered with low rounded granules, dorsal margin with incomplete granular ridge. Ambulatory legs relatively shorter, fourth merus 0.8 times as long as carapace width. Male abdominal somite 6 as long as telson; male telson relatively broader, 1.3 times wider than long. G1 relatively long, slender, shaft more or less evenly tapering, distal chitinous part gently bent laterad at 45°, chitinous part relatively broad, long, gently curved.

Description of holotype male. Carapace ( Fig. 1A ) subsquarish, almost as long as wide; lateral margins subparallel; dorsal surfaces slightly convex, rough, with low granules; gastric and branchial regions swollen, hepatic region depressed; grooves moderately deep, regions well defined. Postfrontal crest straight to slightly concave, divided into 4 dentiform postfrontal lobes, reaching or extending slightly beyond frontal margin in dorsal view; anterior margins unevenly granulate; median cleft deep, moderately broad, leading to deep mesogastric groove; 2 distinct, sharp protogastric protuberances present behind lateral frontal lobes; front prominently deflexed from dorsal carapace at right angles, frontal margin sinuous, with broad median concavity; sublateral areas gently lobiform. Orbital carapace margin gently curved. External orbital tooth broadly triangular, directed antero-laterad, tip sharp, pointed; first anterolateral tooth distinctly smaller than external orbital angle, broadly triangular, pointing dorso-laterad, tip acute; second anterolateral tooth very low, inconspicuous; lateral margins finely granular, cristate. Posterolateral regions with fine oblique striae.

Third maxillipeds with rhomboidal gap when closed ( Fig. 1B ); merus and ischium subequal in size; combined length of carpus, propodus and dactylus (palp) slightly shorter than merus; merus longitudinally ovate, widest subdistally; median and anterior rims, and oblique crista with densely setose fringe; ischium elongately subtrapezoidal; sulcus shallow; entire rim with setose fringe; base with large patch of soft thick setae that extends to base of cheliped; exopod behind ischium, slender, apical median rim with dense setose fringe; flagellum long, reaching beyond width of merus.

Surfaces of thoracic sternites smooth ( Fig. 1B ), but with scattered bristles; sternites 1 and 2 completely fused; sternite 2 separated from sternite 3 by setose ridge; sternites 3 and 4 fused; sternoabdominal cavity reaching to midpoint of fused sternites 3 and 4. Telson relatively broader, ca. 1.2 times wider than long, lateral margins very gently convex on distal part, but almost straight proximally, tip rounded; somite 6 about as long as telson, distal part of lateral margin convex, proximal part almost straight; abdominal somites 3–5 increasingly trapezoidal; somites 1 and 2 transverse, narrow.

Left cheliped ( Fig. 1C ) large, distinctly longer than carapace; outer surfaces covered with distinct rounded granules and scattered setae; ischium short subcylindrical, with few prominent, conical granules at ventral and anterior margins, and several inconspicuous setiferous granules; merus approximately as long as palm, ventral margins with sharp granules, dorsal margin serrate, ventral and inner sides smooth, inner side with regularly arranged setae and 2 additional longitudinal rows of setae, lower (ventral) one much more distinct; carpus subovate, slightly longer than broad, subtrapezoidal in dorsal view, with short row of setae at basal inner margin near mero-carpal joint, without distinct inner tooth. Chela relatively stout, median upper (dorsal) margin and outer surface with conspicuous rounded granules; dorsal margin with incomplete granular ridge; lower (ventral) margin and inner surface with lower, smaller granules; fingers subequal to palm in length; dorsal margin of dactylar finger with small sharp tubercles on proximal half; cutting edges of both fingers with prominent teeth, distal half with small gape when closed ( Fig. 1C ); dorsal and ventral finger margins with conical granules.

Ambulatory legs ( Fig. 1A, B ) slender, very long; third ambulatory leg longest (combined length of merus, carpus, propodus and dactylus about 2 times of carapace width). Meri moderately slender, very long; second ambulatory merus slightly overreaching frontal carapace margin; fourth ambulatory merus about 0.8 times as long as carapace width; lateral margins almost straight, with distinct subdistal spine; dorsal surfaces with scattered micro-granules; ventral side smooth; margins serrate, subcristate. Carpi slender; fourth ambulatory carpus ca. 0.5 times as long as fourth ambulatory merus, with subparallel dorsal ridge; surfaces smooth; margins partly granulose, not serrate. Propodus and dactylus slender; fourth ambulatory propodus ca. 0.8 times as long as fourth ambulatory merus; fourth ambulatory dactylus ca. 0.5 times as long as fourth ambulatory merus, surfaces smooth, margins with short dark amber-coloured spines and scattered bristles.

G1 ( Fig. 4A–C ) moderately long, slender, reaching half length of abdominal somite 6, straight; subdistal inner margin with long setae that do not overreach tip; base rounded, relatively less prominent ( Fig. 4B ); shaft more or less evenly tapering towards distal chitinous part in dorsal and ventral views ( Fig. 4A, C ); apically comparably gently bent laterad at 45° in ventral view ( Fig. 4A ); distal part slightly bent dorsad in lateral view ( Fig. 4B ), moderately broad, moderately long, entirely gently curved. G2 ( Fig. 4D ) very short; base subtriangular; distal part moderately slender, outer margin somewhat abruptly curved at half length.

Colour in life. Carapace and legs brown with yellowish crested margin of carapace with reddish tinge anteriorly, becoming yellowish posteriorly; tubercles and spinules of chelipeds reddish; abdomen and ventral surfaces pale yellow ( Fig. 5 ).

Etymology. Named after the Bataks, the oldest indigenous tribe in the Philippines who reside in Puerto Princesa and the rest of Palawan. The name is used as a noun in apposition.

Remarks. As discussed earlier, the two new species share with G. lawrencei the same prominent four postfrontal lobes and wide male abdominal somite 6 ( Manuel-Santos & Yeo, 2007: fig. 1A–C). The G1 is also similar in form, being slender but the chitinous distal part is only gently bent from the vertical ( Manuel-Santos & Yeo, 2007: fig. 2A, B). In addition, the ambulatory legs are relatively shorter in G. lawrencei compared to the two new species (cf. Manuel-Santos & Yeo, 2007: fig. 1A). As discussed in Manuel-Santos & Yeo (2007), G. lawrencei is only know from three relatively small specimens collected from the southern part of Palawan (Brooke’s Point) (all about 10 mm in carapace width), and they may not be fully adult as yet. Geosesarma batak is most closely related with G. tagbanua , new species (described below). However, their G1 structures are different. The G1 of Geosesarma tagbanua is proportionately more slender, abruptly tapering subapically ( Fig. 4G–I, L ) (versus evenly tapering towards distal chitinous part in G. batak , Fig. 4A–C, F ), and its distal chitinous part is distinctly more slender, with only the apical area curved ( Fig. 4G–I, L ) (versus moderately wider and entirely curved in G. batak , Fig. 4A–C, F ). In addition, G. tagbanua can be distinguished from G. batak by its relatively more slender male telson ( Fig. 2B ) (ca. 1.2 times versus 1.3 times wider than long in G. batak , Fig. 1B ); and the shorter male abdominal somite 6 ( Fig. 2B ) (slightly shorter than telson versus as long as telson in G. batak , Fig. 1B ). The ambulatory legs of G. tagbanua are also slightly longer ( Fig. 2A ) (fourth ambulatory merus about 0.9 times versus 0.8 times as long as carapace broad in G. batak , Fig. 1A ).

With regards to the slender G1 with a long and slender chitinous distal part that is bent laterad at 45°, G. batak and G. tagbanua are most similar to G. bicolor [western Java], G. dennerle [central Java], G. hagen [central Java], G. krathing [eastern Thailand] and G. peraccae [southern Malaysia and Singapore]. However, both new species can easily be distinguished from these species by its relatively larger adult size (adults in excess of 20 mm in carapace width) and prominently longer ambulatory legs. In addition, the carapace of G. peraccae is distinctly trapezoidal ( Ng, 1988: fig. 56A) whereas those of G. batak and G. tagbanua are squarish ( Figs. 1A , 2A , 3A).

With regards to the squarish form of the carapace, general appearance of the external orbital tooth and lateral carapace margin, G. batak and G. tagbanua resemble G. sabanum and G. danumense from Sabah, Borneo (Ng, 1992: fig. 1A; Ng, 2002: figs. 1a, 3B, 4a, b). These two species also have longer ambulatory legs compared to most Geosesarma , although they are still relatively shorter than the two new species from Palawan (Ng, 1992: fig. 1c; Ng, 2002: figs. 1a, 3B, 4a). The two species from Sabah, however, have the postfrontal lobes less distinctly separated (Ng, 1992: fig. 1A; Ng, 2002: figs. 1a, 3B, 4a, b); have no flagellum on their third maxilliped exopod (cf. Ng, 1992: fig. 1B; Ng, 2002: 304); possess a male abdominal somite 6 which is proportionately less wide (cf. Ng, 1992: fig. 1L; Ng, 2002: figs. 2c, 3C); and have stout G1s in which the chitinous distal part is relatively short and spatuliform (cf. Ng, 1992: 1E–J; Ng, 2002: fig. 3D–H) Geosesarma batak and G. tagbanua , like other Geosesarma species now known from the Philippines, do not have pectinate tubercles on the dorsal margin of the dactylus of their chela. While the condition of the carapace, third maxilliped, chela, male abdomen, and/or G1 are not known in G. rathbunae and G. vicentense , the second author has examined the types in the U.S. National Museum of Natural History, and that information is added in this discussion for completeness. Geosesarma batak and G. tagbanua resemble G. rathbunae in the squarish carapace. However, G. rathbunae , from Panay Island, has proportionately much shorter ambulatory legs ( Serène, 1968: pl. 1 fig. 4). Its G1 superficially resembles those of G. batak and G. tagbanua in the general shape and angle but the distal chitinous part is relatively shorter ( Serène, 1968: figs. 5, 6). Geosesarma rathbunae shares the same wide male abdominal somite 6 as G. batak and G. tagbanua ; but the exopod of its third maxilliped has no flagellum (second author, unpublished data). Geosesarma batak and G. tagbanua differ distinctly from G. hednon (from Cebu, Visayas) and G. protos (from Mindanao) in the squarish carapace shape ( Figs. 1A , 2A ) (distinctly wider than long in G. hednon , trapezoidal in G. protos , cf. Ng et al., 2004: fig. 9A, B; Ng & Takeda, 1992: fig. 1A); longer ambulatory legs ( Figs. 1A , 2A , 3A) (much shorter in G. hednon and G. protos , cf. Ng et al., 2004: fig. 9A; Ng & Takeda, 1992: fig. 1D); and the presence of a long flagellum of the exopod of the third maxilliped (short or absent in G. hednon , always absent in G. protos , cf. Ng et al., 2004: 241; Ng & Takeda, 1992: fig. 1B). In G. protos , the G1 is also short and stout ( Ng & Takeda, 1992: fig. 1G–I), very different from that of G. batak and G. tagbanua ( Fig. 4A–C, F, G–I, L ). The poorly known G. vicentense belongs to same group of species as G. hednon and G. maculatum , with a squarish carapace and short ambulatory legs, the exopod of the third maxilliped has a distinct or short flagellum (sometimes missing), and the G1 is straight with the distal chitinous part directed vertically ( Ng et al., 2004: figs. 4, 7B–E, 13C–G; unpublished data).

Distribution. Only known from Palawan Island, the Philippines.

Ecological notes. The species was only found in forested areas near streams. Specimens were rarely found at the ground, but more commonly on trees where they dwell in wet knotholes (and other phytothelmata). Some were detected on rocks where they hide in crevices when disturbed or when resting during daytime. The species is probably nocturnal.

One specimen from Puerto Princesa, Concepcion, Taranaban River, possessed relatively large eggs (diameter 1.12–1.39 mm, on average ca. 1.2 mm) ( Fig. 5B ); suggesting this species undergoes direct or semi-abbreviated development ( Ng, 1988; Ng & Tan, 1995).

Figures

Fig. 1. Geosesarma batak, new species, holotype male (22.8 × 22.4 mm) (NMCR-40105), Concepcion, near Cleopatra Needle. A, overall habitus; B, ventral view of cephalothorax; C, left chela and carpus, outer view.

Fig. 4. A–D, Geosesarma batak, new species, holotype male (22.8 × 22.4 mm) (NMCR-40105), Concepcion, near Cleopatra Needle; E, F, G. batak, new species, paratype male (18.9 × 18.5 mm) (ZRC 2015.291), from Laptay/Napsan; G–J, G. tagbanua, new species, holotype male (21.8 × 21.8 mm) (NMCR-40107), Lipuun Point, Tabon Caves; K, L, G. tagbanua, new species, paratype male (21.2 × 21.7 mm) (NMCR-25052), Narra, Tuas, Estrella Creek. A–C, F, G–I, L, left G1 (from different angles); D, E, J, K, left G2.

Fig.5.Geosesarma batak, new species,in vivo.A, frontodorsal view of paratype female (20.6 × 20.1 mm) (NMCR-40106), Concepcion, Taranaban River; B, ventral view of an ovigerous female from Concepcion, Taranaban River (specimen not collected)

Fig. 2. Geosesarma tagbanua, new species, holotype male (21.8 × 21.8 mm) (NMCR-40107), Lipuun Point, Tabon Caves. A, overall habitus; B, ventral view of cephalothorax; C, left chela and carpus, dorsal view; D, left chela, outer view.