Exagorium fidelisi, Naruse & Chung & Tangah, 2015

Naruse, Tohru, Chung, Arthur Y. C. & Tangah, Joseph, 2015, Description of a new genus and a new species of the family Camptandriidae Stimpson, 1858 (Crustacea: Decapoda: Brachyura) from Lower Kinabatangan-Segama Wetlands, Sabah, Malaysia, Raffles Bulletin of Zoology 63, pp. 327-333 : 328-332

Exagorium fidelisi , new species

( Figs. 1 , 2 , 3a , 4 , 5 )

Material examined. All type specimens were collected from Sungai [= River] Kulamba, Tundon Bohangin, Sabah, Malaysia. Holotype: Male (7.6 × 10.6 mm) (IPMB-Cr. 08.1), 5°35.188’ N 118°37.391’ E, coll. T. Naruse & F. Koret, 18 June 2014. Paratypes: 1 ovig. female (5.7 × 7.9 mm) (IPMB-Cr. 08.2), same data as holotype ; 2 males (4.9 × 6.5, 5.4 × 7.2 mm) (RUMF-ZC-3680) 5°35.010’ N 118°37.545’ E, coll. T. Naruse & F. Koret, 20 June 2014 ; 1 male (5.9 × 7.7 mm), 1 female (4.9 × 6.6 mm) (RUMF-ZC-3682), same data as RUMF-ZC-3680 ; 1 female (7.0 × 9.5 mm) (RUMF- ZC-3681), 5°35.188’ N 118°37.391’ E, coll. T. Naruse & F. Koret, 19 June 2014 ; 1 juv. (2.8 × 3.7 mm) (IPMB-Cr. 08.3), 5°35.530’ N 118°36.894’ E, coll. T. Naruse & F. Koret, 19 June 2014 ; 1 juv. (2.5 × 3.1 mm) (IPMB-Cr. 08.4), 5°36.021’ N 118°35.588’ E, coll. T. Naruse & F. Koret, 20 June 2014 . Comparative material. Cleistostoma dilatatum (De Haan, 1833) : 1 male (13.4 × 19.1 mm) ( ZLKU 11072 ), river mouth of Nakdong-gang , Busan, Korea, coll. Y. Ishii, 13 September 1996 ; 2 females (11.8 × 16.4, 12.1 × 17.4 mm) ( ZLKU 429–431 ), near Hakomatsu Elementary School , Umi River, Kyushu, Japan, coll. S. Miyake et al., 15 July 1954 . Deiratonotus cristatum (De Man, 1895) : 2 ovig. females (4.3 × 5.9, 4.7 × 6.8 mm) (RUMF-ZC-298), Sumiyo River , Amami-ohshima Island, Ryukyu Islands, Japan, coll. S. Shokita et al., 24–27 December 2001 ; 1 male (4.2 × 5.7 mm) (RUMF-ZC-3688), Tekebu , Kasari , Amami-ohshima Island, Ryukyu Islands, Japan, coll. T. Maenosono, 25 April 2012 . Deiratonotus japonicum ( Sakai, 1934) : 1 ovig. female (6.4 × 8.2 mm) (RUMF-ZC-295), Oura River , Okinawa Island, coll. T. Naruse & C.-C. Han, 23 May 2002 ; 3 females (4.4 × 5.6 – 7.2 × 9.1 mm) (RUMF-ZC-296), Hentona River , Okinawa Island, Ryukyu Islands, Japan, coll. T. Naruse et al., 10 January 2004 ; 3 males (2.6 × 3.4 – 4.3 × 5.0 mm), 3 females (2.9 × 3.6 – 3.5 × 4.5 mm), 1ovig. female (5.4 × 7.2 mm) (RUMF-ZC-297), Tima River , Okinawa Island, Ryukyu Islands, Japan, coll. T. Naruse, 25 December 2004 ; 5 males (4.0 × 4.7 – 5.2 × 6.3 mm), 8 females (3. × 4.5 – 6.4 × 8.1 mm), 1 ovig. female (7.4 × 9.3 mm) (RUMF-ZC-3687), Konase , Setouchi , Amami-ohshima Island, Ryukyu Islands, Japan, coll. T. Maenosono, 26 April 2012 . Ilyogynnis microcheirum ( Tweedie, 1937) : 11 males (5.0 × 5.9 – 7.3 × 8.3 mm), 3 females (4.7 × 5.5 – 5.6 × 7.0 mm), 6 ovig. females (4.6 × 5.3 – 5.6 × 6.8 mm) (RUMF-ZC-357) Sungei Buloh East , Singapore, coll. T. Naruse et al., 13 September 2001 . Moguai aloutos Tan & Ng, 1999: 1 ovig. female (6.8 × 5.9 mm) (IPMB-Cr. 08.6), Sepilok Laut Reception Center , Sabah, Malaysia, coll. T. Naruse, F. Koret & J. Aribin, 4 March 2014 ; 1 male (4.8 × 4.3 mm) (RUMF-ZC-3683), Sungai Kulamba , Tundon Bohangin, Sabah, Malaysia, 5°35.530’ N 118°36.894’ E, coll. T. Naruse & F. Koret, 17 June 2014 ; 1 female (7.2 × 6.1 mm) (RUMF-ZC-3684), Sungai Kulamba , Tundon Bohangin, Sabah, Malaysia, 5°35.010’ N 118°37.545’ E, coll. T. Naruse & F. Koret, 17 June 2014 . Moguai elongatum ( Rathbun, 1931) : 1 male (2.7 × 2.4 mm), 2 females (2.3 × 2.1, 3.3 × 3.0 mm) (RUMF-ZC-32), Motonagura , Ishigaki Island, Ryukyu Islands, Japan, coll. T. Naruse & T. Nagai, 21 December 2004 ; 1 female (5.0 × 4.7 mm) (RUMF-ZC-33), Motonagura , Ishigaki Island, Ryukyu Islands, Japan, coll. T. Naruse & T. Nagai, 20 March 2005 . Mortensenella forceps Rathbun, 1909: 1 male (3.3 × 4.6 mm) (RUMF-ZC-299), Tsunoko , Amami-ohshima Island, Ryukyu Islands, Japan, coll. J. Nawa, 23 April 2005; 1 female (5.4 × 8.8 mm) (RUMF-ZC-300), Shirahama , Iriomote Island, Ryukyu Islands, Japan, coll. T. Naruse & T. Nagai, 3 August 2005 ; 1 juv. (2.9 × 4.0 mm) (RUMF-ZC-3690), Funaura Bay , Iriomote Island, Ryukyu Islands, Japan, coll. T. Naruse et al., 1 July 2001 . Paracleistostoma depressum De Man, 1895: 2 males (4.8 × 6.2 – 6.4 × 9.0 mm), 1 female (6.8 × 9.6 mm) (RUMF-ZC-341), Sungei Buloh East , Singapore, coll. T. Naruse et al., 13 September 2001 . Paramoguai pyriforme ( Naruse, 2005) : 1 male (4.3 × 3.6 mm), 2 ovig. females (4.9 × 5.0, 6.1 × 5.7 mm) (RUMF-ZC-3689), Konase , Setouchi , Amami-ohshima Island, Ryukyu Islands, Japan, coll. T. Maenosono, 26 April 2012 . Takedellus ambonense ( Serène & Moosa, 1971) : 2 males (3.5 × 3.6, 4.0 × 4.2 mm), 2 females (4.6v4.9, 5.3 × 5.8 mm), 3 ovig. females (5.1 × 5.3 – 6.7 × 7.8 mm), 1 juv. (2.3 × 2.3 mm) (IPMB-Cr. 08.5), Sungai Kulamba , Tundon Bohangin, Sabah, Malaysia, 5°35.010’ N 118° 37.545’ E, coll. T. Naruse & F. Koret, 20 June 2014 ; 1 male (2.9 × 3.0 mm), 1 ovig. female (5.2 × 5.5 mm) (RUMF-ZC-3685) Sungai Kulamba , Tundon Bohangin, Sabah, Malaysia, 5°35.010’ N 118° 37.545’ E, coll. T. Naruse & F. Koret, 18 June 2014 ; 1 male (2.9 × 3.1 mm) (RUMF-ZC-3686), Sungai Kulamba , Tundon Bohangin, Sabah, Malaysia, 5°35.188’ N 118°37.391’ E, coll. T. Naruse & F. Koret, 18 June 2014 ; 1 male (3.7 × 4.0 mm), 1 female (3.7 × 4.0 mm) (RUMF-ZC-302) Udara River , Iriomote Island, Ryukyu Islands, Japan, coll. T. Naruse & T. Nagai, 23 November 2004 .

Description. Carapace ( Fig. 1 ) hexagonal, CW 1.24–1.40 times CL (mean 1.33, n = 9), dorsal surface gently convex longitudinally, transversely, entirely punctate. Regions poorly defined, epigastric region with one pair of weak convexities, H-shaped gastric groove shallow. Frontal, supraorbital, anterolateral margins connected by rounded, granular ridge; similar ridges present on posterolateral margins (short, oblique), metabranchial regions (short, horizontal), and on intestinal region (long, transverse) just anterior to posterior margin with either end reaching posterolateral corner of carapace. Supraorbital margin slightly convex dorsally, weakly concave above cornea, with triangular ventral projection between mesial margin of orbit and antennular fossa ( Fig. 2a ). Exorbital angle rounded, smoothly continuous with anterolateral margin. Orbit ( Fig. 2a ) laterally bordered by low, thin ridge on upper half, lined with long setae, lower half open. Infraorbital crista sinuous, lined with granules, convex dorsally at middle, mesial end forming high triangular inner orbital tooth. Suborbital ridge gently arcuate,, lined with small granules, granules becoming longer laterally, ridge lateral to orbit directed downwards, without granules. Suborbital, pterygostomial regions ( Fig. 2b ) punctate, posterior margin of pterygostomial region rimmed, lined with granules, arcuate anteriorly, forming distinct Milne-Edwards aperture.

Epistome ( Fig. 2a ) trilobate, median lobe triangular, long, sharp.

Antennular fossa ( Fig. 2a ) relatively high, antennule folded obliquely. Antenna entering into orbit, with long flagellum.

Eyes ( Fig. 2a ) weakly compressed dorsoventrally, dumbbellshaped, enlarged at distal and proximal ends; cornea placed in disto-internal portion (when retracted);, outer-lower portion of eystalk punctate, outer-upper portion granular.

Male thoracic sternum ( Fig. 2b ) shiny, punctate around sutures, episternite of sternites 4–6, posterior half of sternite 7, entire sternite 8. Sterno-abdominal cavity deep, long, reaching posterior border of buccal cavern. Sternal pressbutton for locking mechanism placed close to suture 4/5 at slope of sterno-abdominal cavity of sternite 5.

Third maxillipeds ( Figs. 2b , 5a ) filling entire buccal cavern. Ischium wider than long, short, about third length of merus, ischium, merus punctuate; merus wider than ischium, anterolateral margin arcuate; carpus, propodus, dactylus articulated by end to end. Exopod narrow, reaching distal third of merus.

Chelipeds symmetrical ( Fig. 1 ), female chelipeds smaller than those of males. Merus simple, slightly granular on outer surface, upper, lower-mesial margins lined with long setae. Carpus rhomboidal in upper view, with inner angle, surface smooth. Palm of chela ( Fig. 2b ) gently swollen downwards and inwards. Movable finger with single oblong tooth subproximally; with double line of granules distal to this tooth and also on cutting margin of immovable finger, continuing to proximal ends of horseshoe-shaped, corneous fingertips.

Ambulatory legs ( Fig. 1 ) stout, short, combined length of merus to dactylus of P4 ca. 0.97 times CW, punctate, setose especially near margins. Merus with low granular ridge on upper, lower posterior margins of P2–5 and upper, lower, anterior margins of P3–5. P4 propodus with mat of setae on inner surface. Dactylus stout proximally, but strongly sharpened, with thin, long corneous tip.

Male abdomen ( Figs. 2b , 5b ) with all somites free, punctate on first to third somites and margin of telson. Somite 1 short, very wide, laterally reaching P5 coxae ( Fig. 3a ); somite 2 about two-thirds width of somite 1, as wide as somite 3, somite 3 to telson gradually tapering.

G1 ( Fig. 5c ) q-shaped, bent 180°, outer margin lined with setae from subproximal portion to bent portion, with small projection just distal to bent portion on outer margin. Distally with two terminal processes, tips of both pointed; process from inner side sparsely lined with four distally curved long bristles; inner process longer than outer one. G2 ( Fig. 5d ) shorter than outer process of G1.

Female characters. Sterno-abdominal cavity reaching posterior border of buccal cavern ( Fig. 4 ). Vulvae ( Fig. 4 ) horizontally elongated, oblong, entire, placed close to each other at mesial to suture 5/6. Abdomen with all sutures distinct, somites 2–6 functionally fused; telson triangular, proximal portion embraced by distal margin of abdominal somite 6.

Colouration. The carapace and the pereopods are light brown, but the cheliped carpus and chela are with paler colour ( Fig. 1 ). This is probably because the cheliped carpus and chela are smoother and therefore do not attract as much dirt and mud as the other parts.

Etymology. The species name is dedicated to Fidelis Edwin Bajau, Deputy Director (Development) of the Sabah Forestry Department, who has facilitated and encouraged the authors’ study to a great extent.

Ecological note. Exagorium fidelisi , new species, was pulled up by a yabbie pump from small vertical burrows that were observed on the surface of muddy sediment with depths of 10–30 cm during low tide. It was found beside the Kulamba River, dominated by the clump-forming palm, Nypa fruticans ( Fig. 6 ).

Figures

Fig. 1. Live colouration of Exagorium fidelisi, new genus & species. Holotype, IPMB-Cr 08.1, 7.6 × 10.6 mm.

Fig. 2. Exagorium fidelisi, new genus & species. Holotype, IPMB- Cr 08.1, 7.6 × 10.6 mm.

Fig. 3. Posterolateral portion of male thoracic sternite and abdomen. a, Exagorium fidelisi, new genus & species, holotype, IPMB-Cr 08.1, 7.6 × 10.6 mm; b, Cleistostoma dilatatum (De Haan, 1833), ZLKU11072, 13.4 × 19.1 mm; c, Ilyogynnis microcheirum (Tweedie, 1937), RUMF-ZC-357, 6.6 × 8.2 mm; d, Takedellus ambonense (Serène & Moosa, 1971), IPMB-Cr 08.5, 4.1 × 4.2 mm (Posterior margin of the carapace is lifted up). Arrow indicates where the posterior margin of the carapace is originally placed. a1–3, abdominal somites 1–3; p5c, coxa of pereopod 5; s7, 8, thoracic sternites 7, 8.

Fig. 4. Female thoracic sternum of Exagorium fidelisi, new genus & species. Paratype, IPMB-Cr. 08.2, 5.7 × 7.9 mm.

Fig. 5. Exagorium fidelisi, new genus & species. Holotype, IPMB-Cr 08.1, 7.6 × 10.6 mm. a, left third maxilliped; b, posterior portion of carapace, abdomen and telson; c, left G1; d, left G2. Scales, a, c, d, 1 mm; b, 5 mm.

Fig. 6. Habitat of Exagorium fidelisi, new genus & species, beside Nypa fruticans forest.