Elamena sira, Rahayu & Nugroho, 2019

Rahayu, Dwi Listyo & Nugroho, Dharma Arif, 2019, Three new species of the genus Elamena H. Milne Edwards, 1837 (Crustacea: Decapoda: Hymenosomatidae) from Lombok Island, Indonesia, Raffles Bulletin of Zoology 67, pp. 171-182 : 180-181

Elamena sira new species

( Figs. 2E, F , 3C, D , 5 )

Material examined. Holotype male (3.3 × 3.0 mm) ( MZB Cru 4898), Sira , Lombok Island, 21 July 2009 . Paratype, female (3.8 × 3.5 mm) ( ZRC2019.0594 ), same locality as holotype .

Description. Carapace slightly broader than long, chestnut shape ( Fig. 5A, G ), dorsal surface slightly concave, smooth, surrounded by thin rim, shallow groove on mesogastric, cardiac, branchial regions. Rostrum truncated, anterior margin slightly convex medially, with sparse bristles, laterally continuous with anterolateral margin of carapace, ventral keel deep dorsoventrally, triangular in lateral view, partially visible from dorsal view, posteriorly continuous with prominent interantennular septum. Postocular tooth distinct, triangular, with rounded tip, not visible from dorsal view.

Anterolateral margin slightly sinuous ( Fig. 1A, G ) slightly concave near base of rostrum; first, second anterolateral teeth replaced by slight convexity, rounded boundary with posterolateral margin, respectively; posterolateral margin slightly convex, not well demarcated from posterior margin; posterior margin slightly convex. Pterygostomian region with 2 lobes ( Fig. 1C ), one lobe at opposite ischio-meral suture of third maxilliped, broadly triangular, one much smaller lobe on anterior to base of cheliped coxa. Epistome length subequal to breadth, posterior margin sinuous, with median notch.

Antennules well developed, basal antennular articles placed between bases of eyes, medially separated by septum (proepistome) with relatively long disto-external protuberance; basal antennal article developed from below base of eye. Eyes well developed, stout, partially visible from anterolateral margin in dorsal view.

Third maxillipeds ( Fig. 5B ) squarish, covering buccal cavern when closed; exopod narrow, distal end not reaching distoexternal angle of merus, with distinct flagellum; ischium broader and longer than merus, distal margin forms oblique border with merus, distal and proximal internal angle rounded, external margin much shorter than internal margin; merus subtriangular, with longitudinal ridge along submedian portion of dorsal surface, internal margin slightly convex, shorter than external margin.

Male thoracic sternum wide, glabre; sternites 1–3 fused, partially hidden by third maxilliped, sunken toward buccal cavity, strong transverse ridge at junction of sternites 3/4; sternoabdominal cavity deep, anterior tip reaching posterior border of sternite 4, without suture, press-button situated at level between sternites 5, 6.

Male chelipeds similar ( Fig. 5A ), more robust than those of female; merus rounded in cross section; carpus rounded, distal inner angle blunt; chela ( Fig.5D ) with slightly swollen palm, fingers shorter than palm, dactylus spoon shaped, no wide gape when closed, cutting edges lined with small teeth, with larger proximal tooth on dactylus. Female chela more slender with slight gap between fingers.P2−P5 slender ( Fig. 5A, E ), all surfaces with sparse, short bristly setae, extensor and flexor margins lined with short setae except for flexor margin of dactyli which lined with longer setae; P3 longest, P5 shortest, meri longer than propodi; meri, carpi of all legs with distal acute extension on extensor margins; distal one-third of dactyli gently curving inward, terminating in a sharp claw, flexor margin with 2 subdistal teeth, directed backwards.

Male pleon with five somites, including pleotelson ( Fig. 5F ). Third, fourth somites fused, gradually narrowed over distal half with slightly convex lateral margins; pleotelson subtriangular, 1.8 as long as fifth somite, apex rounded. G1 with slight S-shaped ( Figs. 2E, F , 3C, D ), two third proximal portion stout, third distal more slender, curved, directed ventrally, tip pointed with single long setae.

Female pleon moderately broad ( Fig. 4H ), 6 somites free including pleotelson, subcircular, covering entire thoracic sternum; pleotelson subtriangular, apex convex, terminal margin with tufts of short setae. Vulvae small, placed on medial fused plate of thoracic sternum, at level of sternite 4. Etymology. The new species is named after the type locality Tanjung Sira , Lombok Island, Indonesia. The name is used as a noun in apposition .

Remarks. In the truncated rostrum group, E. sira , new species is the only species with single setae on the male G1, except for E. simplidenta that is known only by female specimens; other species have two or more setae ( Ng & Chuang, 1996). The broad ischium of the third maxilliped (broader than merus) resembles those of E. simplidenta but the two species can be separated by the more prominent posterolateral angle of the carapace, more slender chelipeds, the dactyli of ambulatory legs with one subdistal tooth on flexor margin, and broader female pleon, with slightly concave apex of the pleotelson in E. simplidenta (cf. Ng & Chuang, 1996: fig. 11A, F, G, H, J) versus less distinct posterolateral angle of the carapace, slightly stouter chelipeds, dactyli of ambulatory legs with two subdistal teeth on flexor margin, and relatively narrower female pleon, with convex apex of the subcircular pleotelson in E. sira ( Fig. 5A, D, E, H ). Compared to E. sundaica , a species described from Koepang, a place not too far from Lombok, these two species easily separated by the shape of carapace and male G1 (the anterolateral margin of the carapace with two strong, broad teeth, male pleon broad with semicircular pleotelson, male G1 with 11 plumose setae on its apex in E. sundaica [cf. Ng & Chuang, 1996: fig. 12A, I, K, J] versus slightly sinuous anterolateral margin of the carapace, no teeth but with two slight concavity, male pleon moderately slender with subtriangular pleotelson, male G1 with one plumose setae on its apex in E. sira [ Figs. 2E, F , 3C, D , 5A, F, G ]).

Type locality. Sira , northern Lombok Island, Indonesia .

Habitat and distribution. Intertidal, among dead coral rubbles, Sira, northern Lombok Island, Indonesia.

Figures

Fig. 2. G1 of Elamena species. A, B, Elamena nara, new species, holotype, male (3.8 × 3.5 mm) (MZB Cru 4895), Teluk Nara, Lombok I., Indonesia, May 2010; C, D, Elamena similis, new species, holotype, male (2.9 × 2.9 mm) (MZB Cru 4897); E, F, Elamena sira, new species, holotype, male (3.3 × 3.0 mm) (MZB Cru 4898). A−D, right G1; E, F, left G1; A, C, F, ventral view; B, D, E, dorsal view. Scale bars = 0.25 mm.

Fig. 3. G1 of Elamena species. A, Elamena nara, new species, holotype, male (3.8 × 3.5 mm) (MZB Cru 4895), Teluk Nara, Lombok I., Indonesia, May 2010; B, Elamena similis, new species, holotype, male (2.9 × 2.9 mm) (MZB Cru 4897), Kecinan, Lombok I., Indonesia, 9 June 2009; C, D, Elamena sira, new species, holotype, male (3.3 × 3.0 mm) (MZB Cru 4898) Sira, Lombok I., Indonesia, 21 July 2009. A, B, right G1,ventral view; C, left G1, dorsal view; D, tip of left G1, ventral view. Not to measure.

Fig. 5. Elamena sira, new species. A−E, holotype, male (3.3 × 3.0 mm) (MZB Cru 4898), Sira, Lombok I., Indonesia, 21 July 2009; F, G, paratype, female (3.8 × 3.5 mm) (ZRC2019.0594), same locality as holotype. A, habitus, dorsal view, left P2, P5, right P2, P3 missing; B, left third maxilliped; C, anterior region, ventral view; D, right chela; E, left P5, bristle partially omitted; F, H, somites 1−5 of pleon, and pleotelson; G, carapace. Scale bars: A, C−G = 1 mm; B = 0.5 mm.

Fig. 1. Elamena nara, new species. A–F, holotype, male (3.8 × 3.5 mm) (MZB Cru 4895), Teluk Nara, Lombok I., Indonesia, May 2010; G, H, paratypes, ovigerous female (4.4 × 4.0 mm) (ZRC2019.0592), Pandanan, Lombok I., Indonesia, 25 October 2009. A, habitus, dorsal view, right P3 missing; B, left third maxilliped; C, anterior region, ventral view; D, right chela; E, right P3, bristle partially omitted; F, H, somites 1−5 of pleon and pleotelson; G, carapace. Scale bars: A, C–G = 1 mm; B = 0.5 mm.

Fig. 4. Elamena similis, new species. A−F, holotype, male (2.9 × 2.9 mm) (MZB Cru 4897), Kecinan, Lombok I., Indonesia, 9 June 2009; G, H, paratype, ovigerous female (3.5 × 3.3 mm) (ZRC2019.0593), same locality as holotype. A, habitus, dorsal view, left P4 missing; B, left third maxilliped; C, anterior region, ventral view; D, right chela; E, left P3, bristle partially omitted; F, H, somites 1−5 of pleon and pleotelson; G, carapace. Scale bars: A, F, G = 1 mm; B–E = 0.5 mm.