Statommatia apta Rathbun 1914, n. comb.
Creators: name: Ng, Peter K. L.
name: Castro, Peter
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Chasmocarcinidae
Statommatia
Statommatia apta

description: Statommatia apta (Rathbun, 1914), n. comb.
(Figs. 16 A‒C; 26A, B; 33A, B; 42M; 45C, D; 46; 54A, B; 61A; 77A‒D; 88A; 91E)
Hephthopelta apta Rathbun, 1914: 148 [type locality: Philippines].— Tesch 1918: 233 [in key].— Estampador 1959: 90 [in list].— Serène 1964a: 240 [in list], 241, 242 [in key]; 1968: 92 [in list].— Zarenkov 1972: 238, fig. 4-3 [Vietnam].—Ng et al. 2008: 76 [in list].—Ng & Rahayu 2014: fig. 2C, D [Philippines].
Type material. Holotype male (7.8 × 9.4 mm) (USNM 46389), Philippines, between Cebu and Bohol, Lauis Point Light, Albatross, stn 5419, 09°58’30”N, 123°46’E, 320 m, 25.03.1909.
Other material examined. Philippines. PANGLAO 2005: 2 males (8.4 × 10.1 mm, 8.5 × 10.3 mm) (ZRC 2015.237), Bohol Sea, stn CP2390, 09°27’N, 123°43'E, 627–645 m, 30.05.2005; 1 female (ZRC 2015.238), stn CP2397, 09°36.6’N, 123°42.9’E, 607‒642 m, 31.05.2005; 1 male (10.1 × 12.3 mm, carapace damaged) (ZRC 2013.1727), stn CP2398, 09°34.2’N, 123°41.8’E, 658‒713 m, 31.05.2005.— AURORA 2007: 2 males (5.6 × 6.4 mm, 5.9 × 7.1 mm) (ZRC 2015.239), stn CP2656, 16°02’N, 121°53’E, 262‒278 m, 20.05.2007.
Papua New Guinea. BIOPAPUA: 1 female (MNHN-IU-2011-1166), Open Bay, stn CP3666, 04°40’S, 151°33’E, 760–866 m, 23.09.2010; 1 female (MNHN-IU-2011-1842), off Sepik River, stn CP3701, 03°57’S, 144°41’E, 198–219 m, 01.10.2010; 9 males, 2 females (MNHN-IU-2014-17790), 4 males, 2 females (ZRC 2015.240, ex MNHN-IU-2014-17790), 1 female (MNHN-IU- 2011-2241), 2 males, 1 ovigerous female (6.1 × 7.3 mm) (MNHN-IU-2011-5200), 3 males (MNHN-IU- 2011-2030), Astrolabe Bay, stn CP3710, 05°22’S, 145°48’E, 372–384 m, 05.10.2010; 2 males (MNHN-IU- 2011-2044), Astrolabe Bay, stn CP3711, 05°23’S, 145°48’E, 434– 447 m, 05.10.2010.— PAPUA NUGUINI: 1 male (MNHN-IU-2013-9020), 2 males, 2 females (MNHN-IU-2013- 11599), W. Kranket I., stn CP3948, 05°12’S, 145°51'E, 363–388 m, 26.11.2012; 1 male, 1 female (MNHN-IU- 2013-9010), 2 males (MNHN-IU-2013-9011), 2 males, 3 females, 1 ovigerous female (MNHN-IU-2013-9017), W. Kranket I., stn CP3949, 05°12’S, 145°51'E, 380–407 m, 26.11.2012; 10 males, 16 females (MNHN-IU-2013- 9023), Astrolabe Bay, stn CP4023, 05°22’S, 145°48'E, 340–385 m, 14.12.2012; 2 males (MNHN-IU-2013-9013), stn CP4024; 1 male, 1 female (MNHN-IU-2013-11664), Astrolabe Bay, stn CP4025, 05°21’S, 145°49'E, 520–525 m, 14.12.2012; 1 female (MNHN-IU-2013-7978), W. Kariru I., Bismarck Sea, stn CP4048, 03°20’S, 143°28'E, 325–345 m, 19.12.2012.
Diagnosis. Carapace (Fig. 16 A‒C) subtrapezoidal, convex dorsally, 1.2 wider than long; front bilobed, with shallow median cleft; anterolateral margins arcuate, minutely granular, without distinct lobes or teeth. Posterior margin of epistome (Fig. 26 A, B) with semicircular median lobe with deep median fissure, semicircular lateral margins. Eye peduncle (Fig. 26 A, B) filling orbit, short, immobile; cornea reduced, pigmented. Third maxillipeds (Fig. 33 A, B) not filling buccal cavern when closed; merus ovate, outer margin curved, anteroexternal angle rounded; ischium quadrate, about same length as merus. Chelipeds (Figs. 16 A‒C; 45C, D; 46) subequal in length, slightly dissimilar in female, heteromorphic in males; fingers of minor chela (Figs. 45 D; 46D‒G) subcircular in cross-section, not distinctly laterally flattened, gently tapering to tip, scissor-like, scissor-like, cutting margins with distinct teeth; cutting margin of major chela of males with short, blunt teeth, dactylus arched (Figs. 45 C; 46A‒C); cutting margin of pollex with proximal 2/3 flattened, shelf-like (Fig. 46 A‒C); lower, proximal portion of propodus of small male cheliped flattened, bordered by thick tubercles forming flat ridge on inner, outer margins (Fig. 46 D‒K), smooth margin in females. Ventral surface of cheliped merus with row of small tubercles (sharp in some individuals) along outer margin, inner margin unarmed (Fig. 42 M), hollow region in median part. Inner margin of cheliped carpus with short distal tooth (Fig. 16 A, B). Inner margin of basis-ischium of adult major cheliped gently granuliform (Fig. 16 A). Ambulatory legs (Fig. 16 A‒C) unarmed, proportionally short. P5 dactylus gently upcurved (Fig. 16 A); P5 merus 0.6 cl. Fused thoracic sternites 1, 2 (Fig. 54 A, B) semicircular, broad, short; fused thoracic sternites 3, 4 (Figs. 54 A, B; 88A; 91E) broad. Male pleon (Figs. 54 A, B; 61A) lateral margins of somite 6, fused somites 3‒5 slightly convex; postero-lateral regions as in rest of somite, not swollen; telson proportionally long. Sterno-pleonal cavity deep, press-button for pleonal holding as small, short tubercle posterior to thoracic sternal suture 4/5 near edge of sterno-pleonal cavity. Male thoracic sternite 8 long, rectangular; “supplementary plate” long, subrectangular; structures tightly appressed with most of penis concealed (e.g., Fig. 61 A). G1 (77A‒C) with stout basal part; distal part slender, straight, tapering, with short spinules. G2 (Fig. 77 D) about half G1 length, straight, slender, thin, distal segment short, straight. Somites of female pleon (Fig. 88 A) with convex lateral margins; telson proportionally long. Sterno-pleonal cavity of female (Fig. 91 E) deep, vulvae relatively close together, located on outer margins of cavity close to suture 5/6.
Remarks. The propodus of the minor cheliped of males of S. apta is flat and surrounded by elevated ridges or crests formed by thick tubercles along the inner and outer margins. The cavity thus formed when the propodus is flexed against the similarly hollow merus was hypothesized by Rathbun (1914: 149, as Hephthopelta apta) as “a passage of water into the left branchial canal.” The large, round gap formed by the closed and strongly curved fingers of the major cheliped (Fig. 46 A‒C) was suggested as resulting, when flexed, into “an oval area fringed with hair” resting on the opening of the opposite branchial chamber. This characteristic shape is absent in females of S. apta (Fig. 16 C). Gaping fingers of the major male cheliped, however, can also be observed in other chasmocarcinines such as Statommatia malagasy n. sp. (Fig. 45 G) and Angustopelta cribrorum (Fig. 41 C).
There is a visible variation in the length of the ambulatory legs, with females and small males on hand having legs that are shorter than in the largest males.
Distribution. Western Pacific Ocean (Philippines, Vietnam, Papua New Guinea). Depth: 198‒ 866 m.
description: Published as part of Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), pp. 1-182 in Zootaxa 4209 (1) on pages 73-75, DOI: 10.11646/zootaxa.4209.1.1, http://zenodo.org/record/272646