Gaeticinae
Creators: name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Varunidae

description: Subfamily GAETICINAE Davie & N. K. Ng, 2007
Brankocleistostoma Štev ě i ć, 2011
Brankocleistostoma Števčić, 2011: 134.
Diagnosis. Carapace transversely rectangular; dorsal surface with 2 parallel transverse ridges; mesogastric, branchial, cardiac regions transversely depressed; 2 short oblique ridges on each hepatic region, closer to anterior transverse ridge (Figs. 3 A–C, 4). Front entire, with shallow indentation medially; anterolateral margin with 2 low, broad teeth (Figs. 3 A, C, 4). Eyes prominent (Figs. 3 A, C, 4, 5A). Posterior margin of epistome with broadly triangular median lobe, lateral margins deeply concave (Fig. 5 A). Third maxillipeds forming prominent broad median gape when closed (Figs. 3 D, 5A, B); palp with carpus, propodus, dactylus subequal in length, dactylus with numerous long setae which reaches to base of merus, partially covers anterior 2 or 3 thoracic sternites; merus joining ischium obliquely; inner margin of ischium with numerous setae, those on basal part very (Figs. 3 D, E, 5A, B). Cheliped relatively short, symmetrical; merus short with rounded distal margin lined with dense setae; chela with prominent subventral longitudinal ridge (Figs. 2, 3 F, G, 4, 5B, D). Dactyli of first to third legs falciform; that of last leg subspatuliform, lined with short plumose setae (Figs. 2, 3 H, 4). Thoracic sternum broad; sternites 1, 2 completely fused, very short; separated from longitudinally narrow sternite 3 by rim; sternites 3, 4 separated by suture (Fig. 5 B). Vulvae relatively large, papilla-like, on anterior half of sternite 5 (Fig. 5 B).
Type species. Paracleistostoma fossula Barnard, 1955, by original designation; gender neuter.
Remarks. Manning & Holthuis (1981: 209) argued that P. fossulum Barnard, 1955, is not a Paracleistostoma and probably not even an ocypodid. Ng et al. (2008: 229) agreed, and commented that the structure of its third maxilliped, ambulatory legs and chelae was closer to those in the Varunidae. Without providing any explanation or discussion, Števčiċ (2011) decided that Paracleistostoma fossula Barnard, 1955, warranted a new genus, Brankocleistostoma Števčiċ, 2011. He also established a new family, Brankocleistostomidae Števčiċ, 2011 (Števčiċ 2011: 127), for the genus.
Although no males are known, all the female characters of the types and fresh material of Paracleistostoma fossulum indicate that this species is close to Gopkittisak Naruse & Clark, 2009 (type species Asthenognathus gallardoi Serène & Soh, 1976). The carapace has the same general pattern of carapace ridges, the third maxillipeds are similar in form, with the ischium and merus connected obliquely, and significantly, there is a long tuft of setae on the dactylus that reaches the anterior thoracic sternites (Figs. 3 D, E, 5B). Brankocleistostoma can nevertheless be recognised as a separate genus from Gopkittisak. Of the four characters used by Naruse & Clark (2009) to separate Gopkittisak from Brankocleistostoma (as “ Paracleistostoma ” fossulum), the positioning of the posterior carapace ridge is not reliable. The structure of the anterolateral margin (entire in Gopkittisak but dentate in Brankocleistostoma) and arrangement of the three short ridges on the hepatic region remain valid differences. The proportions of the ambulatory dactyli are also different, being relatively shorter in Brankocleistostoma (Figs. 2, 3 H, 4; Naruse & Clark 2009: fig. 3). In addition, the merus and ischium of the third maxilliped of Brankocleistostoma are relatively broader and more quadrate, with the dactylus proportionately longer (Figs. 3 D, E; Naruse & Clark 2009: fig. 1c).
As already discussed by Naruse & Clark (2009), the structure of the third maxilliped clearly places Gopkittisak in the Gaeticinae as defined by Davie & N. K. Ng (2007) (see also Komai 2011). Števčiċ (2011: 129) established a new tribe, Gopkittisakini for Gopkittisak, in Gaeticinae, without explanation. None of the characters listed by Števčiċ (2011) in his diagnosis of the tribe differ significantly from the rest of the Gaeticinae. As such, Gopkittisakini Števčiċ, 2011, should be synonymised under Gaeticinae Davie & N. K. Ng, 2007. As already discussed, since Brankocleistostoma is so close to Gopkittisak, Brankocleistostomidae Števčiċ, 2011, should also be regarded as a junior subjective synonym of Gaeticinae Davie & N. K. Ng, 2007. Preliminary molecular studies done on Brankocleistostoma and Gopkittisak confirm both as distinct genera as in the Varunidae (K. Y. Ming and K. H. Chu, unpublished data).
Brankocleistostoma fossulum (Barnard, 1955) (Figs. 2–5)
Paracleistostoma fossula Barnard, 1955: 24, fig. 7a–e.
Paracleistostoma fossulum — Serène 1968: 101; Manning & Holthuis 1981: 209. “ Paracleistostoma ” fossulum —Ng et al. 2008: 226, 229.
Brankocleistostoma fossulum — Števčić 2011: 134.
Material examined. Holotype—female (5.0 × 3.5 mm) (SAM A10778), Delagoa Bay, 25°58' 60”S, 32°42'E, Mozambique. Others— 1 female (8.14 × 4.57 mm) (MNHN) (photographed), station TP8, Lokaro, Madagascar, 24 ° 56.6’S 47 ° 06.7−9’E, 5−15m, sand and algae substrate, coll. Expedition ATMO VATAE, 2 May 2010; 1 female (6.95 × 4.08 mm) (MNHN), station TP19, Ambinanibe, Madagascar, 24 ° 04.4−7’S, 46 ° 55.3−56.3’E, 19−25m, sand and shell substrate, coll. Expedition ATMO VATAE, 12 May 2010.
Redescription. Carapace transversely rectangular; dorsal surface almost smooth, with 2 parallel transverse ridges which are relatively more weakly defined medially in larger specimens; mesogastric, branchial, cardiac regions transversely depressed; 2 short oblique ridges on each hepatic region, closer to anterior transverse ridge (Figs. 3 A–C, 4). Front entire, with shallow indentation medially; lateral margins gently angular to rounded, not forming lobe or supraorbital angle; supraorbital margin gently sinuous, without fissures (Figs. 3 A, C, 4, 5A). External orbital angle low, broadly triangular, not projecting anteriorly beyond frontal margin; anterolateral margin subcristate, with 2 low, broad teeth; teeth separated by shallow depressions; junction between antero-, posterolateral margins indistinct, with margin curving onto posterolateral, branchial region, branching to form start of posterior transverse ridge (Figs. 3 A, C, 4). Posterior carapace margin gently concave to almost straight (Figs. 3 A, C, 4). Eyes prominent, entirely filling orbit; cornea distinctly pigmented; peduncle short, stout (Figs. 3 A, C, 4, 5A). Antennules folding transversely (Fig. 5 A). Antenna relatively short, basal articles not fused to carapace; flagellum shorter than length of orbit (Fig. 5 A). Suborbital, subhepatic, sub-branchial surfaces smooth; ptergostomial ridge lined with setae; suborbital margin entire (Fig. 5 A, B). Epistome longitudinally narrow; posterior margin with broadly triangular median lobe, lateral margins deeply concave (Fig. 5 A).
Third maxillipeds forming prominent broad median gape when closed, anterior part filled by long palp (carpus, propodus, dactylus) (Figs. 3 D, 5A, B). Palp with carpus, propodus, dactylus subequal in length, dactylus conical, distal part with numerous long setae which reaches to base of merus, partially covers anterior 2 or 3 thoracic sternites (Figs. 3 D, E, 5A, B). Merus squarish with prominent inner sulcus, joining ischium obliquely; inner margin lined with numerous setae (Fig. 3 D, E). Ischium longer than merus with outer margin distinctly shorter than dentate inner margin; inner margin with numerous setae, those on basal part much longer, reaching across gape between third maxillipeds (Figs. 3 D, E, 5B). Exopod slender, gently sinuous, reaching to below distal part of merus, flagellum long, reaching beyond width of merus (Fig. 3 D, E).
Cheliped relatively short, symmetrical (Figs. 2, 3 F, 4). Merus short with rounded distal margin, margins lined with dense setae (Figs. 2, 3 F, 4, 5B). Carpus ovate, without obvious inner tooth or spine (Figs. 2, 3 F, 4). Chela relatively long, with prominent subventral longitudinal ridge, scattered short setae on inner subdorsal margin; fingers shorter than palm, cutting edges with series of distinct teeth (Figs. 3 F, G, 5D).
Ambulatory legs relatively long, second, third legs longest (Figs. 2, 4). Merus laterally flattened; proximal dorsal margins lined with dense long setae (Figs. 2, 3 H, 4). Propodus laterally flattened, with row of short setae along subventral margin (Figs. 2, 4). Dactyli of first to third legs falciform; that of last leg subspatuliform, lined with short plumose setae (Figs. 2, 3 H, 4).
Thoracic sternum broad; sternites 1, 2 completely fused, very short; separated from longitudinally narrow sternite 3 by rim; sternites 3, 4 separated by distinct suture (Fig. 5 B). Vulvae relatively large, papilla-like, on anterior half of sternite 5 (Fig. 5 B). Abdomen rounded; covering most of thoracic sternum; all somites freely articulating; telson broadly triangular, lateral margins gently convex, sitting in depressed distal margin of somite 6 (Fig. 5 C).
Colour. The dorsal surfaces of the carapace, chelipeds and ambulatory legs are a patchwork of grey and white, with patches of blue. The setae on the carapace and appendages are yellow to orange (Fig. 2).
Type locality. Delagoa Bay, Mozambique.
Remarks. The two recent specimens of B. fossulum were trawled off southern Madagascar, a site 1400 km east of Delagoa Bay, Mozambique. They differ from the holotype female in having a proportionately broader carapace, the lateral angles of the frontal margin relatively sharper, the transverse dorsal carapace ridges are relatively lower and the last ambulatory dactylus is relatively shorter. These differences are probably the consequence of size. The type female of B. fossulum is only 5.0 × 3.5 mm. Of the two recent specimens from Madagascar, the smaller female (6.95 × 4.08 mm) has slightly sharper lateral angles of the frontal margin compared to the larger one (8.14 × 4.57 mm). In addition, its carapace width to length ratio is 1.70, intermediate between that of the holotype (1.43) and that of the largest female (1.78). This suggests that like many varunids, the carapace of B. fossulum gets relatively broader as it grows larger. This is not associated with maturity as the holotype female is mature, being ovigerous. The same is true of the transverse dorsal carapace ridges, which is relatively lower in the largest female. The transverse dorsal carapace ridges are actually not as sharp and cristate as drawn by Barnard (1955: 7a) (Fig. 3 A). They represent the raised parts of the regions that are transversely swollen, and Barnard himself was clear about this as he figured the cross-section of the carapace to show this (Barnard 1955: 7a; present Fig. 3 B). In the present two specimens from Madagascar, the two ridges are distinct laterally, but get less pronounced medially (Figs. 3 C, 4). The ridges are more distinct in the smaller female (Fig. 4 B, C), being slightly more rounded in the larger female (Fig. 4 A). The ambulatory dactylus is relatively short as depicted by Barnard (1955: fig. 7e) (Fig. 3 H) and although he does not say which leg it was from, the structure shows it must be from the last pereiopod. The dactyli of all the other legs are much longer and styliform. The larger female from Madagascar has slightly longer dactyli compared to the smaller one in the small holotype and this character is also probably associated with size.
The long setae at the tip of the dactylus of the third maxilliped are distinctive and reach the anterior thoracic sternites (Figs. 3 E, 5B). However, there is also another group of long setae at the base of the inner margin of the ischium (Fig. 3 E). These transversely arranged setae almost bracket the anterior part of the first two thoracic sternites when the third maxillipeds are closed. Together with the long dactylar setae, these ischial setae form almost a net-like structure.
description: Published as part of Ng, Peter K. L., 2012, The systematic status of two enigmatic ocypodoid crabs, " Paracleistostoma " dentatum Tesch, 1918, and " Paracleistostoma " fossulum Barnard, 1955 (Crustacea: Decapoda: Brachyura), pp. 58-68 in Zootaxa 3206 on pages 62-67, DOI: 10.5281/zenodo.208599