GAETICINAE

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), Zootaxa 3206, pp. 58-68 : 62-67

publication ID	https://doi.org/ 10.5281/zenodo.208599
DOI	https://doi.org/10.5281/zenodo.6170627
persistent identifier	https://treatment.plazi.org/id/F224110F-ED1F-D03D-FF2F-6FF2FE9DFC0A
treatment provided by	Plazi
scientific name	GAETICINAE
status

Treatment

Subfamily GAETICINAE View in CoL 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 View FIGURE 3 A–C, 4). Front entire, with shallow indentation medially; anterolateral margin with 2 low, broad teeth ( Figs. 3 View FIGURE 3 A, C, 4). Eyes prominent ( Figs. 3 View FIGURE 3 A, C, 4, 5A). Posterior margin of epistome with broadly triangular median lobe, lateral margins deeply concave ( Fig. 5 View FIGURE 5 A). Third maxillipeds forming prominent broad median gape when closed ( Figs. 3 View FIGURE 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 View FIGURE 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 View FIGURE 2 , 3 View FIGURE 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 View FIGURE 2 , 3 View FIGURE 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 View FIGURE 5 B). Vulvae relatively large, papilla-like, on anterior half of sternite 5 ( Fig. 5 View FIGURE 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 View FIGURE 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 View FIGURE 2 , 3 View FIGURE 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 View FIGURE 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) View in CoL ( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Paracleistostoma fossula Barnard, 1955: 24 , fig. 7a–e.

Paracleistostoma fossulum — Serène 1968: 101; Manning & Holthuis 1981: 209. “ Paracleistostoma View in CoL ” fossulum —Ng et al. 2008: 226, 229.

Brankocleistostoma fossulum View in CoL — Števčić 2011: 134.

Material examined. Holotype—female (5.0 × 3.5 mm) ( SAM A10778 View Materials ), 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 View FIGURE 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 View FIGURE 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 View FIGURE 3 A, C, 4). Posterior carapace margin gently concave to almost straight ( Figs. 3 View FIGURE 3 A, C, 4). Eyes prominent, entirely filling orbit; cornea distinctly pigmented; peduncle short, stout ( Figs. 3 View FIGURE 3 A, C, 4, 5A). Antennules folding transversely ( Fig. 5 View FIGURE 5 A). Antenna relatively short, basal articles not fused to carapace; flagellum shorter than length of orbit ( Fig. 5 View FIGURE 5 A). Suborbital, subhepatic, sub-branchial surfaces smooth; ptergostomial ridge lined with setae; suborbital margin entire ( Fig. 5 View FIGURE 5 A, B). Epistome longitudinally narrow; posterior margin with broadly triangular median lobe, lateral margins deeply concave ( Fig. 5 View FIGURE 5 A).

Third maxillipeds forming prominent broad median gape when closed, anterior part filled by long palp (carpus, propodus, dactylus) ( Figs. 3 View FIGURE 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 View FIGURE 3 D, E, 5A, B). Merus squarish with prominent inner sulcus, joining ischium obliquely; inner margin lined with numerous setae ( Fig. 3 View FIGURE 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 View FIGURE 3 D, E, 5B). Exopod slender, gently sinuous, reaching to below distal part of merus, flagellum long, reaching beyond width of merus ( Fig. 3 View FIGURE 3 D, E).

Cheliped relatively short, symmetrical ( Figs. 2 View FIGURE 2 , 3 View FIGURE 3 F, 4). Merus short with rounded distal margin, margins lined with dense setae ( Figs. 2 View FIGURE 2 , 3 View FIGURE 3 F, 4, 5B). Carpus ovate, without obvious inner tooth or spine ( Figs. 2 View FIGURE 2 , 3 View FIGURE 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 View FIGURE 3 F, G, 5D).

Ambulatory legs relatively long, second, third legs longest ( Figs. 2 View FIGURE 2 , 4 View FIGURE 4 ). Merus laterally flattened; proximal dorsal margins lined with dense long setae ( Figs. 2 View FIGURE 2 , 3 View FIGURE 3 H, 4). Propodus laterally flattened, with row of short setae along subventral margin ( Figs. 2 View FIGURE 2 , 4 View FIGURE 4 ). Dactyli of first to third legs falciform; that of last leg subspatuliform, lined with short plumose setae ( Figs. 2 View FIGURE 2 , 3 View FIGURE 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 View FIGURE 5 B). Vulvae relatively large, papilla-like, on anterior half of sternite 5 ( Fig. 5 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 3 B). In the present two specimens from Madagascar, the two ridges are distinct laterally, but get less pronounced medially ( Figs. 3 View FIGURE 3 C, 4). The ridges are more distinct in the smaller female ( Fig. 4 View FIGURE 4 B, C), being slightly more rounded in the larger female ( Fig. 4 View FIGURE 4 A). The ambulatory dactylus is relatively short as depicted by Barnard (1955: fig. 7e) ( Fig. 3 View FIGURE 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 View FIGURE 3 E, 5B). However, there is also another group of long setae at the base of the inner margin of the ischium ( Fig. 3 View FIGURE 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.