Rathbunaria Ward 1933
Creators: name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Planopilumnidae
Rathbunaria

description: Rathbunaria Ward, 1933
Rathbunaria Ward, 1933: 386.
Type species. Rathbunaria sculptissima Ward, 1933, by original designation.
Diagnosis. Carapace broader than long (Figs. 5 A, 6A, 8C, D); carapace, pereiopods covered with relatively dense, short, relatively coarse pubescence partially obscuring surfaces, with teeth, ridges still visible; setae on carapace forming approximately hexagonal patterns in parts (Fig. 5 A); dorsal carapace regions almost flat (Fig. 5 C); epigastric cristae short, relatively low, lined with 1–3 small granules, separated by Y-shaped groove; mesogastric cristae discernible but relatively low, lined with some small granules, posterior to, not contiguous with epigastric cristae, gently sloping towards centre of carapace; postorbital cristae very short, low, with small granules, near base of first anterolateral tooth, clearly separated from mesogastric cristae (Figs. 5 A, 6A, 8C, D); postorbital region prominently sunken (Figs. 5 A, C, 6A, 8C, D); posterolateral, posterior carapace regions with distinct transverse submarginal grooves demarcated by rows of granules which connect to prominent grooves in sub-branchial region (Figs. 1 A, 6A, D, 8C, D); subhepatic region with distinct tooth (Figs. 5 B, C, 6B); grooves on sub-branchial region lined by rows of medially eroded granules (Fig. 9 B). Frontal margin with 2 truncate lobes separated by fissure or narrow U-shaped cleft; inner angle of supraorbital margin prominent, almost reaching or slightly exceeding frontal margin, sloping, with median fissure that divides margin into 2 parts, the outer part longer (Figs. 5 A, 6A, 8C, D). Suborbital margin sinuous, appearing sublobate (Figs. 5 B, C, 6B). Surfaces of third maxilliped with numerous eroded depressions of varying sizes, anteroexternal angle distinct but not prominently auricuiliform (Fig. 6 C). External orbital tooth truncate, margin uneven to sinuous; first, second anterolateral teeth subequal, dorsoventrally flattened, appearing foliaceous, with first tooth sometimes subtruncate, without obvious median ridge; third anterolateral tooth small (Figs. 5 A, B, 6A, B). Chelipeds of adult males, females subequal or with one chela slightly larger; dorsal margin of chela with 2 prominent ridges; carpus, merus, palm with prominent ridges, surfaces with numerous eroded depressions of varying sizes; merus with a prominent sharp submedian tooth, prominent subdistal tooth; inner distal tooth of carpus large, lobiform; setae dense but covering only flattened, depressed areas of articles, ridges glabrous, clearly visible; on chela, only fingers, ridges glabrous; outer surfaces of palms of both sexes never completely glabrous (Figs. 5, 6 E). Ambulatory leg with numerous eroded depressions of varying sizes (Figs. 5 A, 6F, G, 10C, D); dorsal margins of merus, carpus, propodus with low crest; merus of first to third ambulatory legs with prominent subdorsal ridge, subdistal tooth large; carpus, propodus with prominent submedian ridges; setae dense but covering only flattened, depressed areas of articles, ridges glabrous, clearly visible (Figs. 5 A, 6F, G, 10C, D). Surface of anterior thoracic sternum, outer surfaces of abdomen with numerous eroded depressions of varying sizes (Figs. 5 B, 6H, 7A); sternites 1, 2 completely fused without trace of suture; s2/3 complete; s3/4 medially interrupted; s4/5, s5/6, s6/7 appears medially interrupted; s7/8 complete; longitudinal median groove present from sternites 6–8; male press button relatively low, on posterior margin of sternite 5; all abdominal somites, telson mobile. G1 relatively more slender, long, gently curved outwards, distal part tapering to sharp tip (Fig. 7 B–D). G2 about half length of G1 (Fig. 7 E).
Remarks. Rathbunaria was described by Ward (1933) at around the same time as Planopilumnus Balss, 1933. Balss (1938: 60) commented that his earlier paper (Balss 1933) preceded Ward (1933) by two months, and he regarded the two genera as synonyms, with Planopilumnus having precedence. This is difficult to verify because Ward's paper had a date of publication but that by Balss did not. Lipke Holthuis (personal communication) checked on this matter in 1984 and commented that on the basis of his notes and library copies, Ward’s paper was probably published earlier than Balss’ but he had no conclusive proof. As such, one has to take Balss at his word that his paper came out earlier, and Planopilumnus is the older name. Balss (1938) also synonymised Rathbunaria sculptissima Ward, 1933, with Planopilumnus spongiosus orientalis Balss, 1933, the latter also having priority. Planopilumnus orientalis has since been regarded as a distinct species (Goh et al. 1990; Davie 2002; Ng et al. 2008).
Although Rathbunaria and Planopilumnus are superficially similar, there are several key characters (dorsal surface of carapace, form of the frontal, orbital, sub-branchial and posterolateral regions, as well as the structures of the chelipeds, ambulatory legs and G1) that argue for their separation (Table 1). The arrangement of setae in Planopilumnus and Rathbunaria also appear to be different. In Planopilumnus, the setae form irregular patterns around the dorsal carapace regions (Fig. 2 A). In Rathbunaria, however, the setae are arranged in small irregular hexagonal patches across the entire dorsal carapace surface, giving it the appearance of a honey-combed structure (Figs. 5 A, 8C). This honey-combed appearance is also obvious on the chelipeds and ambulatory legs (Fig. 5) although relatively less pronounced. In Planopilumnus, the setae form an even covering on the chelipeds and legs (Fig. 2). As such, Rathbunaria is here recognised as a separate genus.
The diagnostic structure of the grooves and ridges on the sub-branchial, posterolateral and posterior carapace regions are almost certainly associated with respiration. Similar structures have been reported for the three Western Pacific xanthid genera Glyptocarcinus Takeda, 1973, Antrocarcinus Ng & Chia, 1994, and Cyrtocarcinus Ng & Chia, 1994 (see Ng & Chia 1994). However, while members of these three genera are generally known from soft substrates that would make such structures useful for respiration (Ng & Chia 1994), little is known about the biology of Rathbunaria. They are known from coral reefs, with two of the specimens collected from coral (see below).
description: Published as part of Ng, Peter K. L., 2010, On the Planopilumnidae Serène, 1984 (Crustacea: Brachyura: Pseudozioidea), with diagnoses of two new pilumnoid genera for species previously assigned to Planopilumnus Balss, 1933, pp. 33-61 in Zootaxa 2392 on pages 43-47, DOI: 10.5281/zenodo.275841