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

description: Planopilumnus Balss, 1933
Planopilumnus Balss, 1933: 39.
Type species. Pilumnus spongiosus Nobili, 1905, by original designation.
Diagnosis. Carapace distinctly broader than long (Figs. 1 A, 2, 4A, 8A, B); carapace, pereiopods covered with dense, short, soft pubescence obscuring most surfaces, teeth; setae usually arranged in distinct patterns (Fig.
2A); dorsal carapace regions gently convex (Figs. 1 B, 3A); epigastric cristae distinct, lined with granules, separated by Y-shaped groove; mesogastric cristae distinct, lined with small granules, posterior to, not contiguous with epigastric cristae, gently sloping towards centre of carapace; postorbital cristae distinct, granular, not contiguous with mesogastric cristae, separated by distinct cervical groove, reaching only to near base of first anterolateral tooth (Figs. 1 A, 2, 8A, B); postorbital region not prominently sunken (Fig. 1 A, B, 2, 3A, 4A, 8A, B); posterolateral, posterior carapace regions with scattered granules but without clear transverse submarginal grooves (Figs. 1 A, 2, 8A, B); subhepatic region with distinct tubercles (Figs. 1 B, C, 3A, B); subbranchial region with scattered, indistinct groups of low granules, without obvious ridges or grooves (Fig. 9 A). Frontal margin with 2 truncate lobes separated by small, V-shaped cleft; separated from supraorbital margin by small fissure or cleft; inner angle of supraorbital margin low, well behind frontal margin, with median fissure dividing margin into 2 parts, the outer part longer (Figs. 1 A, 2, 4A, B). Suborbital margin concave with distinct inner, outer teeth, not cristate (Figs. 1 B, C, 3A, B, 4B). Surfaces of third maxilliped with pits, granules, not eroded; anteroexternal angle auriculiform (Fig. 3 A, C). External orbital tooth truncate, margin uneven to sinuous, usually divided into approximately 2 parts by cleft or fissure; first, second anterolateral teeth subequal with first tooth sometimes subtruncate in larger specimens, each with a low median longitudinal ridge; third anterolateral tooth small (Figs. 1 A, B, 2, 3A, 4A, B). Chelipeds in adult males, females distinctly unequal (Figs. 2, 3 D, E); dorsal margin of chela rounded without ridges although shallow subdorsal or dorsal longitudinal groove may be present; carpus, merus, varying parts of chela covered with scattered granules but without ridges, pits or eroded depressions; merus with low subdistal tooth; inner distal tooth of carpus low, dentiform; dense setae evenly covering, obscuring almost all surfaces except for tips of larger granules, outer, inner surfaces of palm, fingers (Figs. 2, 3 D, E); outer surfaces of larger palms in both sexes almost completely glabrous (Fig. 3 D, E). Surfaces of ambulatory leg articles without spines, ridges, pits or depressions; dorsal margins of merus, carpus, propodus rounded, without spines or crests; merus of first to third legs with low subdistal tooth; dense setae evenly covering, obscuring almost all surfaces (Figs. 2, 10 A, B). Surface of anterior thoracic sternum, outer surfaces of abdomen with scattered granules but without depressions (Figs. 1 C, 3B); 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 distinct, positioned on posterior margin of sternite 5, adjacent to s5/6; all abdominal somites, telson mobile. G1 relatively short, stout, almost straight, tip prominently dilated, appearing flared (Fig. 4 C, D). G2 about half length of G1 (Fig. 4 E, F).
Remarks. Although Planopilumnus has long been synoymised with Rathbunaria Ward, 1933, the present study shows that the two are distinct (see remarks below for Rathbunaria). Actually, Planopilumnus is closest to Platychelonion Crosnier & Guinot, 1969 (type and only species Platychelonion planissimum Crosnier & Guinot, 1969), originally described from relatively shallow waters off Congo, West Africa (see also Manning & Holthuis 1981). Although the carapace of Platychelonion was described as being only weakly pubescent, in contrast to Planopilumnus, their carapace features and pereiopodal characters are very similar. They share the same carapace form, with an almost identical frontal and anterolateral armature (Figs. 11 A, B, 12A, B), although the dorsal surface of Platychelonion is distinctly flatter (Figs. 11 A, B, 12A) than that of Platypilumnnus (Figs. 1 B, 3A). In addition to the degree of pubescence on the carapace and ambulatory legs (much more extensive in Planopilumnus), other differences that separate Platychelonion from Planopilumnus include the junction of the antero- and posterolateral margins being distinct, the third anterolateral tooth been large and distinct, with the posterolateral margin lined only with small granules (Figs. 11 A, 12A) (third anterolateral tooth small, followed by progressively smaller granules towards posterolateral margin in Planopilumnus, Figs. 1 A, 2, 4A, 8A, B), relatively weaker subhepatic tubercles (Figs. 11 B, C, 12B) (distinct in Planopilumnus, Figs. 1 B, C, 3A, B), the dorsal margins of the ambulatory meri are armed with small spines (Fig. 12 E) (smooth or almost so in Planopilumnus, Figs. 2 B, 10A, B), and the G1 is proportionately much stouter with the distal part tapering (Fig. 12 G–I) (relatively more slender with the tip flared in Planopilumnus, Fig. 4 C, D).
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 35-36, DOI: 10.5281/zenodo.275841