Geosesarma vicentense ( Rathbun, 1914 )

Ng, Peter K. L. & Lemaitre, Rafael, 2017, On the taxonomy of two poorly known species of Geosesarma De Man, 1892 (Crustacea: Brachyura: Sesarmidae) from the Philippines, Zootaxa 4250 (5), pp. 475-483 : 476

publication ID	https://doi.org/ 10.11646/zootaxa.4250.5.5
publication LSID	lsid:zoobank.org:pub:5448198D-7CF2-47CE-A3CF-E7760EC5DDB6
DOI	https://doi.org/10.5281/zenodo.6028323
persistent identifier	https://treatment.plazi.org/id/03B88780-FF91-EC43-60A1-320DFA70B5D8
treatment provided by	Plazi
scientific name	Geosesarma vicentense ( Rathbun, 1914 )
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Treatment

Geosesarma vicentense ( Rathbun, 1914) View in CoL

( Figs. 1 View FIGURE 1 , 5A–D View FIGURE 5 )

Sesarma (Sesarma) vicentense Rathbun, 1914: 74 View in CoL .

Sesarma (Geosesarma) vicentensis — Serène 1968b: 106.

Geosesarma vicentensis — Serène & Soh 1970: 402 (list); Ng 1988: 119 (list). Geosesarma vicentense —Ng et al. 2008: 221 (list).

Type material. Holotype: male (9.2 × 8.5 mm), Port San Vicente (Luzon side), Palaui Island, off northern Luzon, 18°31′N 122°7′60″E, along beach, coll. 15 November 1908 ( USNM 45758 View Materials ) GoogleMaps .

Comparative material. Geosesarma maculatum (De Man, 1892) : 1 male (12.4 × 11.9 mm), station MALU 47, Halmahera, coll. MALU Expedition, L. Deharveng, July 1988 (ZRC 2017.0113).

Diagnosis. Carapace almost quadrate, wider than long, width to length ratio 1.1, lateral margins subparallel ( Fig. 1 View FIGURE 1 A, B); dorsal surface with regions weakly demarcated, anterior regions densely covered with low, small rounded, flattened granules ( Fig. 1 View FIGURE 1 A, B); front deflexed, frontal lobes broad with subtruncate margins, separated by shallow broad concavity; postfrontal, postorbital cristae moderately low, distinct ( Fig. 1 View FIGURE 1 A, B, E); external orbital tooth acutely triangular, directed anteriorly, outer margin almost straight, first epibranchial tooth low, second epibranchial tooth barely demarcated ( Fig. 1 View FIGURE 1 A, B). Merus of third maxilliped subovate, subequal in length to ischium; exopod slender, with long flagellum ( Fig. 5A View FIGURE 5 ). Outer surface of palm of adult male with numerous low granules, shallow pits; inner surface granular but without distinct transverse ridge; dorsal margin of dactylus with 3–5 low conical granules on proximal part, tips not chitinous, distal half uneven but without distinct granules ( Fig. 1 View FIGURE 1 F–H). Ambulatory legs each with relatively stout merus having sharp subdistal spine on dorsal margin and lateral, mesial surfaces gently rugose ( Fig. 1 View FIGURE 1 A); propodus without brush-like setae on ventral margin. Male pleon triangular, relatively wide; somite 6 with convex lateral margins; telson semicircular ( Fig. 1 View FIGURE 1 C, D). G1 slender, distal chitinous part elongated, almost straight, directed upwards, subspatuliform, tip dilated, medially clefted ( Fig. 5B–D View FIGURE 5 ).

Remarks. The taxonomic position of Geosesarma vicentense has been uncertain, with Ng & Takeda (1992: 81) questioning its placement in Geosesarma , especially since the only known specimen was obtained from a beach. Geosesarma species are otherwise found further inland in freshwater habitats (Ng 1988). Geosesarma vicentense , however, belongs to the same group of species as G. maculatum (De Man, 1892) , G. ternatense ( Serène, 1968a) , and G. hednon Ng, Liu & Schubart, 2004 , in which the G1 is slender, straight, with the chitinous distal part subspatuliform and directed upwards. Most of the species in this group have small eggs and almost certainly have planktotrophic larvae that must be released into the sea.

Compared to G. maculatum , the frontal orbital lobes of G. vicentense are more convex ( Fig. 1 View FIGURE 1 A, B) (lobes truncate in G. maculatum ; Fig. 2 View FIGURE 2 A, B); the external orbital tooth is relatively less prominent and separated from rest of margin by a shallow cleft ( Fig. 1 View FIGURE 1 A, B) (tooth more prominent and separated from margin by deep cleft in G. maculatum ; Fig. 2 View FIGURE 2 A, B); the ambulatory meri are relatively slender ( Fig. 1 View FIGURE 1 A) (meri broader in G. maculatum ; Fig. 2 View FIGURE 2 A); and the male pleonal somite 6 is proportionately broader ( Fig. 1 View FIGURE 1 D) (somite 6 proportionately longer in G. maculatum ; Fig. 2 View FIGURE 2 C) (see also Ng et al. 2004: figs. 1A, B, 2A). Geosesarma ternatense is distinct in that the male pleonal somite 6 is proportionately very broad with strongly convex lateral margins and the telson is relatively wider (Ng et al. 2004 fig. 8B) (somite 6 and telson less wide in G. vicentense ; Fig. 1 View FIGURE 1 D). Geosesarma vicentense is closest to G. hednon in general form, but can be distinguished by its external orbital tooth being distinct and separated from the rest of the margin by a small cleft ( Fig. 1 View FIGURE 1 A, B) (tooth subparallel to the rest of the lateral margin and separated by a fissure in G. hednon ; cf. Ng et al. 2004: figs. 9B, 11B) and the slender chitinous part of the G1 is relatively shorter ( Fig. 5B–D View FIGURE 5 ) (chitinous part relatively longer in G. hednon ; cf. Ng et al. 2004: figs. 13C–G,14C– H).

Geosesarma protos Ng & Takeda, 1992 View in CoL , also described from Luzon, is very different from G. vicentense View in CoL in possessing an external orbital tooth that is prominent and directed obliquely laterally, a third maxilliped in which the exopod has no flagellum and the G1 is stout with a short chitinous part (Ng & Takeda 1992: fig. 1A, B, G–I)