Geosesarma rathbunae Serene 1968
Creators: name: Ng, Peter K. L.
name: Lemaitre, Rafael
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Geosesarma
Geosesarma rathbunae

description: Geosesarma rathbunae (Serène, 1968a)
(Figs. 3, 4, 5 E–H)
Sesarma (Geosesarma) rathbunae Serène, 1968a: 1086, figs. 5, 6; pl. 1 fig. 4. Sesarma (Geosesarma) rathbunae — Serène 1968b: 106.
Geosesarma rathbunae — Serène & Soh 1970: 403; Ng 1988: 119 (list); Ng et al. 2008: 221 (list).
Type material. Holotype (missing, see Remarks): male (13.0 × 12.2 mm), on trunks of forest trees, Culasi, Panay Island, 800 m altitude, Philippines, coll. McGregor, 18 May 1918 (USNM 54315). Paratype: 1 female (13.3 × 12.0 mm), same locality and other data as holotype (USNM 1277697).
Non-type material. 4 males (14.9 × 14.5 mm, 13.1 × 12.3 mm, 11.1 × 9.7 mm, 10.4 × 9.4 mm), 1 female (14.1 × 12.6 mm), 4 immature juveniles, locality and data same as holotype and paratype (USNM 123208).
Diagnosis. Carapace quadrate to subquadrate, just wider than long, width to length ratio 1.0–1.1, lateral margins parallel (Figs. 3 A, B, 4A, B, H, I); dorsal surface with regions just visible, anterior regions densely covered with low, small, rounded, flattened granules and rugosities (Figs. 3 A, B, 4A, B, H, I); front deflexed, frontal lobes broad with subtruncate margins, separated by shallow concavity; postfrontal, postorbital cristae low but relatively sharp (Figs. 3 A, B, E, 4A, B, C, H, I); external orbital tooth triangular, directed obliquely, outer margin convex, tip not distinctly extending beyond lateral margin (Figs. 3 A, B, 4A, B, H, I). Merus of third maxilliped subovate, subequal in length to ischium; exopod slender without trace of flagellum (Fig. 5 E). Outer surface of palm of cheliped of adult male covered with numerous low granules; inner surface granulated but without transverse ridge; dorsal margin of dactylus with 6–8 low granules on proximal half or two-thirds, granules not chitinous, unarmed on distal half (Figs. 3 F–I, 4F, G). Ambulatory legs each with relatively slender merus having sharp subdistal spine on dorsal margin and lateral, mesial surfaces gently rugose (Figs. 3 A, 4A, B, H, I); propodus without brush-like setae on ventral margin. Male pleon triangular, relatively broad; somite 6 wide, with convex lateral margins; telson semicircular (Figs. 3 C, D, 4D, E). G1 relatively slender, distal chitinous part bent obliquely laterally, tapering to sharp tip (Fig. 5 F–H).
Remarks. While examining the type material of Geosesarma rathbunae, some discrepancies were discovered in the contents of the jars that were supposed to contain the holotype and paratype specimens of this species. Serène (1968a: 1086, 1087) based his description on only two specimens, one male and one female, loaned to him by the USNM. His two specimens were part of a lot (USNM 54315), containing as per the labels and USNM records, a total of five males and two females collected in Culasi, on the west coast of Panay Island, Philippines. The specimens in this lot had been identified by M. J. Rathbun as “ Sesarma (Sesarma) sylvicola (de Man), var” but never reported in the literature. Of the two specimens that Serène borrowed, he designated as holotype the male measuring 13.0 × 12.2 mm, which he illustrated and photographed (Serène 1968a: figs 5, 6, pl. 1, fig. 4), and as paratype the female measuring 13.3 × 12.0 mm. The holotype and paratype were then returned to the USNM where the holotype was assigned for itself the same original catalogue number used for all the Culasi material, USNM 54315. A new catalogue number, USNM 123208, was then issued for the female paratype.
When the two USNM jars with Serène’s (1968a) type material of Sesarma (Geosesarma) rathbunae were pulled from the shelves for this study, we discovered that the lot that should contain the male holotype, USNM 54315, actually contained a female specimen (Fig. 4 A). Furthermore, the lot that should contain the single female paratype, USNM 123208, actually contained four males, one female, and a vial with four small and dismembered immature juveniles unaccounted for in the labels and USNM records. It should be noted that Serène (1968a) only examined and reported in his description the male and female types; thus, the rest of the Culasi material, even though it has been found to be conspecific with Serène’s species, cannot be part of the type series.
After measuring and comparing all the specimens from Culasi with Serène’s (1968a) description, we determined that the female mistakenly found in the holotype jar matches precisely Serène’s female paratype, and this female specimen has now been assigned a new catalogue number, USNM 1277697. However, none of the males found still in USNM 54315 could be matched with confidence to the size and features of the holotype photographed and illustrated by Serène (1968a) (Fig. 3 A), and moreover, none was found to have the G1 dissected and Serène had a well-known practice of dissecting out the G1 for illustration. More conclusive, one of the five males in the original jar with all the Culasi material, is missing and we have concluded it must be the holotype. Given the possibility, even if remote, that Serène’s holotype may be found in the future, we prefer to be cautious and make a note in the records of the missing holotype in USNM 54315. Finally, the status of lot USNM 123208 that was originally to contain the female paratype but found during this study to contain non-paratypes from Culasi, has been adjusted to reflect that the specimens therein are non-types.
The identity of the species, however, is not in doubt as the series of remaining specimens all agree very well with the type descriptions and figures by Serène (1968a).
Geosesarma rathbunae is unique among known Philippine Geosesarma in that the exopod of the third maxilliped does not have a flagellum (Fig. 5 E). All the other species have a long flagellum on the exopod (e.g., Fig. 5A). This is a character, however, present in many highland species from Peninsular Malaysia and Borneo (e.g., see Ng, 1988, 2015). These species also have G1 structures similar to that of G. rathbunae, with the distal chitinous part relatively shorter and laterally bent.
description: Published as part of 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, pp. 475-483 in Zootaxa 4250 (5) on pages 477-482, DOI: 10.11646/zootaxa.4250.5.5, http://zenodo.org/record/495550