Pilumnus dasypodus Kingsley 1879
Creators: name: Clark, Paul F.
name: Trewhella, Stephen M.
name: Michie, Laura A.
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Pilumnidae
Pilumnus
Pilumnus dasypodus

description: Pilumnus dasypodus Kingsley, 1879
(Figs. 4B, 5A–C, 6, 7A–D, 8B)
Common name. Shortspine hairy crab (McLaughlin et al. 2005).
Material examined. 1 male (8.7– 7.1 mm), eastern end of Chesil Beach, Chesil Cove, 50º33'34.20" N 002º26'53.52" W, Portland, Weymouth, Dorset, England, coll. Steve Trewhella, 2 February 2016 (NHM 2024.89). 3 males (9.1– 6.4 mm –10.6– 7.3 mm), 7 females (4.6–3.1–10.0–6.4), off Florida (26º17ʹ52ʺN 082º12ʹ37ʺW), Gulf of Mexico, USA, coll. Continental Shelf Associates, 5 December 1982 (USNM 271436, Acc. # 345592).
Comparative material. Pilumnus hirtellus (Linnaeus, 1761) (Figs. 4A, 8A): 1 male (14.4–9.4 mm), stn 112, 1¼ miles WSW of Breakwater Buoy, Port Erin, Isle of Man, 21 fathoms, muddy sand and shell gravel, coll. R. Hartnoll (NHM 1960.VII.25.121-125). Pilumnus vinaceus A. Milne Edwards, 1880 (Figs. 5G–I, 7E–F, 8C): 9 males (4.5–3.3 mm–13.1–9.7 mm), 6 females (4.5–3.8 mm–10.8–6.9 mm), 6 ovig. females (7.7–5.4 mm–10.3–7.2 mm), Black Rocks, off New River, North Carolina, USA, coll. A.S. Pearce, 14 June 1949 (USNM 89618, Acc. # 183351). 1 female (9.9–7.4 mm), Aracruz, Espírito Santo, Brazil, coll. 16 March 1991 (ZRC 2008.0161). 1 male (29.1–22.7 mm), stn T1, Golfo de Morrosqillo, 09º36.21'N 075º51.77' W –09º35.30'N 075º52.67'W, Caribbean Sea, Colombia, 38–40m, coll. Exped CIOH-INVEMAR-Smithsonian 1995E, 3 August 1995 (USNM 1071706, Acc. # 2036588). 1 ovig. female (24.4–18.0 mm), stn T14, SE of Ceycen Island (Caymen Islands), 09º41.04'N 075º46.08'W, Caribbean Sea, 29 m, coll. Exped CIOH-INVEMAR-Smithsonian1995 E, 6 August 1995 (USNM 1071590, Acc. # 2036588). 1 male (11.2–8.3 mm), Brazil, coll. 11 December 1993 (ZRC 2008.0162). 1 female (10.1–7.3 mm), Meireles, Fortaleza, Ceará, Brazil, coll. A. Anker, 15 June 2011 (ZRC). 1 male (6.4–4.7 mm), Paracuru, Ceará, Brazil, coll. P. Pachelle, 28 August 2011 (ZRC). 1 female (9.6–7.5 mm), Icapri, Brazil; coll. A. Anker & P. Pachelle, 28 July 2012 (ZRC 2013.0817).
Discussion. The G1s of Pilumnus species are generally sigmoidal in shape with a similar distal morphology if viewed under a microscope, although there appear to be differences distally (Fig. 7). Michie et al. (2021) used confocal scanning microscopy to differentiate the details in the G1 distal morphology of 10 fiddler crab (Uca spp.) species living sympatrically on an Indonesian beach. Therefore, this technique was also adopted for the present and there appears to be subtle differences in the distal morphology distinguishing P. dasypodus, P. hirtellus and P. vinaceus such as setal length that may not apparent using normal light microscopy (Fig. 6 versus 7).
Carapace characters are perhaps more obvious especially since Magalhães et al. (2021) discussed three distinguishing features they used to separate P. vinaceus from P. dasypodus. The first of these is the granulation on the mesobrachial region of the carapace being distinctly granular in P. vinaceus (Fig. 4G, J) (versus not granular in P. dasypodus; Fig. 4A, D). The present study, however, did not find this character particularly helpful as the mesobranchial region of the carapace in both species appears to be granular. Although that on P. vinaceus is relatively stronger, it is not always the case as there is some variation. The surface of the mesobranchial region is gently granular in P. dasypodus as well, just not as strong. Magalhães et al. (2021: 552) also noted that P. vinaceus has distinct granulations on the hepatic region and there is a row of granules at the base of the last anterolateral spine towards the gastric region, these being absent in P. dasypodus. Although the granulation on the hepatic region is relatively more distinct in P. vinaceus (Fig. 5G, J) (versus weakly granulated in P. dasypodus; Fig. 5A, D), but this is not always easy to distinguish. Magalhães et al. (2021) also seem to indicate that the pterygostomial region is smooth in P. dasypodus but this is not the case as the surface is in fact distinctly granulated (Fig. 5C, F). In comparison, these granules are present in P. vinaceus and are distinctly larger and sharper (Fig. 5I, L). The shape and structure of the granules on the pterygostomial region are useful characters to separate the two species. Another diagnostic character discovered in this study was the strength of the subhepatic spine present between the first and second anterolateral carapace spines. This subhepatic spine is large and sharp in P. vinaceus (Fig. 4H, K) (versus absent or extremely low and granular in P. dasypodus; Fig. 4B, E). This character was the most distinctive and useful feature to separate the two species.
As discussed, there are also small differences in the G1 structures. In P. dasypodus, the distal part of the G1 is evenly subconical with the tip rounded (Figs. 7A–D, 8B). In P. vinaceus, the distal part of the G1 is proportionately longer and is asymmetrically conical, with the tip sharper (Figs. 7E–H, 8C). Both G1s are quite different from that of P. hirtellus, which has the distal part longer and sharply tapering (Fig. 8A). In addition, the two subterminal setae on the ventral margin just before the distal curves are short and slender in P. hirtellus (Fig. 8A); in P. dasypodus and P. vinaceus, these two setae are much stouter and prominently elongate (Fig. 8B, C).
Although several morphological characters have been identified that appear to separate P. dasypodus from P. vinaceus, it must be noted that none are particularly robust. This reflects the taxonomy of Pilumnus which comprises many species that are similar in appearance with characters that often vary. To have greater confidence in the diagnostic characters proposed, a much larger sample size from across the distribution of the two species, including juveniles and subadults, will need to be accessed. The paper by Magalhães et al. (2021) which regards P. dasypodus and P. vinaceus as distinct, is based mainly on genetic data. While the Brazilian population was shown to belong to a distinct molecular genetic clade, for which they applied the name P. vinaceus, it must be noted that the type locality for this species and P. dasypodus was the Florida Keys! It is imperative that additional samples from across the distribution of both supposed taxa be assembled for a more substantive genetic study. Furthermore, while Magalhães et al. (2021) stated that they examined the types of P. dasypodus and P. vinaceus, these were not figured. Consequently, the actual identities of the two species they treated remains uncertain.
description: Published as part of Clark, Paul F., Trewhella, Stephen M., Michie, Laura A. & Ng, Peter K. L., 2025, An American in Chesil Cove, England: Pilumnus dasypodus Kingsley, 1879 (Crustacea: Decapoda: Brachyura: Pilumnidae), with notes on its taxonomy, pp. 159-168 in Zootaxa 5569 (1) on pages 162-167, DOI: 10.11646/zootaxa.5569.1.6, http://zenodo.org/record/14704024