Discoplax longipes A. Milne-Edwards, 1867

Ng, Peter K. L. & Shih, Hsi-Te, 2015, The land crabs of the Discoplax longipes A. Milne-Edwards, 1867 species group, with description of a new species from Guam (Crustacea: Decapoda: Brachyura: Gecarcinidae), Zootaxa 3980 (3), pp. 379-405 : 383-388

Discoplax longipes A. Milne-Edwards, 1867

( Figs. 1–3 , 6 A–D, 7A–F, 8, 10A–D, G–J, 11–13, 14A–D, 15A, B, 16A, B)

Discoplax longipes A. Milne-Edwards, 1867: 284 ( New Caledonia); 1873: 294, pl. 15 ( New Caledonia); De Man 1902: 548 (discussion); Tesch 1918: 137 (list); Sendler 1923: 23, pl. 20 fig. 1a, b (Makatea, Tuamotu Archipelago, French Polynesia); Forest & Guinot 1961: 74 (list); Serène 1968: 110 (list); Guinot 1985: 454 (list); 1994: 168 (list); 1988: 6 (Loyalty Islands); Türkay 1987: 145 (list); Poupin 1996: 5, 66 (list); Ng & Guinot 2001: 317 (part), fig. 5 (Loyalty Island, New Caledonia); Ng et al. 2008: 214 (list); Poupin & Juncker 2010: 56 (Makatea, Tuamotu Archipelago, French Polynesia).

Cardisoma rotundum —Anonymous 1970: 2, fig. ( Niue) (not Thelphusa rotunda Quoy & Gaimard, 1824 )

Cardisoma longipes — Yaldwyn 1970: 2, fig. ( Niue); 1972: 508 (list); Türkay 1974: 236, figs. 4, 10, 15 ( New Caledonia; Ocean [Pleasant] Island, Nauru; Kandavu Island, Fiji; Niue; Cook Islands; Tuamotu Archipelago, French Polynesia); Yaldwyn & Wodzicki 1979: 25 (part) (in key); Hartnoll 1988: 21 (list); Tavares 1989: 35 (in list); McLay & Ryan 1990: 115, tab. 2 ( Fiji); Ng 1998: 1151 (part); Omori & Holthuis 2000: 38, fig. 32.19 (list).

Material examined. Holotype: male (54.6 × 48.5 mm) ( MNHN –B3763 S), “ New Caledonia ”, no other data. Loyalty Islands, New Caledonia: 1 male (71.9 × 61.7 mm) ( MNHN –B20150), Cong–Ouloup Cave, Ouvea Atoll, coll. J.-P. Guillerm, 26 September 1987; 1 female (soft, freshly moulted) ( MNHN), Cong–Ouloup Cave, Ouvea Atoll, coll. P. Wea & L. Deharveng, 14 November 2000; 1 adult female (49.0 × 43.0 mm), 1 young male (30.6 × 26.9 mm) ( MNHN –B24812), Xodre Cave, Lifou Island, by hand, coll. B. Séret, 1 September 1993; 1 male (37.2 × 32.7 mmm), 1 juvenile female (32.8 × 27.6 mm) ( MNHN –B24815), 1 male (43.3 × 37.7 mm), 1 juvenile female (30.3 × 25.9 mm) ( ZRC 2001.1150), Inegoj Cave, Lifou Island, by hand, coll. B. Séret, 2 February 1993; 2 females (36.8 × 32.6 mm, 26.9 × 23.7 mm) ( MNHN –B26944), station K10, "siphon cristal", Inegoj Cave, Lifou Island, in water, coll. B. Séret, 12 August 1995; 1 specimen (17.7 × 15.7 mm, dried, badly damaged) ( MNHN –B26945), in closed pool, near a siphon, Mexel Cave, Lifou Island, coll. 2 August 1995; 1 male (carapace damaged, 37.2 × 33.9 mm), 1 female (56.0 × 50.0 mm) ( MNHN –B27949), Kumo Cave, Lifou Island, coll. “Workshop Lifou 2001”; 1 juvenile male (19.0 × 16.2 mm) ( MNHN), station NC00–073, Pekepié Cave, Drueulu, Lifou Island, coll. L. Deharveng & A. Bedos, 21 October 2000; 1 male (58.9 × 51.1 mm) ( MNHN –B28463), 1 juvenile (8.2 × 7.5 mm) ( ZRC), station NC00–114, Peng Cave, Hapetra, Lifou Island, coll. L. Deharveng & A. Bedos, 26 October 2000; 1 male (68.2 × 57.4 mm), 2 juvenile females (20.7 × 17.8 mm, 17.2 × 14.0 mm) ( ZRC 2002.0050), station NC00– 144, Peng Cave, Hapetra, Lifou Island, coll. L. Deharveng & A. Bedos, 29 October 2000; 1 juvenile (9.0 × 8.0 mm) ( MNHN –B26949), from small pool, station 88–057, in fresh water, limestone cave, Panace Cave, Tiga Island, coll. T.M. Iliffe & S. Sarbu, 16 June 1988; 1 female (24.9 × 22.4 mm) ( ZRC 2002.0051), 2 juveniles (7.3 × 6.1 mm, 7.8 × 6.7 mm) ( MNHN), station NC00–165, Wea Cave, Tiga Island, coll. L. Deharveng & A. Bedos, 2 November 2000; 1 female (61.2 × 53.4 mm), 1 juvenile male (18.0 × 15.3 mm), 1 juvenile female (21.8 × 18.6 mm) ( MNHN), station NC00–150, Wea Cave, Tiga Island, coll. L. Deharveng & A. Bedos, 1 November 2000. Niue — 2 males (57.0 × 50.2 mm, 54.0 × 47.0 mm), 1 female (61.5 × 53.5 mm) ( SMF 6680), coll. C.H. Thomson, 1970, don. Dominion Museum, Wellington; 1 male (74.9 × 62.6 mm) (UF 2194), supratidal to well inland, Hakupu area, Niue Island, coll. B. Holthuis & G. Paulay, 9 April 1991; 2 males (57.6 × 50.1 mm, 56.0 × 48.0 mm) (UF 2197), on road between Alofi & Tuapa, Niue island, coll. G. Paulay, 6 April 1986. French Polynesia: 1 male (68.9 × 61.3 mm) ( SMF 4293), 1 male (65.0 × 55.7 mm) ( SMF 5849), Tubuai Island, Makatea, Tuamotu, Hanseatische Südsee Expedition, coll. E. Wolff, 16 July–20 July 1909.

Diagnosis. Frontal, epigastric, epibranchial and anterior part of mesobranchial regions covered with numerous small rounded granules, those on anterior part flattened; mesogastric, metagastric regions distinctly granulated; posterior part of meso-, metabranchial regions with prominent striae, granules; epigastric regions well defined, margin relatively sharp; postorbital cristae relatively strong ( Figs. 1 A–C, 2, 3, 6A–D, 7A–F). Surfaces of adult chelae distinctly granulated to rugose ( Fig. 1 A). Ambulatory legs long; ratios of maximum length to maximum width of second to fourth ambulatory meri 3.6–4.4, 3.5–4.3, 2.9–3.6, respectively; ratios of maximum length to maximum width of second to fourth ambulatory legs (dactylus, propodus, merus) 13.9–16.0, 13.5–15.0, 11.1–12.1, respectively; surfaces covered with distinct granules and/or striae, appearing very rugose; dorsal margins of merus prominently granulated; lateral margins of propodus, dactylus lined with strong, stiff spines or setae, propodus always distinctly armed ( Figs. 1 A, B, 2, 3, 10A–D, G–J). Male abdomen relatively broader; lateral margin of somite 6 distinctly convex ( Figs. 1 D, G, 8). Adult G1 strongly curved, appearing almost C-shaped when viewed from ventral perspective; tip bent at an angle of about 90° from vertical; outer margin of distal part meets curved distal part of pectinated part abruptly, forming gentle shelf–like structure; base of pectinated distalmost part (outer marginal view) prominently broad; inner surface with relatively deep median longitudinal depression ( Figs. 11–13 , 14 A–D, 15A, B, 16A, B). Loyalty Islands to French Polynesia.

Remarks. Alphonse Milne-Edwards (1867: 284) established Discoplax longipes for a specimen of unspecified sex measuring 55.0 by 54.0 mm from New Caledonia. He later elaborated on this species and figured it (A. Milne- Edwards 1873: 294, pl. 15), with the drawing clearly depicting a male specimen. A male specimen measuring 54.6 by 48.5 mm (MNHN–B3763 S) is labelled as the presumptive type of the species ( Fig. 1 ). The discrepancy in carapace lengths (48.5 mm versus 54.0 mm) can easily be explained by A. Milne-Edwards including the abdomen in his measurement. Türkay (1974: 239) had also treated this specimen (his measurements are 59.0 by 49.0 mm agree well with the present ones) as the holotype.

The differences between D. longipes and D. michalis n. sp. are relatively small, and certainly not as distinct between these two species and D. gracilipes , which differ in the carapace and pereopod granulation, ambulatory leg proportions, and G1 structure (cf. Ng & Guinot 2001: 326). The molecular analysis shows that three groups are present ( Fig. 17 ). One clade contains two subclades; one with the Philippine population ( D. gracilipes ) and the other has specimens from Loyalty Islands and Niue that are D. longipes s. str. We could not obtain DNA from the French Polynesian specimens, which appear to have been previously preserved in formalin. The other clade with the Guam specimens had previously been identified as D. longipes by Ng & Guinot (2001). Morphologically, however, the Guam specimens and those from Loyalty Islands, Niue, and French Polynesia are very close.

Fortunately, there is a large series of specimens from Guam, Loyalty Islands, Niue, and French Polynesia that include juveniles and specimens of various sizes so variation can be studied in detail. The one character that is consistently different between the specimens from Loyalty Islands (including Niue and French Polynesia) (here referred to as D. longipes s. str.) and Guam is the structure of the G1. In D. longipes s. str., the adult G1 is strongly curved when viewed in situ from the ventral perspective, forming a distinct C, with the distal pectinated part gently curved laterally ( Figs. 11–13 , 14 A–D, 15A, B). In the material from Guam, the adult G1 is only gently curved from the ventral perspective and the distal part is curved slightly more strongly and appears to be more right angled ( Figs. 14 E–H, 15C–H, 16C, D). It is important to compare specimens of similar size and observe the G1 from the same angle. The shape of the structure is such that the G 1 may superficially appear to be almost straight if viewed from a different angle (see Figs. 12 C, D, 13D). The G1 difference is very reliable. Even in smaller specimens (carapace widths of 55 mm or less), the G1 of D. longipes s. str. is relatively more curved ( Fig. 16 A, B) than in the Guam specimens ( Fig. 16 C, D). The consistency of this difference, together with the molecular data ( Fig. 17 ), argues for the recognition of the Guam material as a separate pseudocryptic species, herein named D. michalis n. sp.

There are no major or consistent differences in the relative proportions of the ambulatory legs between D. longipes s. str. and D. michalis n. sp. ( Fig. 10 ). There appears to be a subtle difference in the shape of somite 6 of the male abdomen. In D. longipes s. str., male abdominal somite 6 appears to be relatively wider and the lateral margins are more convex (cf. Fig. 8 A–E, G–J). In D. michalis n. sp., male somite 6 is proportionately less broad and the lateral margins less convex (cf. Fig. 9 A, B, D). One large male of D. longipes s. str. from Loyalty Island (68.2 × 57.4 mm, ZRC 2002.0050), however, has proportionately the most narrow somite 6 of all the specimens of both species examined, being relatively long with the lateral margins only gently convex ( Fig. 8 F). Its G1, however, is typical for the species, being distinctly C-shape ( Fig. 14 A, B). All other specimens of D. longipes s. str. examined (including the holotype male) have a relatively wider male abdominal somite 6.

In his synopsis of the fauna of French Polynesia, Poupin (1996: 5) noted “ SENDLER (1923) recorded about 30 species from Makatea, Rimatara and Tahiti, from the collections made during the Hanseatischen Südsee- Expedition. Some of them, like Coenobiia cavipes or the gecarcinid Discoplax longipes , have never been collected since.” Poupin & Juncker (2010: 56) nevertheless later published a photograph of a specimen from Makatea. The specimens from French Polynesia are large ( Fig. 3 A, B; Sendler 1923: pl. 20, fig. 1a, b; Türkay 1974: fig. 15), but the G1 structure is distinctly C-shaped, a character that identifies them with D. longipes s. str. The same is true for the specimens from Niue. There seems little doubt now that the specimens from Niue and French Polynesia are conspecific with D. longipes s. str. from Loyalty Islands. Their G1 structures are of the same form (distinctly Cshape), and this is supported by the molecular analysis, with a Niue specimen clustering with the Loyalty Island material ( Fig. 17 ). This indicates that specimens from Fiji and Cook Islands that have been reported by Türkay (1974) and McLay & Ryan (1990), respectively, are probably also D. longipes s. str. as these localities are between the Loyalty Islands and French Polynesia.

Distribution. Loyalty Islands (type locality); Niue; Fiji; Cook Islands; Makatea, Tuamotu, French Polynesia.

Figures

FIGURE 1. Discoplax longipes A. Milne-Edwards, 1867, holotype male (54.6 × 48.5 mm) (MNHN – B 3763 S), “ New Caledonia ”. A, E, overall habitus; B, frontal view of cephalothorax; C, buccal cavity and third maxillipeds; D, G, anterior thoracic sternum and abdomen; F, carapace. A – D after A. Milne-Edwards (1873: pl. 15).

FIGURE 2. Discoplax longipes A. Milne-Edwards, 1867, overall habitus. A, male (68.2 × 57.4 mm) (ZRC 2002.0050); B, male (43.3 × 37.7 mm) (ZRC 2001.1150); C, male (37.2 × 32.7 mm) (MNHN – B 24815). All specimens from Loyalty Islands.

FIGURE 3. Discoplax longipes A. Milne-Edwards, 1867, overall habitus. A, male (68.9 × 61.3 mm) (SMF 4293), Makatea, French Polynesia; B, male (65.0 × 55.7 mm) (SMF 5849), Makatea, French Polynesia; C, male (54.0 × 47.0 mm) (SMF 6680), Niue.

FIGURE 6. Discoplax species, dorsal views of carapaces. A, D. longipes A. Milne-Edwards, 1867, male (68.2 × 57.4 mm) (ZRC 2002.0050), Loyalty Islands; B, D. longipes A. Milne-Edwards, 1867, male (43.3 × 37.7 mm) (ZRC 2001.1150), Loyalty Islands; C, D. longipes A. Milne-Edwards, 1867, male (68.9 × 61.3 mm) (SMF 4293), Makatea, French Polynesia; D, D. longipes A. Milne-Edwards, 1867, male (57.0 × 50.2 mm) (SMF 6680), Niue; E, D. michalis n. sp., paratype male (68.3 × 60.0 mm) (ZRC 2000.0571), Guam; F, D. michalis n. sp., paratype male (41.8 × 36.0 mm) (ZRC 2001.0701), Guam.

FIGURE 8. Discoplax longipes A. Milne-Edwards, 1867, anterior thoracic sternums and abdomens. A, male (37.2 × 32.7 mm) (MNHN – B 24815), Loyalty Islands; B, male (37.2 × 33.9 mm) (MNHN – B 27949), Loyalty Islands; C, male (43.3 × 37.7 mm) (ZRC 2001.1150); D, male (58.9 × 51.1 mm) (MNHN – B 28463), Loyalty Islands; E, male (71.9 × 61.7 mm) (MNHN – B 20150), Loyalty Islands; F, male (68.2 × 57.4 mm) (ZRC 2002.0050), Loyalty Islands; G, male (68.9 × 61.3 mm) (SMF 4293), Makatea, French Polynesia; H, male (65.0 × 55.7 mm) (SMF 5849), Makatea, French Polynesia; I, male (57.0 × 50.2 mm) (SMF 6680), Niue; J, male (54.0 × 47.0 mm) (SMF 6680), Niue.

FIGURE 9. Discoplax michalis n. sp. A, C, paratype male (68.3 × 60.0 mm) (ZRC 2000.0571), Guam; B, paratype male (41.8 × 36.0 mm) (ZRC 2001.0701), Guam; D, paratype male (69.7 × 57.8 mm) (ZRC 2000.5072), Guam.

FIGURE 10. Discoplax species, ambulatory legs. A – F, right second ambulatory legs; G – L, left fourth ambulatory legs. A, G, D. longipes A. Milne-Edwards, 1867, male (68.2 × 57.4 mm) (ZRC 2002.0050), Loyalty Islands; B, H, D. longipes A. Milne- Edwards, 1867, male (43.3 × 37.7 mm) (ZRC 2001.1150), Loyalty Islands; C, I, D. longipes A. Milne-Edwards, 1867, male (65.0 × 55.7 mm) (SMF 5849), Makatea, French Polynesia; D, J, D. longipes A. Milne-Edwards, 1867, male (54.0 × 47.0 mm) (SMF 6680), Niue (laterally transposed to facilitate comparisons); E, K, D. michalis n. sp., paratype male (68.3 × 60.0 mm) (ZRC 2000.0571), Guam; F, L, D. michalis n. sp., paratype male (41.8 × 36.0 mm) (ZRC 2001.0701), Guam.

FIGURE 11. Discoplax longipes A. Milne-Edwards, 1867. A, anterior thoracic sternums, sternoabdominal cavities and G 1 s, male (58.9 × 51.1 mm) (MNHN – B 28463), Loyalty Islands; B, sternoabdominal cavity and G 1 s, male (71.9 × 61.7 mm) (MNHN – B 20150), Loyalty Islands; C, D, left G 1 (basal part broken off), holotype male (54.6 × 48.5 mm) (MNHN – B 3763 S), “ New Caledonia ”. C, ventral view; D, dorsal view.

FIGURE 12. Discoplax longipes A. Milne-Edwards, 1867, right G 1 (laterally transposed to facilitate comparisons, denuded); male (68.9 × 61.3 mm) (SMF 4293), Makatea, French Polynesia. A – C, F, G, ventral views (photographed at different angles); D, E, H, I, dorsal views (photographed at different angles); F – I, distal parts of G 1.

FIGURE 13. Discoplax longipes A. Milne-Edwards, 1867, left G 1, male (74.9 × 62.6 mm) (UF 2194), Niue. A – C, E, F, ventral views; D, G, H, dorsal views. E – H, distal parts of G 1; B – H, denuded.

FIGURE 14. Discoplax species, left G 1 s. A – D, D. longipes A. Milne-Edwards, 1867, male (68.2 × 57.4 mm) (ZRC 2002.0050), Loyalty Islands; E – H, D. michalis n. sp., paratype male (68.3 × 60.0 mm) (ZRC 2000.0571), Guam. A, C, E, G, ventral views; B, D, F, H, dorsal views; C, D, G, H, distal parts (denuded).

FIGURE 16. Discoplax species, left G 1 s (denuded). A, B, D. longipes A. Milne-Edwards, 1867, male (43.3 × 37.7 mm) (ZRC 2001.1150), Loyalty Islands; C, D, D. michalis n. sp., paratype male (41.8 × 36.0 mm) (ZRC 2001.0701), Guam.

FIGURE 17. A Bayesian inference (BI) tree of the genus Discoplax from the Indo-West Pacific region and the sister genus Cardisoma spp., based on the combined 16 S rDNA and cytochrome oxidase subunit I genes (COI). Probability values at the nodes represent support values for BI, maximum likelihood (ML) and maximum parsimony (MP).