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

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http://dx.doi.org/10.11646/zootaxa.3980.3.3

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scientific name

Discoplax longipes A. Milne-Edwards, 1867
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Discoplax longipes A. Milne-Edwards, 1867 

( Figs. 1 –3View FIGURE 1View FIGURE 2View FIGURE 3, 6View FIGURE 6 A –D, 7 A –F, 8, 10A –D, G –J, 11 –13, 14A –D, 15 A, B, 16 A, 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. 1 a, 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 –B 3763 S), “ New Caledonia ”, no other data. Loyalty Islands, New Caledonia: 1 male (71.9 × 61.7 mm) ( MNHN – B 20150View Materials), 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 – B 24812View Materials), 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 – B 24815View Materials), 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 – B 26944View Materials), station K 10, "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 – B 26945View Materials), 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 – B 27949View Materials), 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 – B 28463View Materials), 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 – B 26949View Materials), 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. 1View FIGURE 1 A –C, 2, 3, 6 A –D, 7 A –F). Surfaces of adult chelae distinctly granulated to rugose ( Fig. 1View FIGURE 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. 1View FIGURE 1 A, B, 2, 3, 10 A –D, G –J). Male abdomen relatively broader; lateral margin of somite 6 distinctly convex ( Figs. 1View FIGURE 1 D, G, 8). Adult G 1 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 –13View FIGURE 11View FIGURE 12View FIGURE 13, 14View FIGURE 14 A –D, 15 A, B, 16 A, 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 –B 3763 S) is labelled as the presumptive type of the species ( Fig. 1View FIGURE 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 G 1 structure (cf. Ng & Guinot 2001: 326). The molecular analysis shows that three groups are present ( Fig. 17View FIGURE 17. A). 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 G 1. In D. longipes  s. str., the adult G 1 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 –13View FIGURE 11View FIGURE 12View FIGURE 13, 14View FIGURE 14 A –D, 15 A, B). In the material from Guam, the adult G 1 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. 14View FIGURE 14 E –H, 15 C –H, 16 C, D). It is important to compare specimens of similar size and observe the G 1 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. 12View FIGURE 12 C, D, 13 D). The G 1 difference is very reliable. Even in smaller specimens (carapace widths of 55 mm or less), the G 1 of D. longipes  s. str. is relatively more curved ( Fig. 16View FIGURE 16 A, B) than in the Guam specimens ( Fig. 16View FIGURE 16 C, D). The consistency of this difference, together with the molecular data ( Fig. 17View FIGURE 17. A), 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. 10View FIGURE 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. 8View FIGURE 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. 9View FIGURE 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. 8View FIGURE 8 F). Its G 1, however, is typical for the species, being distinctly C-shape ( Fig. 14View FIGURE 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. 3View FIGURE 3 A, B; Sendler 1923: pl. 20, fig. 1 a, b; Türkay 1974: fig. 15), but the G 1 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 G 1 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. 17View FIGURE 17. A). 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.

MNHN

Museum National d'Histoire Naturelle

ZRC

Zoological Reference Collection, National University of Singapore

SMF

Forschungsinstitut und Natur-Museum Senckenberg

DNA

Department of Natural Resources, Environment, The Arts and Sport

Kingdom

Animalia

Phylum

Arthropoda

Class

Malacostraca

Order

Decapoda

Family

Gecarcinidae

Genus

Discoplax

Loc

Discoplax longipes A. Milne-Edwards, 1867

Ng, Peter K. L. & Shih, Hsi-Te 2015
2015
Loc

Cardisoma longipes

Omori 2000: 38
McLay 1990: 115
Tavares 1989: 35
Hartnoll 1988: 21
Yaldwyn 1979: 25
Turkay 1974: 236
Yaldwyn 1970: 2
1970
Loc

Discoplax longipes

Poupin 2010: 56
Ng 2001: 317
Poupin 1996: 5
Turkay 1987: 145
Guinot 1985: 454
Serene 1968: 110
Forest 1961: 74
Sendler 1923: 23
Tesch 1918: 137
Man 1902: 548
Milne-Edwards 1867: 284
1902