Alox latusoides ( Sakai, 1937 )

Ohtsuchi, Naoya & Kawamura, Tomohiko, 2016, Redescription of Alox chaunos Galil & Ng, 2007 (Crustacea: Decapoda: Brachyura: Leucosiidae) new to Japan; with notes on the male characters of A. latusoides (Sakai, 1937), Zootaxa 4111 (1), pp. 41-52 : 49-51

Alox latusoides ( Sakai, 1937)

[Japanese name: Tsuno-karuishi-kobushi] ( Fig. 6 )

Oreophorus (Oreotlos) latusoides Sakai, 1937: 119 , text fig. 14 [type locality: Nagasaki]; 1976: 81, pl. 25, fig. 1.— Miyake 1961: 14; 1983: 201 (list); 1998: 201 (list).

Tlos petraeus — Alcock 1896: 176 (not A. Milne Edwards 1874).

Tlos latus — Sankarankutty 1962: 157, fig. 4, 5.

Alox latusoides — Tan & Ng 1995: 122 –124.— Minemizu 2000: 202, unnumbered figure; 2002: 202, unnumbered figure.— Marumura & Kosaka 2003: 26.

Material examined. WMNH-Na-Cr 0 160, 1 male (5.5 × 7.2 mm), Kamiura, Kushimoto, Wakayama, August 1979, coll. S. Nagai; 1 female (7.5 × 10.2 mm), off Yamada Onsen, Onna-son, Okinawa, 21 m, 7 July 1992, coll. S. Nagai.

Supplementary description on basis of male specimens from Japan. Thoracic sternum ( Fig. 6 B) densely covered by flattened tubercles of regular size, deeply sunk medially, with distinct ridges interspaced with 3 deep granule-lined grooves on surface. Sterno-abdominal cavity deep, reaching buccal cavity ( Fig. 6 B).

Abdomen ( Fig. 6 B, D) hastate, densely covered with flattened tubercles irregularly on surface; first, second somites short; third to fifth somites fused; third, fourth somites depressed medially, elevated laterally; fourth to sixth somites elevated medially, with pair of depression aside, eroded laterally, with a few flattened tubercles on floor of eroded parts; fifth somite demarcated from fourth somite by deep groove which continuous to submedian depression of fourth somite; sixth somite slightly longer than width, weakly narrowed distally; telson triangular, 1.6 times longer than basal width, 1.1 times longer than sixth somite.

G1 ( Fig. 6 E, F) stout, 2.5 times longer than G2, distal half dilated, covered with long setae on lateral, mesial surface; tip with wide opening. G2 ( Fig. 6 G) narrow; tip with petaloid process.

Female characters. See Tan & Ng (1995: 123, 124).

Size. The largest male is 8.3 × 11.2 mm ( Sakai 1976, as Oreophorus (Oreotlos) latusoides); the largest female is 8.1 × 11.3 mm ( Tan & Ng 1995); the smallest ovigerous female is 6 × 9 mm ( Sankarankutty 1962, as Tlos latus ).

Color in life. See Minemizu (2000: 202, unnumbered figure; 2002: 202, unnumbered figure).

Distribution. Pacific coast of Japan, from Suruga Bay to Kii Peninsula ( Minemizu 2000, 2002; Marumura & Kosaka 2003; this study), northwest Kyushu ( Sakai 1937, 1976; Miyake 1961, as Oreophorus (Oreotlos) latusoides ), Okinawa Island ( Marumura & Kosaka 2003); Andaman Sea ( Tan & Ng 1995); Bay of Bengal ( Alcock 1896, as Tlos petraeus ).

Habitat. Sandy bottom ( Sakai 1976), or bottom of sand mixed with shell debris and gravel ( Minemizu 2000, 2002), at 10–50 m deep ( Minemizu 2000, 2002; Marumura & Kosaka 2003).

Remarks. A male specimen at hand agreed well with the morphological characteristics described by Sakai (1937) and Tan & Ng (1995), though both of them are based on female specimens. However, the carapace is less expanded laterally in male (CW/CL = 1.3, Fig. 6 A) than in females (CW/CL = 1.4±0.1, N = 3, cf. Tan & Ng 1995: 123). In the third maxillipeds, a round circular depression on the outer surface of the merus and a shallow granulelined groove along three-quarters of mesial to posterior margins of the ischium are both present, but they are shallow, not distinct as drawn in Tan & Ng (1995: fig. 9D) in the specimens at hand. Female specimen figured by Tan & Ng (1995: 8.1 × 11.3 mm, USNM uncatalogued) is not much larger than female specimen at hand (7.5 × 10.2 mm), and therefore, we regarded these differences as individual variation.

Alcock (1896) examined eight specimens (at least one male) from the Andaman Islands and the Pedro Shoal, Sri Lanka, under the name “ Tlos petraeus ”, and described that male abdomen has a denticle in the middle line on fourth and sixth somites. It is nevertheless an important male diagnostic character of the genus Oreotlos . Tan & Ng (1995) examined two female specimens, which may represent part of eight specimens examined by Alcock (1896), and concluded that Alcock (1896) examined females of A. latusoides and that he had probably confused it with a male of an Oreotlos species. As a result and despite the lack of information of male characters, Tan & Ng (1999) removed Oreophorus (Oreotlos) latusoides to Alox based on the other diagnostic characters of this genus. Our examination of a male specimen from Kii Peninsula, revealed the absence of a median denticle on the third to sixth somite. The present generic status of A. latusoides is thus supported.

As discussed above, according to the key of Tan & Ng (1995), A. chaunos is closest to A. latusoides . Shared characters include: a broad, non-demarcated median keel; a median depression in the third maxilliped; and the stout, scoop-like chelae with broad immovable fingers. Nevertheless, A. chaunos can be readily distinguished from A. latusoides by the following characters: (1) anterolateral part of the carapace is moderately eroded and has a deep sigmoid groove in A. chaunos (Figs. 2A, D, 3A) but it is strongly eroded, and without distinct groove in A. latusoides ( Fig. 6 A; Tan & Ng 1995: pl. 4D); (2) subhepatic protuberance is more prominent in A. chaunos (Figs. 2A, D, 3A) than in A. latusoides ( Fig. 6 A; Tan & Ng 1995: pl. 4D, F); (3) hepatic and anterolateral carapace margins are divided by a broad concavity in A. chaunos (Figs. 2A, D, 3A) but such a concavity is absent in A. latusoides ( Fig. 6 A); (4) groove along on the mesial to posterior margin of the third maxilliped is absent in A. chaunos (Figs. 2C, F, 3C) but it is present in A. latusoides ( Fig. 6 B; Tan & Ng 1995: fig. 9D); (5) male thoracic sternum is relatively less depressed medially in A. chaunos (Fig. 2B, G) than in A. latusoides ( Fig. 6 B); (6) G1 is tapering, twisted, tips directed dorsally, without setae on the lateral surfaces in A. chaunos ( Fig. 3 J, K), but the shaft is dilated subdistally, not twisted, tips directed ventrally, with short setae densely on lateral surface in A. latusoides ( Fig. 6 B, C); and (7) the G2 is one-third the length of the G1, and the tip is spoon-like in A. chaunos (Fig. 2L, M) but it is more than a half in length of G1, and the tip is elongate and petaloid in A. latusoides ( Fig. 6 G). Furthermore, it is shown here that the male telson of A. chaunos is proportionally longer (TL/TW = 2.5±0.0, Fig. 2G) than those of A. latusoides (TL/TW = 1.6, Fig. 6 B, D) when similar-sized specimens are compared. The habitat also appears to be different in the two species. All known specimens of A. chaunos were recorded from reef flats or sandy bottoms shallower than 3 m, whereas those of A. latusoides were from subtidal rocky reefs 20–62 m deep ( Alcock 1896; Sakai 1976; Marumura & Kosaka 2003).

Figures

FIGURE 3. Alox chaunos Galil & Ng, 2007. Males (A – G, J – M, 7.2 × 8.9 mm, NSMT-Cr 24073; H, 3.8 × 4.9 mm, NSMT-Cr 24075; I, 3.3 × 4.4 mm, NSMT-Cr 24071), Nagura Bay, Ishigaki Island. A, carapace (dorsal view); B, anterior part of carapace, frontal view; C, right third maxilliped (outer surface); D, E, right cheliped, outer (D) and inner views (E); F, right fourth ambulatory legs; G – I, abdomens; J, K, left first gonopod in lateral (J) and mesial views (K); L, M, left second gonopods in mesial view (L), and its tip (M). Indistinct flattened tubercles were omitted in A – E. Scales = 2.0 mm for A, 1.0 mm for B – M.

FIGURE 6. Alox latusoides (Sakai, 1937). Male (WMNH-Na-Cr 0 160, 5.5 × 7.2 mm), Kamiura, Kushimoto, Wakayama Prefecture. A, dorsal view; B, ventral view; C, frontal view; D, abdomen; E, F, left first gonopod in lateral (E) and mesial views (F); G, left second gonopods in mesial view. Scales = 1.0 mm.