Macrophthalmus ( Euplax ) dagohoyi Mendoza & Ng, 2007

Macrophthalmus ( Euplax) dagohoyi Mendoza & Ng, 2007 View in CoL

( Figs. 2E–H, 3D–F, 4D–F, 5D–F)

Macrophthalmus ( Euplax) dagohoyi Mendoza & Ng, 2007: 677 View in CoL , figs. 3–5 [ type locality: Bohol Island, Philippines]; Ng et al., 2008: 237 (list).

Macrophthalmus dagohoyi View in CoL – Barnes, 2010: 36 (key).

Euplax leptophthalmus View in CoL – Kishino et al., 2011: 14, figs. 1–3 (Amami Island, Ryukyus); Koyama, et al. 2022: 64, fig. 1 (Kyushu, Japan); Nunobe et al., 2023: 35, fig. 1 (Shikoku, Japan) (not Euplax leptophthalmus H. Milne Edwards, 1852 View in CoL ).

Euplax dagohoyi View in CoL – Sasaki, 2023: 15152 (list).

Material examined. Holotype: 1 male (14.9 × 13.4 mm) ( NMCR 27008 ), subtidal mangrove mud, Abatan River Estuary, Bohol Island, Philippines, coll. Panglao 2004 Expedition, 28 June 2004 . Paratypes: 1 male (13.5 × 12.1 mm) ( NMCR 27009 ) , 1 female (17.5 × 15.6 mm) ( ZRC 2007.0004 View Materials ), subtidal mangrove mud, Abatan River Estuary, Bohol Island, Philippines, coll. Panglao 2004 Expedition, 28 June 2004 . Others : 2 males (17.2 × 14.2, 15.0 × 12.5 mm), 1 female (14.0 × 11.8 mm) (NCHUZOOL 17340), Amami Island , Japan, coll. T. Yonezawa, 4 September 2024 ; 1 male (19.5 × 15.8 mm), 1 female (13.3 × 11.6 mm) (NCHUZOOL 17293), Yakugaki River , Amami Island, Japan, coll. T. Yonezawa, 6 October 2013 ; 1 male (16.2 × 13.7 mm), 1 female (13.3 × 11.6 mm) ( ZRC 2024.0077 View Materials ), Yakugaki R., Amami Island, Japan, coll. T. Yonezawa, 6 October 2013 ; 5 males (24.4 × 20.3, 20.9 × 17.4, 20.6 × 16.9, 19.4 × 16.3, 17.6 × 14.7 mm), 2 females (21.2 × 17.2, 17.2 × 14.4 mm) (NCHUZOOL 17294), Wenchang , Hainan Island, China, coll. X. Zhang, 30 November 2023 ; 1 male (20.7 × 16.9 mm), 1 female (20.3 × 16.7 mm) ( ZRC 2024.0598 View Materials ), Wenchang , Hainan Island, China, coll. X. Zhang, 30 November 2023 ; 1 male (18.9 × 16.1 mm) (NCHUZOOL 17295), Sanya , Hainan Island, China, coll. You-Qi Hao, 18 March 2023 .

Diagnosis. Carapace ( Fig. 2E–G) subquadrate, almost circular, 1.15–1.23 times wider than long; surface granular, with scattered, short setae. Supraorbital margin ( Fig. 3D–F) distinctly backward-sloping. Anterolateral margin ( Fig. 3D–F) granulated, setose, with 3 relatively weak teeth (including exorbital tooth). First tooth (exorbital tooth) broadly subtriangular, never acutely tipped; second tooth broad, lobular or subrectangular, with rounded tip, directed upwards and outwards; U-shaped incision between the first and second teeth wide, less pronounced, shallow; third tooth relatively indistinct, small, bluntly triangular, directed upwards and outwards. Front moderate in width. Eyestalk ( Fig. 3D–F) relatively more curved, more tapering, cornea more inflated. Male chelipeds subequal. Merus inner and outer margins with fringe of long setae. Inner surface of carpus with dense long setae; outer surface smooth. Palm short, inflated; upper margin and inner surface with thick setae. Ambulatory legs ( Fig. 2E–G) long, slender. Male pleon ( Fig. 4D–F) tapering gradually toward telson, tip rounded anteriorly. G1 ( Fig. 5D–F) relatively slender; subdistal part tapering, long and curved.

Habitat. Subtidal muddy bottoms of mangrove estuaries or creeks at water depths ranging from 20 cm to 10 m ( Mendoza & Ng, 2007; Kishino et al., 2011; Koyama et al., 2022; this study). On Amami Island, the habitat is a muddy slope in a mangrove area with gentle flow and minimal freshwater influence. The area remains submerged even at low spring tides, with soft, deeply deposited mud and occasional plant debris, sometimes forming a reduced (anoxic) layer ( Fig. 6C, D). In Hainan, specimens were captured using entangling nets from soft bottoms at a depth of about 10 m.

Size. Largest male CW 24.4 mm (NCHUZOOL 17294); largest female CW 21.2 mm (NCHUZOOL 17294).

Distribution. Japan (Shikoku, Kyushu, and Ryukyu Islands), China ( Hainan Island) and the Philippines ( Bohol Island) ( Mendoza & Ng, 2007; Kishino et al., 2011; Koyama et al., 2022; Nunobe et al., 2023; this study) (Fig. 1).

Remarks. Since its original description ( Mendoza & Ng, 2007), this species has not been recorded under this name, with only a few studies mentioning it in lists (e.g., Ng et al., 2008; Sasaki, 2023) or keys ( Barnes, 2010). Based on the morphological and molecular results of our study, this species is now confirmed to also occur in Amami Island, Ryukyu Islands, Japan ( Kishino et al., 2011, as “ Euplax leptophthalmus ”) and Hainan, China (this study). By extension, the record of Euplax leptophthalmus from Miyazaki Prefecture in Kyushu, Japan, should also be treated as M. dagohoyi . Although M. dagohoyi and M. leptophthalmus are very similar in morphology, they can be distinguished by differences in the carapace and male G1 (see “Morphological differences and variation” in the Discussion).

Molecular analyses. The analysis has revealed a number of distinct haplotypes for each species for both 16S and COI genes ( Table 1). The mean pairwise nucleotide divergences of K2P distances and bp differences for the COI haplotypes are shown in Table 2. K2P values (and bp differences) for M. leptophthalmus are 0.15–1.38% (1–9 bp), and for M. dagohoyi are 0–0.61% (0–4 bp). Conversely, interspecific differences between these two species range from 0.76% to 2.48% (5–16 bp). Both species differ from M. latreillei and M. barnesi by larger values of ≥ 13.51% ( ≥ 80 bp).

The phylogenetic analysis based on these sequences (Fig. 7) shows that M. leptophthalmus and M. dagohoyi are closely related, but the support values are not high. The two species and M. latreillei form a highly supported monophyletic group. However, the support values for a larger clade comprising this group of three species together with M. barnesi are weak.