Takedaplax, Ng & Ahyong & Shane T., 2024

Ng, Peter K. L., Ahyong, & Shane T., 2024, Redefining Lophoplax Tesch, 1918: recognising Myopilumnus Deb, 1989, and the establishment of three new genera, Hosekia, Takedaplax, and Striacoeloma (Crustacea: Brachyura: Pilumnidae), Raffles Bulletin of Zoology 72, pp. 335-355 : 347-348

Takedaplax , new genus

Type species. Lophoplax sextuberculata Takeda & Kurata, 1984 , by present designation. Gender of genus feminine.

Included species. Only Lophoplax sextuberculata Takeda & Kurata, 1984 .

Diagnosis. Carapace rectangular; epigastric, postorbital and hepatic areoles well developed with anterior margin cristate to subcristate; epigastric region gently convex, smooth, setose, not areolate; protogastric, cardiac, mesobranchial and cardiobranchial regions may be raised to form areole in larger specimens, barely or not visible in smaller specimens; intestinal region not prominently raised, no visible intestino-branchial areole; surface adjacent to posterior carapace margin almost flat, not forming ridge, no transverse channel visible; orbit clearly visible in dorsal view, supraorbital margin breaking general carapace outline, forming distinct concavity; eyes freely movable, ocular peduncle relatively long; lateral lobe of frontal margin low, indistinct; anterolateral margin with 4 visible teeth or spines (including external orbital tooth), last one often small; posterolateral margins sinuous, gently converging towards posterior carapace margin. Endostome not obliquely recessed posteriorly into buccal cavern, subparallel to adjacent pterygostomial surface, low, short endostomial ridges. Posterior margin of epistome entire, without lateral fissures, median part triangular, lateral parts distinctly concave. Third maxilliped ischium subquadrate, length about 1.3× width. Adult male chelipeds almost symmetrical; dorsal surface of carpus with prominent longitudinal areole, separated from swollen lateral fringe by groove; chela relatively slender with external surface covered with tubercles and granules. Ambulatory legs elongate, slender, P4 longest, about 2.0× carapace width; P2–5 merus without crest on extensor margin, distally unarmed, outer surface smooth, without medio-longitudinal swelling; P4 merus length about 4.3× height, distinctly longer than half carapace width. G1 strongly sinuous, tip recurved.

Etymology. The genus is named after Masatsune Takeda, whose work on the genus has been invaluable in the present revision, and we thank him for encouraging us to “finish the job” by revising the generic position of all species previously placed in Lophoplax . The name is derived from his family name, in arbitrary combination with Lophoplax . Gender is feminine.

Remarks. The six prominent areolets on the anterior half of the carapace of Lophoplax sextuberculata is the only character that links the species to Lophoplax , although the position of the areolets are different. Compared to Lophoplax sensu stricto, however, L. sextuberculata has a distinctly wider carapace which appears rectangular in form, in sharp contrast to the more quadrate form. Most markedly, it differs in having the posterior margin of the epistome entire, without any lateral fissures ( Figs. 8E , 9D ). In Lophoplax sensu stricto, as well as Myopilumnus , Hosekia , new genus, and Striacoeloma , new genus, the posterior epistomial margin is divided into three distinct lobes by well-defined fissures (e.g., Figs. 3B , 4E , 5E , 6C, D ). The form of the epistome is the same as in the pilumnid genus Pseudolitochira Ward, 1942 (sensu Ng et al., 2021). Species of Pseudolitochira , however, are very setose, with long silky setae that partially or completely obscure the margins and surfaces, and lack any trace of areoles on the carapace, with the regions smooth and hardly demarcated ( Ng & Clark, 2022a, b; Ng & Lin, 2023; Ng, 2024a).

In the general appearance of the carapace, especially in the overall shape and the reduced size of the fourth anterolateral tooth/spine, Lophoplax sextuberculata is superficially similar to Viaderiana typica Ward, 1942 , the type species of Viaderiana Ward, 1942 . Viaderiana typica (and congeners), however, have the extensor margin of the ambulatory merus armed with at least one spine, the regions are never prominently raised to form granules, the ischium of the third maxilliped is distinctly more elongate, and the posterior epistomal margin is divided into three distinct lobes by distinct fissures (see Ng, 2023, 2024b).

As such, Lophoplax sextuberculata is made the type species of Takedaplax , new genus.

Figures

Fig. 8. Takedaplax sextuberculata (Takeda & Kurata, 1984), new combination, male (4.0 × 3.2 mm) (NSMT-Cr S 1253), Japan. A, dorsal habitus (right side partially brushed); B, carapace (right side denuded); C, left third maxilliped; D, frontal view of cephalothorax; E, epistome; F, anterior thoracic sternum and part of pleon; G, left chela; H, dorsal view of right cheliped.

Fig. 9. Takedaplax sextuberculata (Takeda & Kurata, 1984), new combination. A–C, holotype female (8.2 × 6.2 mm) (NSMT-Cr S 8949) (after Takeda & Kurata, 1984: figs. 14–16); D–J, male (4.0 × 3.2 mm) (NSMT-Cr S 1253), Japan. A, carapace; B, dorsal view of left cheliped; C, right third maxilliped; D, epistome; E, right P4; F, right P5; G, pleon (missing somite 6 and telson) showing exposed sternite 8 lateral to somite 2; H, right G1 (ventral view); I, right G1 (dorsal view); J, right G2. Scales: D, G = 0.5 mm; E, F = 1.0 mm; H–J = 0.2 mm.

Fig. 3. Lophoplax bicristata Tesch, 1918, lectotype male (5.8 × 4.3 mm) (ZMA D103002), Kei Islands. A, right third maxilliped; B, epistome; C, left P4; D, left P5; E, pleon, showing exposed sternite 8 lateral to somite 2; F, left G1 (ventral view); G, distal part of left G1 (ventral view); H, distal part of left G1 (dorsomedial view); I, distal part of left G1 (dorsal view); J, left G2. Scales: A, B = 0.5 mm; C–E = 1.0 mm; F, J = 0.25 mm; G–I = 0.1 mm.

Fig. 4. Lophoplax takakurai Sakai, 1935a, male (5.0 × 4.2 mm) (NSMT-Cr S 1254), Japan. A, dorsal habitus (right side partially brushed); B, carapace (right side denuded); C, left third maxilliped; D, frontal view of cephalothorax; E, epistome; F, anterior thoracic sternum and pleon; G, right chela; H, left chela; I, dorsal view of right cheliped.

Fig. 5. Lophoplax takakurai Sakai, 1935a. A–D, holotype male (11.5 × 9.0 mm) (after Sakai, 1935a: text-fig. 15; pl. 7, fig. 2); E–K, male (5.0 × 4.2 mm) (NSMT-Cr S 1254), Japan. A, overall dorsal habitus; B, right third maxilliped; C, left chela; D, female pleon; E, epistome; F, left P4; G, right P5; H, pleon, showing exposed sternite 8 lateral to somite 2; I, right G1 (ventral view); J, right G1 (dorsal view); K, right G2. Scales: E, H = 0.5 mm; F, G = 1.0 mm; I–K = 0.2 mm.

Fig. 6. Hosekia symmetrinuda (Edmondson, 1951), new combination, holotype male (6.5 × 5.0 mm) (BPBM 5109), Samoa. A, dorsal view of carapace (right side denuded); B, subfrontal view of cephalothorax (right side denuded); C, frontal view of cephalothorax (right side denuded); D, frontal view showing buccal cavity; E, buccal cavity, anterior thoracic sternum and sternopleonal cavity; F, left chela.