Rhizophoracepon, Williams & Boyko & Tri, 2023

Williams, Jason D., Boyko, Christopher B. & Tri, Ngo Van, 2023, Description of a new genus and species of bopyrid (Isopoda: Epicaridea: Bopyridae) from the pinnotherid crab, Plenotheres coarctatus (Bürger, 1895), associated with mangrove clams from Vietnam, Raffles Bulletin of Zoology 71, pp. 531-541 : 534-535

Genus Rhizophoracepon , new genus

Type species. Rhizophoracepon magnagibbus , new species, by present designation.

Etymology. The genus name is a combination of Rhizophora , to denote the mangrove habitat of the host clams and pea crabs, and - cepon, a commonly used suffix for bopyrid genera, especially in Keponinae . The gender is masculine.

Diagnosis. Female head subovate, frontal lamina thin and extending to lateral margins of head. Eyes absent. Antennules and antennae with two and five articles each, respectively. Barbula with two slender subequal falcate pointed lateral projections on each side, middle region smooth. Maxilliped with large palp present. Coxal plates on pereomeres 1–7 rounded with crenulate surface and small thin projections; dorsolateral bosses and tergal projections absent. Mid-dorsal projections on pereomeres absent. Oostegites enclosing brood pouch; oostegite 1 with subcircular anterior article, subequal in size to posterior article, internal ridge digitate, posterior article rounded with distolateral triangular projection. Pereopods subequal in structure, posterior pairs slightly longer than anterior. Pleon with six segments, first five pleomeres each bearing a pair of biramous digitate pleopods and uniramous digitate lateral plates, surfaces crenulate. Endopodites, exopodites, and lateral plates subequal in size. Terminal pleomere ending in uniramous uropods, surface smooth, margins slightly crenulate. Male head ovate, distinctly separated from first pereomere. Minute eyes near posterolateral corners. Antennules of three articles each; antennae of six articles each. No pereomeres with mid-ventral tubercles. Pereopods subequal in size and structure except anterior three pairs with longer dactyli. Pleon with six pleomeres. First five pleomeres with low, rounded pleopods bearing nipple-like extension, mid-ventral tubercles present on pleomeres 1–4. Pleomere 6 without uropods, posterolaterally extended into two flat, broad, smooth rami separated by large triangular median indentation.

Remarks. Rhizophoracepon , new genus, belongs to Keponinae as the females and males possess all the diagnostic characters of that subfamily ( Boyko et al., 2013), particularly the five pairs of lateral plates of the female with weakly tuberculate to filamentous marginal projections. The new genus differs from all others in Keponinae in having females with rounded coxal plates with crenulate surfaces and small thin projections (apomorphy), no dorsolateral bosses, tergal projections or mid-dorsal projections on the pereomeres, and five pairs of short, subequal digitate biramous pleopods and uniramous lateral plates and uniramous uropods. No species in any other keponine genera have this combination of characters. The male has a slightly tapered pleon with the pleomeres splayed out laterally, mid-ventral tubercles on pleomeres 1–4, and broad, widely separated lobes on the pleotelson, a combination of characters that distinguishes it from the males of other keponine genera. Interestingly, the shape of the male pleon is similar to the males of species of Rhopalione Pérez, 1920 ; however, the females of the new genus and species do not show any similarity to those of species of Rhopalione .