Haplodendron Just, 2003, gen. nov.
Creators: name: Just, Jean
Publisher: name: Zenodo
Year: 2003
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Haplomunnidae
Haplodendron

description: Haplodendron gen. nov.
Type species. Haplodendron buzwilsoni sp. nov. —here designated. Species included. Type species only.
Etymology. The name of the genus alludes to the family Haplomunnidae and the similarity to Dendrotion (Dendrotiidae) of the stalked insertion of the antennulae and antennae.
Diagnosis. Head broader than long, laterally rounded in dorsal view, with distinctive neck near base; width less than pereonite 1, lateral depth equal to pereonite 1, with low frons­clypeal ridge, antennulae and antennae on joint tall projection dorsally on head, projections joined by low, concave ridge. Body vaulted in lateral view; surfaces and margins of head and pereon with scattered thin, simple setae; pleotelson more densely covered with similar setae; head, pereon and pleotelson, and larger appendages, including mouthparts, with dense felt of tiny setules. Pereonite 1 slightly longer than subequal 2–4, 5–7 dorsomedially compressed to narrow strips along body axis. Pleon with free pleonite 1, longest ventrally. Pleotelson strongly inflated, longitudinal axis nearly perpendicular to pereonal axis, wider than pereonite 5, reaching forward to about pereonite 2, anterodorsally heartshaped in true dorsal view, distal tip smooth, projecting at right angle between uropods. Mandible molar process wedge­shaped, apical ridge with row of small stout curved setae; palp elongate, longer than body of mandible, articles of subequal length. Maxilliped palp with article 2 distinctly broader than 1 and 3; epipodite rounded rectangular, apex reaching to distal part of palp article 2. Pereopod I subchelate, major hinge between carpus and propodus, length approximately 1.5 head­pereon length; ischium longer than basis, carpus strongly elongate; distinct rows of many sharp robust setae on opposing margins of carpus and propodus. Pereopod II slender, length about 2.5 head­pereon length, (II­VII not known); ischium longer than basis. Pereopod I with, pereopod II without, second dactylar claw. Opercular pleopods with long simple setae on ventral surfaces. Uropods tiny, biarticulate, directed ventroposteriorly. Preparatory female with external developing oostegites.
Remarks. Penile papillae in males of the Janiroidea normally protrude from the midposterior margin of pereonite 7 to insert in a mid­proximal pouch in pleopod I, thus crossing externally a first free pleonite if present. In Haplodendron, the vasa deferentia run internally through the first free pleonite to emerge on its posterior margin, from where they insert into an open, V­shaped slit in the midventral proximal surface of pleopod I (Fig. 3, pl1 vv). This construction is likely to be an adaptation to the reflexed pleotelson, because the papillae would be unlikely to be able to reach pleopod I if starting on pereonite 7 and lying externally on pleonite 1. Previous illustrations of males in other genera of Haplomunnidae do not make clear whether this configuration is common to all species in the family, hence the character is not included in the diagnosis of the new genus. As far as I am aware, the only other janiroid, indeed asellote, family known to have the vasa deferentia running internally through the first pleonite is the Paramunnidae. In that family, the vasa deferentia tips emerge into an enclosed pocket on the dorsoproximal surface of pleopod I.
description: Published as part of Just, Jean, 2003, Haplodendron buzwilsoni gen. nov., sp. nov., the first record of Haplomunnidae from the southern Indo­Pacific (Isopoda: Asellota), pp. 1-10 in Zootaxa 372 on pages 3-4, DOI: 10.5281/zenodo.156634