Haplomunna Richardson, 1908

Cunha, Marina R. & Wilson, George D. F., 2003, Haplomunnidae (Crustacea: Isopoda) reviewed, with a description of an intact specimen of Thylakogaster Wilson & Hessler, 1974, Zootaxa 326, pp. 1-16 : 8-9

Genus Haplomunna Richardson, 1908

Munna Richardson, 1905: 483 (part).

Haplomunna Richardson, 1908: 79 ; Menzies, 1962: 32; Wilson, 1976: 574.

Aryballurops Gamô, 1983: 13–16 , figs 8 and 9; Saito, Itani & Nunomura, 2000: 25.

Type species. Munna caeca Richardson, 1905 , by monotypy.

Species included: Haplomunna caeca ( Richardson, 1905) ; Haplomunna hubbsi Wilson & Hessler, 1976 ; Haplomunna japonica ( Gamô, 1983) .

Diagnosis (modified from Wilson 1976): Head rounded in dorsal view; depth and width less than pereonite 1, with distinct frons­clypeal ridge, antennae on low projection. Body ovate in dorsal view, vaulted in lateral view; surfaces and margins spinose, with two distinctly different sizes of spines: large robust spines, often on raised portions of the cuticle, and small thin spines (‘stiff hairs’ in Richardson 1905), pereonites 5–7 with spines only on lateral edges, dorsal surfaces smooth. Pereonites 1–4 sculptured, dorsal surfaces often with parallel transverse ridges arching across dorsum; lengths subequal. Female coxal developing oostegites external to sternal surface. Pereonites 5–7 dorsomedial axis compressed; lateral portions extending posteriorly beneath elevated pleotelson. Preparatory female with external developing oostegites. Pleotelson longitudinal axis nearly perpendicular to pereonal axis; inflated, width subequal to pereonite 5 width, somewhat bilobed anterodorsally, heart shaped in dorsal view; distal tip smooth, produced ventroposteriorly. Mandible molar process truncate with two distal ridges: distal ridge finely denticulate; proximal ridge with inner row of stout spines, and outer row of long sharp, minutely serrate spines; palp elongate, longer than body of mandible, article 1 longer than articles 2–3, article 3 subequal to article 2, with elongate setae in group at distal tip. Maxillipedal palp with segment 2 distinctly broader, segment 3 only slightly broader than segment 1. Pereopod I strong, subchelate; carpus somewhat elongate; distinct rows of many stiff unequally bifid setae on occlusive margins of both carpus and propodus. Pereopods II– VII similar to each other. All pereopods with two dactylar claws. Opercular pleopods with strong spines. Uropod tiny, uniarticulate, directed ventroposteriorly.

Remarks: We propose a synonymy of Haplomunna Richardson, 1908 and Aryballurops Gamô, 1983 . The species H. japonica differs from the East Pacific species H. caeca and H. hubbsi in having a much more inflated pleotelson, but in all other respects, the three species are similar. Gamô (1983) provides the first description of a male in the Haplomunna clade, details of which we can confirm from specimens of an undescribed species provided by S. Beaulieu ( SIO). In particular, the tip of the male pleopod I is rounded and not laterally produced (i.e., not saggitate) as in Thylakogaster , thus having a form more like that of Abyssaranea or Munella . An elongate mandibular palp, another similarity with the latter two genera, and the less modified form of pereopods II– VII clearly separates Haplomunna from Thylakogaster . Nevertheless, Thylakogaster and Haplomunna are similar in several respects, the most conspicuous being the reflexed and inflated pleotelson.