Exosphaeroma Stebbing, 1900

Bruce, N. L., 2003, New genera and species of sphaeromatid isopod crustaceans from Australian marine coastal waters, Memoirs of Museum Victoria 60 (2), pp. 309-369 : 327

Exosphaeroma Stebbing

Exosphaeroma Stebbing, 1900: 553 ; 1902: 54 (part).— Stebbing, 1910a: 220.— Stebbing, 1910b: 428.— Hansen, 1905: 103, 118.— Richardson, 1905: 287.— Barnard, 1914: 374.— Monod, 1933: 9–20.— Menzies, 1962: 132.— Menzies and Frankenberg, 1966: 45.— Menzies and Glynn, 1968: 65.—Schultz. 1969: 131.— Hurley and Jansen, 1977: 55.— Kussakin, 1979: 398.— Harrison, 1984a: 381.— Brusca and Iverson, 1985: 26.— Jacobs, 1987: 67.— Kensley and Schotte, 1989: 229.— Harrison and Ellis, 1991: 939 (key).

Type species: Sphaeroma gigas Leach 1818 , by original designation.

Diagnosis. Pereonite 7 posterior margin even or forming a mesial point, without processes; pleon and pleotelson without process. Pleonite 1 dorsal posterior margin with pair of flat and flush submedian lobes. Pleotelson posterior margin entire, ventrally excavate, without distinct exit channel. Maxilliped palp articles 2–4 mesial margin with distinct lobes. Pereopods 1–3 with inferior margins of merus–propodus densely setulose; ischium superior margin usually with cluster of long simple setae at midpoint. Penial process basally set apart, slender usually between 3–5 times as long as basal width. Pleopod 2 appendix masculina slender, basal in position, extending well beyond distal margin of ramus, apex may be glandular in appearance; pleopods 3–5 exopods with complete transverse suture; pleopods 4 and 5 exopods with or without thickened ridges or folds. Uropods with both rami prominent in dorsal view, lamellar, subequal in length, margins not serrated. Mouthparts not metamorphosed. Brood pouch (Harrison,1984) formed of four pairs of oostegites that do not overlap at the midline.

Species included and distribution. See Appendix. Exosphaeroma appears to be distributed world-wide, though apparently absent from the North Atlantic with those species currently known from the western Atlantic and Caribbean being incorrectly placed. Its presence in the eastern South Atlantic is uncertain as there are insufficient data from the African coast to be sure of its absence. Loyola e Silva (1979) reviewed the distribution of the genus as then composed.

Remarks. Characters which best serve to identify Exosphaeroma include the lamellar uropodal rami with the exopod being about as large as the endopod, with both rami lacking serrate margins, the entire posterior margin to the pleotelson which lacks a ventral exit channel, and the superior margin of the ischium of pereopods 1–3 provided with long setae. Pleopod 2 usually has the appendix masculina longer than the endopod, and the distal portion is often folded back on itself. Pleonite 1 has two flat submedian lobes forming part of the pleonite outline, a character shared with at least Isocladus Miers, 1976 . That genus is readily separated by males having a prominent backwardly-directed process on pereonite 7.

Exosphaeroma is in critical need of revision, the most recent diagnosis being that of Kensley and Schotte (1989). A minimal diagnosis is offered here, based on those species for which the characters mentioned are described. Currently 32 species are included (Appendix), although many more species have been incorporated, and some removed, notably to Gnorimosphaeroma Menzies, 1954 , Harrieta Kensley, 1987 , Ptyosphaera Holdich and Harrison, 1983 , Thermosphaeroma Cole and Bane, 1978 , Tholozodium Eleftheriou, Holdich and Harrison, 1980 and also Clianella Boone, 1923 , Cymodoce Leach, 1814 , Paracerceis Hansen, 1905 , Pseudosphaeroma Chilton, 1909 , Sphaeroma Bosc, 1892 and Sphaeromopsis Holdich and Jones, 1973 .

The relationship of Exosphaeroma to the similar Isocladus Miers, 1976 and Zuzara Leach, 1818 is unresolved ( Bruce and Holdich, 2002). Isocladus and Zuzara are not precisely defined and include numerous ill-defined and poorly described species. Many of the 39 species, including those regarded as incertae sedis (see Appendix), have minimal descriptions. All of the Southern Hemisphere species need to be redescribed for there to be sufficient data to assess species differences, relationships or the biogeography of this genus.