Cassidias Richardson, 1906

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 : 319-320

Cassidias Richardson

Cassidias Richardson, 1906: 20 .— Barnard, 1920: 374.— Kensley, 1978: 87.— Harrison, 1984a: 373.— Harrison and Ellis, 1991: 934.

Type species. Cassidias argentinea Richardson, 1906 , by monotypy. Types held at USNM, Smithsonian Institution , Washington, DC, USA .

Diagnosis. Pleotelson with prominent median process; posterior margin with simple median notch and distinct ventral exit channel. Antennule peduncle article 1 more than twice as long as article 2, articles 1 and 2 robust; article 3 slender, all articles collinear. Maxilliped palp articles 2–4 with distomesial angle moderately produced, mesial margins with numerous setae. Pleopods 1–3 with both rami longitudinally oblique. Pleopod 2 with appendix masculina distally attached. Male uropods attached subdistally on pleon, endopod reduced to short stub, exopod round in section with apical spike, entire ramus extending beyond posterior margin of pleotelson.

Description of male. Body stout, about twice as long as greatest width, strongly vaulted; dorsal surface finely granular, with scattered setae; unable to conglobate. Head weakly immersed in pereonite 1. Eyes large, lateral, facets distinct, prominent posterior lobe. Pereon segments without raised posterior margins. Coxae not distinctly demarcated, overlapping anterior over posterior, ventrally directed. Membrana cingula absent. Pleon of 4 segments, segment 1 largely concealed by pereonite 7, segments 2–4 indicated by 2 distinct suture lines running to lateral margins of pleon. Pleotelson with prominent median process; posterior margin with simple median notch and distinct ventral exit channel. Pleonal sternite present.

Antennule and antenna anteriorly positioned on head. Antennule peduncle articles 1 and 2 robust, article 1 more than twice as long as article 2; article 3 slender, all articles collinear; flagellum shorter than peduncle, extending to anterior of pereonite 1. Antenna peduncle article 1 and 2 short, subequal, shorter than 3–5, which become progressively longer; flagellum about as long as peduncle, extending to posterior of pereonite 1.

Epistome anteriorly acute, with weak mesial constriction; with indistinct ventral tubercle Labrum unornamented. Mandible incisor multicuspid; molar process prominent, crushing, provided with marginal scale teeth; left mandible with prominent lacinia mobilis both mandibles with spine row of 5 or 6 spines; palp article 1 longest, 3 shortest. Maxillule lateral lobe with about 13 RS on gnathal surface, most of which are serrate; mesial lobe with 5 long RS, 3 of which are prominently serrate. Maxilla with all articles well developed; lateral and middle lobes with flat strongly curved and finely serrate RS, mesial lobe with several and acute long RS, some of which are basally CP. Maxilliped endite distal margin numerous long acute CP setae and 3 long CP RS on distomesial margin; palp articles 2–4 each with distomesial angle produced, mesial margins with numerous setae, lateral margins of articles 2 and 3 without setae, article 4 with 1 seta.

Pereopods all ambulatory, pereopods 1–3 subsimilar, more robust than 4–7; inferior margins of merus, carpus and propodus with serrate and CP RS; setulose fringe weakly developed; dactylus with prominent simple secondary unguis and 1 flattened seta arising at lateral margin, 2 flat setae at distolateral margin. Pereopods 6 and 7 inferior and distal margins of merus, carpus and propodus with numerous serrate and biserrate RS.

Penes paired, separated by about basal width of penial process; short, not reaching pleopod peduncles.

Pleopods 1–3 both rami with PMS, longitudinal axis of both rami oblique Pleopod 1 exopod extending beyond endopod distal margin subtruncate, proximolateral angle with single short acute RS; endopod distinctly triangular in shape. Pleopod 2 with appendix masculina distally attached on mesial margin. Pleopod 3 exopod with complete suture, suture not distinct on pleopod 4 and incomplete on pleopod 5. Pleopods 4 and 5 exopod and endopods with well-developed transverse thickened ridges; pleopod 5 endopod with 3 lobate scale patches and transverse suture. Uropod exopod 3 times as long as wide, subdistally attached on pleon, endopod reduced to short stub, exopod round in section with apical spike, entire ramus extending beyond posterior margin of pleotelson.

Female. Pleotelsonic process considerably smaller than in the male; uropods with both rami lamellar, positioned midlaterally on pleon, endopod extending only slightly beyond posteri- or margin of pleotelson; both rami with numerous CP setae. Mouthparts metamorphosed. Brood pouch of the type species made up of 4 pairs of oostegites on pereonites 1–4 (Harrison 1984, but see remarks).

Composition. Cassidias argentinea Richardson, 1906 , C. australiensis sp. nov., C. africana Barnard, 1920 . Cassidias trituberculata Thielemann, 1910 has been synonymised with Holotelson tuberculatus Richardson, 1909 ( Kwon, 1990).

Remarks. Harrison (1984a), on the basis of differences in brood-pouch morphology, excluded Cassidias africana Barnard, 1920 from the genus. The type species is known only from females ( Richardson, 1906), and until such time as males are known it is impossible to assess the generic characters for this genus. Although brood-pouch morphology is generally consistent within sphaeromatid genera, there is insufficient evidence to consider such differences to be axiomatically of generic merit, and this character is known to vary in Sphaeroma ( Harrison, 1984a) and now also in Margueritta (present study). At present it seems appropriate to retain the genus, diagnosed on the basis of the known males, with recognition that its status is uncertain. A new genus cannot adequately be differentiated from Cassidias on the basis of type material.

Males of this genus, as here defined can be readily recognised by subterminal uropods which have the endopod reduced in size, by the presence of a broad, blunt, posteriorly directed process on the pleotelson and by the terminal appendix masculina. In addition, the posterior margin of the pleotelson has a distinct simple median notch. Females have the uropods in a more midlateral position and both rami are flat. The process on the pleotelson is reduced compared with that of the male, but does allow identification of females.

The most similar genus is Neonaesa Harrison and Holdich, 1982b which is readily differentiated by the males having the appendix masculina mesially attached, the pleotelson posterior margin with three small notches and the pleotelson dorsal surface with a small median boss flanked by two low submedian bosses. Females of Neonaesa are separated by having a cylindrical uropodal exopod and a reduced endopod in contrast to female Cassidias which have uropodal rami both present and flat.