Austrasphaera, Bruce, 2003

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 : 310-311

Austrasphaera gen. nov.

Type species. Austrasphaera berentsae sp. nov., here designated.

Diagnosis. Anterior margin of head overriding antennule and antennae bases. Pleon with all segments entirely fused, with no visible sutures, entirely fused to pleotelson. Antennule peduncle articles 1 and 2 subequal in length, each about twice as long as article 3; article 3 posteriorly offset. Pereopods basis and ischium subequal in length, short, about two-thirds as long as propodus. Pleopod 1 operculate, rami collinear, endopod with mesial margin indurate. Male appendix masculina massive, 0.8–1.0 as wide as endopod, 1.2–1.5 times as long as endopod, distally widest. Uropods subterminal.

Description of female. Body elongate, 3–4 times as long as greatest width, strongly vaulted; dorsal surface smooth; lateral margins subparallel to weakly ovate; unable to conglobate. Head weakly to strongly anteriorly produced, weakly immersed in pereonite 1, anteriorly overriding antennule and antennal bases; rostral process minute. Eyes small, lateral. Pereon segments without raised posterior margins. Coxal plates distinct, overlapping anterior over posterior. Membrana cingula absent. Pleotelson without foramen or excision, but with shallow ventral exit channel. Pleonal sternite present.

Antennule and antenna in ventral position on head. Antennule peduncles narrowly separated by epistome; peduncle articles 1 and 2 robust, anteriorly flattened, expanded; article 2 inferodistal angle produced forming a lobe, plane of articles 1 and 2 of projecting ventrally; peduncle article 3 short, about 0.17 as long as articles 1 and 2, posteriorly offset at midpoint of article 2; flagellum of 3 articles. Antenna slender, held beneath body, peduncle articles 1–3 short, together about 1.3 times as long as article 4, article 5 longest; flagellum as long as or slightly shorter than peduncle.

Epistome narrow, unornamented, anteromedian portion weakly produced. Labrum unornamented. Mandible incisor unicuspid or with weakly defined cusps; left mandible with or without prominent lacinia mobilis; molar process smooth, without serrations or ridges; palp article 1 longest, 3 shortest. Maxillule with lateral lobe with 13 RS on gnathal surface, mesial lobe with 2 long CP slender setae and 1 short slender seta. Maxilla with all articles well developed; lateral and middle lobes with flat finely serrate RS, mesial lobe with blunt and acute long RS, some of which are basally CP. Maxilliped endite distally with cactus and club setae, laterally with 1 long curved CP seta; palp articles not mesially produced, mesial margins with numerous setae, lateral margins without setae.

Pereopods all robust, inferior margins flattened; dactylus with prominent recurved trifid secondary unguis; propodus longest, about 1.0–1.6 times as long as basis. Pereopods lacking serrate and trifid RS.

Brood pouch composed of an anterior and posterior pocket.

Pleopods with all rami elongate, pleopods 1–3 with PMS, 4 and 5 without PMS. Pleopod 1 exopod 1.3–1.6 as long as endopod, endopod about half as wide as exopod, apex distally narrowed. Pleopods 3 and 4 without transverse suture. Pleopods 4 and 5 exopod and endopods with transverse thickened ridges; pleopod 5 endopod with 2 scale patches and transverse suture. Uropods endopod and exopod lamellar, exopod smaller than endopod.

Male. Similar to female except for sexual characters. Pleopod 2 appendix masculina basally or subbasally attached. Penes short, adjacent, basally not widely separated. Pereopod 1 lateral margin with 2 proximally positioned submarginal serrate RS.

Composition. Austrasphaera berentsae sp. nov.; A. springthorpei sp. nov.

Etymology. From Latin australis (meaning south, in reference to the ‘South Land’, i.e., Australia), with the ending - sphaera indicating the family affinity (feminine).

Remarks. This distinctive genus is characterised by the following characters: elongate and strongly vaulted body; pleonite and pleotelson entirely fused; posterior margin of the pleotelson entire; antennules ventrally positioned on head, with articles 1 and 2 expanded, plane of articles ventrally directed; antennule peduncle articles 1 and 2 subequal in size, article 2 with an anterior lobe and article 3 posteriorly offset on article 2; pereopods robust with a very short basis and a long propodus; operculate pleopods, pleopod 2 exopod about half as long as endopod, in the male endopod with a massive appendix masculina; pereopods 5–7 without the usual serrate and trifid setae; and uropods with the exopod smaller than the endopod (but not minute).

Pleopods 4 and 5 have thickened ridges on both rami placing this genus within the broad subfamily concept of Dynameninae Bowman, 1981. Bruce (1995) defined the Ischyromene -group, an informal grouping of genera within the Dynameninae. Austrasphaera shows all the characters of that group of genera: proportions of the antennule peduncle articles, pleopod 1 with the endopod mesial margin being indurate, and pleopod 2 with the exopod distinctly shorter than the endopod. Austrasphaera is similar to four southern Australian genera ( Juletta Bruce, 1993 , Maricoccus Poore, 1994 and Margueritta Bruce, 1993 ) which share: anterior margin of the head produced, overriding the antennule and antennal peduncles, antennule peduncle article 3 being posteriorly offset (also present in Diclidocella Bruce, 1995 , and some species of Cymodocella Pfeffer, 1887 , see Bruce, 1995), pleopod 1 being operculate, pereopods 5–7 with none (or very few) trifid or serrate setae and the pleotelson largely fused to the pleon. The body shape of the four genera varies from scale-like in Maricoccus , flattened in Juletta , vaulted in Margueritta , to elongate and semicylindrical in Austrasphaera .

Two South African species, incorrectly placed in Dynamenella , are similar to Austrasphaera and to the Ischyromene- group. These are “ D.” taurus Barnard, 1940 and “ D.” navicula Barnard, 1940 . “ D.” taurus has a similar antennule with peduncular article 2 being large and anterodistally produced, and the anterior margin of the head produced with ventral antennules and antennae (rather than anterior). “ Dynamenella” navicula has a similar head and body shape to Austrasphaera , but those appendages that were figured by Barnard otherwise differ. Both species have a pleon with four segments and collinear antennule peduncle articles; pereopod and pleopod morphology is unknown and further comparison is not possible without the redescription of the South African species.