Nannoniscus Sars, 1870

Wilson, George D. F., 2008, A review of taxonomic concepts in the Nannoniscidae (Isopoda, Asellota), with a key to the genera and a description of Nannoniscus oblongus Sars, Zootaxa 1680, pp. 1-24 : 13-14

Nannoniscus Sars, 1870

Nannoniscus Sars, 1870: 164 ; Hansen, 1916: 87 –89; Gurjanova, 1932: 51; Menzies, 1962b: 133; Birstein, 1963: 78; Siebenaller & Hessler, 1981: 241; Kussakin, 1999: 68.

Saetoniscus Brandt, 2002: 11 , figs. 6–13.

Type species. Nannoniscus oblongus Sars, 1870 .

Composition. N. acanthurus Birstein, 1963 ; N. aequiremus Hansen, 1916 ; N. affinis Hansen, 1916 ; N. analis Hansen, 1916 ; N. antennaspinis Brandt, 2002 ; N. arcticus Hansen, 1916 ; N. arctoabyssalis Just, 1980 ; N. australis Vanhöffen, 1914 ; N. bidens Vanhöffen, 1914 ; N. bidens sensu Brandt, 1992 ; N. camayae Menzies, 1962 ; N. caspius G. O. Sars, 1897 b; N. cristatus Mezhov, 1986 ; N. coalescus ( Menzies & George, 1972) ; N. detrimentus Menzies & George, 1972 ; N. inermis Hansen, 1916 ; N. laevis Menzies, 1962 ; N. laticeps Hansen, 1916 ; N. menziesi Mezhov, 1986 ; N. meteori ( Brandt, 2002) , comb. nov.; N. minutus Hansen, 1916 ; N. muscarius Menzies & George, 1972 ; N. oblongus G. O. Sars, 1870 ; N. ovatus Menzies & George, 1972 ; N. perunis Menzies & George, 1972 ; N. plebejus Hansen, 1916 ; N. profundus Svavarsson, 1982 ; N. reticulatus Hansen, 1916 ; N. robustus Birstein, 1963 ; N. simplex Hansen, 1916 ; N. spinicornis Hansen, 1916 ; N. teres Siebenaller & Hessler, 1981 .

Diagnosis (modified from Siebenaller & Hessler 1981:241). Pereonal tergites projecting laterally from pereopodal coxae; pereonites 6–7 dorsal articulation absent medially. Pleon distinctly shorter than pereonites 5–7. Antennula with 5 segments, distal article bulbous, article 4 distal margin with ventromedial often angular projection. Mandible with palp. Pereopods I–II equally robust. Uropods biramous.

Remarks. Siebenaller & Hessler (1981: 241) noted that further division of Nannoniscus was possible, and described several substantially different species that were retained in the genus under their concept. The pleotelson varies considerably within Nannoniscus , with species having posterolateral or posterior spines or substantially different widths to length ratios. The presence and position of ventral spines is also variable amongst the described species in the genus. All species, however, are broad bodied with distinct tergal plates extending over and laterally from the ventrally placed coxae. As discussed below, N. intermedius Siebenaller & Hessler, 1981 is transferred to Nannonisconus owing to its distinctly enlarged pleotelson, compared to all other species in the genus. Hebefustis Siebenaller & Hessler, 1977 is similar to some species of Nannoniscus , given the latter's variability in such features as ventral spination and posterolateral spines on the pleotelson. This variability leaves the absence of antennal article 4 projection as the only definitive character of Hebefustis . Siebenaller & Hessler (1981: 241) left this character out of the diagnosis of Nannoniscus .

A possibly new species was found among the published descriptions of species of Nannoniscus . Brandt (1992) did not provide evidence that specimens found in the eastern Weddell Sea were conspecific with N. bidens Vanhöffen, 1914 from Gauss­Station. Brandt's "redescription" is in fact a new record because Vanhöffen's type material was not newly described or illustrated. Brandt (1992: 147) mentions Vanhöffen's illustrations but does not discuss the appearance of his specimens, and states that specimens from the Weddell Sea were used for "redescription" (p.141). A comparison of Brandt's illustrations with those of Vanhöffen suggests that the two species are not conspecific. In particular, the antennular articles and the head shape differ substantially between the two descriptions. Because other asellote taxa in Antarctic oceans have proven to be narrow range endemics (e.g., Paramunnidae ; Just & Wilson 2004), this identification should be tested by a study of Vanhöffen's 3 specimens. In the meantime, this record of N. bidens , and perhaps that of Amar & Roman (1974) should be considered as possibly new species.