Natatolana gracilis ( Hansen, 1890 )

Keable, Stephen J., 2006, Taxonomic Revision of Natatolana (Crustacea: Isopoda: Cirolanidae), Records of the Australian Museum 58 (2), pp. 133-244 : 182

Natatolana gracilis ( Hansen, 1890)

Synonymy in Keable & Bruce, 1997: 682, figs. 11–12.

Type material. Holotype: 3, 8 mm, ZMUC CRU152 (examined). Type locality: the only type specimen was without location data but Hansen (1890) indicates that there is a high probability that it was collected at St Thomas, Virgin Islands [c. 18°20'N 64°55'W].

Diagnosis. Eyes: well developed ( Hansen (1890) describes the eyes as large with a few large ommatidia, these have faded in the holotype and are now barely apparent). Interocular furrow: absent. Frontal lamina: lateral margins concave but not medially constricted, narrowing toward apex. Antenna: c. 0.4–0.5× as long as body, reaching to posterior of pereonite 4. Coxal plates: furrows moderately developed, on all coxae. Pleonite 4: apex slightly rounded. Pleotelson: broad, length 0.87× basal width; anterodorsal depression absent (although the anterior margin is thickened, and there is a smooth curve to a depression, this is not equivalent to the distinct and abrupt depression found in species such as N. pellucida ); anterolateral margins almost straight and angling posteriorly toward the midline; posterolateral margins straight, markedly angled to anterolateral margins and meeting at an obtuse angle; apex produced into a small point; with 7–8 RS. Pereopod 2: propodus with 4 RS on palm (illustrated by Hansen (1890), pereopod 2 propodus now missing from holotype). Pereopod 3: propodus with 3 RS on palm. Pereopod 7: basis narrow, width 0.38× length; distance between anterior margin and medial carina less than between posterior margin and medial carina; posterior margin with setae completely absent along entire length. Penes: unknown (the only specimen that can be identified with certainty is damaged and fragile, there appear to be 2 flattened lobes present, these may be penes but because of the fragile nature of the specimen these could not be examined closely enough to conclude that they were penes). Pleopod 2 appendix masculina: extending beyond tip of endopod, 1.07× length of endopod; margins very strongly curved laterally; slender; apex not at angle to adjacent margins, bluntly rounded. Uropods: exopod slightly shorter than endopod, 0.8× the length of the endopod.

Sexual dimorphism. Based on the record of Koening (1972), females apparently differ from males only in the primary sexual characters and do not have the pleopod 2 appendix masculina. The possibility of further sexual dimorphism, however, is uncertain until samples from the type locality, containing both sexes, have been examined.

Size. Only measured specimen reported is 8 mm.

Remarks. The most distinctive feature of Natatolana gracilis is the shape of the male appendix masculina. The holotype is the only male specimen that has been reported and is, therefore, the only specimen that can be attributed to the species with certainty. Further specimens from the vicinity of the type locality are needed in order to expand upon the redescription of Keable & Bruce (1997).

Distribution. The type locality is uncertain but is probably St Thomas, U.S. Virgin Islands. Also reported from northern Brazil at depths of 7–85 m ( Koening, 1972; Pires-Vanin, 1998) but this requires verification (Keable & Bruce, 1997).