Nannoniscidae

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 : 12-13

Key to the genera of the Nannoniscidae

Because the posterior somite articulation is an unreliable character but nevertheless is used in previous keys ( Siebenaller & Hessler 1981; Kussakin 1999), this key uses different characters, and recognises useful features such as the form of the pleotelson. Micromesus , added to the family by Svavarsson (1984), is included. This key is also designed to be used without dissection; although the mandibular palp is used, this character can be determined on intact specimens. The composition of some genera, like Panetela (discussed above) and Austroniscus , need to be reconsidered as some species differ from the generic concepts established by Siebenaller & Hessler (1981) and may not key out properly here. For example, the narrow­bodied species A. coronatus Schiecke & Modigh­Tota, 1976 , although accepted to be Austroniscus by Kaiser & Brandt (2007), probably needs to be placed elsewhere. This species may key out as Nannoniscoides .

1. Antennula with 5 articles, distal article bulbous...........................................................................................2

­ Antennula with 6 or more articles, distal article tubular or rounded............................................................3

2. Antennula article 4 distomedial margin with shelf­like process...................................................................5

­ Antennula article 4 distomedial margin unmodified, lacking projections..................................................10

3. Pereonites and pleon broadly expanded laterally (distance from midline to posterior coxae subequal or less than distance from coxae to lateral margin); pleopodal operculum (pleopods I–II) in ventral view width less than half pleotelson width ......................................................................................... Austroniscus

­ Pereonites and pleon not broadly expanded laterally (distance from midline to posterior coxae greater than distance from coxae to lateral margin); pleopodal operculum (pleopods I–II) in ventral view more than half pleotelson width.....................................................................................................................................4

4. Head anterolateral margin rounded, not projecting; mandibles prognathous, often projecting anteriorly in dorsal view; pleopod II of female with ventromedial spines or projections ........................ Thaumastosoma

­ Head anterolateral margin projecting and angular; mandibles projecting anteroventrally, not prognathous, not visible in dorsal view; pleopod II of female smooth, without ventromedial spines or projections.......... .............................................................................................................................................. Nannoniscoides

5. Body narrow—pereonal margins rounded in cross­section, tergites curving ventrally, pereonites 4–5 longer than wide; ventral surfaces never with spines...................................................................................6

­ Body moderately broad—tergites projecting laterally, especially in pereonites 5–7; pereonites 4–5 wider than long; ventral surfaces often with spines or keels..................................................................................7

6. Head with projecting rostrum; antennula tiny, not projecting anteriorly; antenna short—article 5 and flagellum altogether near length of proximal articles, flagellum strongly tapering distally; mandible palp absent ............................................................................................................................................ Exiliniscus

­ Head without projecting rostrum; antennula projecting beyond margin of head; antenna normal lengtharticle 5 and flagellum altogether distinctly longer than proximal articles, flagellum weakly tapering; mandible palp present ...................................................................................................................... Panetela

7. Pleon broad and elongate—wider than head or pereonites 5–7, distinctly longer than pereonites 5–7; pleopods near length of pleotelson ............................................................................................... Nannonisconus

­ Pleon small—less than or near width of head or pereonites 5–7, subequal or shorter than pereonites 5–7; pleopods distinctly shorter than pleotelson...................................................................................................8

8. Pereopod I robust, all podomeres distinctly wider than those of pereopod II, carpus and propodus with robust elongate ventral setae ........................................................................................................ Rapaniscus

­ Pereopod I not robust, podomeres near width to those of pereopod II, carpus and propodus with simple ventral setae..................................................................................................................................................9

9. Pereon or pleopodal surfaces with at most one ventromedial spine; pereopod I and II similar in setation and width of carpus and propodus ............................................................................................. Nannoniscus

­ Pereon or pleopodal surfaces with 2 or more ventromedial spines; pereopod II carpus and propodus broader and with more robust setae than pereopod I ................................................................. Regabellator

10. Uropod biramous, antennula article 2 distal margin without projections; pleotelson broad (length near width) and shield shaped, with distolateral spines ......................................................................... Hebefustis

­ Uropod uniramous, antennula article 2 distal margin with flat dorsal spine; pleotelson narrow (much longer than wide) and ovoid, without distolateral spines ........................................................... Micromesus