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 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 narrow-bodied species A. coronatus Schiecke & Modigh-Tota, 1976, although accepted to be Austroniscus by Kaiser & Brandt (2007), probably needs to be placed elsewhere. This species may key out as Nannoniscoides. For more information on the Nannoniscidae, see Wilson (2008).
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 shelf-like 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 cross-section, 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 distal; mandible palp absent ...
Exiliniscus
- Head without projecting rostrum; antennula projecting beyond margin
of head; antenna normal length-article 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 broadly (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
References
Kaiser, S., & Brandt, A. (2007) Two new species of the genus Austroniscus Vanhoeffen, 1914 (Isopoda : Asellota : Nannoniscidae) from the Antarctic shelf. Zootaxa, 47-68.
Kussakin, O.G. (1999) Morskye I solonovatovodnye
ravnonogie rakoobrasnye (Isopoda) cholodnix I umerennix vod sevgernogo
polushariya [Marine and brackishwater likefooted Crustacea (Isopoda) from
the cold and temperate waters of the Northern Hemisphere] Suborder Asellota.
Part 2. Families Joeropsididae, Nannoniscidae, Desmosomatidae, Macrostylidae).
Opredeliteli po Faune SSSR [Determinants of the Fauna], Izdavaemye Zoologischeskim
Institutom
Rossiiskiya Akademiya Nauk. (Ed A. F. Alimov.) St. Petersburg, NAUKA.
Vol. III, pp. 1-383.
Sars, G.O. (1870) Nye Dybvandscrustaceer fra Lofoten. Forhandlinger I Videnskabs-Selskabet I Kristiania, 1869, 145-286.
Schiecke, U., & Modigh-Tota, M. (1976) Erstfund eines Vertreters der Nannoniscidae (Isopoda: Asellota) im Mittelmeer: Austroniscus coronatus n. sp. aus dem Golf von Neapel. Pubblicazioni della Stazione Zoologica di Napoli, 40, 105-133.
Siebenaller, J., & Hessler, R.R. (1981) The genera of the Nannoniscidae (Isopoda, Asellota). Transactions of the San Diego Society of Natural History, 19, 227-250.
Svavarsson, J. (1984) Description of the male of Pseudomesus brevicornis Hansen, 1916 (Isopoda, Asellota, Desmosomatidae) and rejection of the family Pseudomesidae. Sarsia, 69, 37-44.
Wilson, G. 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: 1-24. (PDF: abstract, complete article 290KB)