Key to Suborder Oniscoidea

Phylum Arthropoda
 Subphylum Crustacea
  Class Malacostraca
   Subclass Eumalacostraca
    Superorder Peracarida
     Order Isopoda

Taken primarily from  Kozloff, 1987, 1996  (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)
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1a  Flagellum of antenna 2 with more than 10 articles (but there may be as few as 6 articles in immature specimens) (picture); up to about 2.5 cm long; found in rock crevices (and sometimes on pilings) just above the high tide line 2
1b Flagellum of antenna 2 with not more than 4 articles; less than 2 cm long; not typically found in rock crevices (generally on uppermost portions of sancy beaches or truly terrestrial) 3
2a Basal article of uropod about as broad as long (picture) Ligia (Ligia) pallasii
2b Basal article of uropod several times as long as broad (rarely found as far north as Oregon) Ligia (Megaligia) occidentalis
3a Flagellum of antenna 2 with 3 or 4 articles; tracheal system absent; under debris on sandy beaches, near uppermost limits of intertidal zone 5
3b Flagellum of antenna 2 with 2 articles; tracheal system present in exopodites of pleopods 1 and 2; truly terrestrial, though occasionally found close to the uppermost limits of the intertidal zone 4
4a Capable of rolling up into a ball; antenna 2 not extending posteriorly beyond pereonite 2; pleotelson blunt Armadillidium vulgare
4b Not capable of rolling up into a ball; antenna 2 not extending posteriorly beyond pereonite 2; pleotelson pointed Porcellioscaber
5a Flagellum of antenna 2 with 3 articles 6
5b Flagellum of antenna 2 with 4 articles 7
6a Pleonites becoming gradually narrower than the pereonites; cephalon with large and tuberculatemedian and anterolateral lobes; antenna 2 not extending beyond pereonite 2 Alloniscus perconvexus
6b Pleonites becoming abruptly narrower than the pereonites; cephalon rounded in front and with only small lateral lobes, if any; antenna 2 long, extending beyond pereonite 2 Littorophiloscia richardsonae
7a Anterior margin of cephalon deeply 3-lobed, the median lobe forming a rostrum; basal article of uropod expanded, forming a large lobe lateral to the endopodite and nearly reaching the distal tip of the latter Armadilloniscus holmesi
7b Anterior margin of cephalon 2-lobed, without a rostrumlikemedian lobe; basal article of uropod not expanded, the endopodite inserted upon it in a posterolateral position Detonella papillicornis



Taxonomic Levels Represented in this Key:
 Ligia (Megaligia) occidentalis
 Ligia (Ligia) pallasii



Page created by Heidee Leno, 7-2002
Edited by:  Dave Cowles 8-2002; 2005
Edited by: Hans Helmstetler 11-2002