Key to Suborder Valvifera

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

Taken primarily from  Kozloff, 1987, 1996 p. 338 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)
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1a Body nearly cylindrical; pereon with only 6 free pereonites (pereonite 1 is fused to the cephalon); pereopods 1-4 smaller and much more setose than pereopods 5-7, and not used for locomotion Idarcturus hedgpethi
1b Body rather definitely flattened dorsoventrally; with 7 free pereonites; all pereopods similar 2
2a Lateral margins of cephalon with a deep incision; eyes decidedly dorsal; in brackish water and fresh water Saduria entomon
2b Lateral margins of cephalon without a deep incision; eyes lateral (photo); mostly marine (a few species, however, occur in situations where the salinity is slightly reduced) 3
3a Pleon consisting entirely of a pleotelson, although a pair of lateral incisions indicate the posterior limits of 1 partly free pleonite 4
3b Pleon consisting of 2 free pleonites plus the pleotelson, which has a pair of lateral incisions which indicate the posterior limits of another partly free pleonite (photo) 9
4a Posterior margin of pleotelson notched 5
4b Posterior margin of pleotelson tapering to a rounded tip Synidotea nodulosa
5a Anterior margin of cephalon either with a pair of distinct spines or divided by notches into sharp-tipped projections 6
5b Anterior margin of cephalon neither with a pair of distinct spines nor divided by notches into sharp-tipped projections 8
6a Pleon decidedly longer than wide; dorsal surface of each pereonite with 3 tubercles, one of which is on the midline (the cephalon also has 3 tubercles, plus a pair of spines close to the midline at the anterior margin) Synidotea pettiboneae
6b Pleon about as wide as long; dorsal surface of each pereonite not with 3 tubercles, but with either a slight transverse ridge or with several tubercles, none of which is on the midline 7
7a Dorsal surface of each pereonite with a slight but distinct transverse ridge (on most pereonites, this is near the posterior border), but without tubercles; anterolateral corners of the cephalon not extending beyond the two more nearly median projections of the cephalon Synidotea consolidata
7b Dorsal surface of each pereonite with several tubercles, all of which are lateral to the midline; anterolateral corners of the cephalon prominent, extending considerably beyond the 2 more nearly median projections of the cephalon Synidotea ritteri
8a Pereonite 4 definitely wider than the preceding and succeeding pereonites Synidotea nebulosa
8b Pereonites 2-7 all about the same width Synidotea angulata
9a Palp of maxilliped consisting of 4 articles 10
9b Palp of maxilliped consisting of 5 articles 13
10a Posteriormost portion of pleotelson either angular or coming to a distinct projection, definitely not concave 11
10b Posteriormost portion of pleotelson concave, but with a slight median projection Idotea (Idotea) rufescens
11a Only the coxal plate of pereonite 7 reaching the posterior limit of the pereonite Idotea(Idotea) fewkesi
11b Coxal plates of pereonites 6 and 7 reaching the posterior limits of these pereonites 12
12a Posterior portion onf pleotelson angular, but the tip not extended as a distinct projection; lateral margins of pleotelson not concave Idotea (Idotea) urotoma
12b Posterior portion of pleotelson tipped with a distinct projection; lateral margins of pleotelson often concave (the margins between the tip and the posterolateral corners may also be concave) (Now it is thought that this species does not occur in our region) Idotea (Idotea) ochotensis
13a Posterior margin of pleotelson concave Pentidotea resecata
13b Posterior margin of pleotelson convex, often with an apical projection 14
14a Posterolateral margin of coxal plate of pereonite 7 acute (photo) 15
14b Posterolateral margin of coxal plate of pereonite 7 bluntly rounded Idotea (Pentidotea) schmitti
15a Pereonite 1 only slightly wider (not more one-tenth) than the cephalon; body slender, all pereonites about the same width 16
15b Pereonite 1 decidedly wider (by at least one-tenth) than the cephalon (photo); pereonites near the middle of the body wider than the more anterior and posterior pereonites 17
16a Frontal process of cephalon (visible in dorsal view) broadly triangular, not extending forward beyond the tip of the frontal lamina (this plate lies between the bases of the second antennae and is visible in ventral view) male Idotea (Pentidotea) montereyensis
16b Frontal process slender, sharp-tipped, extending forward considerably farther than the tip of the frontal lamina Idotea (Pentidotea) kirchanskii
17a Width of pleotelson about equal to that of the cephalon (lateral margins of pleotelson straight or slightly concave; blunt apical projection of pleotelson conspicuous) [found in central and southern California] Idotea (Pentidotea) aculeata
17b Pleotelson wider than the cephalon 18
18a Pleonite 1 decidedly narrower laterally than along the midline (photo); eyes kidney-shaped (common intertidal species) Idotea (Pentidotea) wosnessenskii
18b Pleonite 1 not significantly narrower laterally than along the midline; eyes not kidney-shaped 19
19a Length less than 2 cm; apex of frontal process without a median notch; eyes almost circular; apical projection of pleotelson inconspicuous female Idotea (Pentidotea) montereyensis
19b Length up to about 5.5 cm; apex of frontal process with a median notch; eyes distinctly elongated; apical projection of pleotelson prominent Idotea (Pentidotea) stenops


Taxonomic Levels Represented in this Key:

  Idotea (Idotea) fewkesi
  Idotea (Idotea) ochotensis
  Idotea (Pentidotea) wosnessenskii
  Pentidotea resecata



Page created by Heidee Leno, 7-26-2002
Edited by:  Dave Cowles 8-2002, 2005, 2006
Edited by:  Hans Helmstetler 10-2002