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)
| Jump to: | ||||
| Lower taxonomic level | Main Page | Alphabetic Index | Systematic Index | Glossary |
| 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 | Idotea (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)
resecata
Idotea
(Pentidotea) wosnessenskii