| 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) |
Pentidotea
wosnesenskii |
| 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 |