| 1a |
With gills on pereonites
2-4; mandible
without molar
process |
2 |
| 1b |
With gills on pereonites
3 and 4 only; mandible
with a molar process |
3 |
| 2a |
Perepods
3 and 4 with 1 article,
pereopod
4 with 1 article;
abdomen small and without obvious segmentation |
Cercops compactus |
| 2b |
Pereopods
3 and 5 with 3 articles, pereopod
4 with 1 article;
abdomen small and without obvious segmentation |
Petrotripus brevis |
| 3a |
With vestigial pereopods
on pereonites
3 and 4; mandible
with a palp |
4 |
| 3b |
Without pereopods
on pereonites
3 and 4; mandible
without a palp |
7 |
| 4a |
Pereopods
3 and 4 consisting of 2 articles;
antenna 2 without long setae |
5 |
| 4b |
Pereopods
3 and 4 consisting of only 1 article;
antenna 2 with long setae
on the larger articles |
6 |
| 5a |
Head with a median dorsal spine (in the male) or a knob (in the female);
pereopod
5 consisting of 6 articles;
gnathopod
2 of male attached to the anterior half of pereonite
2 |
Deutella californica |
| 5b |
Head without a median dorsal spine or knob; pereopod
5 consisting of 3 articles;
gnathopod
2 of male attached to the posterior half of pereonite
2 |
Mayerella banksia |
| 6a |
Next-to-last article
of antenna 2 about 4 times as long as wide, with setae
not appreciably longer than its width; short spines on pereonites
directed more nearly anteriorly than laterally |
Tritella laevis |
| 6b |
Next-to-last article
of antenna 2 about 6 times as long as wide, with some setae
about twice as long as its width; short spines on pereonites
directed more laterally than anteriorly |
Tritella pilimana |
| 7a |
Width of propodus
of gnathopod 2 about four-fifths the length of this article; length of
adults about 4 mm; with a pair of grasping spines on the proximal half
of the propodus
of pereopods
5-7 (found on the surface of the sea star Henricia leviuscula, as
well as on hydroids and other organisms) |
Caprella greenleyi |
| 7b |
Width of propodus
of gnathopod
2 less than two-thirds the length of this article;
length of adults generally greater than 5 mm; with a single grasping spine
or tooth on the propodus
of pereopods
5-7 |
8 |
| 8a |
With a ventral spine between the bases of gnathopods
2 |
9 |
| 8b |
Without a ventral spine between the bases of gnathopods
2 |
12 |
| 9a |
|
|
| 9b |
|
|
| 10a |
|
|
| 10b |
|
|
| 11a |
|
|
| 11b |
|
|
| 12a |
Head without any dorsal spines, knobs, or tubercles |
13 |
| 12b |
Head with 1 or a pair of dorsal spines, knobs, or
tubercles |
18 |
| 13a |
|
|
| 13b |
|
|
| 14a |
|
|
| 14b |
|
|
| 15a |
|
|
| 15b |
|
|
| 16a |
|
|
| 16b |
|
|
| 17a |
|
|
| 17b |
|
|
| 18a |
Head with a single dorsal spine or knob |
19 |
| 18b |
Head with a pair of dorsal spines or tubercles |
23 |
| 19a |
Dorsal spine on head an anteriorly directed, triangular projection |
20 |
| 19b |
Dorsal projection on head a knob that is directed upward |
22 |
| 20a |
Tubercles
on dorsal surface of pereonites
small or absent (if present at all, lacking on pereonite
1); gnathopod
2 of male attached near the anterior end of pereonite
2 |
Caprella angusta |
| 20b |
Tubercles
on dorsal surface of pereonites
distinct, present on all pereonites;
gnathopod
2 of male attached near the middle of pereonite
2 |
21 |
| 21a |
|
|
| 21b |
|
|
| 22a |
|
|
| 22b |
|
|
| 23a |
Head with a pair of tubercles |
24 |
| 23b |
Head with a pair of rather sharp spines |
25 |
| 24a |
|
|
| 24b |
|
|
| 25a |
Flagellum
of antenna 1 longer than the peduncle;
pereonites
1 and 2 of male not more than twice as long as wide. |
Metacaprella anomala |
| 25b |
Flagellum
of antenna 1 shorter than the peduncle
(photo);
pereonites
1 and 2 of male more than twice as long as wide (photo)
(Metacaprella kennerlyi in key) |
Caprella kennerlyi |