| 1a |
Article
4 of antenna 2 extraordinarily thickened and bearing large ventral
spines
or teeth; urosome
dorsoventrally flattened; ramus
of uropod
3 flattened and paddlelike (Corophium) |
2 |
| 1b |
Article
4 of antenna 2 not especially thickened and without spines or teeth; urosome
laterally compressed; ramus
of uropod
3 somewhat conical or bladelike |
8 |
| 2a |
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| 2b |
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| 3a |
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| 3b |
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| 4a |
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| 4b |
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| 5a |
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| 5b |
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| 6a |
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| 6b |
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| 7a |
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| 7b |
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| 8a |
Coxa
1 much reduced and coxa
4 greatly enlarged (often more than 3 times the width of coxa
2); ramus
of uropod
3 with distinct articles |
Stenotheidae |
| 8b |
Coxae
1-4 nearly equal in size (although becoming slightly wider
posteriorly);
obvious ramus
of uropod
3 with a minute second article
or uniarticulate |
9 |
| 9a |
Eyes borne on prominent anteriorly-directed lateral
lobes of head;
proximal posterior margin of coxa
4 without a deep concavity; peduncle
of uropod
3 slender and distinctly longer than the telson;
telson
thick and fleshy, not cleft |
10 |
| 9b |
Eyes not borne on lateral lobes; proximal posterior
margin of coxa
4 with a deep concavity in its posteroproximal portion; peduncle
of uropod
3 stout, never greatly exceeding the length of the telson;
telson
sometimes thickened, but usually thin and cleft |
18 |
| 10a |
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| 10b |
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| 11a |
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| 11b |
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| 12a |
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| 12b |
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| 13a |
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| 13b |
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| 14a |
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| 14b |
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| 15a |
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| 15b |
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| 16a |
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| 16b |
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| 17a |
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| 17b |
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| 18a |
Ramus
of uropod
3 vestigial;
scarcely one-fourth as long as the peduncle |
19 |
| 18b |
Ramus
of uropod
3 distinct; at least one-half as long as the peduncle |
20 |
| 19a |
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| 19b |
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| 20a |
Antenna 1 longer than the peduncle
of antenna 2; telson
bearing no more than 2 stiff spines |
21 |
| 20b |
Antenna 1 shorter than the peduncle
of antenna 2; telson
with more than 2 spines (Talitridae, "beach hoppers") |
27 |
| 21a |
Antenna 1 slightly longer than antenna 2; uropod
3 bearing a minute inner ramus
(hidden in lateral view); telson
bearing 2 stiff spines |
Parallorchestes spp. |
| 21b |
Antenna 1 shorter than, or about as long as antenna 2; uropod
3 truly uniramous; telson
naked or bearing setae or small, flexible spines |
22 |
| 22a |
Antenna 1 of female only slightly shorter than antenna
2 (in males,
it is distinctly shorter than antenna 2); apex of uropod
3 bearing only setae or flexible spinules; telson
not cleft to its base (Allorchestes) |
23 |
| 22b |
Antenna 1 of both sexes distinctly shorter than antenna
2; apex of
uropod
3 bearing stiff spines; telson
cleft to its base |
24 |
| 23a |
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| 23b |
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| 24a |
Flagellum
of antenna 2 long (with 20 or more articles
in adult specimens); uropod
1 with an enlarged peduncular
spine at the base of the rami
(this spine lateral to the rami);
telson
naked (Keyed as Hyale frequens in Kozloff key) |
Protohyale
sp. |
| 24b |
Flagellum
of antenna 2 short (with less than 20 articles
in adult specimens); uropod
1 with or without an enlarged peduncular
spine at the base of the rami
(when present, this spine is between the rami);
telson
bearing slender spinules |
25 |
| 25a |
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| 25b |
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| 26a |
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| 26b |
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| 27a |
Gnathopod
1 subchelate
(especially in males), its dactyl
not longer than the width of article
6; pereopod
6 not exceeding the length of pereopod
7; ramus
of uropod
3 shorter than the peduncle
and tapering to a point |
28 |
| 27b |
Gnathopod
1 simple, its dactyl
longer than the width of article
6; pereopod
6 slightly longer than pereopod
7; ramus
of uropod
3 at least as long as the peduncle,
not tapering distally (Megalorchestia) |
31 |
| 28a |
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| 28b |
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| 29a |
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| 29b |
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| 30a |
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| 30b |
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| 31a |
Flagellum
of antenna 2 shorter than peduncle;
bases of peduncles
of pleopods
only slightly expanded; inner margin of outer ramus
of uropod
2 without spines |
Megalorchestia pugettensis |
| 31b |
Flagellum
of antenna 2 not shorter than the peduncle
(in males it is much longer than the peduncle);
bases of peduncles
of pleopods
nearly twice as wide as their distal ends; inner margin of outer ramus
of uropod
2 with spines |
32 |
| 32a |
Article
5 of gnathopod
1 of female with a posterodistal tubercle;
ventral margins of epimera
2-3 each bearing several small spines; rami
of pleopods
less than half the length of the peduncles
(the antennae are pinkish orange in life) |
Megalorchestia
californiana |
| 32b |
Article
5 of gnathopod
1 of female without a tubercle;
ventral margins of epimera
without spines; rami
of pleopods
at least one-half the length of the peduncles |
Megalorchestia columbiana |