Taken primarily from Kozloff, 1987, 1996 p. 348 (Copyright 1987, 1996, University of Washington Press. Used in this web page by permission of University of Washington Press)
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| Lower taxonomic level | Main Page | Alphabetic Index | Systematic Index | Glossary |
| 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 |
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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 |
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| 16b | ||
| 17a | ||
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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 | ||
| 19b | ||
| 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 | ||
| 23b | ||
| 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 | ||
| 25b | ||
| 26a | ||
| 26b | ||
| 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 |
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| 28b | ||
| 29a | ||
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| 30a | ||
| 30b | ||
| 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 |
Megalorchestia
californiana
Protohyale sp.