Taken primarily from Kozloff, 1987, 1996 p. 341 (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 | Protandric hermaphrodites in which the last larval stage (cryptoniscus), after functioning as a free-living male, becomes transformed into a parasitic female; this loses all or most appendages and becomes hypertrophied in such a way that the body has 2 to several lobes (section Cryptoniscina) | 2 |
| 1b | Sexes separate and both parasitic, the male being much smaller and more isopodlike than the female (there is usually a male closely associated with each female)(section Bopyrina) | 3 |
| 2a | Parasitic in barnacles (Balanus glandula, Chthamalus dalli); adult female conserving only the cephalon and some of the more anterior segments of the cryptoniscus, the rest of the body consisting of several lobes; basal article of antenna 1 and coxal plates of male toothed | Hemioniscus balani |
| 2b | Hyperparasitic on the rhizocephalans Peltogaster paguri and Peltogasterella gracilis, which are parasites of hermit crabs; adult female, after a period of completely internal parasitism, becomes constricted into 2 nearly spherical portions, the anterior one being buried in the host, the posterior one being external; basal article of antenna 1 and coxal plates of male smooth | Liriopsis pygmaea |
| 3a | Endoparasitic (not visible externally) in the visceral cavity of the crabs Hemigrapsus oregonensis and H. nudus (body of female bent into a V, the cephalon divided into 2 hemispheres, the pereopods reduced to stubs, the pleon with 5 pairs of wrinkled lateral lobes; male with only 6 pairs of pereopods | Portunion conformis |
| 3b | Ectoparasitic, either located in the branchial chamber of the crustacean host, attached to the dorsal surface, or attached to the underside of the abdomen | 4 |
| 4a | Attached to the dorsal surface of the host, which is either a decapod or mysid (female asymmetrical, with only 5 pairs of pereopods, these grouped around the oral region, and with most of the posterolateral portion covered by a pair of enlarged oostegites) | 5 |
| 4b | In the branchial chamber or under the abdomen of decapod crustaceans | 7 |
| 5a | Parasitic on the shrimp Pasiphaea pacifica; female with all pereonites and pleonites fused or so nearly fused that they are indistinct (male with pleonites fused) | Holophryxus alaskensis |
| 5b | Parasitic on mysids (possibly other planktonic crustaceans); female with at least some pereonites and pleonites distnct dorsally | 6 |
| 6a | Female with all pereonites and pleonites distinct dorsally (male with all pleonites distinct)(parasitic on the mysid Eucopia australis, collected in very deep water, and perhaps associated with other mysids) | Arthophryxus beringanus |
| 6b | Female with pereonites 1-3 and pleonites distinct dorsally (type specimen found in a collection of mysids from very deep water) | Prophryxus alascensis |
| 7a | Female symmetrical or only slightly asymmetrical, with all pereonites distinct, and with 5 pairs of nearly equal oostegites; female with 7 pars of pereopods and generally with 6 distinct pleonites | 8 |
| 7b | Abdominal parasites of shrimps in the genera Lebbeus, Spirontocaris, Eualus, and Heptacarpus; female very asymmetrical, with pereonites not completely separated dorsally; on the swollen side, the oostegites are large and form a closed brood pouch, and generally only pereopod 1 persists; on the nearly straight side, oostegites 2-4 are reduced to small plates and there are 7 pereopods; pleon with 5 pleonites, 4 pairs of leaflike lateral plates, and small uniramous pleopods; male with fused pleonites | Hemiarthrus abdominalis |
| 8a | Parasitic on the underside of the abdomen of the thalassinid Upogebia pugettensis (pleon of female without lateral plates but with well developed biramous pleopods and uniramous uropods; pleon of male with lateral plates) | Phyllodurus abdominalis |
| 8b | Parasitic in the branchial chamber of thalassinids, hermit crabs, galatheids, and shrimps of the families Crangonidae, Hippolytidae, and Pandalidae | 9 |
| 9a | On the thalassinid Neotrypaea californiensis; pleon of female with 6 pairs of lateral plates which are long and thin and whose posterior margins are fringed by slender outgrowths (brood pouch of female closed; pleon of male with elongated lateral plates but these are not fringed) | Ione cornuta |
| 9b | On hermit crabs, galatheids, or shrimps; pleon either with 5 pairs of lateral plates, with rudimentary plates, or without any plates | 10 |
| 10a | Pleon with 5 pairs of lamellar and smooth lateral plates; brood pouch closed; pleonites of male fused or not fused | 11 |
| 10b | Pleon either without lateral plates or with rudimentary plates; brood pouch open; pleonites of male fused (photo) | 13 |
| 11a | On the galatheid Munida quadrispina (see also choice 12b); female with 2 pars of lateral lamellae on the posteroventral border of the cephalon; coxal plates of the pereon well developed; pleopods visible when the animal is viewed from the dorsal side; pleotelson elongated and swollen near its tip and bearing biramous uropods; pleonites of male fused | Munidum parvum |
| 11b | Female with 1 pair of lateral lamellae on the posteroventral border of the cephalon; pereon without coxal plates; pleopods not visible when the animal is viewed from the dorsal side; pleotelson short, rounded or truncate at its tip and bearing uniramous uropods; pleonites of male not fused | 12 |
| 12a | On hermit crabs; endopodites of pleopods of female much longer than the exopodites, their surfaces more or less tuberculated | Pseudione giardi |
| 12b | On the galatheid Munida quadrispina (see also choice 11a); endopodites of pleopods of female only slightly longer than the exopodites, their surfaces smooth | Pseudione galacanthae |
| 13a | On shrimps of the family Crangonidae (Crangon, Argis); female with well developed biramous pleopods and uniramous uropods | Argeia pugettensis |
| 13b | On shrimps of the families Hippolytidae (Spirontocaris, Eualus, Heptacarpus) and Pandalidae; female either without pleopods or with pleopods reduced to tubercles, and without uropods | Bopyroides hippolytes |