Note

Guide to the Coastal Marine Isopods of California

Richard Brusca, Vania R. Coelho, and Stefano Taiti

Table of Contents

Key to the Suborders of Isopoda

1. With five pairs of pereopods (thoracomere 2 entirely fused to cephalon, with its appendages modified as pylopods and functioning as a second pair of maxillipeds; thoracomere 8 reduced, without legs); adult males with mandibles grossly enlarged, forceps-like, projecting in front of head; adult females without mandibles. Gnathiidea
- With seven pairs of pereopods (thoracomere 2 not fused with cephalon, with one pair of maxillipeds and seven pairs of pereopods); males without projecting, forceps-like mandibles; females with mandibles. 2
2. Adults obligate parasites on other crustaceans; bilateral symmetry reduced or lost in females; male a small bilaterally symmetrical symbiont living on the body of the female; antennae (antennae 2) vestigial; antennules (antennae 1) reduced to three or fewer articles; without maxillules (maxillae 1). Epicaridea
- Not obligate parasites on other crustaceans; bilateral symmetry retained in both sexes; male not as above; antennae never vestigial; antennules variable; usually with maxillules 3
3. Body cylindrical or tubular in cross-section, but often appearing laterally compressed (amphipod-like) due to ventrally elongated abdominal pleura; with distinct row of filter setae along medial margin of maxilla (maxilla 2); penes located on coxae of male pereopod 7; apex of pleotelson curves dorsally; pleonite 5 elongate, markedly longer than any other pleonites (known only from Southern Hemisphere and India). Phreatoicidea
- Body variable, but not appearing laterally compressed as above; without row of filter setae along medial margin of maxilla; penes on sternum of male pereonite 7 (or on sternum of pleonite 1); apex of pleotelson does not curve dorsally; pleonite 5 rarely elongate (markedly longer than other pleonites only in Limnoriidae) 4
4. Terrestrial; antennules vestigial, minute; pleon always of 5 free pleonites, plus the pleotelson. Oniscidea
- Aquatic; antennules normal, or if reduced not minute; pleon variable, with or without fused pleonites. 5
5. Anus and articulating base of uropods positioned terminally (or subterminally) on pleotelson; uropods styliform. 6
- Anus and articulating base of uropods positioned at base of pleotelson; uropods flattened. 8
6. With lateral coxal plates; antenna peduncle 5-articulate; maxillipeds without coupling setae; penes of male arise from articulation between pereonite 7 and pleonite 1; mandible without palp; pleopodal exopods broad and opercular to the thick tumescent endopods; female pleopod 1 present. Calabozoidea
- Without lateral coxal plates (pereopodal coxae small); antenna peduncle 6-articulate; maxillipeds with or without coupling setae; penes of male arise on sternum of pereonite 7; mandible with palp; pleopods not as above; female pleopod 1 absent. 7
7. Minute, usually less than 3 mm long; long and slender, length about 6 times width; antenna peduncle without a scale; antennule reduced, peduncle indistinguishable from flagellum; maxilliped without coupling setae on endite; female pleopod 2 biramous; male pleopod 2 endopod not geniculate; interstitial. Microcerberidea
- Rarely minute, usually greater than 4 mm long; body not elongate (length less than 6 times width); antenna peduncle usually with a scale; antennule rarely reduced, peduncle and flagellum distinct; maxilliped almost always with coupling setae on endite; female pleopod 2 uniramous; male pleopod 2 endopod large and geniculate; rarely interstitial. Asellota
8. Body elongate, length usually more than 6 times width; uropodal exopod curving dorsally over pleotelson; coxae of maxillipeds fused to head (i.e. not freely articulating); mandible with lamina dentata in lieu of spine row and lacinia mobilis (lamina dentata, spine row and lacinia mobilis lacking in Paranthuridae); maxillule an elongate stylet with apical hooks or serrate margin; maxilla vestigial and fused with paragnath (or absent). Anthuridea
- Body not markedly elongate, length usually less than 4 times width; uropodal exopod not curving over pleotelson; coxae of maxillipeds not fused to head; mandible without lamina dentata; maxillule variable; maxilla well developed, never fused with paragnath. 9
9. Uropods modified as a pair of ventral opercula covering the entire pleopodal chamber; males with penes arising on sternum of pleonite 1, or on articulation between pereonite 7 and pleonite 1; mandibular molar process a stout, flattened grinding structure. Valvifera
- Uropods not modified as ventral opercula covering pleopods, but positioned laterally; males with penes arising on sternum of pereonite 7; mandibular molar process usually a thin, bladelike, cutting structure, or absent (flattened only in Sphaeromatidae). Flabellifera
About This Page

Richard Brusca
Arizona-Sonora Desert Museum, Tucson, Arizona, USA

Vania R. Coelho
Dominican University of California, San Rafael, California, USA

Stefano Taiti

Correspondence regarding this page should be directed to Richard Brusca at and Vania R. Coelho at

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