Note

Guide to the Coastal Marine Isopods of California

Richard Brusca, Vania R. Coelho, and Stefano Taiti

Table of Contents

Suborder Asellota

(Key references: Richardson, 1905; Menzies, 1951A, B, 1952; Menzies and Pettit, 1956; Menzies and Barnard, 1959; Kussakin, 1962A, B, 1988; George and Strömberg, 1968; Thistle, 1979; Wilson, 1994, 1997; Wilson and Wägele, 1994)

Asellotans are easily recognized by the following combination of features: uropods terminal and styliform; pleonites 4-5, and often pleonite 3, fused to pleotelson, creating an enlarged terminal piece; pleonite 1, 2, or 3 forming an operculum over the more posterior pleopods; male pleopods 2 with specialized copulatory apparatus consisting of an enlarged protopod, a geniculate (knee-like) endopod, and typically a well-muscled exopod; pereonites without coxal plates.

The Asellota are one of the most diverse groups of isopods, comprising about 25% of all marine species. They are most successful and diverse in the deep sea. Thirty-eight species of Asellota, in nine families, are known from California waters; eighteen (in four families) occur in California's intertidal region.

(figures 13-15, 16-20, 21-25, 26-30)

Key to Intertidal Species of Asellota

1. Eyes on lateral, peduncle-like projections; terminal article (dactylus) of pereopods 2-7 with two claws. 2
- Eyes (if present) dorsolateral on head, not pedunculate; dactylus of pereopods 2-7 with two or three claws. 3
2. Pleotelson somewhat pear-shaped; uropods greatly reduced, barely visible dorsally. Munnidae 4
- Pleotelson broad, shieldlike; uropods short but clearly visible in dorsal view.
(Only one species of this family, Santia hirsuta, is known from California).
Santiidae
3. Both pairs of antennae small, flagella lacking or rudimentary; antenna articles of peduncle dilated; uropods short, inserted in subterminal excavations of pleotelson, not extending much beyond its posterior margin, if at all. Joeropsididae 7
- Antennae, long with multiarticulate flagella (caution: often broken off); antenna articles of peduncle not dilated; uropods well developed. Janiridae 8
4. Uropods minute, without serrate distal margin; male first pleopods with apices tapering to tip. Uromunna ubiquita
- Uropods not minute, with serrate distal margin; male first pleopods with apices laterally expanded. 5
5. Uropods without large acute spinelike protuberances on distal margin; dentate suburopodal shelf visible in dorsal view. Munna halei
- Uropods with large acute spinelike protuberances on distal margin; no dentate suburopodal shelf visible in dorsal view. 6
6. Pleotelson broad (length about 0.8 times width); body stout (length about 1.7 times width). Munna stephenseni
- Pleotelson narrow (length about 1.6 times width); body relatively elongate (length about 2.6 times width). Munna chromatocephala
7. Pleotelson with five to seven spines on each lateral border. Joeropsis dubia dubia
- Pleotelson with three spines on each lateral border. Joeropsis dubia paucispinis
8. Eyes lacking. 9
- Eyes present. 10
9. Body not elongate, length less than 3 times width; not a minute interstitial species. Caecijaera horvathi
- Body elongate, length about 6 times width; minute (< 2 mm long) interstitial species. Caecianiropsis psammophila
10. Propodus (next to last article) of first pereopod with conspicuous serrated margin on proximal third of ventral margin; basal three articles of maxillipedal palp as wide as endite. Janiralata 11
- Propodus of first pereopod with proximal third of inferior border smooth; maxillipedal palp with second and third articles much wider than endite. Ianiropsis 12
11. Pleotelson with distinct, medially curved, spinelike posterolateral angles. Janiralata occidentalis
- Pleotelson with posterolateral angles evenly curved, lacking distinct angles or spinelike processes. Janiralata davisi
12. Lateral borders of pleotelson with spinelike serrations. 13
- Lateral borders of pleotelson spineless (fine setae may be present). 15
13. Pleotelson with four to seven spinelike serrations on each side; lateral apices of first male pleopod not directed abruptly posteriorly. Ianiropsis analoga
- Pleotelson with two to three spinelike serrations on each side; lateral apices of first male pleopod directed abruptly posteriorly. 14
14. Pleotelson with two spinelike serrations on each side. Ianiropsis epilittoralis
- Pleotelson with three spinelike serrations on each side. Ianiropsis tridens
15. Uropods half or less length of pleotelson. 16
- Uropods considerably exceeding half pleotelson length. 17
16. Pleotelson with distinct posterolateral angles lateral to uropod insertions. Ianiropsis derjugini
- Pleotelson lacking posterolateral angles lateral to uropod insertions. Ianiropsis minuta
17. Uropods exceeding length of pleotelson; lateral apices of first male pleopod bifurcate. Ianiropsis montereyensis
- Uropods not exceeding pleotelson length; lateral apices of first male pleopod not bifurcate. Ianiropsis kincaidi
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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