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 |
