Suborder Oniscidea (Terrestrial Isopods)
(Key references: Van Name, 1936, 1940, 1942; Mulaik and Mulaik, 1942; Schultz, 1970, 1972, 1984; Garthwaite et al., 1985, 1992; Taiti and Ferrara, 1986; Garthwaite 1988, 1992; Leistikow and Wägele, 1999)
The Oniscidea (formerly "Oniscoidea") are the only group of crustaceans fully adapted to live on land. They are distinguished by: extreme reduction (1-3 articles) of the antennules; endopods of male pleopod 1 and/or 2 elongate, styliform, specialised as a copulatory apparatus; and, presence of a complex water-conducting system (Hoese, 1981, 1982A). In species best adapted to terrestrial life (e.g. Porcellionidae, Armadillidiidae, Armadillidae) the exopods of pleopods 1-2 or 1-5 bear respiratory structures, called pseudotracheae or "lungs." Terrestrial isopods possess general body morphologies correlated to their ecological strategies and behaviour, and can be grouped in three main categories (Schmalfuss, 1984): the runners, with an elongate, slightly convex body and long pereopods; the clingers, with a flat broad body and short strong pereopods; and the rollers, with a highly convex body able to roll up into a ball (pillbugs).
With over 4,000 described species, Oniscidea is the largest isopod suborder. They occur in any kind of terrestrial habitat, from littoral to high mountains, from forests to deserts. In California twenty-two species in nine families occur in littoral biotopes, but only species of Ligia, Tylos, Littorophiloscia and the Scyphacidae are typical inhabitants of the eulittoral zone.
(figures 94-98, 99-103, 104-109, 110-115)Key to Littoral Species of Oniscidea
The key and species list include all the strictly littoral oniscid species, some of which have wide distributions or have been introduced to North America, and some of which occur on both coasts.
| 1. | Uropods ventral, hidden by pleotelson and not visible in dorsal view of the animal. | Tylidae: Tylos punctatus |
| - | Uropods terminal, clearly visible in dorsal view. | 2 |
| 2. | Flagellum of antenna with more than ten articles; eye with more than fifty ommatidia. | Ligiidae 3 |
| - | Flagellum of antenna with two to seven articles; eye with less than thirty ommatidia, or eyes absent. | 6 |
| 3. | Pleotelson with posterolateral projections; uropod with insertion of exopod and endopod at the same level. | Ligia 4 |
| - | Pleotelson without posterolateral projections; uropod with insertion of exopod distinctly proximal to that of endopod. | Ligidium 5 |
| 4. | Distance between eyes equal to length of one eye; peduncle of uropod several times longer than broad. | Ligia occidentalis |
| - | Distance between eyes equal to twice length of one eye; peduncle of uropod about as broad as long. | Ligia pallasii |
| 5. |
Surface of body smooth and shiny; eye ovoid, far from posterior margin of cephalon; endopod of second male pleopod with rounded apex. |
Ligidium gracile |
| - | Surface of body rough with sparse scales; eye subtriangular, almost reaching posterior margin of cephalon; endopod of second male pleopod with pointed apex. | Ligidium latum |
| 6. | Flagellum of antenna tapering to a point, with articles distinguishable only in micropreparations. | Trichoniscidae 7 |
| - | Flagellum of antenna with two to four clearly distinct articles. | 8 |
| 7. | Flagellum of antenna of three minute articles; eye consisting of a single black ommatidium. | Haplophthalmus danicus |
| - | Flagellum of antenna of six or seven minute articles; eyes lacking. | Brackenridgia heroldi |
| 8. | Flagellum of antenna with four articles. | Scyphacidae (part) 9 |
| - | Flagellum of antenna with two or three articles. | 12 |
| 9. | Uropods with peduncle subcylindrical, exopod inserted terminally and distinctly protruding from body outline. | Detonella papillicornis |
| - | Uropods with peduncle lamellar, exopod inserted on medial margin and not protruding from body outline. | 10 |
| 10. | Body markedly convex and capable of rolling into a ball; cephalon with median lobe truncate. | Armadilloniscus lindahli |
| - | Body not markedly convex and incapable of rolling into a ball; cephalon with median lobe pointed. | 11 |
| 11. | Penultimate article of peduncle of antenna with spurlike process on lateral margin; dorsal body surface of adult female covered with conspicuous tubercles; seventh male pereopod with a strong spine caudally directed and a rounded lobe on carpus. | Armadilloniscus coronacapitalis |
| - | Penultimate article of peduncle of antenna without spurlike process on lateral margin; dorsal body surface rough with low, rounded tubercles; seventh male pereopod without spine and lobe on carpus. | Armadilloniscus holmesi |
| 12. | Flagellum of antenna with three articles. | 13 |
| - | Flagellum of antenna with two articles. | 15 |
| 13. | Cephalon with cone-shaped lateral lobes protruding frontwards; pleon not abruptly narrower than pereon. | Scyphacidae (part): Alloniscus 14 |
| - | Cephalon without cone-shaped lateral lobes; pleon abruptly narrower than pereon. | Philosciidae: Littorophiloscia richardsonae |
| 14. | Peduncle of uropod with posterolateral margin produced, rounded. | Alloniscus mirabilis |
| - | Peduncle of uropod with posterolateral margin not produced, oblique. | Alloniscus perconvexus |
| 15. | Body moderately convex, unable to roll into a ball; uropod subcylindrical, distictly protruding backwards compared with pleotelson tip. | 16 |
| - | Body very convex, able to roll into a ball; uropod flattened, reaching pleotelson tip. | 21 |
| 16. | Dorsal surface of body covered with fine but distinct scales; first article of flagellum of antenna distinctly shorter than second. | Platyarthridae 17 |
| - | Dorsal surface of body with no distinctly visible scales; first article of flagellum of antenna as long or longer than second. | Porcellionidae 18 |
| 17. | Eyes with about ten ommatidia; pleotelson tip reaching distal margin of uropodal peduncle. | Niambia capensis |
| - | Eyes lacking; pleotelson much shorter than uropodal peduncle. | Platyarthrus aiasensis |
| 18. | Cephalon with a V-shaped suprantennal line; pereonite 1 with regularly convex posterior margin. | Porcellionides floria |
| - | Cephalon with no suprantennal line; pereonite 1 with posterior margin concave at sides. | Porcellio 19 |
| 19. | Pleotelson with a rounded apex. | Porcellio dilatatus |
| - | Pleotelson with an acute apex. | 20 |
| 20. | Dorsal surface of body granulated; posterior margin of first pereonite distinctly concave at sides. | Porcellio scaber |
| - | Dorsal surface of body smooth; posterior margin of first pereonite slightly concave at sides. | Porcellio laevis |
| 21. | Cephalon with a triangular frontal scutellum; eyes with twenty to twenty-five ommatidia; posterolateral corner of first pereonite entire; uropod with large flattened exopod filling gap between pleotelson and fifth pleonite. | Armadillidiidae: Armadillidium vulgare |
| - | Cephalon with no triangular frontal scutellum; eyes with four to eight ommatidia; posterolateral corner of first pereonite cleft; uropod with large flattened peduncle filling gap between pleotelson and fifth pleonite, exopod minute inserted dorsally. | Armadillidae: Venezillo microphthalmus |
