| 1a |
Flagellum
of antenna 2 with more than 10 articles
(but there may be as few as 6 articles
in immature specimens) (picture);
up to about 2.5 cm long; found in rock crevices (and sometimes on
pilings)
just above the high tide line |
2 |
| 1b |
Flagellum
of antenna 2 with not more than 4 articles;
less than 2 cm long; not typically found in rock crevices (generally on
uppermost portions of sancy beaches or truly terrestrial) |
3 |
| 2a |
Basal article
of uropod
about as broad as long (picture) |
Ligia
(Ligia)
pallasii |
| 2b |
Basal article
of uropod
several times as long as broad (rarely found as far north as Oregon) |
Ligia
(Megaligia)
occidentalis |
| 3a |
Flagellum
of antenna 2 with 3 or 4 articles;
tracheal system absent; under debris on sandy beaches, near uppermost
limits
of intertidal zone |
5 |
| 3b |
Flagellum
of antenna 2 with 2 articles;
tracheal system present in
exopodites
of pleopods
1 and 2; truly terrestrial, though occasionally found close to the
uppermost
limits of the intertidal zone |
4 |
| 4a |
Capable of rolling up into a ball; antenna 2 not
extending posteriorly
beyond pereonite
2; pleotelson
blunt |
Armadillidium vulgare |
| 4b |
Not capable of rolling up into a ball; antenna 2 not
extending posteriorly
beyond pereonite
2; pleotelson
pointed |
Porcellioscaber |
| 5a |
Flagellum
of antenna 2 with 3 articles |
6 |
| 5b |
Flagellum
of antenna 2 with 4 articles |
7 |
| 6a |
Pleonites
becoming gradually narrower than the pereonites;
cephalon
with large and tuberculatemedian
and anterolateral lobes; antenna 2 not extending beyond pereonite
2 |
Alloniscus perconvexus |
| 6b |
Pleonites
becoming abruptly narrower than the pereonites;
cephalon
rounded in front and with only small lateral lobes, if any; antenna 2
long,
extending beyond pereonite
2 |
Littorophiloscia richardsonae |
| 7a |
Anterior margin of cephalon
deeply 3-lobed, the median
lobe forming a rostrum;
basal article
of uropod
expanded, forming a large lobe lateral to the endopodite
and nearly reaching the distal tip of the latter |
Armadilloniscus holmesi |
| 7b |
Anterior margin of cephalon
2-lobed, without a rostrumlikemedian
lobe; basal article
of uropod
not expanded, the endopodite
inserted upon it in a posterolateral position |
Detonella papillicornis |
