1a.

Terrestrial species. First pair of antennae inconspicuous, rudimentary and not 1/4 as long as the second pair; abdominal segments distinct.

[2]

 1b.

Aquatic species. First pair of antennae plainly visible and at least 1/4 long as second pair; posterior segments of abdomen fused.

[17]

2a.

Uropods not extending beyond the terminal abdominal segment; capable of rolling into a ball

[3]

2b. 

Uropods extending beyond the terminal abdominal segment; not capable ofrolling into a ball (except Cylisticus convexus)

[5]

3a.

Median lobe of head extending dorsally and interiorly as a flat, truncate horn, with a deep groove in back of the horn.

Armadillidium nasatum

3b.

No horn or groove extending from median lobe of head.

[4]

4a.

Telson hour glass shaped, not triangular in form; all five pairs of pleopods bear pseudotracheae.

Venezillo evergladensis 

4b.

Telson triangular, not hour glass shaped; First two pairs of pleopods bear pseudotracheae, very common in sunny areas under boards and foundations.

Armadillidium vulgare 

5a.

Flagellum of second antennae with 2 or 3 articles, and adults larger than 6mm.

[6]

5b.

Flagellum of second antennae with 4 to many articles, those with less than 5 articles, less than 6mm in length, those with 10 or more articles may be up to 9mm in length.

[11]

6a.

Flagellum of second antennae with 3 articles, prominent lobes on either side of head.

Oniscus asellus

6b.

Flagellum of second antennae with 2 articles.

[7]

7a.

Abdomen abruptly narrower than the thorax; antennae usually conspicuously banded with white at the joints.

Porcellionides pruinosus

7b.

Abdomen not abruptly narrower than the thorax; banding of antennae absent or inconspicuous.

[8]

8a.

Tergites 3, 4, and 5 distinctly narrower than the other tergites, deep triangular notches between the lateral expansions of tergites 2 and 3, 3 and 4, and 4 and 5; median lobe of head acute; outline of body in cross section strongly arched, capable of rolling into a ball.

Cylisticus convexus

8b.

Tergites 3, 4, and 5 the same width as other tergites, all notches between lateral expansions of tergites have parallel sides; median lobe of head not acute; outline of body in cross section, not strongly arched; not capable of rolling into a ball. 

[9]

9a.

All five pairs of pleopods with pseudotracheae (not visible in 70% alcohol) and appear opaque white in color, posterior margin of first segment of pereon strongly curved.

Trachelipus rathkei

9b.

First two pairs of pleopods with pseudotracheae (not visible in 70% alcohol) and only first two pairs appear opaque white the rest appear translucent; posterior margin of first segment of the pereon more or less straight.

[10]

10a.

Antennal segments 2-4 strongly carinate, dorsal carinae of segments 2 and 3 produced into strong spines; head and body with conspicuous tubercles; median head lobe broad and truncate; posterio-lateral corner of first tergite produced posteriorly head dark gray; body yellowish gray with brown patches and a row of light spots on either side of mid-dorsal line.

Porcellio spinicornis

10b.

Antennal segments 2-4 not strongly carinate, no spines; head and body with conspicuous tubercles; median head lobe triangular posterio-lateral corner of first tergite produced posteriorly; head and body dark gray.

Porcellio scaber

10c.

Antennal segments 2-4 not strongly carinate, no spines; head and body smooth without conspicuous tubercles median head lobe triangular; posterio-lateral corner of first tergite not produced posteriorly; head and body light gray with tiny light spots on the head and with a cluster of light spots on each side of the tergites.

Porcellio laevis

11a.

Flagellum of second antennae with 10 or more distinct segments; inner branch of uropods longer than outer branch.

Ligidium elrodii

11b.

Flagellum of second antenna with less than 5 articles; inner branch of uropods shorter than or equal to the outer branch.

[12]

12a.

Dorsal surface with pronounced longitudinal ridges, less than 4mm in length, white, slow moving and easily mistaken for juveniles of other species.

Haplophthalmus danicus

12b.

Dorsal surface without pronounced longitudinal ridges; dorsal surface smooth or with bumps or spines.

[13]

13a. .

Dorsal surface appears smooth

[14]

13b.

Dorsal surface appears rough.

[15]

14a.

Three ocelli; color pinkish. 

Trichoniscus pusillus

14b.

One ocelli; deep purple color.

Hyloniscus riparius

15a.

Body yellowish-white with gut apparent through the translucent integument; eyes with one ocellus and flagellum with two articles.

Trichorhina tomentosa

15b.

Body rose or pink in color, or completely white.

[16]

16a.

Eyes with one tiny ocellus, body white, antennae short.

Miktoniscus medcofi 

16b.

Eyes with one large ocellus, body pink or rose-red color (occasionally white), with a double yellow longitudinal stripe, antennae long.

Androniscus dentiger

17a.

Lateral margins of head expanded and with conspicuous cleft, frontal margin with carina projection between basal segments of second antenna.

Lirceus spp.

17b.

Lateral margins of head not expanded, not notched or cleft, no frontal carina.

Caecidotea spp.