Key to Order Cephalaspidea

[Cephalaspideans have a shield-shaped head (cephalic shield) which is often used to plow through the substrate.  Nearly all also have an internal or external shell, though one pelagic family has no shell.  None have rhinophores, though some have rolled extensions of mantle on the head that may look somewhat like rhinophores.]

Taken primarily from  Kozloff, 1987, 1996  p. 237 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

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1a	Shell either not visible externally or too small to accommodate the animal when it retracts	2
1b	Shell large enough tot accommodate the animal when it retracts	7
2a	Shell visible externally, but partly covered by the mantle	3
2b	Shell not visible externally	4
3a	Width of the aperture, at the level where the shell is broadest, slightly more than one-third the width of the shell; height up to about 2 cm	Haminoea vesicula
3b	Width of the aperture, at the level where the shell is broadest, about two-thirds the width of the shell; height up to about 1.5 cm	Haminoea virescens
4a	Body completely dark brownish purple or blue-black	Melanochlamys diomedea
4b	Body not completely dark brownish purple or blue-black	5
5a	Body light to dark reddish brown, with numerous yellow spots; with yellow lines on the edge of the cephalic shield, foot, and borders of the mantle flaps	Aglaja ocelligera
5b	Body not reddish brown; and without yellow spots; without yellow lines on the cephalic shield, foot, and mantle flaps	6
6a	Body pale yellow, with scattered clusters of small red dots	Gastropteron pacificum
6b	Body pale yellow to white, without clusters of red dots	Philine bakeri
7a
7b
8a
8b
9a
9b
10a
10b
11a
11b
12a
12b