Taken primarily from Kozloff, 1987, 1996 pp. 217, 497 (Copyright 1987, 1996, University of Washington Press. Used in this web page by permission of University of Washington Press)
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| Lower taxonomic level | Main Page | Alphabetic Index | Systematic Index | Glossary |
| 1a | Aperture oval, considerably higher than wide; periostracum generally with small ridges that diverge as they approach the edge of the aperture (associated with the solitary ascidians Styela gibsii, Pyura haustor, and Chelysoma productum) (Velutina plicatilis in key) | Velutina velutina |
| 1b | Aperture about as wide as high; periostracum without spiral ridges | Velutina prolongata |