Taken primarily from Kozloff, 1987, 1996 p154. (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 | Relatively large worms, length often exceeding 10 cm, width often exceeding 1 cm; not secreting tubes; posterior one-third of the body, behind the region bearing gills, without setae, and therefore resembling a teai; gills pinnate or bushy | 2 |
| 1b | Small worms, up to about 2.5 cm long and 0.5 mm wide; secreting membranous tubes coated with fine sand; gills and setae continuing nearly to the posterior end of the body, so that there is nothing that resembles a tail; gills consisting of 1-4 simple filaments | Branchiomaldane simplex |
| 2a | With several pairs of esophageal caeca, those of 1 pair being much longer than the others; neuropodia of more posterior gill-bearing segments not closely approaching the midventral line | 3 |
| 2b | With only 1 pair of esophageal caeca; these short; neuropodia of more posterior gill-bearing segments closely approaching the midventral line | Arenicola marina |
| 3a | Nephridiopores completely exposed; with 4-7 pairs of esophageal caeca; typically inhabiting muddy sand at the inner margins of bays | Abarenicola pacifica |
| 3b | Ventral portions of nephridiopores covered by a flap of skin; with 8 or more pairs of esophageal caeca; typically inhabiting rather clean sand at the mouths of bays or on beaches exposed to some wave action | 4 |
| 4a | Usually with 8-12 pairs of esophageal caeca; usually on beaches exposed to some wave action | Abarenicola claparedi subsp. oceanica |
| 4b | Usually with 12-19 pairs of esophageal caeca; usually near the mouths of sandy bays | Abarenicola claparedi subsp. vagabunda |