Distinguishing the genera Apomatus Philippi, 1844 and Protula Risso, 1826 (Polychaeta: Serpulidae). A further Plea for a Methodical approach to Serpulid Taxonomy

Ventral thoracic bloodvessel-patterns were defined in a random sample of 152 living specimens of the Apomatus/Protula- complex. Two main patterns and a derived one could be recognized. Eight characters, often used in Serpulid taxonomy and retraceable in preserved material, were determined too: e.g. presence or absence of an operculum and pattern of thoracic setae. These parameters were correlated to the vascular patterns. It was shown that (a) all operculate specimens possess a vascular system of one main pattern; 86% of those closely studied have "Apomatus-setae" at least from setiger 4 onwards; all have radioles with paired rows of compound eyespots. (b) The non-operculate specimens generally possess the other main vascular pattern; the thorax often has limbate setae throughout (56°/o) or "Apomatus-setae" in posterior segments only (31%); 70% show paired rows of simple eyespots. (c) The depths of occurrence of operculate worms differ significantly from those of nonoperculate specimens, (d) The derived vascular pattern occurs in five ou