Raphidrilus Monticelli, 1910a

Magalhães, Wagner F., Bailey, Julie H., Brock, - & Davenport, Jennifer S., 2011, On the genus Raphidrilus Monticelli, 1910 (Polychaeta: Ctenodrilidae) with description of two new species, Zootaxa 2804, pp. 1-14 : 2-3

Genus Raphidrilus Monticelli, 1910a

Type species: Raphidrilus nemasoma Monticelli, 1910a

Type locality. Gulf of Naples in the Mediterranean Sea.

Diagnosis (emended after Monticelli, 1910a). Raphidrilinae with peristomium obviously delimited from prostomium and first achaetous segment both dorsally and ventrally; nuchal organs shallow depressions with cilia; 1–2 dorsally biannulated achaetous segments between peristomium and first chaetiger; posterior end indistinct from posterior segments. Heart body always present from chaetiger 4. Serrate capillaries throughout; more abundant anteriorly. Reproduction sexual and asexual.

Remarks. The presence of at least one dorsally biannulated achaetous segment between the peristomium and chaetiger 1 is constant in R. harperi sp. nov., R. hawaiiensis sp. nov., and R. nemasoma , and has not been described from other ctenodrilid species.

Dean (1995) points out that the origin of the heart body should not be used as a diagnostic character for the genera Raphidrilus and Raricirrus , because in Raricirrus variabilis it begins at chaetiger 4 (4–6) as well as in all Raphidrilus species. The position and extent of the heart body in the three described species of Raphidrilus seems to be a species level character given that the heart body begins at chaetiger 4 in all three but differs in how the heart body projects anteriorly or posteriorly to one or more chaetigers.

Monticelli’s description of Raphidrilus nemasoma reports a male phase with distinctive smooth curved spines in segments 5–8. All incomplete specimens from the Mediterranean that were examined under SEM do not bear such spines. Petersen and George (1991) pointed out that the possible undescribed Raphidrilus described by Qian and Chia (1989) as having short genital spines, may in fact have normal neurochaetae. Because such genital spines have not been found in any specimen examined of R. harperi sp. nov., or R. hawaiiensis sp. nov., we believe this feature should be species specific (if truly present), rather than being generic in diagnosis.

The morphological characters useful in differentiating species within the genus Raphidrilus , not in order of importance, are: 1) Shape of prostomium; 2) Presence/distribution of short sensory cilia in addition to the nuchal organs on the prostomium; 3) Number of dorsally biannulated anterior achaetous segments; 4) Shape of thoracic and abdominal segments; 5) Position and extent of the heart body; 6) General shape of the digestive tube; 7) Presence of sensorial tufts on parapodia ( Qian & Chia 1989); 8) Number, length and distribution throughout the body of the capillary chaetae; 9) Arrangement of the capillary fibrils seen under SEM; and 10) Position of the anal aperture and presence of fields of cilia.