Raphidrilus nemasoma 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 : 4-5

Raphidrilus nemasoma Monticelli, 1910a

Figure 1 (A–D)

Raphidrilus nemasoma Monticelli, 1910a : p. 61–64.

Raphidrilus nemasoma ; Monticelli, 1910b: p. 403–406, pls. 12–13; Banse, 1959a: p. 307; possibly Banse, 1959b: p. 170–171, fig. 2; possibly Bellan, 1964; not Harris, 1971: p. 706, fig. 14; Katzmann, 1972: p. 136; not Qian & Chia, 1989: p. 2350, figs. 1–18.

Ctenodrilus branchiatus Sokolow, 1911a : p. 548–565, plates XXVII–XXIX.

Material examined. Croatia: Vrsar Harbor, northern Adriatic Sea, 45°08,989ʹ N 13°35,776ʹ E, collected from the thallus of Caulerpa racemosa (Forsskål) J. Agardh , coll. Barbara Mikac, 08/12/2008 (9 anterior fragments mounted on stub, USNM 1150464).

Description. Small and incomplete specimens, 1–2.5 mm long, 0.05–0.1 mm wide with 5–11 anterior chaetigers. First four chaetigers (thorax) wider than long; abdominal chaetigers twice longer than wide with sub–annulations.

Prostomium short, broadly round; peristomium single achaetous annulation followed by one dorsally biannulated achaetous segment ( Fig. 1 A, B). Parapodia with serrated capillaries throughout ( Fig. 1 C, D). Anterior chaetigers with 4 serrated capillaries in each noto– and neuropodia; number of chaetae reduces from chaetiger 5–6 to 1– 2 serrated capillaries in posterior chaetigers. Distance between the insertion point of two capillary fibrils along the capillary chaetae approximately the same as the width of a single fibril ( Fig. 1 C, D). Branchial filaments arising posterodorsal to notochaetae. Posterior end and pygidium not observed.

Distribution. Raphidrilus nemasoma seems to be widely distributed in the Ligurian and Tyrrhenian seas ( Castelli et al. 1995) and the northern Adriatic Sea.

Remarks. The specimens analyzed from the northern Adriatic Sea agree well with the description of R. nemasoma by Monticelli (1910a, b). Monticelli (1910b) reported an achaetous segment before chaetiger 1, but referred to it as the peristomium; however, SEM analysis of R. nemasoma specimens newly collected showed an additional achaetous segment posterior to the peristomium. The dorsal distinction between prostomium and peristomium, however, is not easily seen using light microscopy, even at 1000x magnification.

The type series of R. nemasoma are believed to be lost or never kept (see discussion in Petersen & George 1991) but the specimens newly collected from the northern Adriatic Sea are not well enough preserved to be assigned as neotypes and were not collected near the type locality (Naples Gulf, Italy). More complete and well preserved specimens are necessary to better assess the external morphology of this species, even though detailed descriptions of the external morphology and internal anatomy are available in Monticelli (1910b) and Sokolow (1911a).

Figures

FIGURE 1. SEM of Raphidrilus nemasoma showing: A, anterior end in lateral view; B, base of ventral proboscis; C, D, serrate capillaries.