Melinna Malmgren, 1865

Gunton, Laetitia M., Zhang, William, Kupriyanova, Elena K. & Hutchings, Pat A., 2023, New Species of Melinna (Melinnidae, Annelida) from the Australian Abyss with Comments on M. albicincta, M. cristata and M. elisabethae, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 125-154 : 130

Melinna Malmgren, 1865

Diagnosis (after Mackie & Pleijel, 1995). Melinnidae with 4 pairs of apinnate branchiae on segments 2–5. Single pair of postbranchial dorsal hooks on segment 3. Segments 4 to 7 forming dorsal depression, posteriorly delimited by transverse membranous fold. Eighteen pairs of thoracic chaetigers, segments 2–5 with neuropodia with slender acicular chaetae, subsequent neuropodia with uncini. Notopodia from segment 4 or 5, with capillary notochaetae. Four pairs of nephridia on segments 4–7. Abdomen with variable number of neuropodia with uncini. Pygidium lobulate, anal cirri absent.

Type species Sabellides cristata Sars, 1851 by monotypy.

Remarks. The above diagnosis is based on Mackie & Pleijel (1995), but is modified with regards to segment number, as Rouse et al. (2022) state that there is an achaetous segment (segment 1) before the first chaetiger (segment 2). While the branchiae arise from segments 2–4, they appear to arise from a dorsal ridge at the level of segments 2–3, and they exhibit varying levels of basal fusion. Nephridia are on segments 4–7. With regard to the segment on which the dorsal hooks appear we do not follow Holthe (1986), instead we follow Stiller et al. (2020) and Rouse et al. (2022) to indicate that they begin on segment 3.

Earlier descriptions of Melinna species can be quite confusing regarding the numbering of segments and chaetigers. Most authors of previous descriptions have failed to recognize or neglected the anterior achaetous segment behind the peristomium, while the anterior notopodia are small and ventrally displaced so may have been missed. While the definition of Mackie & Pleijel (1995) indicates that notopodia begin from segment 4 or 5, we cannot find any records of species with notopodia from segment 5, and the confusion in the literature about anterior segment numbering does not help. Table 3 lists the numbering of anterior segments which will facilitate the interpretation of earlier descriptions of species of Melinna as many lack the presence of an anterior achaetous segment.

We have also followed more recent papers in referring to segments by numbers and not by Roman numerals. Given the confusion of some species from northern Europe, including the type species of the genus Melinna , M. cristata , we have provided expanded descriptions and figures to supplement those provided by Mackie & Pleijel (1995).