Erseia oligochaeta, Nygren, Arne, Sundkvist, Tobias, Mikac, Barbara & Pleijel, Fredrik, 2010

Nygren, Arne, Sundkvist, Tobias, Mikac, Barbara & Pleijel, Fredrik, 2010, Two new and two poorly known autolytines (Polychaeta: Syllidae) from Madeira and the Mediterranean Sea, Zootaxa 2640, pp. 35-52 : 42-44

Erseia oligochaeta , new genus, new species

( Fig 2 A–D)

Material examined. Holotype. Croatia, Istria, 2 km west of Rovinj, 45°05.220'N 13°36.517'E, 27 m, sponges, hydroids, and Holothuria sp., Agassiz trawl, 17 Sept 2008, preserved in alcohol ( GNM Polychaeta 13180). Paratypes. Same locality as holotype, four specimens preserved in formalin ( GNM Polychaeta 13181– 13184), two specimens preserved in alcohol ( GNM Polychaeta 13185, 13186), seven specimens preserved on slides ( GNM Polychaeta 13187a–13189a, 13190–13193), of which five rear ends preserved in alcohol, of which two are used up for DNA extraction ( GNM Polychaeta 13187b–13189b). Other material. Same locality as holotype, two specimens preserved in alcohol, used up for DNA extraction, two specimens preserved on slides, rear ends preserved in alcohol.

Diagnosis. Procerini with only 1–2 unidentate simple chaetae in all chaetigers, and a trepan with single large, and 25–28 smaller teeth.

Description. Length 2.1–3.0 mm for 24–27 chaetigers, width at level of proventricle, excluding parapodial lobes, 0.2 mm. Live specimens pale gray, sometimes faintly reddish, without colour markings ( Fig. 2 A). Body shape, excluding parapodial lobes, cylindrical in transection, ventrally flattened. Body fairly constant in width, with tapering posterior end. Ciliation on nuchal epaulettes. Prostomium rounded rectangular. Four eyes with lenses, anterior pair larger, confluent in dorsal view; eye spots present. Palps small, invisible in dorsal view ( Fig. 2 A), not possible to evaluate degree of fusion. Nuchal epaulettes extending to anterior part of tentacular segment ( Fig. 2 A, indicated with arrow). Prostomium with three antennae; median antenna inserted medially on prostomium, lateral antennae on anterior margin. Tentacular cirri two pairs. Median antenna reaching chaetiger 4–5. Lateral antennae and first dorsal cirri about 2/3 as long as median antenna. Dorsal tentacular cirri half as long as median antenna, ventral tentacular cirri c. half as long as dorsal pair. Dorsal cirri from chaetiger 1 with following alternation in direction, where D=cirri pointing down and U=cirri pointing up: U DDU DU DDU followed by eight DU-groups. From chaetiger 2 dorsal cirri alternating in length; short cirri as long as 1–1.5 times body width, long cirri as long as 2–2.5 times body width. Cirrophores on tentacular cirri and all dorsal cirri. Cirrophores and cirrostyles alternating in length along the body; cirrophores and cirrostyles on short cirri c. half as long as its counterpart in long cirri; cirrophores on short cirri with thin base, cirrophores on long cirri with broad base; cirrophores shorter than parapodial lobes; cirrophores shorter than their cirrostyles. Antennae, tentacular cirri, first dorsal cirri, and short cirri cylindrical; long cirri, and anal cirri clavate ( Fig. 2 A, but note that most of the long cirri have been lost). Parapodial lobes of medium size, rounded. Aciculae 1–2 in all chaetigers ( Fig. 2 D). Chaetal fascicle with 1–2 unidentate simple chaetae in all chaetigers ( Fig. 2 C, D). Bayonet chaetae not observed. Pharynx with small sinuation in front of proventricle ( Fig. 2 A). Trepan in tentacular segment, with single large dorsal tooth and 25–28 small teeth in single ring ( Fig. 2 B). Basal ring present, infradental spines present. Proventricle as long as 1–1.5 segments in chaetiger 3–4 ( Fig. 2 A) with c. 23 rows of muscle cells. Length of anal cirri c. as long as body width.

Reproduction. Schizogamous reproduction by anterior scissiparity. One specimen with developing small antennae after chaetiger 13, and one specimen with newly regenerating posterior end after chaetiger 13.

Habitat. Sponges, hydroids, 25 m.

Distribution. Mediterranean, Adriatic Sea, only known from type locality.

Intraspecific genetic variation. Two haplotypes of COI separated by a single mutation, and a single haplotype of 16SrDNA were found in the five sequenced specimens.

Remarks. Erseia oligochaeta , new genus, new species is unique among autolytines in having a trepan with one large dorsal tooth and 25–28 smaller teeth, and only 1–2 simple unidentate chaetae in all chaetigers. These chaetae are reminiscent of those found in the anterior chaetigers of Virchowia spirifer ( Augener, 1913) and Imajimaea draculai . However, both species have additional types of simple and/or compound chaetae, which are absent in E. oligochaeta , new genus, new species. In other morphological respects E. oligochaeta , new genus, new species is most similar to Virchowia species, with its alternating long clavate dorsal cirri and short cylindrical dorsal cirri, situated on unequally sized cirrophores. One character that E. oligochaeta , new genus, new species do not share with Virchowia (even though the situation for V. pectinans (Hartmann- Schröder, 1983) is uncertain) is the nuchal epaulettes which are not situated on outgrowths but instead extends on the dorsum.

Etymology. The species epithet oligochaeta is derived from the Greek oligos meaning few, and the Greek khaite meaning long hair, and refers to the few chaetae this species is provided with.

Figures

FIGURE 2. Erseia oligochaeta, new genus, new species. A. Holotype, dorsal view. B. Trepan, dorsal view (spm 2). C. Simple chaeta, chaetiger 2 (spm 2). D. Simple chaeta and aciculae, chaetiger 10 (spm 2). Scale lines A 0.5 mm, and B – D 10 µm.