Amphiglena vulcanoensis Giangrande & Putignano & Licciano & Gambi 2021, sp. nov.

Amphiglena vulcanoensis sp. nov.

(Figs 16, 17)

Material examined. Holotype: (MNCN 16.01 /18911): Italy: Vulcano Island-Baia di Levante vent system, 8 May 2013, 38°25’10.10”N 14°57’43.38”E; 1.5 m depth (Vizzini et al. 2017).

Paratypes: MNCN 16.01 /18912: 3 specimens from same locality and date as the holotype; 49 specimens, all collected in the same locality and date as the holotype PCZL S.A. 8.1. Material fixed ethanol 95% (including holotype and paratypes).

Description. Holotype complete, with eight thoracic and 32 abdominal chaetigers. Body length 4.2 mm, branchial crown 1.5 mm; maximum body width 0.5 mm, abdomen largely flattened. Yellow colouration presents especially in the thorax, highlighting the mid-dorsally faecal groove, and ventral shields (Fig. 16A). Crown with 7 pairs of radioles with 16 pairs of pinnules arranged in two longitudinal rows alternating along the radiolar length. The gap between pinnule pairs remaining constant along the radiole, with only the first basal pair more separated from the successive one. The pinnules show a variable length appearing very short and with a characteristic swell on the end, not observed in other species. The tip of radioles short and blunt (Fig. 16C). Dorsal lips with very long and rounded dorsal radiolar appendages, (1/3 of radiolar length). Radiolar skeleton with two rows of cells. Anterior peristomial ring not visible. Posterior peristomial ring low with two small ventral projections with low margin, ventral basal flanges thick and extending as prominent ridge from the base of the ventral-most radioles. Base of crown distinctly thick (Fig. 16D, E). Peristomial eye not visible. Pygidial eyes present as cluster of brown spots on lateral margins of pygidium. Thorax longer than wide. First thoracic chaetiger bearing only 3 chaetae similar in shape to the superior chaetae of the other thoracic segments. From the second to the eighth thoracic chaetiger, 7 uncini in each torus, with approximately five rows of similar-sized small teeth above the main fang and well-developed breast, going beyond the main fang and with large distance above main fang. Medium-short handles long around 1/3 of the total uncinus length (0.35); the uncini are also larger in height than the other species (Fig. 17A). Companion chaetae present, with straight shaft and short mucro (Fig. 17B). Second to eighth thoracic chaetigers with 5 chaetae of which one superior chaeta broadly hooded and four inferior paleate chaetae of two different typologies, one having a mucro long as the hood, the second showing a very short mucro and a reduced length (Fig. 17D, E, H). Four abdominal uncini on each torus with 4 teeth, uncini higher than longer and with a medium handle (Fig. 17C). Four broadly hooded abdominal neurochaetae similar to the inferior paleate chaetae both in the first and median abdominal segments, but the last becoming longer (Fig. 17F, G). Spermathechae light brown/coloured.

Staining pattern. In both thorax and abdomen stain only ventral shields, intensely coloured on the peristomial ring, and abdomen with a narrow stained string (Fig. 16B).

Variation. Individuals always with 8 thoracic chaetigers and up to 32 abdominal chaetigers. Mean body length of 3.7 mm and mean crown length of 1.3 mm. Up to 10 thoracic uncini on each torus and 7 abdominal uncini (Table 1).

Remarks. This is a species larger than the other congeneric species, with a compact appearance and with the largest number of radioles of all Mediterranean species, and non Mediterranean species. In this aspect, it resembles the Australian species A. magna Capa & Rouse, 2007 from which it is distinguished by the length of handles of thoracic uncini, but also by the ventral peristomial shape. This feature is similar to A. terebro Rouse, 1993, which is a smaller species with fewer radioles and 12 thoracic chaetigers.

Etymology. The species is named from type locality, the Island of Vulcano (Aeolian Archipelago, north Sicily).

Distribution and Ecology. The species up to date has been collected only in Baia di Levante hydrothermal vent’ system of Vulcano island. This vent’s system is unique since it is not only acidified due to CO 2 emissions from the primary vent source (approx. 300 m from the collection area), but has also some sulphur (H 2 S) and is enriched by metal ions (see Vizzini et al. 2017, and references herein for a description of the system and its benthic community). Amphiglena vulcanoensis sp. nov. was collected with a few other polychaetes, among which Platynereis cf. massiliensis Moquin-Tandon, 1869 was the dominant species (Waege et al. 2017, Vizzini et al. 2017).