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

Amphiglena aeoliensis sp. nov.

(Figs 18, 19)

Material examined. Holotype (MNCN 16.01 /18913): Italy: Panarea Island (Aeolian Archipelago), near the Bottaro crater, 27 September 2016, 8 m depth; station B2, 38°38’14.49”N 15° 6’34.47”E).

Paratypes: MNCN 16.01 /18914: 8 specimens from the same locality and date as the holotype; PCZL: 19 specimens B2 site, 27 September 2016; PCZLS.A. 9.1. 79 specimens B3 site, 27 September 2016; PCZL S.A. 9.2. 39 specimens B3 site, September 2018 PCZL S.A. 9.3. The remaining material is in the MCG collection. Most material fixed in ethanol 70% (including the holotype and paratypes), and some in ethanol 95 %.

Description. Holotype complete, with eight thoracic and 28 abdominal chaetigers. Body length 2.8 mm, branchial crown 1 mm long, maximum body width 0.43 mm. Natural dark brown colouration presents especially in the thorax and highlighting the mid-dorsal faecal groove, and ventral shields. (Fig. 18A). Crown with five pairs of radioles with 14 pairs of pinnules arranged in two longitudinal rows alternating along the radiolar length. Gap between pairs decreasing along the radiole from the base to the distal end, with the first two basal pairs more separated from the others. Pinnules slender and elongated, showing a similar length (1/4 of the total radiolar length) with the distal pairs and the first two basal pairs slightly shorter. Tip of radioles elongated as long as pinnule length (measuring 1/4 of the total radiolar length) and with a blunt end (Fig. 18C). Radiolar skeleton with two rows of cells. Dorsal lips with pointed dorsal radiolar appendages clearly shorter and wider than the pinnule, being 1/7 of the total radiolar length. Anterior peristomial ring even in height all around and visible also ventrally. Posterior peristomial ring low. Ventral basal flanges high, extending as prominent ridge from base of ventralmost radioles, across anterior peristomial ring but appearing not connected (Fig. 18D, E). Peristomial eyes not visible. Pygidial eyes present, as clusters of brown spots on lateral margins of pygidium. Thorax longer than wide. First thoracic chaetiger bearing only 3 chaetae similar in shape to the thoracic superior chaetae. From the second to the eighth thoracic chaetiger, 6 uncini in each torus with well developed breast, large distance to main fang, with approximately four rows of long teeth above main fang, and short handles long 1/3 of the total uncinus’ length (0.30) (Fig. 19A). Companion chaetae with straight shaft and short mucro (Fig. 19B). Second to eighth thoracic chaetigers with 4 chaetae, of which one superior broadly hooded chaeta (Fig. 19D) and three paleate chaetae on each thoracic chaetiger, with short mucro (Fig. 19E). Five abdominal uncini with similar-sized small teeth above the main fang, higher than thoracic ones and with short handle; the uncini are also larger in height than the other species, as in A. vulcanoensis sp. nov. (Fig. 19C). Up to 3 abdominal broadly-hooded neurochaetae, becoming narrower and with a more geniculate appearance in the last segments (Fig. 19G, F). A pair of brown/red spermathechae present at the base of dorsal lips.

Staining pattern. In both, thorax and abdomen stain only ventral shields overlapping the natural brown colouration. Colouration pattern wide on both thorax and abdomen following the shape of the segments, but not reaching the tori (Fig. 18B).

Variation. Individuals always with 8 thoracic chaetigers and up to 28 abdominal chaetigers. Mean body length of 2.55 mm and mean crown length of 1.08 mm. Peristomial eyes visible only in few specimens. Up to 8 thoracic uncini and 6 abdominal one (Table 1).

Remarks. The new taxon is very characteristic in its colouration, although variable in intensity among specimens, as well as for its very compact appearance. This dark brown colour pattern is quite unusual among Amphiglena species.

Peristomial rings and basal ventral flanges are quite similar to A. cf. mediterranea, from which it is distinguished for the first peristomial ring visible also ventrally, for the staining pattern, for a more compact appearance with wider and lower segments, but especially for the short handle of thoracic uncini.Among the non Mediterranean species, the new taxon is similar to A. nishi Capa & Rouse, 2007 described from Japan, especially in the shape of peristomial rings and ventral basal flanges. This species is however a smaller taxon with only 4 radioles.

Etymology. The species is named from the type locality, the Aeolian Archipelago (north Sicily) where the species was collected.

Distribution and ecology. This species is one of the most abundant taxa of the benthic community associated to the brown macroalga Cystoseira brachycarpa, dominating the rocks around the Bottaro crater and the hydrothermal system around it (see Auriemma et al. 2019, for a description of the collection area). Its local distribution in the area and its relationship with another new congeneric species are discussed below.