Amphiglena panareensis, Giangrande & Putignano & Licciano & Gambi, 2021

Giangrande, Adriana, Putignano, Matteo, Licciano, Margherita & Gambi, Maria Cristina, 2021, The Pandora’s box: Morphological diversity within the genus Amphiglena Claparède, 1864 (Sabellidae, Annelida) in the Mediterranean Sea, with description of nine new species, Zootaxa 4949 (2), pp. 201-239 : 227-229

Amphiglena panareensis sp. nov.

( Figs 20 ; 21 ).

Material examined. Holotype ( MNCN 16.01 /18915): Italy: Panarea Island (Aeolian Archipelago), Bottaro crater, 27 September 2016, 8 m depth; station B3, 38°38’14.49”N 15° 6’34.47”E.

Paratypes: MNCN 16.01 /18916: 9 specimens from the same locality and date as the holotype; 53 specimens B3 site, 27 September 2016 PCZL S.A. 10.1; 7 B1 site, 27 September 2016 PCZ S.A. 10.2.; 63 specimens, B3 site, 23 September 2018; PCZL S.A. 10.3: 76 specimens, B2 site 23 September 2018 ; 33 specimens, B1 site, 23 September 2018, 10 m depth, PCZL S.A. 10.4. Remaining specimens in MCG collection. Most of the material fixed in ethanol 70% (including the holotype and paratypes); some material fixed in ethanol 95 %.

Description. Holotype complete, with eight thoracic and 40 abdominal chaetigers. Body length 5.5 mm, branchial crown 1.5 mm, maximum body width 0.26 mm. Natural brown colouration present especially in the thorax, highlighting the mid-dorsally faecal groove, and ventral shields ( Fig. 20A ). Crown holding five pairs of radioles with 15 pairs of long pinnules in two symmetrical not alternating rows. 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 of similar length (1/4 of the total radiolar length) and with the last two distal pairs and the first two basal pairs slightly shorter. Radiolar bare tips long1/3 of the total radiolar length, with a blunt end ( Fig. 20C ). Radiolar skeleton with two rows of cells. Dorsal lips almost identical in length to pinnules, being 1/4 of the total radiolar length. Anterior peristomial ring visible, high and with similar height all around. Anterior peristomial ring low. Both peristomial rings appeared connected to highly developed ventral basal flanges, which extend as prominent ridges from base of ventralmost radioles ( Fig. 20D, E ). Peristomial eyes not visible. Pygidial eyes present as brown cluster spots on lateral margins of pygidium. Thorax longer than wide. First thoracic chaetiger bearing only 3 chaetae similar in shape to the superior thoracic ones. Second to eighth thoracic chaetigers with 4 uncini per torus, having well-developed breast, large space to main fang, approximately four rows of long teeth above main fang, and a medium handle (0.40) ( Fig. 21A ). Companion chaetae with straight shaft and long mucro ( Fig. 21B ). Second to eighth thoracic chaetigers with 4 chaetae, of which one is a superior broadly hooded chaeta ( Fig. 21D ), and three paleate chaetae in inferior row on each thoracic chaetiger, with long mucro (longer than the hood) ( Fig. 21E ). Four abdominal uncini on each torus higher than longer and with similar-sized small teeth above the main fang, with a medium handle, and also in this species with a large height as observed in A. vulcanoensis sp. nov. and A. aeoliensis sp. nov., ( Fig. 21C ). Two abdominal broadly hooded neurochaetae similar to the thoracic paleate in the first abdominal chaetigers, becoming more geniculate in the middle segments ( Fig. 21G, F ). Spermathechae light brown/red coloured, not conspicuous.

Staining pattern. In both thorax and abdomen stain only ventral shields, showing a square shape in the thorax and a longer double thin rectangular shape in the abdomen ( Fig. 20B ).

Variation. Individuals always with 8 thoracic chaetigers and up to 42 abdominal chaetigers. Mean body length of 4 mm and mean crown length of 1.3 mm. Peristomial eyes visible in some specimens. Up to 6 thoracic uncini on each torus and 6 thoracic uncini one on each torus ( Table 1).

Remarks. The main feature distinguishes this new taxon is its elongate appearance, that also includes the base of the crown. Moreover, members of this species have the highest and more developed ventral basal flanges, extending as prominent ridges, observed in the genus. The elongate base of the crown appears similar to a web and in some specimens makes difficult to see the base of the peristomial ring. This is similar to A. gravinae sp. nov., described from the Adriatic Sea, from which it is distinguished especially for the different development of both the peristomial rings, but also for the length of handle of abdominal uncini, for the highest number of thoracic paleate chaetae, and for the shape of abdominal chaetae. Moreover, A. panareensis sp. nov. is longer than A. gravinae sp. nov. In addition, this is the second Mediterranean taxon showing pinnules arranged in pairs not alternating along the radiole. Among the non Mediterranean taxa, high developed ventral flanges are present also in A. bondi Capa & Rouse, 2007 , however, this is a thin and more compact species, with a longer branchial crown bearing 6 radioles with similar length. Lastly, the brown colouration appears clearer and more homogeneous than that observed in specimens of A. aeoliensis sp. nov. described in the present paper from the same area.

Etymology. The species is named from type locality, the island of Panarea (Aeolian Archipelago) (see Auriemma et al. 2019 for a description of the collection area).

Distribution and Ecology. This species represents, together with A. aeoliensis sp. nov., one of the most abundant taxa of the benthic community associated to the macroalga Cystoseira brachycarpa , the brown habitat-former alga dominating the rocks of the Bottaro crater and the hydrothermal system around it ( Auriemma et al. 2019). Its local distribution in the area and its relationship with A. aeoliensis sp. nov. are discussed below.

Figures

FIGURE 20. Amphiglena panareensis sp. nov. A. entire worm, photo from the holotype; B. staining pattern; C. tip of the radiole; D. photo from anterior end, ventral view, material coloured with Shirlastain A; E. scheme of the anterior end ventral view.

FIGURE 21. Amphiglena panareensis sp. nov. A. thoracic uncinus; B. companion chaeta; C. abdominal uncinus; D. superior thoracic chaeta; E. inferior thoracic chaeta; F. abdominal chaeta from anterior abdominal segment; G. abdominal chaeta from a middle abdominal segment.