Amphiglena aenariensis, 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 : 207-208

Amphiglena aenariensis sp. nov.

( Figs 4 , 5 )

Material examined. Holotype: ( MNCN 16.01 /18721): Italy: Ischia Castello Islet 25.11.2011 station S3 (south side acidified station of the CO 2 vent system), 40°43’51.99”N 13°57’47.63”E; 2 m depth.

Paratypes: MNCN 16.01 / 18722: 6 specimens from the same locality and date as the holotype: 16 specimens all collected in the same locality and date as the holotype ; PCZL S.A.2.1.: 22 specimens from the same site, 19.6.2012, in station N3 (north side of the CO 2 vent’s system, 1.5 m depth), 40°43’54.98”N 13°57’48.34”E PCZL S.A.2.2. Material fixed in formalin 4% and preserved in ethanol 70%; some material fixed in ethanol 95%.

Description. Holotype complete, with eight thoracic and 24 abdominal chaetigers. Body length 2.3 mm and crown length 1.5 mm; width 0.4 mm. Body brown coloured on ventral side, quite flattened abdomen ( Fig. 4A ). Crown bearing five pairs of radioles with 12 pairs of pinnules arranged in two longitudinal rows slightly alternating along the radiolar length. Pinnules appear slightly swollen and with a similar length shorter than the radiolar tip, measuring about 1/5 of the total radiolar length ( Fig. 4C ). Most distal pairs of radioles having pinnules decreasing in length with longer pinnules in median position along the radiole. The radiole’s distal end is 1/4 of the total radiolar length and appears elongate, slender but with a blunt, slightly swollen finger-like end. Radiolar skeleton with two rows of cells. Dorsal lips short, almost 1/7 of the total radiolar length.Anterior peristomial ring not visible, posterior peristomial ring slightly higher ventrally and showing a mid-ventral incision with well separated margins where the ventral basal flanges are fused. Ventral basal flanges low, connected as prominent ridges from the base of ventralmost radioles. ( Fig. 4D, E ). Peristomial eyes slight brown and difficult to see. Pygidial eyes brown as double clusters on lateral margins of pygidium. Thorax longer than wide. First thoracic chaetiger bearing only 3 chaetae similar in shape to superior chaetae of the following chaetigers. From the second to the eighth thoracic chaetiger, 6 uncini in each torus, with rounded and flattened breast, with approximately four rows of long teeth above main fang, and short handles (0.23 ratio) ( Fig. 5A ). Companion chaetae present, with straight shaft and long mucro ( Fig. 5B ). Four thoracic chaetae, one superior thoracic hooded chaeta ( Fig. 5D ), 3 inferior paleate chaetae, with mucro longer half of the tip of the superior chaetae ( Fig. 5E, F ). Six abdominal uncini on each torus with 3 teeth of similar-size and short handle ( Fig. 5C ). First abdominal chaetigers bearing three broadly-hooded neurochaetae similar in shape to the inferior thoracic paleate chaetae, but longer ( Fig. 5G ), and becoming longer and more geniculate in the median abdominal segments ( Fig. 5F ). Spermathechae brown/red coloured.

Staining pattern. In both thorax and abdomen stain only ventral shields. Peristomial rings and first thorax segment well coloured. Abdomen paler, showing a double square design in each chaetiger ( Fig. 4B ).

Variability. Individuals can have up to 29 abdominal chaetigers, up to 8 thoracic uncini and 6 abdominal ones ( Table 1). Some specimens were observed to have 5 radioles in one lobe and 6 in the other, and in some specimens the presence of a bifid radiole was also detected. Spermathechae were very pale in the holotype, and darker in some paratypes.

Remarks. This species is distinguished from the specimens here reported as A. cf. mediterranea in the staining pattern, especially in the abdomen, and in the more connected ventral basal flanges. Moreover, specimens appeared more compact and shorter with a flattened abdomen and a higher body/crown ratio ( Table 1). In addition, specimens belonging to this taxon are characterized by having a very short-handle of thoracic uncini, the shortest observed in all the taxa here reported. The features of the peristomial rings of A. aenariensis sp. nov. resemble A. Jimenezi Capa & Lopez, 2004, described from Panama, from which it is distinguished by the length of the radiolar appendage, but especially for the short-handles of thoracic uncini. The short-handle of thoracic uncini distinguishes this species from most of the other known species of Amphiglena . Among the non Mediterranean species, only A. nishi Capa & Rouse, 2007 has a similar handle length, however, it differs from A. aenariae sp. nov. in the higher number of thoracic uncini, in the relative length of the crown and in the higher number of radioles having shorter pinnules, moreover A. nishi has more developed ventral basal flanges. Lastly, thoracic uncini of A. aenariensis are the largest in the genus when compared to the worm size, together with very long abdominal neurochaetae.

Etymology. Named from the collection site which is part of the Bay of Cartaromana, where the ancient Roman submerged town Aenaria, was discovered. Aenaria is also the name used to designate the Island of Ischia during the ancient Roman colonization.

Distribution and Ecology. This species is one of the most abundant polychaetes in the CO 2 vents at the Castello ( Ricevuto et al. 2014; Gambi et al. 2016). The collection site, the Castello Aragonese at Ischia, is a rocky islet, the remains of a volcanic structure that, along its south and north sides, is characterized by gas emissions from the seafloor, composed by more than 95% by CO 2. This CO 2 surplus causes a natural acidification of the surrounding waters (down to <6.4 pH units in the most intense bubbling on the southern side) ( Kroeker et al. 2011; Hofmann et al. 2011). However, both salinity and temperature remain similar to the ambient waters, and the site is therefore intensively used as a natural laboratory to study the effect of ocean acidification for the benthic biota since 2006 ( Hall-Spencer et al. 2008, see Foo et al. 2018 for a review of studies at this site).

Figures

FIGURE 4. Amphiglena aenariensis 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 5. Amphiglena aenariensis sp. nov. A. thoracic uncinus; B. companion chaeta; C. abdominal uncinus; D. superior thoracic chaeta; E. inferior thoracic chaeta; F. abdominal chaeta from a middle abdominal segment; G. abdominal chaeta from the anterior abdominal segment.