Amphiglena pithecusensis, 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 : 210-212

Amphiglena pithecusensis sp. nov.

( Figs 6 , 7 )

Material examined. Holotype ( MNCN 16.01 /18901): Italy: Lacco Ameno (Ischia), 40°45’24.38”N 13°53’6.26”E, June 2012, 2– 3 m depth, on hard bottoms covered by macroalgae, mainly the brown alga Halopteris scoparia .

Paratypes: MNCN 16.01 /18902: 5 specimens from the same locality and date as the holotype, 13 specimens from the same site of the holotype ; PCZL S.A. 3.1.; 5 specimens from S. Anna rocks ( Ischia-Cartaromana Bay ), 40°43’34.58”N 13°57’35.98”E, 26 August 2014 . PCZL S.A. 3.2. Most material fixed in formalin 4% (including holotype and paratypes) and preserved in 70% ethanol, some material fixed in ethanol 95 %.

Description. Holotype complete, with eight thoracic and 24 abdominal chaetigers. Body length 2.5 mm (branchial crown 1.5 mm); width 0.4 mm ( Table 1). Body light brown coloured on ventral side and with a flattened abdomen ( Fig. 6A ). Crown with five pairs of radioles with 12 pairs of pinnules arranged in two longitudinal rows slightly alternating along the radiolar length. Gap between pinnules pairs decreasing along the radiole, with the first basal pair appearing slightly more separated from the others. Pinnules all of similar length, measuring about 1/4 of the total radiolar length, except first basal pair and the two distal pairs slightly shorter. Tip of radioles elongated, reaching almost 1/3 of the total radiolar length, thinning toward its blunt end ( Fig. 6C ). Anterior peristomial ring not visible. Posterior peristomial ring higher ventrally with a well separated ventral incision and margins with an inflated appearance ( Fig. 6D, E ), connected to ventral basal flanges extending as prominent ridges from the peristomial ring to the base of ventral-most radiole. Peristomial eyes brown. Dorsal lips measuring 1/5 of the radiolar length. Pygidial eyes present as small clusters of red spots on lateral margins of pygidium. Thorax longer than wide. First thoracic chaetiger bearing only 2 chaetae similar in shape to superior chaetae of the following chaetigers. From the second to the eighth thoracic chaetiger, 7 uncini in each torus, with a short handle approximately 1/4 of the total uncinus length (0.31), with approximately four rows of teeth above main fang, and with rounded and flattened breast ( Fig. 7A ). Companion chaetae present, with straight shaft and short mucro ( Fig. 7B ). Two superior broadly hooded chaetae ( Fig. 7D ); 3 inferior paleate chaetae with short mucro as long as the paleate region ( Fig. 7E ). Three abdominal uncini, with similar-sized small teeth above the main fang, with short-handle and appearing higher than long ( Fig. 7C ). Two abdominal broadly hooded chaetae, similar, but longer, to the thoracic paleate chaetae both in anterior and median abdominal segments ( Fig. 7F, G ). Spermathechae visible brown/red coloured.

Staining pattern. In both thorax and abdomen stain only the ventral shields, with a very narrow pattern especially in the abdomen remaining poorly stained ( Fig. 6B ).

Variation. Individuals with 8 thoracic chaetigers and up to 24 abdominal segments. Mean body length of 2.1 mm and mean crown length of 1.3 mm ( Table 1). Crown asymmetrical in some specimens composed of 11 radioles (5 pairs +1).

Remarks. Specimens similar in external morphology to A. aenariensis sp. nov. previously described, but distinguished from that species by having slightly longer handles of the thoracic uncini, although not as long as in A. cf mediterranea . Moreover, hooks are proportionately smaller. Other differences are in a different ratio between body and crown ( Table 1), in the narrow paleate chaetae in the thorax and abdominal chaetae of the mid body chaetigers which in A. aenariensis appear more geniculate and longer. Differences also in the ventral shape of the posterior peristomial ring with slight inflated margin, and in the shorter dorsal lips, and the ventral shield stain in this taxon appears less intense and narrower especially in the abdomen. Finally, the space between the pinnules in the radioles appears wider than in A. aenariensis sp. nov..

Etymology. Named from type locality. Lacco Ameno represents the first site of settlement of the ancient Greek populations (Eubei) at Ischia in the 8 th century BC, who called the island Pithekoussai, or Pithecusae in ancient Latin, due to the production of the local clay pottery.

Distribution and Ecology. This species belongs to a group of similar taxa that are abundant around the coast off the Ischia Island. This species is present all around Ischia on hard bottoms with different algal cover, as well as on Posidonia oceanica seagrass beds under “normal pH condition”, except at the San Pietro site, where a form similar to A. mediterranea is present.

Figures

FIGURE 6. Amphiglena pithecusensis 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 7. Amphiglena pithecusensis 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 anterior abdominal segment.