Amphiglena cf. mediterranea ( Leydig, 1851 )

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 : 204-206

Amphiglena cf. mediterranea ( Leydig, 1851)

( Figs 2 , 3 )

Material examined. 32+ 18 specimens Italy: from Ischia S. Pietro promontory (Ischia Island, Tyrrhenian Sea), 40°44’47.78”N 13°56’40.93”E; collected on macroalgae (mainly Halopteris scoparia ) during the years 1975 ( Fresi et al. 1983) and 2005 (Gambi M.C.) at 1-2 m depth; PCZL S.A.1.4; 36 specimens from Leghorn (Tyrrhenian Sea), 43°28’28.92”N 10°19’42.54”E, collected in 1986 at 3 m depth on rocky substrate covered by coralline algae ( Giangrande 1988) PCZL S.A.1.2; 141 specimens from Portofino (Genoa, Ligurian Sea), 44°18’10.70”N 9°12’56.29”E, collected in 1980 from 3 to 5 m depth, on hard substrate with algal cover PCZL S.A.1. All the material fixed in formalin 4% and preserved in ethanol 70%.

Description. Specimens from S. Pietro (Ischia Island, Italy) have 8 thoracic chaetigers and up to 27 abdominal ones ( Fig. 2A ), a mean body length of about 3.10 mm of which about 0.80 mm is the crown, maximum wide of 0.36 mm ( Table 1). The crown is composed of up to 10 radioles (5 pairs) each bearing up to 20 pinnules (10 pairs), arranged in two longitudinal rows alternating along the radiolar length. The gap between pairs remaining quite constant along the radiole. The pinnules show a similar length (about 1/3 of the total radiolar length), with only the first two basal pairs and the last two distal pairs appearing shorter (between 2/3 and 1/2 of the pinnule in medial position). Radiolar tip measuring almost 1/2 of the total radiolar length, with a pointed end; the dorsal lips are around 1/5 of the total radiolar length.

Spermathechae and peristomial eyes not visible, pygidial eyes ellipsoid red. First peristomial ring flattened and visible only dorsally ( Fig. 2E ). Second peristomial ring slightly higher ventrally, appearing separated and with rounded margins ( Fig. 2D, F ). High ventral basal flange not connected to the peristomial ring ( Fig. 2D, F ). Up to six thoracic uncini with handle of medium length (48) and with four teeth ( Fig. 3A ). Companion chaetae with long mucro ( Fig. 3B ). Superior thoracic chaetae broadly hooded ( Fig. 3D ). Three paleate chaetae with short mucro on each thoracic chaetiger ( Fig. 3E ). Abdominal uncini with short handle ( Fig. 3C ), abdominal chaetae as in the genus, appearing all similar from the first chaetigers to the last one ( Fig. 3F, G ).

Staining pattern. Thorax and abdomen intensely coloured and appearing dark blue with the exception of the intersegmental grooves, abdominal segments completely stained ( Fig. 2B, C ).

Remarks. Amphiglena mediterranea is the type species for the genus and is also the most common name used for material collected around the world, and widely reported as a cosmopolitan species ( Day 1967; Hartmann-Schröder & Rosenfeldt 1989; Hartmann-Schröder 1990; Knight-Jones et al. 1991, 2017; Dauvin et al. 2003; Dorgham et al. 2013; Faulwetter et al. 2017), and is still reported in recent ecological and biodiversity studies ( Gambi et al. 2016; Hutchings & Kupriyanova 2018) as well as in Mediterranean polychaete check-lists (e.g., Castelli et al. 2008; Faulwetter et al. 2017). However, no type material was deposited from the type locality in Nice ( France), and the original description by Leydig (1851) (in German) was not highly informative. Other authors gave a description of this taxon: Claparéde (1864), Saint Joseph (1894) and Rioja (1923), or commented on it ( Banse 1957; Fitzhugh 1990). The last detailed re-description was by Rouse & Gambi (1997) from individuals collected off Ischia Island (Gulf of Naples, Italy), however, due to the location, far from the type locality, it was not possible to designate a neotype from this material.

A comparison of the descriptions of A. mediterranea over time suggests that a large morphological variability exists concerning size, number of chaetigers, and number of radioles that need further exploration ( Tilic et al. 2019).

The taxon here re-described and collected from Ischia S. Pietro is the most similar and well corresponding to the re-description of A. mediterranea by Rouse & Gambi (1997), for material collected in Ischia in 1994 (Castello Islet), on hard substrate with Cladophora sp. and Halopteris scoparia algal cover, at 1-2 m depth. It corresponds well with regards to the shape and length of handles of thoracic uncini, and in the number of radioles and compact appearance ( Fig. 2A ), even though the small basal flanges in the description of these authors were connected to the peristomial ring. Similar features are also present in specimens from Portofino having a crown/body ratio of 0.3. By contrast, specimens from Leghorn examined during this study are slightly smaller and with a crown/body ratio of 0.49 ( Table 1). In the specimens examined from all these sites located along the Tyrrhenian coast, also the ventral peristomial ring is similar to that described in the material of Rouse & Gambi (1997), even if in the material from San Pietro (Ischia) the peristomial ring appears ventrally more opened and rounded ( Fig. 2F ) compared to that of material from Leghorn. Therefore, all these forms showed a very similar external appearance including the staining pattern with the abdomen fully coloured ( Fig. 2B, C ), this latter feature was not provided in the description by Rouse & Gambi (1997).

Figures

FIGURE 2. Amphiglena cf. mediterranea A. entire worm, specimen from Ischia, Naples; B. staining pattern of a specimen from Ischia, Naples; C. staining pattern of a specimen from Leghorn; D. photo from anterior end ventral view of a specimens from Ischia, material coloured with Shirlastain A; E. scheme of the anterior end dorsal view; F. scheme of the anterior end ventral view.

FIGURE 3. Amphiglena cf mediterranea A. thoracic uncinus; B. companion chaeta; C. abdominal uncinus; D. superior thoracic chaeta; E. inferior thoracic chaeta; F. abdominal chaeta from a first abdominal segment; G. abdominal chaeta from a middle abdominal segment.