Chone usticensis, Giangrande & Licciano & Castriota, 2006

Giangrande, Adriana, Licciano, Margherita & Castriota, Luca, 2006, Description of Chone usticensis sp. nov. (Polychaeta, Sabellidae) from the Mediterranean Sea, Zootaxa 1168, pp. 51-58 : 53-57

Chone usticensis sp. nov.

Figures 2 –4

Material examined

Type material: Holotype, MNCN 16.01/10325, collected by L. Castriota at station A, 38°41.50’ N 13°09.78’ E, in November 1997, at 50 m depth on a soft­bottom mainly composed of medium sand, biogenic and volcanic particles, together with a significant amount of red calcareous algae . Paratypes, MNCN 16.01/10326, 3 specimens from the same station.

Non­type material from the same locality (held in the personal collection of A. Giangrande): station A, 20 specimens Nov 96, 11 specimens July 97, 25 specimens November 97; station B, 48 specimens November 96, 40 specimens July 97, 59 specimens November 97; station C, 35 specimens November 96, 8 specimens July 97, 522 specimens November 97.

Description

Holotype complete, with 8 thoracic and 30 abdominal chaetigers ( Fig. 2A ). Branchial crown length 10 mm, total thorax­abdomen length 20 mm, maximum width 2.5 mm. Branchial lobes each with 10 fully developed radioles and one to two ventral radiolar appendages ( Fig. 3A ); radioles with palmate membrane for less than half of their length; radiolar flanges present distally to palmate membrane, but with radioles terminating as very long filaments ( Fig. 2B ). All pinnules of similar length. Radiolar skeleton axis composed of two rows of cells; outer surfaces of radioles flat. Dorsal lips pointed, longer than wide, radiolar appendages not visible, with one or two pinnular appendages. Ventral lips rounded, with radiolar appendage ( Fig. 3A, B ). Collar high with a mid­dorsal narrow gap, and slightly higher ventrally ( Fig. 2C ), ventral lobe of anterior peristomial ring pointed and extending slightly beyond ventral collar margin ( Fig. 2D ).

Thoracic notopodia in chaetiger 1 with 4 narrowly hooded chaetae. Notopodial fascicle from chaetigers 2–8 with superior group of 3–4 elongate narrowly hooded chaetae (Fig. 4C) and inferior group with 4–5 paleate chaetae posteriorly and 4–5 bayonet type anteriorly. Paleate chaetae with long tip (Fig. 4D). Neuropodial acicular uncini in number of about 13 per torus, with a series of small teeth of similar size over the main fang, with hood present, and breast only developed as slight swelling; handles very long (Fig. 4E, F). Abdominal neuropodial fascicles with modified, elongate narrowly hooded chaetae, longer in the posterior segment (Fig. 4A, B). Abdominal notopodia with 12–13 avicular uncini, with main fang surmounted by 5–6 rows of small teeth, breast rectangular, not extending beyond distal end of proximal tooth, handles absent. Intertorus variation in morphology present, with uncini from anterior abdominal segments as in Fig. 4H, and uncini from posterior abdominal segments as in Fig 4I. Intratorus variation present as well (Fig. 4G). Pygidium triangular with long cirrus ( Fig. 2A, E ). Thoracic ventral glandular shields visible in thoracic chaetigers. Body cream coloured. Tube not observed.

Remarks

Chone usticensis together with another Mediterranean species, C. filicaudata Southern, 1914 , and C. americana Day, 1973 , have a pygidial cirrus filament. Chone usticensis and C. filicaudata differ in the radiolar flanges which in C. filicaudata are developed until the end of radioles, in the length of palmate membrane, shorter in C. usticensis , in the shape of the paleate chaetae, wider in C. usticensis , and in the shape of the anterior peristomial ring lobe, entire and not incised in C. usticensis . Concerning the latter feature, C. usticensis is similar to C. americana , but differs in the shape of the thoracic uncini, which in C. americana are provided with teeth of unequal size above the main fang ( Tovar­Hernández 2005), in the shape of the collar, ventrally lower in C. americana , in the shape of thoracic paleate chaetae, which has a longer tip in C. usticensis , and in the shape of abdominal uncini, which in C. americana have a smaller number of teeth over the main fang. Chone usticensis also shows similarity to some Mediterranean specimens previously collected and reported as Chone sp. ( Giangrande 1992). However, the features of the branchial crown, a lower palmate membrane and a shorter filiform tips of the radioles, distinguishes this taxon from C. usticensis .

Most of the specimens of the examined population were small sized (around 10 mm in total length). The holotype was selected from the best­preserved larger specimens because we assume it to be an adult, although gametes were not detected. Oocytes in the abdomen have been observed in some non­type material of a similar size as the holotype. The number of dorsal pinnular appendages seems to vary according to the size of individuals, with only one in smaller ( Fig. 3A ), and two in larger specimens ( Fig. 3B ).

Type locality Offshore on South Coast of Ustica Island at 38°41.50’ N 13°09.78’ E.

Etymology The species is named after the type locality.

Figures

FIGURE 2. Chone and ventral views of the anterior end removing of the branchial crown, E) detail of the pygidial filiform cirrus.

FIGURE 3. Chone dissected specimen showing internal structures, B) internal structure from a large specimen. Dpa = dorsal pinnular appendage; dl = dorsal lip; vra = ventral radiolar appendage; vl = ventral lip.