Oxydromus digitifera, Çinar & Dağli & Erdoğan-Dereli, 2022

Çinar, Melih Ertan, Dağli, Ertan & Erdoğan-Dereli, Deniz, 2022, The diversity of polychaetes (Annelida: Polychaeta) in a longterm pollution monitoring study from the Levantine coast of Turkey (Eastern Mediterranean), with the descriptions of four species new to science and two species new to the Mediterranean fauna, Journal of Natural History 56 (33 - 36), pp. 1383-1426 : 1393-1399

Oxydromus digitifera sp. nov.

( Figures 2–6 )

Type material

Levantine Sea, Turkey, holotype. ESFM-POL/2018-158 , 14 August 2018, SAMSWR, 36.048889°N, 35.935833°E, 79 m, mud with shell fragments .

Paratypes. ESFM-POL/2017-205 14 August 2017, ERDSWR, 36.589722°N, 34.316667°E, 32 m, mud with shell fragments, 1 specimen; ESFM-POL/2017-206 , 16 August 2017, BTCSW1 , 36.862222°N, 35.961944°E, 31 m, mud, 1 specimen; ESFM-POL/2017-207 , 23 August 2017, ISKSW2 , 36.521389°N, 35.975833°E, 37 m, mud with shell fragments, 1 specimen; ESFMPOL/2017-208, 16 August 2017, BTCSW1 , 36.862222°N, 35.961944°E, 31 m, mud, 1 specimen; ESFM-POL/2018-158 , 14 August 2018, SAMSWR, 36.048889°N, 35.935833°E, 79 m, mud with shell fragments, 2 specimens; ESFM-POL/2019-69 , 09 September 2019, EDRSWR, 36.589722°N, 34.316667°E, 37 m, mud, 2 specimens .

Non-type material

Levantine Sea, Turkey. ESFM-POL/2019-57 , 06 September 2019, Mersin Bay, off Mersin, 36.671833°N, 34.555558°E, 55 m, mud, 6 specimens; ESFM-POL/2019-60 , 06 September 2019, Mersin Bay, off Narlıkuyu, 36.421086°N, 34.126275°E, 60 m, mud, 3 specimens; ESFMPOL/2019-61, 09 May 2019, Mersin Bay, off Akyatan Lagoon, 36.590797°N, 35.089811°E, 22 m, mud, 4 specimens; ESFM-POL/2018-157 , 15 August 2018, BTCSW1 , 36.862222°N, 35.961944°E, 33 m, mud, 3 specimens; ESFM-POL/2018-159 , 14 August 2018, ISKSW2 , 36.521389°N, 35.975833°E, 41 m, mud with shell fragments, 2 specimens; ESFM-POL/2019- 62 , 25 July 2019, Antalya Bay, off Anitli, 36.048889°N, 32.555556°E, 55 m, mud, 8 specimens; ESFM-POL/2019-63 , 07 September 2019, Iskenderun Bay, off Arsuz, 36.392564°N, 35.803300°E, 60 m, maerl bed, 5 specimens; ESFM-POL/2019-64 , 25 July 2019, Mersin Bay, off Narlıkuyu, 36.421086°N, 34.126275°E, 60 m, mud, 5 specimens; ESFM-POL/2019-65 , 25 July 2019, Mersin Bay, off Taşucu, 36.233553°N, 33.894669°E, 25 m, sandy mud with shell fragments, 3 specimens; ESFM-POL/2019-66 , 06 September 2019, Mersin Bay, off Mersin, 36.671711°N, 34.555558°E, 55 m, mud, 9 specimens; ESFM-POL/2019-67 , 06 September 2019, Mersin Bay , off Narlıkuyu , 36.421086°N, 34.126275°E, 60 m, mud, 2 specimens; ESFMPOL/2019-68, 09 May 2019, Mersin Bay , off Akyatan Lagoon , 36.590797°N, 35.089811°E, 22 m, mud, 8 specimens .

Description

Holotype complete, 6.4 mm long, 0.9 mm wide (chaetiger 1), with 30 chaetigers. Complete paratype 4 mm long, 0.55 mm wide (chaetiger 1), with 24 chaetigers. Body pale yellowish, no colour markings in preserved specimens ( Figure 6 (a,b)). Body dorso-ventrally flattened in holotype and subrectangular in cross-section in some paratypes ( Figure 4 (a,b)); gradually becoming narrower and flattened towards posterior end. Ventral side flattened, without furrow. Anterior segments (from prostomium to chaetiger 7) robust, placed very close to each other, making intersegmental furrows indistinct; intersegmental furrows distinct after chaetiger 7.

Proboscis everted in holotype, and in some paratypes; cylindrical, massive, muscular, 0.8 mm long, 0.5 mm wide, with dense, minute ciliae, completely surrounding subdistal part of pharynx, near opening ( Figures 2 (a,b), 4(a–d), 5(a), 6(a,b)). Papillae absent.

Prostomium subrectangular, wider than long (by almost 3 times), with two pairs of reddish eyes ( Figures 2 (a), 6(a)); anterior pair largest, almost 2 times larger than posterior one; anterior pair almost reniform in shape, posterior pair rounded. Palps biarticulate; palpophore stout, cylindrical, 1/3 − 1/4 of palpostyle; palpostyle conical, tapered ( Figure 2 (a)). A pair of lateral antennae present, emerging on anterior part of prostomium, slender, tapering to tip, almost as long as palps, antennophore short. Median antenna missing in holotype; present in some paratypes, placed on anterior end of prostomium, minute, bottle-shaped, median part expanded ( Figures 2 (a), 4(e)). A pair of nuchal organs present on posterior-lateral part of prostomium, distinct, mid-dorsally separated from each other ( Figure 4 (e)).

Tentacular cirri six pairs, each pair present on three separate segments; segments enlarging from anterior to posterior; cirri placed dorsally on each segment always with more developed cirrophores; anterior pair placed closely side by side in a nearly horizontal line; middle pair well separated, placed in a nearly oblique line, posterior pair placed closely in a vertical line ( Figures 2 (b), 4(d), 6(b)). Cirrostyles are missing on holotype and most paratypes; one paratype with cirrus on posterior segment extending back to chaetiger 3, long, tapered.

Parapodia with noto- and neuropodia. Notopodia poorly developed, represented by a small ridge placed just on cirrophores of dorsal cirri; neuropodia well developed in all chaetigers (especially in middle part of body); subtriangular in shape, with a prominent digitiform projection near tip, placed on anterior face of parapodia; as a protuberance in anterior parapodia, first distinctly appearing on chaetiger 3, becoming triangular or digitiform shape in middle and posterior parapodia, again appearing as a small tubercle on posterior-most chaetigers ( Figures 3 (a–c), 5(b,c,f), 6(d)). Parapodia in first two chaetigers smaller than others; parapodial lobes (neuropodia) (250 µm) smaller than body width (750 µm) on chaetiger 3; parapodial lobes (600 µm) almost same length as body width (650 µm) on chaetiger 10; parapodial lobes (700 µm) always longer than body width (450 µm) after chaetiger 13; parapodial lobes (550 µm) almost 2 times longer than body width (300 µm) on posterior parapodia.

Dorsal cirri present on all chaetigers, placed on dorsal side of parapodia; cirrophores well developed ( Figure 3 (a–c)), generally bending towards posterior side of body; cirrostyles of dorsal cirri missing on holotype and most paratypes; cirrostylus on chaetiger 2 on paratype reaching back to chaetiger 7, slender, tapering.

Ventral cirri present on all chaetigers, smooth, placed slightly posteriorly on ventral side of neuropodia, near tips; not extending beyond or slightly extending beyond parapodial lobes; subdistal part bottle-shaped, proximal part narrow, gradually increasing in size towards middle part and then gradually decreasing in size towards distal end ( Figure 3 (a–c)).

Chaetiger 1 and 2 without notochaetae and notoaciculae; with only neuropodial falcigers, numbering 20–25, with blades indistinctly bidentate and serrate; blade lengths ranging from 27.5 µm to 65 µm; shafts heterogomph, long piece sharply triangular, small piece notched with two rounded lobes; shafts with fine striae ( Figures 3 (d), 5(d,e)). Neuroaciculae numbering two in chaetiger 1 with pointed tips, protruding from parapodial lobe ( Figure 3 (a–c), 6(d)).

Notopodial chaeta first appearing on chaetiger 3, placed on ventral side of cirriophore, slender, slightly bending, furcated, 130 µm long, coarsely serrated subdistally; serrated part with tips 87.5 µm long; long branch 18.7 µm long, short branch 8.7 µm long ( Figure 3 (e), 5(f)). Notoacicula single, with pointed tip, bending ventrally, protruding from parapodia on ventral side of cirrophores. Neuropodia well developed with only heterogomph falcigers; numbering 32, with finely serrated blades, measuring 45–175 µm long.

In middle chaetigers (chaetiger 11), notopodial furcate chaetae numbering maximally 4, slightly bending, 205 µm long, long branch 21 µm long, short branch 6 µm long, subdistally finely serrated; serrated part 75 µm long. Notoacicula present, numbering one, with pointed tip, bending ventrally, protruding from parapodial lobe. Neuropodia with heterogomph falcigers, numbering 37, blades finely serrated, measuring 87.5–250 µm long.

In posterior chaetiger, notopodial furcate chaetae numbering two, slightly bending, 225 µm long, long branch 21.5 µm long, short branch 3.7 µm long; subdistal spines indistinct. Neuropodial falcigers numbering 18, with blades measuring 90–250 µm long.

Pygidium rounded, with one pair of long anal cirri.

Reproduction

Some specimens collected in early September have oocytes within the pharynx and anterior segments, about 50–60 µm in diameter ( Figure 6 (c)).

Remarks

This species is characterised by having a subrectangular prostomium with a minute, bottle-shaped antenna; two pairs of reddish eyes (posterior ones larger); maximally four furcate notochaetae in the middle parapodia; and a prominent triangular, digitiform projection, placed anteriorly near tips of neuropodia. The specimens of O. digitifera sp. nov. have also small body size (6–8 mm), with a small number of chaetigers. The previous described Oxydromus species do not have such a projection on the parapodia. Oxydromus digitifera sp. nov. is mostly similar to O. pugettensis ( Johnson 1901) , originally described from the Puget Sound region (US Pacific coast) ( Johnson 1901), in the shape of prostomium (longer than wide), the size of eyes (anterior ones larger), the placement of eyes (not close to each other) and the number of notopodial chaetae (fewer than 10), but differs from it in having a bottle-shaped median antenna (slender, tapering in O. pugettensis ) and a digitiform projection on parapodia (absent in O. pugettensis ). A minute antenna was also previously reported on O. angustifrons from the Philippines ( Grube 1878), on O. berrisfordi from the South Africa ( Day 1967) and on O. microantennata from the Australian coast ( Hutchings and Murray 1984), but O. digitifera sp. nov. mainly differs from these species in the shape of the antenna (bottle-shaped in O. digitifera sp. nov. vs very small, minute, slender in O. microantennata ; triangular, tapering in O. angustifrons and O. berrisfordi ) and having a digitiform projection on the neuropodium (lacking in other species). The new species is mainly distinguished from the other Oxydromus species ( O. pallidus Claparède, 1864 , O. agilis (Grube, 1874) , O. fasciatus (Grube, 1855) and O. flexuosus (delle Chiaje, 1827)] so far reported from the Mediterranean Sea in having a minute antenna (larger in other species), notopodia with 1–4 chaetae (more than 10 in O. flexuosus ), a somewhat rectangular prostomium (rounded in O. fasciatus ), and a digitiform projection on parapodia (absent in other species).

Etymology

The epithet digitifera (Latin digitus, finger-shaped, and fera, bearing) refers to the digitiform projection on the parapodia.

Distribution

This species was only found in the Levantine Sea, Turkey, eastern Mediterranean, at depths between 22 and 79 m. This species recently appeared in the shallow-water softbottom samples from the region (after the year 2016), known as a hot-spot area for alien polychaete species ( Çinar 2009; Çinar and Dağli 2013), so it might have been introduced to the area via an unknown vector. However, more data about its distribution are needed to reach a reliable conclusion. At the moment, this species can be categorised as likely alien species or cryptogenic species.

Figures

Figure 2. Oxydromus digitifera sp. nov. paratype (ESFM-POL/2018-158): (a) anterior end, dorsal view; (b) anterior end, lateral view. Scale bar: 0.5 mm.

Figure 3. Oxydromus digitifera sp. nov. paratype (ESFM-POL/2018-158): (a) anterior parapodium (chaetiger 2), anterior face; (b) middle parapodium (chaetiger 10), anterior face; (c) posterior parapodium (chaetiger 20), posterior face; (d) neuropodial falciger (chaetiger 10); (e) notopodial furcate chaeta. Scale bar: a–c = 200 µm; d = 26 µm; e = 20 µm.

Figure 4. Oxydromus digitifera sp. nov. paratype (ESFM-POL/2018-158): (a) whole body (posterior part missing), dorsal view; (b) whole body, lateral view; (c) anterior end,dorsal view; (d) anterior end, lateral view; (e) prostomium, dorsal view. Scale bar: a, b = 0.5 mm; c = 0.7 mm; d = 0.6 mm; e = 0.2 mm.

Figure 5. Oxydromus digitifera sp. nov. paratype (ESFM-POL/2018-158): (a) anterior part of proboscis, dorsal view; (b) middle parapodia, dorsal view; (c) middle parapodium, posterior face; (d) tip of falciger, middle parapodium; (e) falciger, middle parapodium; (f) notopodial furcate chaeta, middle parapodium. Scale bar: a = 170 µm; b = 60 µm; c = 55 µm; d = 4 µm; e, f = 21 µm.

Figure 6. Oxydromus digitifera sp. nov. non-type material (ESFM-POL/2019-65): (a) anterior end, dorsal view; (b) anterior end, lateral view; (c) anterior end, dorso-lateral view; (d) tip of a middle parapodium with a characteristic digitiform projection. Scale bar: a, b = 0.6 mm; c = 0.3 mm; d = 25 µm.