Sphaerosyllis pontica, Martín, 2017

Martín, Guillermo San, 2017, Taxonomic contribution to the genus Sphaerosyllis (Annelida: Syllidae: Exogoninae) in the Black Sea, Zootaxa 4329 (3), pp. 281-291 : 284-288

Sphaerosyllis pontica sp. nov.

( Figs 2–4 )

Material examined. Black Sea, Bulgarian coast, off Varna, Sta. 191-4 (VA2), 43.1382°N, 28.2447°E, 33.7 m depth, muddy sand, POS 363 cruise of R/V “Poseidon”, 23 March 2008, holotype ( MNINGA PLY084 ) ; same data for 10 paratypes ( MNINGA PLY085 ) ; same data for 2 paratypes mounted on SEM stub ( MNINGA PLY 086 ) ; Romanian coast, off Constanța, Sta. BS 07/CT04, 44.0835°N, 29.0336°E, 44.5 m depth, grey mud, April 2007, 6 paratypes ( MNINGA PLY090 ) ; Romanian coast, off Eforie Nord, Sta. S-RO1-003, 43.8306°N, 30.1347°E, 100.5 m depth, well compressed, whitish mud with Modiolula phaseolina (Philippi, 1844) , SESAME 1 cruise of R/V “Mare Nigrum”, 8 April 2008, 4 paratypes (MNINGA PLY087); same data for 2 paratypes mounted on permanent slides ( MNINGA PLY089 ) .

Additional material: Black Sea, without collection data, 8+ specimens ( MNINGA 30.268).

Description. Body small, slender, with well-marked segments, pale yellowish, without colour markings, 1.5– 3.1 mm long, 0.16–0.32 mm wide, for 23–33 chaetigers ( Fig. 3A ). Holotype 2.7 mm long, 0.21 mm wide for 31 chaetigers. Small glandular papillae scattered over dorsum ( Figs 2A , 3D ). Prostomium rectangular, wider than long ( Fig. 2A ). Two pairs of red-brownish, coalescent (touching each other on lateral sides) lensed eyes in trapezoidal arrangement on posterior half of prostomium; anterior pair (16.3–22.4 µm in diameter) slightly larger than posterior ones (12.2–19.3 µm in diameter). Antennae short, similar in length, pyriform with bulbous bases and short narrow distal tips, of similar length to or slightly shorter than prostomium ( Figs 2A , 3B ). Median antenna (31.6–41.8 µm) inserted more posteriorly than lateral antennae (30.6–45.9 µm), approximately on middle of prostomium; lateral antennae inserted on anterior margin of prostomium. Palps broad, fused along their entire length, similar in length to prostomium, with a dorsal notch, sometimes directed downwards. Peristomium well developed, of similar length to subsequent segments, with a dorsal fold dorsally covering posterior part of prostomium. One pair of pyriform peristomial cirri (16.3–27.5 µm), much shorter than antennae, situated slightly anteriorly to anterior eyes, antero-laterally directed ( Fig. 2A ). Dorsal cirri small (30.6–47.9 µm), shorter than parapodial lobes, with bulbous bases and short tips. Dorsal cirri absent on chaetiger 2. Parapodial lobes conical, short, with few subterminal, digitiform papillae ( Fig. 3E ). Parapodial glands present from chaetiger 4 to last chaetiger, spherical, with fibrillar material ( Fig. 2A–C ), a rounded papilla on dorsal part of each gland ( Fig. 3C–E ); parapodial glands apparently absent in some segments of some specimens. Ventral cirri digitiform, shorter than parapodial lobes ( Figs 2B , 3E ). Anterior parapodia with 5–6 compound heterogomph chaetae with short unidentate blades of similar size, about 10.7–15.3 µm in length ( Figs 2E , 4A ). Blades of one or two dorsalmost compound chaetae with up to 7 moderately long spines along cutting edges; blades of ventral compound chaetae smooth. Tips of shafts always smooth. Towards posterior of body, number of chaetae per parapodium and length of blades slightly decrease; only 3–4 compound chaeta in last parapodia, all with smooth blades, about 10.2–14.3 µm in length ( Figs 2H, K , 4B, C ). Dorsal simple chaetae unidentate, straight, smooth, pointed, present from chaetiger 1, stouter in posterior chaetigers ( Figs 2D, G, J , 4D ). Ventral simple chaetae more slender than dorsal ones, unidentate, slightly curved, pointed, present on posterior chaetigers (in last 7–11 chaetigers) ( Fig. 2L ). Anterior parapodia (approx. first 5–7 chaetigers) with two aciculae each, one straight and thin and other stouter, with tip bent forward at about right angle ( Fig. 2F ); single acicula in each remaining parapodia, of latter type, most posterior ones thicker ( Fig. 2I, M ). Pygidium short, rounded lobe, with a pair of anal cirri (45.9–71.4 µm), similar in shape to dorsal cirri but stouter and 2–2.5 times longer than posterior dorsal cirri ( Figs 2C , 3C ). Pharynx slender, extending over 2–3 chaetigers, opening with a crown of around 10 small, soft papillae; pharyngeal tooth conical, bluntly rounded anteriorly, located terminally. Proventricle short, barrel-shaped, 138–204 µm long, 110–154 µm wide, extending through 1.5–2.5 chaetigers, with about 12–15 indistinct muscle cell rows ( Fig. 2A ).

Biology. Two epigamic males (2.4 and 3.1 mm long, both with 33 chaetigers) with natatory chaetae were present in sample MNINGA PLY090. They had masses of spermatozoa, two per chaetiger, from chaetiger 9 to chaetigers 22–27. Natatory chaetae slender, up to 721 µm long, decreasing gradually in length towards posterior end, first present from chaetiger 10. Last 2–3 chaetigers without natatory chaetae. No other epitokal modifications were observed in those two specimens.

Remarks. The new species most closely resembles Sphaerosyllis climenti del Pilar Ruso & San Martín, 2012, described from off Alicante, Spain, Western Mediterranean Sea, Sphaerosyllis parabulbosa San Martín & López, 2002 , described from off Sisargas Islands, A Coruña, NW Spain, and Sphaerosyllis thomasi San Martín, 1984 , described from the Balearic Islands but also reported in other parts of the Mediterranean. All these species have in common the median antenna inserted more posteriorly than the lateral antennae, pyriform dorsal cirri, with bulbous bases and narrow, short tips, shorter than the parapodial lobes, lacking on chaetiger 2, and the anterior parapodia with two aciculae each, one straight and one with bent tip.

Sphaerosyllis pontica sp. nov. differs from Sphaerosyllis parabulbosa in having conical parapodial lobes rather than rounded, dorsal simple chaetae beginning from the anterior parapodia rather than from the midbody parapodia, dorsal simple chaeta without spines on margin, shaft heads without spines, and blades without subdistal spine on posterior dorsalmost chaetae. Also, the blades of compound chaetae (10–15 µm long) are slightly shorter than in Sphaerosyllis parabulbosa (13–17 µm).

Sphaerosyllis pontica sp. nov. differs from Sphaerosyllis thomasi in having the blades of compound chaetae longer than in Sphaerosyllis thomasi (7–8 µm), with smoother serrations, and the shaft with smooth tips. In addition, in Sphaerosyllis pontica sp. nov. the eyes are arranged in a wide trapezium rather in a rectangle.

Finally, Sphaerosyllis pontica sp. nov. differs from Sphaerosyllis climenti in having the blades of compound chaetae slightly longer than in the latter (7–10 µm) and having the parapodial glands with fibrillar material instead of granular. In spite of the filling of some parapodial glands in Sphaerosyllis pontica sp. nov. sometimes appears as granular (depending on the angle of view), they are in fact fibrillar (better seen with phase contrast).

Sphaerosyllis levantina Faulwetter, Chatzigeorgiou, Galil, Nicolaidou & Arvanitidis (2011) , from Israel, and S. boeroi Musco, Çinar & Giangrande (2005) , from Italy and Cyprus, are also species with fibrillar glands, described from relatively near areas. However, these species have longer blades on compound chaetae, especially the latter, with more spines on margin, very different from those of Sphaerosyllis pontica sp. nov., which are short and smooth or provided with short spines on margin of blades.

Type locality. Black Sea (Bulgarian and Romanian coasts).

Habitat. Mud and muddy sand at 33.7–100.5 m depth.

Geographical distribution. So far known only from the Black Sea.

Etymology. The species epithet pontica (Latin, adjective, feminine) is derived from the ancient name of the Black Sea ( Pontus Euxinus ), the type locality of the species.

Figures

FIGURE 2. Sphaerosyllis pontica sp. nov., holotype (MNINGA PLY 084): (A) Anterior end, dorsal view; (B) Mid-body parapodia, dorsal view; (C) Posterior end, dorsal view; (D) Dorsal simple chaeta from anterior parapodium; (E) Compound chaetae from anterior parapodium; (F) Aciculae from anterior parapodium; (G) Dorsal simple chaeta from mid-body parapodium; (H) Compound chaetae from mid-body parapodium; (I) Acicula from mid-body parapodium; (J) Dorsal simple chaeta from posterior parapodium; (K) Compound chaetae from posterior parapodium; (L) Ventral simple chaeta from posterior parapodium; (M) Acicula from posterior parapodium. Scale bars: A – C = 0.1 mm; D – M = 20 µm.

FIGURE 3. Scanning electron microscopy (SEM) micrographs of Sphaerosyllis pontica sp. nov., paratype (MNINGA PLY 086): (A) whole specimen, dorsal view; (B) Anterior end, dorsal view; (C) Posterior end, dorsal view; (D) Chaetigers 14 – 17, dorsal view, showing papillae scattered over dorsum; (E) Chaetigers 19 – 25, dorsal view, showing dorsal cirri, ventral cirri, papillae of parapodial glands, and subterminal digitiform papillae on parapodia. ac — anal cirri; dc — dorsal cirri; dp — dorsal papillae; la — lateral antenna; ma — median antenna; pg — papillae of parapodial glands; pp — subterminal parapodial papilla; vc — ventral cirrus. Scale bars: A = 0.5 mm; B = 0.2 mm; C – E = 0.1 mm.

FIGURE 4. SEM micrographs of Sphaerosyllis pontica sp. nov., paratype (MNINGA PLY 086): (A) Tip of dorsalmost compound chaeta, chaetiger 9; (B) Tip of ventral compound chaeta, chaetiger 16; (C) Tip of ventral compound chaeta, chaetiger 23; (D) Dorsal simple chaeta, chaetiger 20. Scale bars: A, C = 5 µm; B = 2 µm; D = 10 µm.