Polycirrus twisti Potts, 1928

Çinar, Melih Ertan, 2009, Alien polychaete species (Annelida: Polychaeta) on the southern coast of Turkey (Levantine Sea, eastern Mediterranean), with 13 new records for the Mediterranean Sea, Journal of Natural History 43 (37 - 38), pp. 2283-2328 : 2315-2317

Polycirrus twisti Potts, 1928

( Figure 11 )

Polycirrus twisti Potts 1928: 698–700 , fig. 212.

Material examined

ESFM-POL/2005-1329 , 19 September 2005, K 17, 2 m, Sarcotragus sp. , 1 specimen ; ESFM-POL/2005-1325 , 19 September 2005, K 19, 4 m, Halophila stipulacea , 3 specimens ; ESFM-POL/2005-2337 , 28 September 2005, K36, 0.3 m, Cy. elegans , 11 specimens ; ESFM-POL/2005-2766 , 29 September 2005, K37, 0.1– 3 m, rocks, 3 specimens ; ESFM-POL/2005-2233 , 29 September 2005, K37, 0.2 m, J. rubens , 3 specimens ; ESFM-POL/2005-2418 , 29 September 2005, K 37, 3 m, Z. marina, 1 specimen ; ESFM-POL/2005-2468 , 29 September 2005, K37, 0.2 m, Brachidontes pharaonis , 4 specimens ; ESFM-POL/2005-1764 , 30 September 2005, Finike Bay , G15, 36°17′34″ N, 30°09′33″ E, 10 m, Z. marina, 1 specimen ; ESFM-POL/2005-2668 , 3 October 2005, K44, 0.1 m, Co. mediterranea , 1 specimen ; ESFM-POL/2005-2319 , 3 October 2005, K44, 0.1 m, Cy. elegans , 1 specimen ; ESFM-POL/2005-2389 , 3 October 2005, K 44, 3 m, Z. marina, 1 specimen ; ESFM-POL/2005-1522 , 5 October 2005, K 50, 5 m, muddy sand, 3 specimens ; ESFM-POL/2005-2432 , 7 October 2005, K 53, 3 m, Sarcotragus sp. , 12 specimens ; ESFM-POL/2005-2453 , 7 October 2005, K 53, 3 m, Aplysina aerophoba , 25 specimens ; ESFM-POL/2005-2277 , 7 October 2005, K53, 0.1 m, Cy. elegans , 8 specimens .

Description

Largest specimen complete 13 mm long, 1 mm wide, with 86 chaetigers. Body pale brownish in general ( Figure 11A ), but specimens collected in Aplysina aerophoba dark brownish. Eye spots absent. Tentacular membrane anteriorly expanded to form large anteriorly directed lobe and laterally expanded as two large lobes with convoluted margins. Buccal tentacles of two types; thin, long, narrow grooved tentacles and thickened, small grooved ones ( Figure 11A ). Ventral lower lip raised, forming a small globular structure. Thorax with 22 pairs of notopodia from segment 2. Notopodia long and elongated in anterior part, becoming smaller towards posterior part. Two types of notochaetae; pinnate and capillary chaetae ( Figure 11B ). Pinnate chaetae numbering 10–12 per parapodia, measuring maximally 300 µm, with a long arista (12.5 µm long) ( Figure 11C ). Capillary chaetae present in inferior part of notopodia, numbering 1–2 (observed on some parapodia), measuring 37.5–75 µm long. Neurochaetae from chaetiger 16 to pygidium placed on small erect globular structure; numbering c. 15–20 per parapodium; uncini large with an extended base, with one tooth above main fang, followed 6–10 minute denticles (dental formula MF: 1: 6–10); attached to torus by elongate tendons ( Figure 11D,E ). Thoracic ventrum with raised ventral pads on segments 2–10, separated medially by deep midventral grooves. Nephridial papillae small rounded, on chaetigers 1–3.

Remarks

Polycirrus twisti was originally described from the Suez Canal (Kabret) by Potts (1928). The main diagnostic features of this species are that it has two types of notochaetae (pinnate and capillary) and one type of neurochaeta (one large tooth above the main fang) starting on the last five or six thoracic chaetigers. The number of thoracic and abdominal chaetigers seems to be size-related in this species. The 13 mm long specimen had 22 thoracic and 86 abdominal chaetigers, whereas the 6.5 mm long specimen possessed 17 thoracic and 48 abdominal chaetigers. The Mediterranean specimens of P. twisti are in accordance with the original description of this species. However, the Mediterranean specimens have neurochaetae on the last five or six thoracic chaetigers, whereas Potts (1928) mentioned that neurochaetae were present only on the last thoracic chaetiger. However, it should be kept in mind that the first thoracic neurochaetae are difficult to determine because they emerge on a very small protuberance and become more discernable towards the posterior part of the thorax.

In the Mediterranean Sea, P. twisti might have been confused with P. plumosus Wollebaeck, 1912 , which also has pinnate chaetae. Polycirrus twisti mainly differs from it in having capillary chaetae on parapodia (lacking in P. plumosus ). Therefore, the previous reports of P. plumosus should be re-examined.

Distribution

Polycirri twisti is only known from the Suez Canal and could have been introduced to the Mediterranean from this region.

Figures

Figure 11. Polycirrus twisti: (A) whole body, dorsal view (ESFM-POL/2005-2432), (B) capillary chaeta on notopodium of chaetiger 10, (C) pinnate chaeta on notopodium of chaetiger 10, (D) neurochaetae on chaetiger 20, (E) neurochaetae on chaetiger 40. Scale bars: (A) 0.5 mm, (B) 14 µm, (C) 13 µm, (D) 15 µm, (E) 12 µm.