Dipolydora keulderae, Simon, 2011

Simon, Carol A., 2011, Polydora and Dipolydora (Polychaeta: Spionidae) associated with molluscs on the south coast of South Africa, with descriptions of two new species, African Invertebrates 52 (1), pp. 39-39 : 43-46

Dipolydora keulderae sp. n.

Figs 3 , 4

Etymology: This species is named for Felicia Keulder who helped with the sampling.

Description: Small species, body equal width along length, narrows for last five chaetigers. Holotype 7.5 mm for 82 chaetigers and 0.4 mm wide at chaetiger 5 (Paratypes ranging from 4 mm for 45 chaetigers to 6 mm for 61 chaetigers). Prostomium notched, caruncle extends to posterior margin of chaetiger 3, but to end of chaetiger 2 in one specimen; no occipital tentacle; in holotype two pairs of eyes arranged in trapezoid, 0–2 pairs in others, posterior pair larger; no pigmentation ( Fig. 3A ). Palps extend back approximately to chaetiger 14.

Chaetiger 1 with finger-like notopodial lobes that usually obscure single, fine notochaeta emerging anterior to lobe ( Fig. 3A ; lobes orientated posteriorly to show short notochaetae), neuropodial lobe small, inconspicuous, tuft of unilimbate neurochaetae; chaetigers 2–4, notochaetae arranged in three tiers, first row short, slightly bent and unilimbate, second row slightly longer than first row and spear-shaped, third row long and lanceolate; chaetigers 6–10 as on anterior chaetigers, but chaetae of first row more sharply bent; in subsequent chaetigers short chaetae fewer, with longer chaetae increasing in number; no modified posterior notochaetae. Neuropodial lobes of chaetigers 2–4, 6 small, neurochaetae unilimbate. Bidentate hooded hooks from chaetiger 7; 3, 5 and 1 per series on anterior, median and posterior chaetigers in holotype; 3–4, 6–7, 1 in paratypes; no constriction on shaft, in anterior hooks angle between main fang and shaft>90°, angle between teeth approximately 45°, accessory tooth decreasing in size until hooks in final eight (up to 11 in other specimens) chaetigers unidentate without hoods ( Fig. 3F ), number of chaetigers with unidentate hooks apparently not proportional to total number of chaetigers ( Fig. 4 ); no companion chaetae with anterior hooded hooks in holotype, but present on one ramus each on chaetigers 7 and 8 in one specimen; last two chaetigers with fine capillary companion chaeta.

Chaetiger 5 1.5× length of preceding and succeeding chaetigers; five modified spines alternating with bilimbate companion chaetae ( Fig. 3B ), modified spines falcate with collar on convex side of curved end of spine, in worn spines collar appears as a narrow ridge or cuff ( Fig. 3C ); dorsal fascicle of 3 or 4 geniculate bilimbate chaetae ( Fig. 3D ); fascicle of short unilimbate neurochaetae.

Branchiae from chaetiger 7 ( Fig. 3A ), first two pairs very small, first obvious pair on chaetiger 9; finger-like, individual branchiae not meeting at dorsal midline; 15 branchiate chaetigers in holotype, 6–12 in paratypes, in specimens with 40 to 60 chaetigers, number of branchiate chaetigers generally proportional to total number of chaetigers ( Fig. 4 ), with longest worm with 89 chaetigers not having more branchiate chaetigers.

Pygidium reduced, with four lobes, dorsal pair smaller than ventral pair ( Fig. 3E ), in some specimens looks cuff-shaped.

Comparison: D. keulderae sp. n. belongs to the D. bidentata / barbilla group (sensu Blake, 1996). The species resembles all other members of this group in having a notched or bilobed prostomium, modified spines with a collar on the convex side of the curved end of the spine, and hooded hooks from chaetiger 7. D. keulderae most closely resembles D. barbilla Blake, 1980 and D. pilocollaris Blake & Kudenov, 1978 . Generally, the length of the caruncle is the same in all three species. Common to D. keulderae and D. barbilla are the maximum number of hooded hooks and the loss of the second tooth in the hooded hooks; however, D. barbilla has heavy posterior notopodial spines ( Blake 1980) that are lacking in D. keulderae . D. keulderae and D. pilocollaris are similar in the start of the branchiae and the absence of posterior notopodial spines, but differ with respect to the maximum number of hooded hooks per fascicle and the presence of unidentate hooks posteriorly ( Blake & Kudenov 1978). D. keulderae differs from both species with respect to the fine structure of the modified spines on chaetiger 5 and companion chaetae: in both D. barbilla and D. pilocollaris the falcate spines have bristled collars, while the latter also has hastate companion chaetae. D. keulderae also has companion chaetae accompanying the hooded hooks for only the last two chaetigers (the presence of a winged chaeta with only the hooded hooks on the right neuropodia on chaetigers 7 and 8 in one specimen suggests that this is an anomaly), while the other two species have companion chaetae with the anterior hooded hooks. D. pilocollaris also lacks notochaetae on chaetiger; in D. keulderae these notochaetae are present but very inconspicuous.

Holotype: SOUTH AFRICA: Eastern Cape: SAMC A60060 , Canon Rocks, Port Alfred , coralline algae, 28.i.2005, C.A. Simon.

Paratypes: SOUTH AFRICA: Western Cape: SAMC A60061 (2), Struisbaai, host Turbo sarmaticus , 7.iii.2005, C.A. Simon ; SAMC A60071 (6), Hermanus, host wild Haliotis midae, Anna Mouton (shells processed by Simone Neethling) . Eastern Cape: SAMC A60062 (ethanol specimens), Port Elizabeth , host Crassostrea gigas , 21 x.2009, C.A. Simon .

Distribution: Found at Haga Haga, Canon Rocks and Kowie Rocks (Port Alfred), Port Elizabeth, Grootbank (Tsitsikamma), Mossel Bay, Struisbaai and Hermanus.

Habitat: Holotype found in coralline algae, but paratype found boring in the shells of Crassostrea gigas (Thunberg, 1793) , Turbo sarmaticus L., 1758 and Haliotis midae L., 1758.

Figures

Fig. 3. Dipolydora keulderae sp. n., SAMC A60060: (A) dorsal anterior; (B–D) chaetiger 5: (B) winged companion chaeta, (C) modified spines on chaetiger 5 with collar on convex side, the collar may be worn andappear as a line inmore worn spines, as inthe spine on theright, (D) long notochaeta; (E) pygidium with four lobes;dorsal pair smaller thanventral; (F) from left to right,hooded hooks, from anterior, late middle and posterior chaetigers. Scale bars: A = 0.05 mm, B–F = 0.02 mm.

Fig. 4. Dipolydora keulderae sp. n., the relationships between number of branchiate chaetigers/chaetigers with unidentate hooks and total number of chaetigers.