Dipolydora Verrill, 1879

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 : 42-43

Genus Dipolydora Verrill, 1879 Dipolydora normalis (Day, 1957) Figs 2A–D

Polydora normalis: Day 1957: 97 , figs 6f–j; 1967: 471, figs 18.3k–l.

Morphology of new material: Up to 4.6 mm for 51 chaetigers. Prostomium bifid, with caruncle extending to posterior margin of chaetiger 3; no occipital tentacle; no eyes; no pigmentation ( Fig. 2A ).

Chaetiger 1 with well-developed notopodial lobes, two capillary notochaetae emerging anterior to notopodial lobe, not always obvious ( Fig. 2A ); chaetigers 2–4, notochaetae arranged in three tiers, first row short, slightly bent, unilimbate, second row slightly longer than first row, spear-shaped, third row long, lanceolate; chaetigers 6–10 similar to anterior chaetigers, but chaetae of first row more sharply bent; in subsequent chaetigers short chaetae fewer and longer, increase in number; no modified posterior notochaetae; chaetigers 1–4 with well-developed neuropodial lobes with two rows of neurochaetae, first row unilimbate, second row lanceolate, neuropodial lobes of chaetigers 6–7 smaller, neurochaetae of chaetiger 6 similar to chaetigers 1–4. Bidentate hooded hooks from chaetiger 7; with 3 or 4, 6 and 1 hooks per series on anterior, median and posterior chaetigers; maximum number 6 hooks; no constriction on shaft; in anterior chaetigers hooks with angle between main fang and shaft>90°, but smaller than is usual for other Dipolydora species, angle between teeth approximately 45° ( Fig. 2B ); chaetigers 7–10 with 1–2 winged companion chaetae; with last 23 or 24 chaetigers with 1–2 inferior needle-like companion chaetae; in one, possibly regenerating, specimen only six chaetigers with companion chaetae.

Chaetiger 5 1.5× length of preceding and succeeding chaetigers ( Fig. 2A ); chaetae include dorsal fascicle of 3–4 geniculate bilimbate chaetae, five modified spines alternating with spear-shaped companion chaetae and fascicle of short unilimbate neurochaetae; younger modified spines generally straight with sharp points, older spines worn, with slight concavity ( Fig. 2C ).

Branchiae from chaetiger 8 ( Fig. 2A ), (from chaetiger 9 in one specimen), depending on length, last 5–13 chaetigers abranchiate, long anteriorly, overlap mid-dorsum, shorten posteriorly.

Pygidium cuff shaped with dorsal notch ( Fig. 2D ).

Comparison: New material mostly corresponding with original description and paratype examined (Day 1957); in the paratype the last 12 chaetigers are abranchiate, falling within the range observed in the new material, posterior inferior companion chaetae are not mentioned in the description but are present in both the new material and the paratype, although they are present on fewer chaetigers in the latter. The specimens differ with respect to the length of the caruncle, which extends to the posterior edge of chaetiger 3 in the new material. In the original description it is described as extending to chaetiger 4, but in fig. 6f (Day 1957) and the paratype the caruncle extends to the beginning of chaetiger 4. The striated structure of posterior notochaetae described by Day (1957) was not observed. Although Day (1957) recorded seven modified spines on chaetiger 5, the paratype examined here only had five, in agreement with the new material. The structure of the spines is also similar; although fig. 6g (Day 1957) shows only a falcate spine; the paratype also has younger spines which are straight and pointed, as described for the new material. The concavities of older spines in the new material were never as pronounced as in the paratype. The differences observed here may be related to the smaller size of the new material examined.

Paratype (examined): MOZAMBIQUE: Inhaca Island : BMNH 1961.16 .56, J.H. Day .

Additional material examined: SOUTH AFRICA: Eastern Cape: SAMC A60058 (4) , SAMC A60059 (ethanol specimens) , Haga Haga, from surface of Haliotis midae , 26.iv.2007, C.A. Simon.

Distribution: Previously found along the north-east coast of southern Africa, with its southernmost distribution at Durban. In the current study the distribution range is extended further south, and it was found only at Haga Haga in the Eastern Cape Province. Habitat: Found in tubes on the surface of farmed Haliotis midae shells.

Figures

Fig.2.Dipolydora normalis: (A) dorsal anterior;(B) hoodedhook;(C) from left to right:bilimbate companion chaeta, pointed and worn modified spines of chaetiger 5; (D) pygidium.Scale bars:A = 0.1 mm, B and C = 0.02 mm, D = 0.5 mm.