Polydora dinthwanyana, 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 : 46-48

Polydora dinthwanyana sp. n.

Fig. 5

Etymology: From isiXhosa dinthwa (spot) and -nyana (diminutive suffix), referring to the pigmented spots that resemble freckles.

Description: Only two specimens, holotype complete, in two fragments, paratype anterior fragment. Holotype 7.5 mm for 70 chaetigers, 0.4 mm wide at chaetiger 5. Squat peristomium, width 0.2 mm, length 0.1 mm ( Fig. 5A ); body narrows posteriorly, penultimate chaetiger 0.2 mm wide ( Fig. 5B ). Prostomium rounded, entire; caruncle extending to end of chaetiger 2; no occipital tentacle; holotype with three eyes ( Fig. 5A ), paratype with four eyes, arranged in trapezoid. Pigmentation: prostomium, caruncle, peristomium and chaetigers 1–3 with yellow-brown spots; in holotype last three chaetigers without pigmentation, preceding 17 chaetigers spotted with yellow-brown pigment, but decreasing in intensity anteriorly ( Figs 5A, 5B ).

Chaetiger 1 notochaetae absent, with rounded notopodial lobes; chaetigers 2–4 notopodial lobes prominent, small, inconspicuous from chaetiger 6 and posteriorly. Chaetigers 2–4, 6–8, notochaetae arranged in three tiers, chaetae of first tier short, slightly bent, unilimbate chaetae, second tier with longer, straight unilimbate chaetae, third tier with long lanceolate chaetae; posterior chaetigers with only simple capillary chaetae of two lengths. No posterior modified spines. Chaetigers 1–6, neurochaetae unilimbate, of approximately equal lengths, neuropodial lobes well-developed. Bidentate hooded hooks from chaetiger 7, 5, 8 and 1 per series on anterior, middle and posterior chaetigers, last two chaetigers without hooded hooks. Hooks with constriction on shaft, with main tooth at a 90° angle to main shaft, 45° between main and accessory teeth ( Fig. 5C ). Single, fine companion chaeta accompanying hooded hooks only on last three chaetigers of paratype.

Chaetiger 5 1.5× size of preceding chaetigers; dorsal chaetae absent; five modified spines present alternating with long winged companion chaetae ( Fig. 5D ), spines curved with lateral flange visible in ventral view, resembling a tooth in some angles of view,

or not visible, unworn spines sharply curved with sharp point ( Fig. 5D ); small tuft of neuropodial chaetae present.

Branchiae from chaetiger 7 ( Fig. 5A ); first two pairs short, with succeeding branchiae longer and thicker, tending to project outwards at 90° to axis of body ( Figs 5B, 5E ), 75% of chaetigers branchiate.

Pygidium small, rounded ( Fig. 5B ).

Glands in chaetigers 7–10 in paratype, with large sacs ( Fig. 5E ).

Comparison: P. dinthwanyana sp. n. belongs to the P. ciliata / P. websteri group (Blake 1996). It resembles P. woodwicki Blake & Kudenov, 1978 and P. umangivora Williams, 2001 with respect to the shape of the prostomium and peristomium, length of the caruncle, and the absence of an occipital tentacle and posterior modified notochaetae. All three species are shell-borers. P. dinthwanyana further resembles P. woodwicki in the shape of the notopodial lobes from chaetigers 1–4, the presence of a flange on the modified spines of chaetiger 5, number of eyes, maximum number of hooded hooks and in having a small pygidium, although the shape differs. Differences include the arrangement of anterior notochaetae in two tiers and the presence of superior dorsal fascicle of geniculate chaetae on chaetiger 5 in P. woodwicki ( Blake & Kudenov 1978) . P. dinthwanyana resembles P. umangivora in the arrangement of anterior notochaetae in three tiers, the number of modified spines on chaetiger 5 and the absence of notochaetae on chaetiger 5; they differ with respect to the shape of the notopodial lobes of chaetiger 1, the modified spines of chaetiger 5 have flange not lateral tooth, size of the pygidia, the maximum number of hooded hooks and lack of bristles on hoods ( Williams 2001). P. dinthwanyana differs from both species by having greatly curved unworn modified spines on chaetiger 5, companion chaetae with the hooded hooks of the last three chaetigers and 75 % of the chaetigers being branchiate.

Holotype: SOUTH AFRICA: Eastern Cape: SAMC A60067 (in two pieces), Haga Haga, host Haliotis midae , 25.ii.2005, C.A. Simon.

Paratype: same data as for holotype, SAMC A60070 (fragments, slides), host Turbo sarmaticus .

Distribution: Found only at Haga Haga on the east coast.

Habitat: Both specimens found boring into mollusc shells ( H. midae and T. sarmaticus ).

Figures

Fig.5. Polydora dinthwanyana sp. n., SAMC A60067: (A) dorsal anterior; (B) dorsal posterior; (C) hooded hook; (D) chaetiger 5, from left to right:long bilimbate companion chaeta, ventral view of modified spine, modified spines from different angles; (E) cross-section of chaetiger 8. Scale bars:A= 0.1 mm, B = 0.5 mm, C–D = 0.02 mm, E = 0.05 mm.