Dipolydora quadrilobata Jacobi 1883

Dipolydora quadrilobata (Jacobi, 1883)

Figure 4

Polydora quadrilobata Jacobi, 1883: 3, 2 pls; Mesnil 1897: 87 –88, pl. 3, figs. 9–11; Fauvel 1927: 54, fig. 18l–r; Uschakov 1955: 272, fig. 94A–D; Blake 1969a: 37 –51, figs. 27–37 (larvae); 1971: 13–15, fig. 9 (synonymy); Rasmussen 1973: 111 –112; Radashevsky 1993: 18–21, fig. 9 (synonymy); Sato-Okoshi 2000: 445.

Polydora (Polydora) quadrilobata. Hartmann-Schröder 1996: 319 –320, fig. 144a–f.

Dipolydora quadrilobata. Blake 1996: 198, fig. 4.32I–N.

Material examined. Bulgaria: Sta. 190–4/VA2, Varna (43°08.17ʹN, 28°14.41ʹE), 33.7 m, muddy seabed, 23 Mar 2008, coll. A. Teacä, MNINGA PLY044 (46); Romania: Sta. 89, Eforie Nord, 10 m, medium-grained sand, 20 Aug 2003, coll. V. Abaza (1); Sta. 91, Tuzla, 10 m, sand mixed with shell debris, 20 Aug 2003, coll. V. Abaza (6); Sta. BS07/MA07 (43°46.47ʹN, 28°31.05ʹE), 33.5 m, silty mud, 20 Apr 2007, coll. A. Teacä, MNINGA PLY045 (2); Sta. BS05/66 (44°13.37ʹN, 29°38.03ʹE), 60.3 m, mud with Modiolula phaseolina (Philippi, 1844), 10 Aug 2007, coll. A. Teacä, MNINGA PLY046 (2); Sta. BS05/01 (44°19.29ʹN, 29°30.27ʹE), 56 m, greenish-grey mud with Mytilus galloprovincialis and M. phaseolina shells, 11 Aug 2007, coll. A. Teacä, MNINGA PLY047 (99); Sta. BS05/03 (44°19ʹ27ʹ N, 29°33ʹ35ʹ E), 54.5 m, mud with M. phaseolina, 11 Aug 2007, coll. A. Teacä, MNINGA PLY048 (357); Sta. BS05/28 (44°11.29ʹN, 29°40.57ʹE), 60.6 m, mud with M. phaseolina, 11 Aug 2007, coll. A. Teacä, MNINGA PLY049 (3); Sta. S–RO1–02 Portiţa (44°38.482ʹN, 29°39.845ʹE), 50.1 m, black muds with Melinna palmata and Mya arenaria, 7 Apr 2008, coll. A. Teacä, MNINGA PLY050 (114); Sta. BS08/91–1 (43°50ʹ29.43ʹ N, 29°15ʹ27.68ʹ E), 62.5 m, mud with M. phaseolina, 21 Jun 2008, coll. A. Teacä, MNINGA PLY051 (2); Sta. BS08/05 (43°59ʹ31.00ʹ N, 29°21ʹ31.18ʹ E), 56 m, greenish-grey mud with Mytilus and Modiolula shells, 22 Jun 2008, coll. A. Teacä, MNINGA PLY052 (92); Sta. BS08/45–1 (43°55ʹ29.71ʹ N, 29°21ʹ24.84ʹ E), 59.8 m, greenish-grey mud with Mytilus and Modiolula shells, 22 Jun 2008, coll. A. Teacä, MNINGA PLY053 (9); Sta. BS08/22 (43°57ʹ31ʹ N, 29°17ʹ81ʹ E), 55.3 m, greenish-grey mud with Mytilus and Modiolula shells, 23 Jun 2008, coll. A. Teacä, MNINGA PLY054 (5); Ukraine: Sta. 140–3/Phy4a (45°39.11ʹN, 31°20.78ʹE), 46.1 m, pelitic sand with shell rubble and Phyllophora, 15 Mar 2008, MNINGA PLY055 (3); Sta. 156–2/DN10 (45°26.95ʹN, 30°59.28ʹE), 45.5 m, pelitic sand with shell rubble and Phyllophora, 17 Mar 2008, MNINGA PLY056 (287); Sta. 159–4/Phy7 (45°34.13ʹN, 30°17.38ʹE), 23.4 m, silty mud with Mytilus shells, 18 Mar 2008, MNINGA PLY057 (2).

Description. Up to 15 mm long, 0.75 mm wide at chaetiger 5, with up to 90 chaetigers. Colour of preserved worms pale yellowish. Body without dorsal pigmentation.

Prostomium more or less distinctly incised anteriorly, forming two rounded lobes; caruncle indistinct, extending to posterior end of chaetiger 3 (Fig. 4 A). Occipital antenna absent. Eyes usually absent in adults; juveniles with four eyes arranged in nearly straight transverse row with the outer pair larger and irregular in shape. Nuchal organs as long, narrow ciliary bands on lateral sides of caruncle. Palps long, flexible, with prominent ciliated groove, extending posteriorly to chaetiger 15.

Chaetiger 1 biramous, with well-developed podial lobes, carrying both short notopodial capillaries and more numerous neuropodial capillaries (Fig. 4 A). Chaetigers 2–4 and 6 with noto- and neuropodial fascicles of winged capillary chaetae (Fig. 4 A–B). Notochaetae arranged in two vertical rows of shorter and thicker capillaries plus a dorsal superior tuft of longer and thinner capillaries. Neurochaetae also as two vertical rows of thick capillaries and a ventral inferior tuft of thinner and shorter capillaries. Number of capillary notochaetae diminishing toward posterior end. In far posterior notopodia capillaries completely replaced by stout, sharply pointed spines arranged in semicircular row (Fig. 4 E–F); number of spines increasing from 1–3 in a tuft up to 16, providing a spinous appearance to posterior end.

Chaetiger 5 modified, larger than adjacent segments, without postchaetal lamellae and carrying a horizontal curved row of 4–6 large spines (Fig. 4 A–B). Modified spines of chaetiger 5 falcate, distally curved, with two nearly equal teeth and a tuft of fine bristles in concavity between teeth. Companion chaetae absent (see Remarks). Dorsal superior fascicle of chaetiger 5 with up to seven geniculate limbate chaetae arranged in a vertical or oblique row (Fig. 4 C–D); ventral inferior fascicle as compact tuft of up to 9 winged capillaries.

Neuropodial bidentate hooded hooks, up to six in vertical row from chaetiger 7. Main fang of hook at obtuse angle to shaft and at reduced angle to distal smaller tooth. Shafts of hooks strongly curved, without constriction and manubrium. In anterior neuropodia up to four inferior capillaries present ventral to hooks. In posterior neuropodia inferior capillaries diminishing in number, becoming narrow and non-winged.

Branchiae from chaetiger 7, short at first, reaching full size by chaetiger 10–12, absent from posterior third of body, not connected to notopodial lobes.

Pygidium with four subequal lobes (Fig. 4 F).

Habitat and ecology. On the Romanian coast D. quadrilobata is found in soft sediments (fine sand, muddy sand, sandy mud, silty mud, and mud) at 10– 100 m. However, the species is most common and abundant between 40–60 m in mud between beds of Modiolula phaseolina, with densities up to 2600 ind. m–2.

The worm constructs permanent tubes that stand erect in the substrate, extending 15–20 mm. Tubes straight, up to 40 mm long and 1.5 mm wide, built of fine sand grains bound by silt and detrital particles. The upper part of tube is smooth and greyish-brown in colour, while the lower part, buried in sediment, is coarser and rusty-coloured.

Reproduction and development. Not known to date in the Black Sea.

Distribution. Arctic-boreal species, reported from the Pacific (Blake 1996) and Atlantic coasts of North America (Blake 1971), Sea of Japan and Sea of Okhotsk (Sato-Okoshi 2000), Bering Sea (Uschakov 1955; Radashevsky 1993), White Sea (Khaitov et al. 1999); North Sea (Rasmussen 1973; Hartmann-Schröder 1996), British Channel, Kiel Bay, Baltic Sea, Atlantic coast of Europe (Fauvel 1927), Adriatic Sea (Castelli et al. 1995; Požar-Domac 1978) and Black Sea (Todorova & Panayotova 2006).

Remarks. There is little confusion regarding the taxonomic position of Dipolydora quadrilobata. This species is closely related to D. caulleryi in having heavy, protruding, awl-shaped notopodial spines in far posterior segments and a pygidium divided into four nearly equal lobes, both falling into the ʹ armata/ caulleryi ʹ subgroup (sensu Blake 1996). Söderström (1920) even considered D. quadrilobata to be a juvenile of D. caulleryi. Nevertheless, Dipolydora quadrilobata is unique among species of the Polydora complex by having modified spines of chaetiger 5 expanded distally into two nearly equal teeth with a bushy tuft of fine bristles between them, and by four eyes arranged in a nearly straight transverse row (Blake 1996).

The Black Sea specimens match the morphological descriptions of specimens from northern Europe (Hartmann-Schröder 1996) or from northern Pacific (Radashevsky 1993). However, brown reticulated pigmentation on anterior end of body reported by many authors (Fauvel 1927; Blake 1971, 1996; Radashevsky 1993; Hartmann-Schröder 1996) was absent in the Black Sea specimens. Sato-Okoshi (2000), however, indicates that in Japan this pigmentation was present only in some specimens. Also, in one individual were observed two limbate capillaries near the bases of the major spines of chaetiger 5, like normal companion chaetae (Fig. 4 D).