Branchiosyllis maculata ( Imajima, 1966 )

Aguado, Teresa, Martín, Guillermo San & Ten, Harry A., 2008, Syllidae (Annelida: Polychaeta) from Indonesia collected by the Siboga (1899 – 1900) and Snellius II (1984) expeditions, Zootaxa 1673, pp. 1-48 : 10-13

Branchiosyllis maculata ( Imajima, 1966)

Figs 3 , 4

Typosyllis maculata Imajima, 1966: 277 , text-figs 59 a–m.

Branchiosyllis maculata .— Licher, 1999: 274.—San Martín et al., submitted.

Material examined. 2 spec. (one spec. mounted for SEM) ZMA V.Pol. 5259, Indonesia, NE coast of Sumba, 09°57'S 120°49'E, sandy bottom and sponges, 45 m, Snellius II, Sta. 4.067, 16 Sept. 1984; 1 spec. ZMA V.Pol. 5260, NE coast of Sumba, 09°57'S 120°48'E, sandy bottom, sponges and gorgonians, 50 m, 1.2 m Agassiz trawl, Snellius II, Sta. 4.068, 16 Sept. 1984; 4 spec. AM W30108, Australia, Western Australia, inshore reef off Ned's Camp, Cape Range National Park, 21°59'S 113°59'E, frilly Caulerpa sp., 1m, 2 Jan. 1984; 3 spec. AM W29519, Australia, Western Australia, N end of beach, Bundegi Reef, 21°49'S 114°11'E, rocky rubble & brown alga with epiphytic growth, sticky sediment, 2m, 4 Jan. 1984; 2 spec. AM W30109, Australia, Western Australia, N end of beach, Bundegi Reef, Exmouth Gulf, 21°49'S 114°11'E, rocky rubble with sediment, brown alga with epiphytic growth, intertidal, 4 Jan. 1984; 3 spec. AM W30110, Australia, Western Australia, Goss Passage, Beacon Is., 28°25'30"S 113°47'E, dead plates of Acropora sp. covered in coralline algae, 8m, 19 May 1994. (Material from Australia identified by San Martín et al., submitted).

Comparative material examined. Branchiosyllis cirropunctata (Michel, 1909) . 2 spec. AM W30091, Western Australia, Goss Passage, Beacon Isl., 28°25'30"S 113°47'E, dead plates of Acropora sp., covered in coralline algae, 8 m, 19 May 1994; 1 spec. AM W30092, NE entrance to Goss Passage, Beacon Isl., 28°27'54"S 113°46'42"E, dead plate-like Acropora sp., covered in coralline algae, 8 m, 25 May 1994 (all identified by San Martín et al., submitted).

Description. Longest specimen incomplete, 8 mm long, 0.7 mm wide, 58 segments. Body cylindrical, ventrally flattened. From proventricular segments backwards, one dorsal spot of black pigment on middle of each segment. Some articles of dorsal cirri partially black, usually two to three articles without pigment alternating with one pigmented ( Fig. 3 A). Prostomium rounded; four eyes in open trapezoidal arrangement, almost on line. Median antenna lost, insertion mark between posterior eyes. One lateral antenna lost, another with only one article, insertion on anterior margin of prostomium. One transversal ciliary band on prostomium, located anterior to eyes and median antenna ( Fig. 4 B). Palps triangular, longer than prostomium, fused at base, with a median groove. Peristomium short, considerably smaller than subsequent segments ( Fig. 3 A, 4A). Dorsal tentacular cirri with about 21 articles, ventral cirri shorter than dorsal ones, with about 14 articles. Dorsal cirri with distinct cirrophores. Dorsal cirri of chaetiger 1 long, with about 50 articles; subsequent most anterior dorsal cirri with 27–32 articles ( Fig. 3 A). Midbody and posterior dorsal cirri alternating long and short, with 36–39 and 21–24 articles respectively. Parapodial lobes distally bilobed, prechaetal and postchaetal lobes digitiform, similar in shape, postchaetal lobe slightly longer than prechaetal one ( Figs 3 I, 4E, F). Ventral cirri digitiform, proximally inserted, not exceeding beyond length of parapodial tip ( Fig. 3 I). Usually eight to nine compound heterogomph chaetae on anterior parapodia; blades falcigerous, bidentate, with spines on edge ( Fig. 3 B) and dorsoventrally decreasing in length (ca. 32.5 µm dorsal-most, ca. 19 µm ventral-most). Midbody parapodia with six to eight compound bidentate chaetae (ca. 30–15 µm), similar to those of anterior parapodia, except two to three most ventrally located with shorter shafts and short blades (ca. 20–25 µm). Dorsal-most blades with spines on edge, and long distal tooth ( Figs 3 F, 4D). Spines decreasing to lacking in ventral-most chaetae ( Fig. 3 F). Posterior chaetigers with six to eight compound chaetae, two to three most ventrally located with short shafts and claw-shaped blades, smooth on margin, unidentate and rotated 180º ( Figs 3 H, 4G, H); remaining four to five chaetae with longer shafts and bidentate blades (ca. 22–16 µm) ( Fig. 3 G). Anterior parapodia each with three slender aciculae, two straight and pointed and one slightly oblique at tip ( Fig. 3 C). Midbody and posterior segments with two to three aciculae protruding from parapodia, one to two straight and pointed, other slightly oblique at tip ( Figs 3 D, E, 4E, F). Pharynx through about seven segments; pharyngeal tooth located anteriorly, surrounded by crown of ten soft papillae. Proventricle longer than pharynx, through 12 segments, with about 43 muscle cell rows, and distinct mid-dorsal line ( Fig. 3 A). Pygidium missing.

Remarks. The specimens agree well with the original description of B. maculata . The claw-shaped chaetae, typical of Branchiosyllis , are difficult to observe in dorsal view, as their shafts are very short, sometimes appearing to be lacking. We compared specimens from Indonesia with those from Australia, and noticed some small differences in details of posterior chaetae: in Australian specimens, the bidentate chaetae are similar, but the proximal tooth is smaller than in specimens from Indonesia. The posterior chaetae in specimens from Indonesia have shafts not as curved in their distal parts, as occurs in specimens from Japan (cf. Imajima, 1966). However, shafts of Indonesian specimens are similar to those of specimens from Australia. These small differences may either be related to the geographic distances between populations or to the presence of a species complex, as postulated for B. exilis .

Branchiosyllis cirropunctata is a similar species, but it possesses claw-shaped chaetae only on its far posterior segments, and the chaetae have distinctly enlarged subdistal spurs on the head of the shaft.

Distribution. West Pacific Ocean (Southern Japan, Australia), Indonesia.

Figures

FIGURE 3. Branchiosyllis maculata ZMA V. Pol. 5260. A: Anterior part, dorsal view; B: Anterior chaetae; C: anterior aciculae; D: Midbody aciculae; E: Posterior aciculae; F: Midbody chaetae; G: Posterior chaetae; H: Posterior clawshaped chaetae; I: Posterior parapodium, anterior view. Scale A: 0.5 mm; B – H: 20 µm; I: 48 µm.

FIGURE 4. Branchiosyllis maculata ZMA V. Pol. 5259. SEM. A: Anterior part, dorsal view; B: Prostomium, dorsal view; C: Anterior chaetae; D: Midbody chaeta; E: Midbody parapodia, dorsal view; F: Midbody parapodium, dorsal view, midbody aciculae; G: Posterior chaetae; H: Posterior claw-shaped chaetae.