Chone costulata ( Grube, 1877 ) Grube, 1877

Tovar-Hernández, María Ana, 2007, On some species of Chone Krøyer, 1856 (Polychaeta: Sabellidae) from world-wide localities, Zootaxa 1518, pp. 31-68 : 39-42

Chone costulata ( Grube, 1877) new combination

Figure 5

Sabella costulata Grube, 1877: 548 –549.

Material examined. Type material. K ē rgu ē len [ ZMB 894, holotype], Great Whale Bay, 24.1 m, Expedition Gazelle.

Additional material. Chone gracilis Moore, 1906 [ USNM 5513, holotype], [ ANSP 1–24, paratype]. Description. Colour, body shape, and size. Body cream coloured. Holotype incomplete (no posterior abdomen). Body length 25 mm, width 6 mm. Tube unknown.

Branchial lobes and branchial crown. Insertion of the branchial crown not exposed beyond collar ( Fig. 5 A). Branchial crown length 24 mm. Radioles: 19 pairs. Radioles with median pinnules three times longer than more proximal pinnules. Radiolar tips medium-sized ( Fig. 5 D). The palmate membrane extends about three quarters the length of the branchial crown. Lateral flanges narrow ( Fig. 5 D). Dorsal lips broadly rounded, as long as wide, without mid-rib. Dorsal pinnular appendages: one short pair. Ventral lips rounded, as long as wide, about one quarter the length of the dorsal lips. Ventral radiolar appendages: 8 short pairs (less than one quarter the length of the branchial crown length).

Peristomium . Anterior peristomial ring lobe not exposed beyond collar, distally entire, triangular. Posterior peristomial ring collar: antero-dorsal ( Fig. 5 A) and lateral margins entire ( Fig. 5 C), ventral margin higher than dorsal, incised ( Fig. 5 B); longitudinal grooves on ventral side of collar; entire length of mid-dorsal collar margin forms a broad gap ( Fig. 5 A). Dorsal pockets well developed ( Fig. 5 A). Ventral shield of collar swollen, horseshoe-shaped, three times wider than long ( Fig. 5 B). Ratio of posterior peristomial ring collar length versus chaetiger 2 length, in lateral view: 1.5:1.

Thorax. Chaetigers 2 to 8: notopodia– two irregular rows of elongate, narrowly hooded chaetae; one anterior row with bayonet chaetae; two posterior rows with symmetrical; paleate chaetae with a medium-sized mucro; neuropodia– two irregular rows of acicular uncini per torus, main fang surmounted by three rows of teeth ( Fig. 5 F), second tooth enlarged, located in the midline, dentition covering one quarter of the main fang length (not illustrated). Glandular ridge on chaetiger 2: narrow.

Abdomen. Abdominal segments: 7. Anterior uncini with the main fang surmounted by four rows of teeth equal in size, occupying less than half the length of main fang, main fang not extending beyond breast, breast rectangular ( Fig. 5 G). Posterior uncini similar but with three rows of teeth ( Figs 5 H). Pygidium unknown.

Gametes. Holotype mature male, spermatozoa with barrel-shaped nucleus, triangular, elongate acrosome and two rounded mitochondria ( Fig. 5 E).

Methyl green staining. Ventral shield of collar stains uniformly, except for a transversal, M-shaped median line ( Fig. 5 B); lateral and dorsal sides of collar darker than following segments ( Fig. 5 C). Thorax and anterior abdomen with epidermis completely glandular, stains uniformly, dorsal and ventrally ( Figs 5 A–C), except for the faecal groove ( Fig. 5 A).

Remarks. Sabella costulata is transferred to Chone because it has branchial lobes fused dorsally; palmate membrane and radiolar flanges present; dorsal lips broadly rounded, as long as wide, without mid-rib; ventral lips present, broadly rounded; dorsal pinnular appendages present; ventral radiolar appendages present; glandular ridge on chaetiger 2; elongate, narrowly hooded chaetae, bayonet and paleate chaetae, acicular uncini with second tooth enlarged, located in the midline; anterior and posterior abdominal uncini with well developed rectangular breast, handles absent, main fang well developed, few rows of small teeth covering one half (or less) of the main fang length.

The unique distinctive features of C. costulata are: anterior margin of collar incised ventrally; entire length of mid-dorsal collar margin forms a broad gap; dorsal pockets well developed; and ventral collar shield is horseshoe-shaped with a median, transversal M-shaped line. Other species with the ventral margin of collar incised is C. gracilis , however, the holotype of this species has the incision probably due to a regeneration process; in the paratype it is entire.

Figures

FIGURE 5. Chone costulata. (A) Anterior end, dorsal view; (B) same, ventral view; (C) same, lateral view; (D) radiolar tip; (E) spermatozoa; (F) thoracic uncinus; (G) anterior abdominal uncinus; (H) posterior, abdominal uncinus. (A – C) Methyl green staining. A – H [ZMB 894, holotype].