Chone gracilis Moore, 1906

Tovar-Hernández, María Ana, 2007, Revision of Chone Krøyer, 1856 (Polychaeta: Sabellidae) from North America and descriptions of four new species, Journal of Natural History 41 (9 - 12), pp. 511-566 : 534-536

Chone gracilis Moore, 1906

( Figure 8 )

Chone gracilis Moore 1906, p 257 –259, Plate 12, Figures 62–66; Berkeley and Berkeley 1952, p 123 –124, Figure 254; Hartman 1969, p 665; Fauchald 1972, p 326 –327.

Material examined

Type material. Alaska [ USNM 5513 (holotype), ANSP AD 2208 (one paratype), ANSP 1- 24 (one paratype), Alitak Bay, Kodiak Island , Sta. 4274, 1903, 4–56.3 m] .

Non-type material. Alaska [ USNM 40723 ], Pavlov Bay , Ms. Stranger, coll. E. and C. Berkeley (3) . Oregon [ LACM-AHF], 000002-62, 44 ° 33.59N, 125 ° 14.69W, 2000 m, Cruise 6207A, AD6, 6 July 1972 (1) ; 000009-25 (1); 000007-12 (4).

Description (based on holotype, in parentheses variation observed in paratypes)

Colour, body shape, and size. Body cream coloured (brown in USNM 40723) with an iridescent epicuticle. Trunk cylindrical. Holotype complete, but pygidium and some radioles are broken, branchial crown almost separate from the body. Body length 21 mm (5–12 mm), width 1.5 mm (0.5–1.5). Tube hyaline.

Branchial lobes and branchial crown. Insertion of the branchial lobes partially exposed dorsally beyond collar ( Figure 8A ). Branchial crown length 11 mm (1.75–3.5). Radioles: nine (seven) pairs. Radioles with median pinnules three times longer than more proximal pinnules. Radiolar tips medium-sized ( Figure 8D, H ). The palmate membrane extends to three-quarters the length of branchial crown. Lateral flanges broad ( Figure 8D–H ). Dorsal lips (dl) broad basally, triangular towards tip, erect, without mid-rib ( Figure 8I ). Dorsal pinnular appendages: (six pairs). Ventral lips (vl) rounded, small, as long as one-quarter the length of dorsal lips ( Figure 8I ). Ventral radiolar appendages: (three pairs).

Peristomium . Anterior peristomial ring lobe not exposed beyond collar, distally entire, triangular. Posterior peristomial ring collar: antero-dorsal margin entire ( Figure 8A ); lateral margins entire ( Figure 8C–F ); ventral margin incised in holotype ( Figure 8B ), entire in paratype ( Figure 8E ) and higher than dorsal ( Figure 8C, F ); entire length of mid-dorsal collar margins forms a broad gap; broad faecal groove ( Figure 8A ); dorsal pockets well developed. Ventral shield of collar swollen, horseshoe-shaped, two times wider than long ( Figure 8B, E ). Ratio of posterior peristomial ring collar length versus chaetiger 2 length, in lateral view: 2:1.

Thorax. Chaetiger 1: two groups of nine elongate, narrowly hooded chaetae. Chaetigers 2– 8: notopodia—two rows of nine elongate, narrowly hooded chaetae; one anterior row with four to five bayonet chaetae ( Figure 8K ); two posterior rows with five symmetrical, paleate chaetae with short mucro ( Figure 8L ); neuropodia—two irregular rows (one row) of 19 (13) acicular uncini per torus, facing in the same direction, the oldest upper parts of the tori have only one row (one-quarter of the torus length), main fang surmounted by four rows of teeth, second tooth enlarged, located in the midline, dentition occupying a quarter the length of main fang ( Figure 8J ). Pre- and post-chaetal lobes well developed. Glandular ridge on chaetiger 2: narrow.

Abdomen. Abdominal segments: (24–43). Anterior segments: two transverse rows of very elongate, narrowly hooded chaetae; uncini with the main faing surmounted by three rows of teeth occupying one-half the length of main fang, main fang not extending beyond breast, breast rectangular ( Figure 8M ). Posterior segments: very elongate, narrowly hooded chaetae; uncini similar to those in anterior abdomen, but larger ( Figure 8N ). Pygidium with rounded posterior margin ( Figure 8G ).

Gametes. Holotype female with oocytes in thorax and abdomen; paratype immature.

Methyl green staining. Anterior end of the ventral shield of collar not coloured, posterior end dark ( Figure 8A ). The epidermis is completely glandular (looks like a mat) and stains uniformly in thorax and abdomen, dorsally and ventrally ( Figure 8E–G ).

Remarks

Chone gracilis Moore, 1906 and Chone gracilis Hofsommer, 1913 described from the Kiel Canal (Baltic Sea) are homonyms. The species of Moore is a senior homonym [according to the Principle of Homonym (Article 52.2) and the Principle of Priority (Article 52.3) from the International Commission on Zoological Nomenclature 2000]. It may be used as a valid name. The holotype of Chone gracilis has the ventral margin of the collar incised probably, due to a regeneration process. However, in paratype and additional material it is entire. Deep-water specimens from Oregon have abdominal elongate narrowly hooded chaetae, extremely long. Chone gracilis is unique among the species of Chone distributed in North American waters in having medium-length radiolar tips. Among species in Group I, Chone gracilis and C. infundibuliformis have a short mucro; however, the ventral margin of the collar is higher than dorsal margin in C. gracilis , and slightly higher in C. infundibuliformis .

Figures

Figure 8. Chone gracilis. (A) Anterior end, dorsal view; (B, E) same, ventral view; (C, F) same, lateral view; (D, H) radiolar tip; (G) posterior end; (I) dorsal and ventral lips; (J) thoracic uncinus; (K) bayonet chaeta; (L) paleate chaeta; (M) anterior abdominal uncinus; (N) posterior abdominal uncinus. (E–G) Methyl green staining. (A–D, J– N) [USNM 5513, holotype]; (E–H) [ANSP 2208, paratype].