Aphelochaeta longisetosa

Aphelochaeta longisetosa (Hartmann-Schröder, 1965)

Figure 13

Tharyx longisetosa Hartmann-Schröder, 1965: 222–223; Carrasco 1977: 81–82, figs. 32–33; Rozbaczylo 1985: 155.

Tharyx spp. Hartman 1967: 118.

Material examined. Off Ecuador, SEPBOP, R / V Anton Bruun, Cr. 18B, Sta. 770-C, 10, coll. 10 Sep 1966, 03.267°S, 81.15°W, Menzies trawl, 932 m, 5 specimens (USNM 1490782).— Off central Chile, Valdivia, 39°58ʹS, 73°44.8ʹW, 15 Mar 1960, 84 m, holotype (ZMH P-15068); off Valparaiso, USNS Eltanin Cr. 9, Sta. 752, 26 Sep 1963, 33.23°S, 71.78°W, 209 m (2, USNM 56085); Sta. 753, 26 Sep 1963, 33.27°S, 71.78°W, 192 m (1, USNM 56081).— Central Chile, LUCE, Bahia San Vicente, Punta Liles, Sta. 121, 09 Jun 1949, 36.727°S, 73.136°W, intertidal, rock pools, by hand (1, SMNH); near Puerto Montt, Estero Reloncavi, Bahía Ralún, Sta. M 88, 01 Apr 1949, 41.408°S, S, 72.316°W, 12 m coarse sand (5, SMNH).— Southern Chile, LUCE, Piedra Azul, NW of Punta Quillaipe, Sta. M16E, 04 Dec 1948, 41.525°S, 72.804°W, 40–50 m, coarse sand, trawl (3, SMNH); Canal Caicaen, W of Calbuco, Sta. M46, 24 Jan 1949, 41.771°S, 73.15°W, 13 m, coarse sand, grab (2, SMNH).

Descriptive remarks. This species was described but not illustrated by Hartmann-Schröder (1965) from samples collected from central Chile in sandy sediments in 26– 260 m. Carrasco (1977) collected the species from several stations in Bahia de Concepcion from low water to ca. 20 m and provided a brief description with illustrations of the anterior and posterior end. The specimens from off Valparaiso in 209 m from the Eltanin collection and the various shallow-water specimens from the LUCE agree well with Hartmann-Schröder’s original description and the holotype as well as the descriptions and the illustrations by Carrasco (1977).

The holotype is large, measuring 35 mm long and 1.5 mm wide for about 200 segments. The three specimens from the USNS Eltanin stations 752 and 753 are each broken into two parts: the largest from Sta. 752 is 14 mm long and 5.5 mm wide across the anterior or thoracic region for about 185 setigerous segments. The segments are short and crowded along the entire body as illustrated by Carrasco (1977: figs. 3–4). The anterior region is wide but narrows moderately in the abdominal segments (Fig. 13 A–B). The dorsum is broadly rounded throughout, with parapodial shoulders evident on either side (Fig. 13A, C). A shallow ventral groove begins in anterior abdominal segments, becoming a deep narrow groove in middle and posterior segments (Fig. 13B). The large inflated posterior end reported by both Hartmann-Schröder (1965) and Carrasco (1977) is missing from each of the new specimens.

The pre-setiger region is about as wide as long; the prostomium is triangular, narrowing anteriorly to a nearly pointed tip (Fig. 13 A–C). The peristomium has three rings, each progressively longer and extending dorsally to the mid-point of setiger 1; dorsal tentacles are positioned on the boundary between the peristomium and setiger 1; the first pair of branchiae are on setiger 1 dorsal to the notosetae, and continue on subsequent segments.

Parapodia are lateral to a broadly elevated and rounded dorsum; parapodia have prominent shoulders and the noto- and neuropodia close together; setae emerge from a low torus. The numerous setae of both noto- and neuropodia are long, silky capillaries.

Methyl Green stain. No pattern evident after differentiation.

Remarks. Aphelochaeta longisetosa is distinctive in the relatively large body, expanded anterior and far posterior regions, the very numerous and crowded short segments throughout bearing dense fascicles of long, silky capillary setae. The ventral groove is newly reported. The prominent parapodial shoulders are distinctive. The dorsal midline is not interrupted by a dorsal groove, although a weak mid-dorsal ridge may be present.

This species, originally described as Tharyx longisetosa, was transferred to Aphelochaeta by Blake (1991) as part of his revision of the genus Tharyx. At the same time, Blake (1991) referred Caulleriella longisetosa Hutchings & Murray, 1984 to Tharyx. Thus, two different species have carried the name T. longisetosa. However, these are not homonyms because they currently reside in different genera.

Distribution. Ecuador to southern Chile, intertidal to 932 m.