Autolytus obliquatus Chamberlin, 1919

Nygren, Arne, 2004, Revision of Autolytinae (Syllidae: Polychaeta)., Zootaxa 680, pp. 1-314 : 110-112

Autolytus obliquatus Chamberlin, 1919 (Fig. 52A–F)

Autolytus obliquatus Chamberlin, 1919: 168 –170, pl. 19, fig. 8, pl. 20, fig. 1–3. Autolytus torquens Chamberlin, 1919: 172 –174, pl. 19, fig. 5–7.

Material examined. Kiribati: holotype of A. obliquatus (male stolon) USNM 19336, and holotype of A. torquens (female stolon) USNM 19338, Gilbert Islands, off Apaiang, at surface, 1 Mar 1900.

Description.

Male. Length 6.5 mm for 6+33+3 chaetigers, width 0.4 mm in region a excluding parapodial lobes, 1.0 mm in region b including parapodial lobes. Preserved material yellowish brown, no colour markings. Ciliation not possible to assess.

Prostomium rounded rectangular, wider than long; anterior margin concave (Fig. 52A). Eyes large, 2 pairs, with lenses, eyes situated on ventral and dorsal side of prostomium, ventral pair larger (Fig. 52A). Palps absent. Nuchal epaulettes as small ridges between median antenna and first dorsal cirri.

Median antenna, inserted on posterior part of prostomium, behind dorsal pair of eyes, reaching chaetiger 11–12. Pair of lateral bifid antennae (Fig. 52A), inserted on anterior margin of prostomium, 2 times as long as prostomial width; basal part 1/2 of total length, rami equal in length. Pair of frontal processes, inserted anterolaterally to dorsal pair of eyes, equal in length to 1/3 of prostomial width. Tentacular cirri 2 pairs, dorsal pair as long as prostomial width, ventral pair 1/ 2 in length of dorsal. First dorsal cirri, equal in length to median antenna; achaetous knobs present (Fig. 52A). Second dorsal cirri situated above first chaetigerous lobes. Cirri in region a reciprocally equal, measuring 1/2 of body width; cirri in region b 2/3 as long as cirri in region a, without any alternation in length; cirri in region c inconspicuous. Median ceratophore, and cirrophores on first dorsal cirri, present; cirrophores otherwise absent; small cirrophores on tentacular cirri possibly present. Frontal processes slightly club shaped, cirri in region a fusiform, all other appendages cylindrical.

Parapodia in region a, and c with rounded conical neuropodial lobes, of small to medium size; parapodia in region b flattened, with additional notopodial lobes, rectangular in outline. Single neuropodial acicula in all chaetigers. Unknown number of notopodial aciculae in region b. Neuropodial chaetal fascicle with 7–10 compounds in all chaetigers. Compound chaetae with large distal tooth (Fig. 52C); serration present. Single thin bayonet chaetae (Fig. 52B), subdistally denticulated beginning at chaetiger 1. Notopodial chaetal fascicle with 15–20 swimming chaetae. Anal cirri lost.

Female. Length c. 15 mm for 6+30+(40–50) chaetigers, width in region a 0.5 mm excluding parapodial lobes, in region b 1.1 mm including parapodial lobes. Preserved material yellow (Fig. 52D); no colour markings. Ciliation not possible to assess.

Prostomium rounded rectangular, wider than long, anterior margin concave. Four eyes, with lenses, in trapezoid arrangement, anterior pair larger (Fig. 52D). Palps absent. Nuchal epaulettes reaching beginning of chaetiger 1 (Fig. 52D).

Median antenna lost. Lateral antennae inserted on anterior margin of prostomium, reaching chaetiger 2. Tentacular cirri 2 pairs (Fig. 52D). Dorsal tentacular cirri as long as 1/2 of prostomial width, ventral tentacular cirri 1/3 as long as dorsal. First dorsal cirri, equal in length to lateral antennae, longer than following dorsal cirri in region a (Fig. 52D). Achaetous knobs present. Second dorsal cirri (Fig. 52D) situated above first chaetigerous lobes. Cirri in region a, reciprocally equal, measuring 1/2 of body width; cirri in region b reciprocally equal, c. 1.5 times longer than cirri in region a; cirri in region c shorter than in region b, tapering towards the posterior end. Cirrophores on dorsal cirri in region a, and b, present; cirrophores otherwise absent; small cirrophores on tentacular cirri possibly present. Cirrophores distinct, shorter than parapodial lobes, slightly stouter in region a than in region b. All appendages cylindrical.

Parapodia in region a, and c with rounded conical neuropodial lobes, of small to medium size; parapodia in region b, slightly larger than in region a, with additional notopodial lobes, much smaller than in male. Chaetiger 20 with 2 neuropodial aciculae; 3 anterodorsal and 10 posteroventral notopodial aciculae in same chaetiger. Neuropodial chaetal fascicle with 5–12 compounds in all chaetigers. Compound chaetae with large distal tooth (Fig. 52E); serration present. Single thin bayonet chaetae (Fig. 52F), subdistally denticulated, beginning at region c. Notopodial chaetal fascicle with 15–20 swimming chaetae. Anal cirri lost.

Distribution. Central Pacific. Only known from type locality.

Remarks. Autolytus obliquatus and A. torquens are considered as male and female of the same species. Both taxa have 6 chaetigers in region a, achaetous knobs, large distal tooth in compound chaetae, and a thin bayonet chaetae. The specimens were also collected at the same locality at the same occasion. Stolons with 6 chaetigers in region a, in combination with achaetous knobs are only found in Procerini , and the only described atokes with thin bayonet chaetae in this group are Proceraea anopla , and Imajimaea spp. None of the known Imajimaea species possess a large distal tooth in their compounds, but P. anopla does. Considering these characters, it is possible, that A. obliquatus closest relative is P. anopla . Mature stolons are unknown for P. anopla , but the colour pattern is very distinct in P. anopla , even in preserved specimens; possible synonomy is thus excluded. However, as the atoke is unknown in A. obliquatus , it is not at present certain to what genus it should be referred, it is here considered as Procerini incertae sedis .