Autolytus pacificus Treadwell, 1943

Nygren, Arne, 2004, Revision of Autolytinae (Syllidae: Polychaeta)., Zootaxa 680, pp. 1-314: 187-189

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Autolytus pacificus Treadwell, 1943


Autolytus pacificus Treadwell, 1943  (Fig. 95 A –D)

Autolytus pacificus Treadwell, 1943: 40  , pl. 2, fig. 28–30.

Material examined. Samoa: 3 syntypes USNMAbout USNM 20089, at surface, Apr 1929.

Description. Length 1.7–2.2 mm for 6 +(10–13)+(4–5) chaetigers, width 0.25 mm in region a excluding parapodial lobes, width 0.4 mm in region b including parapodial lobes (Fig. 95 A). Preserved material yellowish, without colour markings. Ciliation not possible to assess.

Prostomium rounded rectangular, wider than long, anterior margin slightly concave. Four eyes, with lenses, laterally positioned on ventral and dorsal side of prostomium, ventral pair larger (Fig. 95 A). Palps absent. Nuchal epaulettes not observed, absent?

Median antenna, inserted on front margin of prostomium, slightly behind lateral antennae, reaching chaetiger 3. Lateral antennae, length 2 / 3 of median antenna. One pair of small tentacular cirri seen on one individual, or these may represent the first dorsal cirri. Antennae cylindrical to slightly clavate, thick. Achaetous knobs absent. Dorsal cirri absent (Fig. 95 A).

Parapodia in region a, and c with rounded neuropodial lobes of very small size; parapodia in region b larger with additional notopodial lobes. Neuropodial aciculae numbering 1–2 in all chaetigers; 3–4 anterolateral and 5–6 posteroventral notopodial aciculae in region b. Neuropodial chaetal fascicle with 4–5 simple knob­like chaetae (Fig. 95 C, D), bifurcated distally, teeth unequal; in addition 1 hook­like bidentate chaetae (Fig. 95 B), with small distal tooth, present in most chaetigers in region b. Notopodial chaetal fascicle with 10–15 swimming setae, length 1 / 2 of body width. Anal cirri lost, absent?

Additional information. According to Treadwell (1943), one of the specimens were found with a ventrally attached egg sac.

Distribution. Central Pacific. Samoa. Only known from type locality.

Remarks. The simple knob­like chaetae are similar to those found in A. emertoni  , but bifurcated; the hook­like chaetae are unique, and nothing similar is found in any other known member of Autolytinae  . There is no described atoke to which A. pacificus  may be referred. The presence of only simple chaetae, absence of bayonet chaetae, very small parapodia in unmodified regions, and absence of dorsal cirri suggest a close affinity with Levidorum  . However, it would be premature to assign A. pacificus  to Levidorum  as very little is known of the stolons in this group. See also A. emertoni  .

Autolytus scheremetevskiyi Averincev, 1982  (Fig. 96 A –D)

Autolytus scheremetevskiyi Averincev, 1982: 21  –22, pl. 3, fig. 1–3.

Material examined. Antarctic Sea: holotype, ZILAbout ZIL 42045View Materials, Amery shelf ice, 45 m, rocks, 18 Feb 1972.

Description. Holotype is an anterior fragment of 12 chaetigers and a few newly achaetous regenerating segments. Length 3.2 mm, width 0.7 mm. Preserved material yellowish, no colour markings. Body, excluding parapodial cylindrical, venter flattened; body width fairly constant. Ciliation as 1 troch per segment (Fig. 96 A).

Prostomium rounded rectangular, wider than long. Four eyes, with lenses, in trapezoid arrangement, anterior pair only slightly larger. Eyes separated; eye spots present (Fig. 96 B). Palps difficult to separate from prostomium (Fig. 96 A), in dorsal view projecting 1 / 3 of prostomial length, fused. Extension of nuchal epaulettes to beginning of first chaetiger, more laterally positioned than is usual (Fig. 96 A).

Antennae lost. Dorsal tentacular cirri reaching chaetiger 1, ventral tentacular cirri 1 / 3 as long as dorsal pair. First dorsal cirri as long as dorsal tentacular cirri, second dorsal cirri as long as following dorsal cirri. Alternation in direction of cirri not assessed. Cirri equal, length 1 / 3 of body width. Cirrophores present on tentacular cirri, and all dorsal cirri. Cirrophores and cirrostyles equal; cirrophores much shorter than parapodial lobes; cirrophores shorter than cirrostyles. Tentacular cirri and first dorsal cirri club shaped (Fig. 96 A), dorsal cirri from chaetiger 2 with precipitation, not possible to evaluate shape.

Parapodial lobes rounded, large (Fig. 96 A). All chaetigers with 2–3 aciculae. Chaetal fascicle with c. 20 compounds in all chaetigers. Compound chaetae with large distal tooth, larger than subdistal tooth (Fig. 96 A); serration present. Bayonet chaetae not found.

Pharynx with sinuation anterior and lateral to anterior part of proventricle. Trepan in chaetiger 4–5, detailed structure not possible to evaluate. Proventricle equal in length to 3 segments in chaetiger 9–11 with c. 50 rows of square shaped muscle cells. Pygidium lost.

Reproduction. Unknown

Habitat. Rocks, 45 m.

Distribution. Antarctic. Only known from type specimen.

Remarks. Autolytus scheremetevskiyi  is a peculiar autolytine, unfortunately only known from this anterior fragment. It is unique in having distal tooth larger than subdistal tooth, and more laterally positioned nuchal epaulettes than usual. The specimen has large parapodial lobes from chaetiger 1, normally the parapodia is slightly smaller in the anterior­most chaetigers. This, in combination with the rather small head with diffuse palps could indicate that the specimen has a regenerated head. As many of the characters, including the trepan, is unknown, it is considered as incertae sedis  within Autolytinae  .


Smithsonian Institution, National Museum of Natural History


Academy of Sciences, Zoological Institute














Autolytus pacificus Treadwell, 1943

Nygren, Arne 2004


Autolytus pacificus

Treadwell 1943: 40


Autolytus scheremetevskiyi

Averincev 1982: 21