Tharyx Webster & Benedict 1887

Genus Tharyx Webster & Benedict, 1887. Emended, Blake, 1991

Type species: Tharyx acutus Webster & Benedict, 1887, by monotypy.

Diagnosis. (Emended). Prostomium conical; peristomium elongate, with pair of grooved dorsal tentacles arising on posterior margin anterior to setiger 1; abdominal segments sometimes beadlike. Noto- and neurosetae arising close to one another, not widely separated. Setae include simple capillaries in anterior and middle setigers, acicular spines present in posterior setigers either in both posterior noto- and neuropodia or only in neuropodia. Long, natatory-like setae present or absent. Acicular spines typically short, curved, sometimes geniculate or sickleshaped, narrowing to expanded tip, typically irregularly notched, or sub-bidentate; tips with pair of stunted or rounded knobs but not with two distinct teeth; spines rarely with oval tips. Capillaries may accompany posterior spines or are absent, when present not alternating with spines. Pygidium with terminal anus and small ventral lobe or disk. Several species with black pigment markings on posterior lateral margin of peristomium.

Remarks. Blake (1991) established that the type species of the genus Tharyx, T. acutus, had knob-tipped hooks or spines in addition to capillaries. This discovery upset the traditional concept of Tharyx, which was based upon specimens having all capillaries (see Hartman 1961). Blake (1991) therefore restricted species of Tharyx to those having knob-tipped acicular spines and moved species having simple and serrated capillaries to the genera Aphelochaeta and Monticellina (now Kirkegaardia), respectively.

Because they have short knobs or lobes on the acicular spines that may appear to be teeth in some views, species of Tharyx have been compared with species of Caulleriella; the two genera are, however, easily distinguished from one another by the position of the noto- and neuropodia. In Caulleriella, the setal fascicles are widely separated from one another, so much so that in cross-section some species appear to have the fascicles at the four corners of body. In Tharyx, on the other hand, the setal fascicles are more laterally placed on the body wall and closer together. Further, the acicular spines of Caulleriella are distinctly bidentate instead of sub-bidentate or with knob-shaped tips.

Although species of Tharyx and Chaetozone both have acicular spines in posterior segments, those of Tharyx are usually smaller, inconspicuous and never form the elaborate cinctured armature so characteristic of Chaetozone (Blake 1996, 2006, 2015). Blake & Göransson (2015) listed 11 species in the genus Tharyx, none of which was from Antarctica. After examination of the holotype and paratypes of Caulleriella obtusa described by Hartmann- Schröder & Rosenfeldt (1990), that species is here referred to Tharyx and is redescribed. In addition, three species, T. coloris n. sp. from the East Antarctic Peninsula, T. moniliformis n. sp. from the deep Weddell Sea, and T. tierralobos n. sp. from off Peru, are new to science bringing the total number of described species of Tharyx to 15.