Tharyx circacutus, Blake, James A., 2015

Blake, James A., 2015, New species of Chaetozone and Tharyx (Polychaeta: Cirratulidae) from the Alaskan and Canadian Arctic and the Northeastern Pacific, including a description of the lectotype of Chaetozone setosa Malmgren from Spitsbergen in the Norwegian Arctic, Zootaxa 3919 (3), pp. 501-552 : 536-538

Tharyx circacutus new species

Figures 21‒22

Tharyx sp. N 1: Provisional name, Washington State Department of Ecology’s Marine Sediment Monitoring Program (MSMP); database (PSEMPMarineBenthicSpeciesList_sortable.xlsx) online: http://www.eopugetsound.org/species/custom-lists/306.

Material examined.— Washington, Strait of Juan de Fuca, east central Port Angeles Harbor, coll. WA Department of Ecology, Puget Sound Ecosystem Monitoring Program ( PSEMP), Sta. 1121, 18 June 2013, 48° 07.9026ʹ N, 123° 23.2853ʹ W, 29.5 m depth, in sandy silt, holotype (LACM-AHF Poly 6556), 12 paratypes (LACM-AHF Poly 6557).

Description. Holotype 14.8 mm long, 0.43 mm wide for ca. 70 setigerous segments; largest paratype 16.4, mm long, 0.32 mm wide with 95 setigers. Body light tan in alcohol; with a cluster of lateral black pigment spots on posterior peristomium, otherwise without pigment except for a few cells surrounding nuchal organs on some specimens. Body long, slender, with first 15‒20 segments expanded, widest part of body with narrow, crowded segments each four times wider than long; following segments becoming as long as wide, with some in middle of body almost moniliform; far posterior segments narrowing to small pygidial segment. Body mostly cylindrical in cross section, with weakly developed ventral groove in far posterior segments.

Prostomium triangular, tapering to pointed anterior margin; eyes absent ( Figs. 21 A–B, 22A‒B); nuchal organs narrow slits surrounded by pigmented cells ( Fig. 21 B). Peristomium wider than long, with one annulation visible laterally and dorsally ( Figs. 21 A‒B, 22A); dorsal midline with a low, weakly developed ridge extending to end of peristomium ( Figs. 21 A, 22A). Paired dorsal tentacles arising from posterior margin of peristomium; first pair of branchiae arising lateral and posterior to tentacles on posterior edge of peristomium ( Figs. 21 A, 22A); second pair of branchiae arising from posterior margin of setiger 1, dorsal to notosetae.

Parapodia low ridges from which setal fascicles arise; noto- and neuropodial setal fascicles positioned close to one another throughout. Notosetae all capillaries throughout ( Fig. 21 D‒E); 5–7 in anterior setigers, reduced to 4–5 in far posterior parapodia. Neurosetae all capillaries in anterior setigers, with ventral-most setae transitioning to shorter, recurved spines in middle body (setiger 38 in holotype and setiger 40 in largest paratype); spines curved, somewhat geniculate with blunt tip; shortest spines in ventral position ( Fig. 21 F‒H); spines accompanied by 2–4 dorsal capillaries at first ( Fig. 21 D), far posterior setigers with 3–5 spines and no capillaries ( Fig. 21 E).

Pygidium with dorsal anus and small ventral lobe ( Figs. 21 C, 22C‒D).

Methyl Green staining pattern. Stain retained in intersegmental grooves of some anterior and middle body segments; weak mid-ventral stain sometimes evident.

Remarks. The nature of the prostomium and peristomium of Tharyx circacutus n. sp. are typical for most species of Tharyx where branchiae begin posterior to the tentacles at the posterior margin of the peristomium and the second pair of branchiae begin on setiger 1. Curved posterior spines are limited to the neuropodia and begin about three-fourths of the way along the body; in far posterior segments the spines assume the blunt, knob-tipped appearance of other Tharyx spp.

T. circacutus n. sp. most closely resembles the type species, T. acutus , from the northeastern United States in having the posterior spines limited to the neuropodia ( Blake 1991). However, the pigmented nuchal organs, the very narrow almost moniliform posterior end, and the very narrow, slender body differ noticeably from T. acutus , which lacks pigmented nuchal organs and in which the entire body and posterior end are more robust with none of the segments appearing moniliform. Further, the body of T. circacutus n. sp. is nearly round in cross section whereas the body of T. acutus is thicker and somewhat dorsoventrally flattened.

Etymology. The Latin circa for around or near is combined with the Latin term acutus for sharp pointed and the species name of the type-species Tharyx acutus , with which this new species is closely related.

Distribution. Known from shallow subtidal habitats in the Puget Sound.

Figures

FIGURE 21. Tharyx circacutus n. sp. A, anterior end, dorsal view; B. anterior end, lateral view; C, posterior end, lateral view; D ‒ E, posterior parapodia, anterior views; F ‒ H, neuropodial acicular spines in posterior parapodia. (A ‒ B, holotype, LACM- AHF Poly 6556; C ‒ H, paratype LACM-AHF Poly 6557).

FIGURE 22. Tharyx circacutus n. sp. Photomicrographs: A, anterior end, dorsal view; B, anterior end, left lateral view; C, posterior end, ventro-lateral view; D, posterior end, right lateral view. (A, holotype, LACM-AHF Poly 6556; B ‒ D, paratype, A LACM-AHF Poly 6557; all stained with Shirlastain A).