Chaetozone malmgreni Blake, 2015, new species

Chaetozone malmgreni new species

Figures 11–12

Chaetozone setosa: Blake 1996: 274 –276, Fig. 8.1. Not Malmgren 1867.

Material examined. Oregon, Clapsop County, off Tillamook Head, Sta. SMG 1937, Scallops Island, 45°53.6ʹN, 124°11.9ʹW, 109 m, 0.1 m 2 Smith-McIntyre grab, coll. 7 Nov 1981, A.G. Carey, Jr. holotype (LACM-AHF Poly 6542), one paratype (LACM-AHF Poly 6543).

Description. A large species, two complete specimens; holotype largest, 25 mm long, 2.5 mm wide for 106 setigers; paratype 18 mm long, 1 mm wide for 82 setigers. Color in alcohol light tan to brown, lacking any distinctive body pigment. Body long, arched dorsally, with shallow, narrow, mid-dorsal groove along entire length of body (Figs. 11 A, 12A), most prominent in anterior setigers, but reemphasized in far posterior segments by overlap of setae and membranes of dorsal cinctures; venter flattened, with deep prominent mid-ventral groove (Fig. 12 B) continuing along entire body through cinctured posterior segments (Fig. 11 F).

Prostomium long, narrow, pointed on anterior end (Figs. 11 A–B, 12B, D); eyes absent; nuchal organs elongated slits on posterior margin of prostomium (Fig. 11 B); peristomium with large anterior inflated buccal region followed by two narrow annulations, second annulation interpreted as an achaetous segment bearing a pair of dorsal tentacles and a pair of branchiae positioned laterally (Fig. 11 A–B). Subsequent setigers with branchiae dorsal to notosetae (Figs. 11 A–B, 12D); anterior branchiae thicker than those of middle segments.

Setiger 1 of approximately same size as preceding achaetous segment and following segments; podial lobes reduced to inconspicuous ridges in anterior setigers, becoming inflated and conspicuous in middle setigers, greatly enlarged with elevated ridges in posterior setigers on deeply cinctured segments bearing conspicuous armature (Fig. 12 A–C); posterior segments separated by deeply cut intersegmental furrows and with highly elevated membranous podial lobes from which spines and capillaries emerge, forming full cinctures (Figs. 11 F, 12A–C); small, ciliated organ present between ventral-most notopodial spine and dorsal-most neuropodial spine (Fig. 11 E); notopodial spines directed ventrally, neuropodial spines directed dorsally.

Noto- and neurosetae from setiger 1 all capillaries, numbering about 6–7 per fascicle; each seta thickened, with short fibrils usually apparent along broadest edge; these capillaries remaining thick and long until far posterior setigers. Acicular spines first present from setigers 20–35 in neuropodia and 40–45 in notopodia, numbering 2–3 at first, accompanied by an equal number of thickened capillaries; neuropodial spines numbering 8–9 per fascicle and notopodial spines numbering 7–8 per fascicle in far posterior setigers, spines forming complete setal cinctures with up to 17 spines on a side (Fig. 9 F); spines accompanied by alternating thin capillaries (Fig. 11 F); spines blunttipped, slightly curved, with weak node or notch at point of emergence from podial lobe (Fig. 11 E); spines with thick borders and fine internal striations.

Last few cinctured setigers narrowing to pointed posterior end (Fig. 12 A–C); pygidium with terminal anus and small flattened ventral lobe (Figs. 11 C–D, 12C).

Methyl Green staining pattern. Stain imparts distinct pattern on prostomium, peristomium, and anterior parapodia (Fig. 12 D). Anterior tip of prostomium unstained, then with transverse band, then clear again; peristomium lightly stained, but with deeper stain on dorsal surface of last achaetous ring. Anterior parapodia deeply stained laterally, with bands extending across venter and sometimes dorsum.

Remarks. Chaetozone malmgreni n. sp. is characterized by having one large and one narrow achaetous peristomial ring followed by another narrow achaetous segment that bears both the tentacles and first pair of branchiae. In addition, this species has deep dorsal and ventral grooves and a distinct MG staining pattern. Other species having the dorsal tentacles and first pair of branchiae on a single achaetous segment include C. lunula Blake, 1996 from northern California, C. corona Berkeley & Berkeley, 1941, from southern California, C. allanotai Blake, 2006 from deep-water offshore California, and C. michellae Magalhães & Bailey-Brock, 2013 from Hawaii. C. lunula, however, has the peristomium shifted posteriorly so that the dorsal tentacles and first pair of branchiae are at the level of setiger 1; further differences with C. malmgreni n. sp. are that the ventral-most neuropodial acicular spine of C. lunula is typically bidentate and the pygidium has a terminal cirrus. C. corona differs from all Chaetozone species in North America in having neuropodial acicular spines beginning on setiger 1. C. allanotai belongs to a group of species having a distinct type of acicular spine where the fine tip curves back and fuses with the shaft. C. michellae has a deep dorsal groove along the entire body, whereas C. malmgreni has both a shallow dorsal groove and a deep ventral groove along the body; the two species have very different MG staining patterns.

There is also some similarity between C. malmgreni n. sp. and C. anasima Doner & Blake, 2006 and C. hystricosa Doner & Blake, 2006, both described from New England waters. However, both of these species have indistinct annulations on the peristomium and the exact origin of the tentacles and first pair of branchiae are vague. Etymology. The species is named for Dr. A. J. Malmgren, who described the first species of Chaetozone, C. setosa, in his classic work on polychaetes from Greenland, Spitsbergen, Iceland, and Scandinavia in 1867.

Distribution. Known only from continental shelf sediments, offshore Oregon, 109 m.