Kirkegaardia chilensis Blake, 2016, new species

Kirkegaardia chilensis new species

Figure 29

Tharyx spp. Hartman 1967:118 (in part).

Material examined. Pacific Ocean, off Western South America, Southwestern Chile, off Valparaiso, USNS Eltanin Cruise 9, Sta. 750, 33.02°S, 71.88°W, 624 m, coll. 26 September 1963, Petersen grab, holotype and paratype (USNM 1013897–8); Cruise 5, Sta. 208, off Concepcion, 35.65°S, 73.13°W 957 m, coll. 11 September 1962, Menzies Trawl, 7 paratypes (USNM 56079), 1 additional paratype (USNM 1013899).

Description. A small species with thin, narrow body; holotype incomplete, 11.7 mm long, 0.35 mm wide across thorax for 56 setigers. Color in alcohol: light tan, no pigment apparent.

Each specimen with very elongate, smooth peristomial region; thoracic region narrow, with 16–20 crowded segments; venter swollen between about setigers 8–14 (Fig. 29 A); long abdominal region with longer segments, sometimes weakly moniliform; posterior end remaining narrow, not expanded in mostly complete paratypes, pygidium missing from all specimens. Abdominal segments with venter flattened, with weak mid-ventral channel containing low ridge extending along midline. Parapodia of thoracic region elevated over dorsal surface producing distinct mid-dorsal channel; middle surface of this channel raised forming a weak and narrow ridge (Fig. 29 B).

Pre-setigerous region elongate, 1.9x as long as wide. Prostomium short, oval, broadly rounded on anterior margin (Fig. 29 A–B); eyes absent; nuchal organs not observed. Peristomium about 1.8x as long as wide, smooth, with two weakly developed lateral grooves, often not apparent (Fig. 29 A–B); mid-dorsal peristomial ridge or crest absent; short proboscis everted on some specimens. Dorsal tentacles arising from posterior part of peristomium (Fig. 29 A–B); first pair of branchiae also on peristomium, posterolateral to dorsal tentacles (Fig. 29 A–B); second pair of branchiae on setiger 1 (Fig 29 B); following branchiae at posterior margin of individual setigers, dorsal to notosetae; branchiae all short, most missing.

Parapodia well developed in thoracic region, dorsally forming lateral borders of dorsal groove (Fig. 29 B); parapodia reduced to setal tori posteriorly. Notosetae long capillaries throughout, up to 7–9 per fascicle in anterior setigers, decreasing to 5–6 posteriorly; denticulated notosetae absent; neurosetae, shorter, thicker than notosetae, numbering 8–10 per fascicle, with very fine denticles along shaft in middle abdominal setigers from setiger 30, visible only at 1000x (Fig. 29 C–D).

Methyl Green stain. Venter of expanded part of thorax stains weakly, otherwise no staining reaction.

Etymology. This species is named for its location on the Chilean continental slope.

Remarks. Kirkegaardia chilensis n. sp. is part of the group of 12 species having the thoracic parapodia elevated over a mid-thoracic channel and is most similar morphologically to K. dorsobranchialis, K. carinata n. sp., and K. cryptica in having an entirely smooth peristomium with no dorsal ridge. Of these, K. carinata n. sp. and K. chilensis n. sp. have a prominent mid-dorsal ridge within the thoracic dorsal channel that is absent in both K. dorsobranchialis and K. cryptica. K. chilensis n. sp. differs from K. carinata n. sp. in having only a weak MG staining pattern limited to the thoracic region instead of the intense and spectacular pattern on the peristomium, thoracic region, and abdominal parapodia of K. carinata n. sp. In addition, the mid-ventral segments of the thoracic region of K. chilensis n. sp. are expanded, whereas all of the thoracic segments of K. carinata n. sp. are the same size.

Distribution. Off western Chile, slope depths of 624– 957 m.