Kirkegaardia carolina Blake, 2016, new species

Kirkegaardia carolina new species

Figures 9, 10 A–C

Tharyx sp. 3: Blake et al. 1987: Appendix C-2; Hilbig 1994: 941.

Material examined. Western North Atlantic, off Cape Lookout, North Carolina, U.S. South Atlantic ACSAR Program Cruise 1, R/ V Columbus Iselin Sta. 2, Rep. 1, 12 November 1983, 34°14.87′N, 75°43.79′W, 1013 m, coll. J.A. Blake, Chief Scientist, holotype (USNM 1407162); Sta. 1, Rep. 2, 11 November 1983, 34°16.36′N, 75°45.50′W, 640 m, coll. J.A. Blake, Chief Scientist, 3 paratypes (USNM 1407163).

Description. An elongate, threadlike, fragile species; holotype from Sta. 2 complete, broken into two parts, 9.4 mm long, 0.2 mm wide across thorax and 0.23 mm wide across middle abdominal segments for about 75 setigers; complete paratype (very fragile) from Sta. 1 complete, 7.3 mm long, 0.3 mm wide with about 65 setigers (Fig. 10 A). Bodies of some paratypes partially covered by remnants of thin, transparent tattered tube (Fig. 10 A–C). Color in alcohol, light tan with no pigment.

Pre-setigerous region about 1.7x as long as wide. Prostomium triangular, narrowing to rounded tip (Fig. 9 A); eyes absent; nuchal organs not observed. Peristomium elongate, slightly wider than anterior setigers, about 1.3x as long as wide, extending posteriorly to between setiger 1; lateral grooves producing three annular rings; dorsal surface elevated with broad dorsal ridge (Fig. 9 A). Dorsal tentacles arising on posterior part of peristomium; first pair of branchiae posterior to tentacles on setiger 1 at posterior margin of setiger 1, dorsal to notosetae (Fig. 9 A). Subsequent branchiae in same position on following thoracic setigers.

Thoracic region with 8–10 setigerous segments, each about 3x as wide as long (Fig. 9 A); thoracic parapodia not elevated, dorsal surface between parapodia continuous over dorsum; body without ventral groove or ridge. Abdominal segments weakly moniliform, increasing in length to about 2.5x as long as wide (Fig. 9 B); far posterior segments becoming narrow again, wider than long, forming elongated, weakly expanded and dorsoventrally flattened posterior section terminating in pygidium with dorsal anus overlying a conical lobe (Fig. 9 C).

Parapodia reduced to low mounds from which setae project; thoracic notosetae consisting of long simple capillaries throughout, numbering 6–8 per notopodium in thoracic setigers, reduced to 4–6 in abdominal segments; denticulated notosetae absent. Thoracic neurosetae 6–8 long simple capillaries, reduced to 4–6 per neuropodium in anterior abdominal segments, becoming shorter, wider basally, with minute denticles along one edge visible from 400– 1000x; denticulated setae first present from setigers 15–20; denticles with short pointed teeth directed lateral to main axis of shaft (Fig. 9 D).

Methyl Green stain. Tip of prostomium stains weakly followed by weak diffuse bands around peristomium; narrow intersegmental grooves of thoracic region retain stain; entire intestinal track absorbs stain, but de-stains rapidly.

Etymology. This species is named for its type locality off Cape Lookout, North Carolina.

Remarks. Kirkegaardia carolina n. sp. is a small, threadlike species that co-occurs at the shallower slope stations off Cape Lookout with two congeners including K. baptisteae and K. kladara n. sp. Of these, K. carolina n. sp. is most similar to the larger, more robust K. baptisteae. Both species have tessellated tubes and 2–3 peristomial annulae. However, K. baptisteae has distinct parapodial shoulders in the thoracic region between which is a broad elevated dorsal surface; in contrast, K. carolina n. sp. has no parapodial shoulders and the surface of the thoracic region is continuous across the dorsum. K. carolina n. sp. has a dorsal ridge along the peristomium, first branchiae on setiger 1, lacks denticulated notosetae, has no expansion of the thoracic segments on the venter, and has a narrow posterior end that is only weakly expanded. In contrast, K. baptisteae has no peristomial dorsal ridge, the first branchiae occur lateral to the dorsal tentacles on the peristomium, has denticulated notosetae, has expanded thoracic segments on the venter, and the posterior end is broadly expanded. Additionally, while K. baptisteae has no MG staining pattern of any kind, K. carolina n. sp. retains stain in the intersegmental grooves of the thoracic region.

Another species that is small and threadlike and that also has tessellated tubes and branchiae from setiger 1 is K. fragilis n. sp. from abyssal depths in the Pacific Ocean. This species however, differs from K. carolina n. sp. in having denticulate notosetae, a more expanded posterior end, and no annular rings on the peristomium.

Biology. Kirkegaardia carolina n. sp. inhabits muddy sediments in upper and middle slope depths on the continental slope off North Carolina. Data from sub-sectioned cores taken and processed individually from box cores collected in South ACSAR Cruise 1 suggest that the species occurred in the lower 2–10 cm of individual cores. Other cirratulids in the same samples were considered to be surface deposit feeders (Blake 1994).

Thin membranous tube material that is readily removed adheres to some of the paratypes (Figs. 10 A–C). This is similar to the same tattered or tessellated tube material reported for K. baptisteae, K. tesselata, and several other species described in this study.

Distribution. Kirkegaardia carolina was collected only from samples along the continental slope off Cape Lookout, North Carolina, in depths of 640–1013 m. The species did not occur on the nearby Cape Hatteras shelf or in the companion surveys off the U.S. Mid- and North Atlantic slopes.