Kirkegaardia baptisteae Blake 1991, new combination

Kirkegaardia baptisteae (Blake, 1991) new combination

Figures 7–8

Tharyx annulosus:? Day 1973: 82; Maciolek-Blake et al. 1985:18 –76; Blake & Baptiste 1985: 140 –178; Maciolek & Grassle 1987: 306. Not Hartman, 1965.

Tharyx sp. 2: Blake et al. 1987: 8 –85, fig. 15; Maciolek et al. 1987: Appendix D-2, 1987b: Appendix D-2; Blake & Grassle 1994: 855.

Monticellina baptisteae Blake, 1991: 24 –26, Fig. 4; Hilbig 1994: 941; Hilbig & Blake 2000 147–164.

Material examined. Western North Atlantic, Off Cape Lookout, North Carolina, U.S. South Atlantic ACSAR Program Cruise 1, R/ V Columbus Iselin Sta. 1, replicate 1, 11 November 1983, 34°16.36′N, 75°45.50′W, 640 m, coll. J.A. Blake, Chief Scientist, 22 specimens (USNM 1407157). — Off New England, Georges Bank, BIMP, Cruise M-3, R/ V Endeavor, Sta. 5-8, February 1982, 40°40.1′N, 67°46.1′W, 80 m, coll. G. Hampson, WHOI, Chief Scientist, 9 specimens (USNM 1407153); Sta. 5-14, February 1982, 40°39.5′N, 67°44.7′W, 86 m, coll. G. Hampson, WHOI, Chief Scientist, 9 specimens (USNM 1407154); Sta. 5-16, February 1982, 40°40.6′N, 67°46.1′W, 78 m, coll. G. Hampson, WHOI, Chief Scientist, 14 specimens (USNM 1407155); Cruise M-6, R/V O ceanus, Sta. 12, 26 Nov 1982, 40°22.2′N, 68°29.8′W, 103 m, coll. G. Hampson, WHOI, Chief Scientist, 4 specimens (01407156).— Off Georges Bank, Lydonia Canyon, US North Atlantic ACSAR Program, Cruise 1, R/ V Cape Hatteras, Sta. 7, replicate 3, 10 Nov. 1984, 40°27.52′N, 67°40.36′W, 560 m, coll. G. Hampson, WHOI, Chief Scientist, 325 specimens (USNM 1407152). — Massachusetts Bay, MWRA long-term monitoring program, 2007 survey, R/ V Aquamonitor, Sta. FF-01A, Rep. 2, 30 Jul 2007, coll. P. Neubert, 42.564°N, 70.676°W, 35.8 m, 15 specimens (MCZ 135292).

Description. An elongate, threadlike species, complete typical specimen from off Georges Bank 14.5 mm long, 0.4 mm wide with 155 setigerous segments. Thoracic region with 10–14 setigers depending upon size; each thoracic segment narrow, 5x wider than long, followed by longer abdominal segments about 2x as wide as long, none appearing moniliform or beadlike; far posterior segments again becoming narrow and crowded producing expanded pre-pygidial region rounded dorsally (Fig. 7 C) and flattened ventrally with a weak mid-ventral groove or channel (Fig. 8 C). Pygidium a rounded segment with narrow terminal lobe (Figs. 7 C, 8C). Color in alcohol light tan with venter of thoracic region sometimes with brownish caste evident on individual segments.

Pre-setigerous region relatively short, about 1.5x as long as wide. Prostomium triangular, tapering to narrow apex (Figs. 7 A–B; 8A, D); eyes absent; nuchal organs as narrow slits on posterior lateral margins (Fig. 7 B). Peristomium incised with two distinct lateral grooves producing three annular rings (Figs. 7 A–B, 8B), but these not extending across dorsum. Dorsal tentacles arising on posterior border of peristomium extending between parapodia of setiger 1 (Fig. 7 A; 8D). First pair of branchiae lateral to dorsal tentacles on peristomium (Fig. 7 A–B); second pair of branchiae on posterior medial border of setiger 1, subsequent thoracic segments with branchiae in similar location (Fig. 7 A–B).

Thoracic region with parapodia forming lateral shoulders, but not elevated and shifted dorsally over midline as in related species; dorsal surface broadly elevated above parapodia, but with each segmental groove continuous across dorsum (Fig. 7 A–B). Branchiae dorsal to notopodia; parapodia with only low tori or mounds from which setae project; notosetae typically longer than neurosetae; long natatory notosetae not observed. Notosetae numbering 10–14 per fascicle in thoracic region, reduced to 5–6 in abdominal segments; neurosetae numbering 8– 10 per fascicle in thoracic segments, reduced to 5–6 in middle and posterior abdominal segments. Capillary setae of thoracic segments long, narrow, with no visible serrations or denticles along margin; from anterior abdominal segments and along most of abdominal region, some notosetae and all neurosetae with distinct denticles along cutting edge. Notosetae of abdominal segments include 2–3 long thin, smooth capillaries and 1–2 short, thicker capillaries with fine denticles (Fig. 7 D). Neurosetae of abdominal segments all short, thick denticulated capillaries (Fig. 7 E). Setae arranged in fascicles such that denticulated edge of notosetae directed ventrally while same edge of neurosetae directed dorsally, vis-à-vis. Denticles visible on both noto- and neurosetae at 400x but details of fine denticles not apparent until 1000x magnification.

Methyl Green stain. There is no MG staining pattern of any kind on K. baptisteae: the stain disappears entirely in clean alcohol.

Remarks. This redescription of K. baptisteae provides additional details and corrects some errors in the original description (Blake 1991). In the original account the peristomium was described as smooth and without annulations. This is not correct: there are actually two lateral grooves variably developed and best seen with SEM or when stained with Shirlastain A. These grooves do not extend over the dorsum, but two or three annular rings are readily apparent laterally. The dorsal tentacles arise at the level of setiger 1 but are on a short extension of the posterior peristomium onto the dorsum between the first two parapodia. The first pair of branchiae actually occur lateral to the dorsal tentacles on the peristomium; these were not reported in the original description and again the scars or stubs of these are best observed with SEM or when stained with Shirlastain A. The second pair of branchiae occur on the posterior border of setiger 1. The far posterior segments containing the pygidium are more expanded and flattened ventrally than reported and illustrated by Blake (1991).

Among the known species of Kirkegaardia including those described in this paper, K. baptisteae is most closely related to K. dutchae n. sp. from the Puget Sound in the northeastern Pacific. The two species differ in that K. baptisteae has ventral thoracic glands that are naturally light tan in color and do not produce a MG staining pattern of any kind, with the stain disappearing entirely in clean alcohol; however, these glands may retain the pink coloration from Rose Bengal for a time after storage. In contrast, the same glands of K. dutchae n. sp. display a distinct MG pattern to the venter of the thoracic region after differentiation. Other differences include details of the denticulated capillaries of the neurosetae and the lack of denticulated notosetae in K. dutchae n. sp. that are present in K. baptisteae. In addition, the first pair of branchiae of K. baptisteae occur lateral to the dorsal tentacles on the posterior edge of the peristomium; in K. dutchae n. sp. the first pair of branchiae are on the anterior margin of setiger 1 and the second pair are on the posterior margin of the same setiger resulting in two pairs of branchiae originating from the first setigerous segment.

Biology. Kirkegaardia baptisteae is one of the most common and widespread species of Cirratulidae along the U.S. Atlantic coast, ranging from the Canadian-US border to off North Carolina in shelf and slope depths. The species is typically found in well-mixed fine sediments and is often among the dominant species in offshore benthic communities (Hilbig & Blake 2000). Specimens have been observed with weakly tattered tubes (Fig. 8 D) through which branchiae may project. However, these tubes consist of light, thin-textured materials that are easily removed from the worm and are similar to those of K. tesselata from off California. They are not the more heavily textured tubes that characterize other species such as K. neotesselata n. sp., which are difficult to remove and result in distortion of the enclosed worms upon preservation.

As part of the 3-year monitoring program on Georges Bank, Blake & Baptiste (1985) developed data on the reproduction and life history of several abundant polychaete species including K. baptisteae, which at the time was misidentified as Tharyx annulosus. At station 13 (ca. 70 m), the species appeared to produce gametes in the winter and spawn in the spring. Reproductive data included the presence of males in November (19.2%) and February (27.9%) and females in July (22.2%), November (42.3%) and February (32.6%). No gametes were observed in individuals collected in May. Size frequency data followed this sequence of reproductive data with the highest percentage of juveniles (6.6%) present in the July collections. A similar pattern was observed for K. baptisteae collected at Station 5-1 (ca. 84 m), except that some males and females were observed in samples collected in May. A distinct difference, however, was observed in the population structure. All collections at Station 5-1, which had higher sand content in the samples, included fewer specimens but larger individuals than those found at Station 13 which has muddier sediments.

Several specimens collected in November from ACSAR Sta. 7 in Lydonia Canyon off Georges Bank were sexually mature females with large yolky eggs that produced swollen segments that were nearly moniliform in shape. The eggs numbered 8–10 per segment and ranged in diameter from 189–256 µm in their longest dimension (average = 231.4 µm, 1 SD = 25.86). The large size of these eggs suggests direct development of embryos that are most likely released in the tubes. The presence of large, mature eggs in November supports the data collected by Blake & Baptiste (1985) where the highest percentage of females was identified in November 1981 with the next highest in February 1982.

Distribution. New England to Cape Lookout, North Carolina, in shelf and upper slope depths, 30– 640 m.