Kirkegaardia hampsoni Blake, 2016, new species

Kirkegaardia hampsoni new species

Figures 12–13

Tharyx dorsobranchialis: Maciolek-Blake et al. 1985: 75, 142, Appendix B-3, Appendix D-8. Not Kirkegaard 1959. Monticellina dorsobranchialis: Blake, 1991 (In part); Hilbig & Blake 2000: 162.

Type Material examined. Western North Atlantic, Offshore New England, Georges Bank, BIMP, Cruise M-8, R/ V Gyre, Sta. 13, 21 May 1983, coll. G. Hampson, WHOI, Chief Scientist, 40°29.5′N, 70°12.6′W, 70 m, holotype and 34 paratypes (USNM 1407138–9); Cruise M-1, R/ V Eastward, Sta. 13, 9 July 1981, coll. M. Rawson, Lamont-Doherty Geological Observatory, Chief Scientist, 40°29.5’N, 70°12.6’W, 70 m, 34 paratypes (USNM 1407140; Cruise M-2, R/V Oceanus, Sta. 13, 0 9 Nov 1981, coll. M. Rawson, Lamont-Doherty Geological Observatory, Chief Scientist, 40°29.5’N, 70°12.6’W, ~ 70 m, 52 paratypes (USNM 1407141); Cruise M-3, R/ V Endeavor, Sta. 13, 11 Feb 1982, coll. G. Hampson, WHOI, Chief Scientist, Sta. 40°29.5’N, 70°29.2’W, 69 m, 65 paratypes (USNM 1407142); Cruise M-4, R/V Cape Henlopen, Sta. 13, coll. G. Hampson, WHOI, Chief Scientist, 18 May 1982, 40°29.3’N, 70°12.5’W, 70 m, 29 paratypes (USNM 1407143); Cruise M-5, R/V Oceanus, Sta. 13, 28 Jul 1982, coll. G. Hampson, WHOI, Chief Scientist, 40°29.3’N, 70°12.6’W, 62 m, 4 paratypes (USNM 1407144); Cruise M-6, R/V Oceanus, Sta. 13, 27 Nov 1982, coll. G. Hampson, WHOI, Chief Scientist, 40°29.3’N, 70°12.4’W, 67 m, 35 paratypes (USNM 1407145); Cruise M-7, R/ V Endeavor Sta. 13, 11 Feb 1983, coll. G. Hampson, WHOI, Chief Scientist, 40°29.3’W, 70°12.5’W, 66 m, 66 paratypes (USNM 1407146).

Other material examined. Offshore New England, Georges Bank, BIMP, Cruise M-6, R/V Oceanus, Sta. 9, 26 Nov 1982, coll. G. Hampson, WHOI, Chief Scientist, 40°26.7′N, 68°09.8′W, 141 m, 10 specimens (USNM 1407148); Sta. 12, 26 Nov 1982, coll. G. Hampson, WHOI, Chief Scientist, 40°22.2′N, 68°29.8′W, 103 m, 28 specimens (USNM 1407147); Sta. 13A, 27 Nov 1982, coll. G. Hampson, WHOI, Chief Scientist, 40°30.0′N, 71°00′W, 78 m, 64 specimens (USNM 1407149). — Cruise M-8, R/ V Gyre, Sta. 12, 20 May 1983, coll. G. Hampson, WHOI, Chief Scientist, 40°22.2′N, 68°29.7′W, 105 m, 21 specimens (USNM 1407150); Sta. 13A, 21 May 1983, coll. G. Hampson, WHOI, Chief Scientist, 40°30.0′N, 71°00.6′W, 80 m, 61 specimens (USNM 1407151). — Massachusetts Bay, MWRA long-term monitoring program, R/ V Aquamonitor, Sta. NF-14, Rep. 1, 31 Jul 2007, coll. P. Neubert, 42.387°N, 70.823°W, 34.2 m, 42 specimens (MCZ 135290); Sta. FF-01A, Rep. 2, 30 Jul 2007, coll. P. Neubert, 42.564°N, 70.676°W, 35.8 m, 8 specimens (MCZ 135291). — Long Island Sound, New London, historical dredged material disposal site, Sta. AC 3, 17 February, 2000, 41°16.471′N, 72°04.459′W, 33 specimens (JAB).

Description. An elongate, often thread-like species with length and number of setigerous segments variable and age dependent. Holotype complete, 10.7 mm long, 0.23 mm wide across thorax and 0.20 mm wide across abdominal segments, with 110 setigers; a mostly complete, slender paratype 14 mm long, 0.2 mm wide across thorax with about 60 setigers compared to more robust paratype 15 mm long, 0.3 mm wide across thorax with 106 setigers. Complete specimens, including holotype, with bodies coiled precluding exact measurements.

Pre-setigerous region about 2.5x as long as wide in smaller, more slender specimens; 2.0–2.3x as long as wide in larger more robust specimens (Figs. 12 A, 13F). Prostomium triangular, tapering to narrow rounded apex (Figs. 12 A–B, 13F); eyes absent; slit-like nuchal organs present on posterior lateral margins. Peristomium elongate, smooth without obvious annulations in smaller specimens, but with 1–2 lateral grooves in larger specimens immediately posterior to prostomium, main part of peristomium remaining smooth (Fig. 12 A–B). Peristomial middorsal ridge present, extending from prostomium to border of setigerous region (Figs. 12 A–B, 13F). Dorsal tentacles on posterior part of peristomium, first pair of branchiae also on peristomium, posterolateral to tentacles, in line with second pair of branchiae on setiger 1 (Figs. 12 A–B, 13F). Branchiae of thoracic segments dorsal to notosetae at border with mid-dorsal channel; thereafter, parapodia shifting to lateral position in abdominal segments; branchiae not observed in far posterior segments.

Parapodia of thoracic region elevated above dorsal midline producing shallow mid-dorsal channel or groove between parapodia (Fig. 12 A), continuing to start of abdominal segments; dorsal thoracic channel with elevated narrow ridge along most of length (Fig. 12 A); thoracic region with 10–15 setigerous segments depending on age of specimens; slender, less mature specimens with fewer, larger more robust specimens with maximal numbers of thoracic setigers. Abdominal region with narrow mid-dorsal furrow or groove over a variable number of segments (Fig. 12 A); far posterior segments becoming shorter and wider, forming weakly expanded posterior section terminating in pygidium with dorsal anus overlying conical lobe (Fig. 12 C).

More slender specimens with most abdominal segments 2– 3x as long as wide (Fig. 12 D–E) with posterior segments becoming shorter, almost moniliform (Fig. 12 F); more robust specimens with most abdominal segments as long as wide with elongate segments limited to far posterior, demonstrating a pattern of growth and maturation of body segments. Larger specimens typically with mature gametes, absent in more slender immature specimens.

Parapodia reduced to low mounds from which setae project; thoracic setae consisting of long simple capillaries numbering 7–12 per notopodium and 6–10 per neuropodium; anterior and middle abdominal segments with about 8–12 setae per noto- and neuropodia (Fig. 13 G); far posterior abdominal segments with 5–8 setae per notopodium and 5–6 per neuropodium; neurosetae becoming shorter, wider basally in middle abdominal segments with minute denticles along one edge (~setiger 50 in largest specimens), visible from 400– 1000x (Figs. 12 G, 13I); notosetae also becoming broad and denticulated in middle abdominal segments, denticles best seen at 1000x (Fig. 13 H). Notosetae with denticles directed ventrally and denticles of neurosetae directed dorsally, vis-à-vis.

Methyl Green stain. Prostomium generally not staining; some specimens, however, with prominent dorsal patch and lateral lines of light green on the peristomium (Fig. 13 B), others with patch lighter, fading rapidly (Fig. 13 A); thoracic region with 8–10 segments with distinct ventral bands of dark blue extending dorsally to near middorsal channel, 4–6 of these bands remaining prominent, being the last stain to fade away (Fig. 13 A–C); prominent mid-ventral longitudinal line present on most anterior abdominal segments (Fig. 13 A–C), broken between segments; lateral intersegmental spots absent but thin lines on dorsal side of abdominal segments represents stain in intersegmental grooves (Fig. 13 B).

Etymology. This species is named for the late Mr. George Hampson, scientist at the Woods Hole Oceanographic Institution. Mr. Hampson was Chief Scientist on the Georges Bank monitoring surveys and the North Atlantic ACSAR surveys in the 1980s. He was also a key field leader on several of our deep-water surveys off northern California in the 1980s and 1990s. He was a mentor to many young marine scientists and provided training on how to collect samples offshore and correctly process them.

Remarks. Kirkegaardia hampsoni n. sp. is most similar to the deeper water U.S. Atlantic species K. annulosa and the shallow-water Mediterranean species K. heterochaeta in general body form and MG staining patterns. Although both K. annulosa and K. heterochaeta have the entire surface of the mid-dorsal channel raised into a ridge, the configuration of this differs from that of K. hampsoni n. sp. because the latter has a separate ridge located on the floor of the channel. As part of the larger review of species in this study, K. hampsoni n. sp. belongs to a group of four species, including K. annulosa, K. kladara n. sp., and K. cristata n. sp. that have a mid-dorsal ridge along the entire length of the peristomium. K. kladara n. sp. differs significantly from each of these species in having the first pair of branchiae on setiger 1 instead of on the peristomium lateral to the dorsal tentacles. K. cristata n. sp. from the northeastern Pacific has a different MG staining pattern and up to four peristomial annular rings instead of up to three annuli in K. hampsoni n. sp.

Biology. Kirkegaardia hampsoni was a dominant species at Station 13, the so-called “mud patch” adjacent to Georges Bank (Maciolek-Blake et al. 1985). The species is generally found in finer-grained sediments than its congener K. baptisteae which, on Georges Bank, prefers sediments having coarser grains.

A few specimens from the February and May 1982 collections at Georges Bank Sta. 13 were females with eggs observed in posterior abdominal segments. At least two specimens were males with numerous sperm packets loose in the coelomic fluid; these sperm had a minute rounded nucleus. The eggs from the February specimens measured 106–122 µm in one specimen and ca. 150–152 µm in another; there were about 4– 6 eggs per segment. In contrast, eggs from the May collection were considerably larger, measuring 160–183 µm in diameter (average = 177.1 µm; 1 SD = 10.6 µm), with four eggs per segment (Fig. 13 D–E). In some segments the largest eggs were compressed anterior to posterior with individual segments being elevated and dorsally rounded due to the contained eggs. There were no apparent females in either the July or November samples. Although scanty, these results suggest that in this area gametes of K. hampsoni develop and mature in January–February and the worms likely spawn in April– May.

Distribution. Kirkegaardia hampsoni n. sp. has been recorded locally as Tharyx and/or Monticellina dorsobranchialis from numerous locations on the U.S. Atlantic continental shelf from the Gulf of Maine to the mid-Atlantic, 30– 150 m. Records from further south and the Gulf of Mexico should be examined as they could possibly belong to different species.