Comprehensive DescriptionRead full entry
“28. Primnoa Lamouroux, 1812
Primnoa Lamouroux, 1812:188.—Studer, 1887:49.—Wright and Studer, 1889:xlviii.—Versluys, 1906:84–85.—Kükenthal, 1915:143 [key to genus]; 1919:357–360 [key to genus]; 1924:265–266 [key to genus and species].— Bayer, 1956:F220; 1961:294 [illustrated key to genus]; 1981b:937 [key to genus].—Bayer and Stefani, 1989:454 [key to genus].—Cairns and Bayer, 2005:226–228 [revision and key to species].
Lithoprimnoa Grube, 1861:174–175.
Diagnosis. Colonies dichotomously branched and usually bushy, some reaching a height of 2 m. Calyces closely spaced and randomly arranged on all branch surfaces, the appressed calyces facing downward. Well developed operculum present, the operculars keeled on inner surface. Polyps large and fleshy, each polyp protected by two rows of four or more large abaxial scales, sometimes arranged in an irregular manner, two short inner-lateral rows of two or three smaller scales (including the marginals), and two even shorter rows of two (including the marginals) adaxial scales, resulting in six longitudinal rows, but four of them composed of very small and few scales; adaxial side of body wall predominantly bare (Figure 13i). There is also a crown of eight large, concave marginals, the adaxial marginals usually smaller than other marginals. Coenenchymal scales arranged in one layer. Tentacular rods are often present (Figure 13j).
Discussion. The four Recent species and one variety (Table 4) in this genus were described, illustrated, and keyed by Cairns and Bayer (2005); the two Paleocene fossil species listed in Table 4 from Denmark (Nielsen, 1913, 1925) are highly doubtful identifications, Bayer (1992) synonymizing one of them, P. gracilis, with the lithotelestid Epiphaxum auloporoides (Lonsdale, 1850). Characters used to distinguish species include the size and shape of the basal scales, size and shape of the polyps, and the shape of the marginal scales. Distribution patterns (Watling and Auster, 2005) and characteristics of the massive axis of this genus have been the subject of many studies, including aspects of growth rate (Andrews et al., 2002), and paleoceanographic isotopic analysis (Heikoop et al., 2002; Sinclair et al., 2005; Sherwood et al., 2005).
Distribution. North Pacific, North Atlantic, subantarctic South Pacific, 9–1,020 m.
Type Species. Primnoa: Gorgonia lepadifera Linnaeus, 1767 (= Gorgonia resedaeformis Gunnerus, 1763), by monotypy. Type not traced.
Lithoprimnoa: L. arctica Grube, 1861, by monotypy. Type not traced.”
(Bayer & Cairns, 2009)
Family Primnoidae Gray, 1858
Primnoa Lamouroux, 1812
Primnoa Lamouroux, 1812: 188; 1816: 442.—Kükenthal, 1919: 357–360; 1924: 265–266 (references).— Bayer, 1956: F220, fig. 157, 1.
Lithoprimnoa Grube, 1861: 174–175
Type species.—Primnoa: Gorgonia lepadifera Linnaeus, 1767 (=Gorgonia resedaeformis Gunnerus, 1763), by monotypy.
Lithoprimnoa: Lithoprimnoa arctica Grube, 1861, by monotypy.
Diagnosis.—Dichotomously branched, arborescent Primnoidae with polyps not arranged in whorls but closely crowded on all sides of the twigs and branches; polyps distinctly curved downward toward the axis. Polyps adaxially naked or nearly so, abaxially armed with scales or plates of variable size, shape, and arrangement. Marginal scales eight, those of the adaxial side of the polyp smaller than those of the abaxial side and may be only indistinctly differentiated. Operculum strongly developed, the adaxial pair of scales smaller than the abaxials and laterals. Tentacles with small, thorny rods.
Remarks.—Kükenthal (1919) recognized only one species of Primnoa, P. resedaeformis, and a variety of it, P. pacifica, a view shared by Madsen (1944). Kükenthal later (1924: 267) treated P. pacifica as a subspecies of the North Atlantic P. resedaeformis: “P. resedaeformis typica.” Both Kükenthal (1924) and Aurivillius (1931) treated P. willeyi as a dubious species, the former considering it probably synonymous with P. resedaeformis.
Broch (1935: 29–33) discussed the status of P. pacifica relative to P. resedaeformis, concluding that the Pacific species is a geographical form of the Atlantic species. His investigation of Norwegian specimens from Trandhjemsfjord showed that the variability of polyp scales is considerably less than in Pacific colonies, and that strongly developed “Basalscleriten” are almost never (“fast nie”) seen in Norwegian colonies. While visiting the Natural History Museum, London, FMB was able to make a drawing of a branch of Hickson’s original material of P. willeyi (Fig. 7C). No type material of P. pacifica is available to us, but samples collected in Japanese waters agree with Kinoshita’s description in most respects and may be taken as representative of his concept.
Specimens of Primnoa trawled in the Pacific sector of the Southern Ocean by USNS ELTANIN are the first record of the genus from Subantarctic waters, although this taxon was reported as a nomen nudum by Heikoop et al. (2002) and Risk et al. (2002). This material demonstrates unequivocally the bipolarity of the genus Primnoa. The few North Pacific specimens available for study show consistent differences from North Atlantic specimens. The numerous specimens from three stations in the Southern Ocean likewise differ somewhat from both North Pacific and North Atlantic specimens.
Kinoshita (1908a) already has remarked upon the Narella-like development of the basal scales in P. pacifica. Pacific specimens of Primnoa in the present collection carry the similarity of the two genera even further. Polyps of a very young colony from the Alexander Archipelago of southern Alaska (USNM 58397) are enclosed in a pair of large, Narella-like basal scales that form a pair of projecting flat horns, a pair of somewhat smaller medial scales, and a circle of buccal scales of which the abaxial pair commonly are the largest. These polyps (Fig. 5A–B, USNM 58397) have a strikingly Narella-like aspect, closely approaching in form the polyps of those Narella species having strongly developed adaxial buccal scales, such as Narella megalepis (Kinoshita, 1908). The most obvious distinction of Primnoa from Narella is the presence of more than four scales in the buccal ring, and the crowded, non-verticillate arrangement of polyps.
Most polyps of North Atlantic colonies of P. resedaeformis have two main rows of large abaxial scales between the marginal scales and the basal scales, the latter of which are not strongly developed and not especially conspicuous. The polyps of Pacific colonies have more numerous, more or less irregularly placed scales between the marginal and basal scales, which usually maintain or increase their size to a variable extent, commonly projecting outward as a pair of strong processes or flat spines.
Although interbreeding populations could be expected to exist around the northern perimeters of the North Pacific and North Atlantic, it is not known at present whether or not the two areas are linked by a continuous population around the Polar Sea (see Broch, 1949). Similarly, it is not known whether or not a continuous population extends from the North Pacific to the South Pacific. Not all possible localities have been sampled by dredge or observed by submersible at appropriate depths. However, the broad scope of explorations at low latitudes in both Pacific and Atlantic Oceans over the past century might have been expected to discover evidence of intermediate populations had such existed.
KEY TO SPECIES AND VARIETIES OF PRIMNOA
1 . Basal scales of most polyps larger than medials, and usually with a prominent marginal spine (Narella-type scale) ..........(P. pacifica) 2
1´. Basal scales roughly the same size as medials, never with marginal spines ..........3
2 . Polyps long and fleshy, often twisted and lacking sclerites on lateral edges of polyps; ratio of mid- to distal polyp diameter 0.25–0.43 .......... P. pacifica var. willeyi
2´. Polyps more robust, straight, with small body wall sclerites on lateral surfaces of polyps; ratio of mid-distal polyp diameter 0.53–0.67 ..........P. pacifica typical
3 . Abaxial medial scales large (to 1.5 mm wide), rectangular, and arranged in 2–5 pairs ..........P. resedaeformis
3´. Abaxial medial scales smaller, elongate or elliptical, not arranged in pairs ..........4
4 . Medial scales elongate and slender (< 0.2 mm wide), restricted to a narrow abaxial tract that is immersed in tissue; operculars spatulate; marginals extremely concave; tentacular rods large and often curved; Aleutians ..........P. wingi sp. nov.
4´. Medial scales elliptical to square (up to 1.0 mm wide), covering abaxial and lateral polyp surface; operculars isosceles-triangular; marginals flat; tentacular rods smaller and straight; Subantarctic ..........P. notialis sp. nov.”
(Cairns & Bayer 2005)