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Description

Primnoa notialis new species

 

(Figs.1 F–G, 11–13)

 

Primnoa resedaeformis notialis.—Heikoop et al. 2002: 118 (nom. nud.).—Risk et al. 2002: 126 (nom. nud.).

 

Material Examined/Types.—Holotype: Eltanin-1346, one colony in alcohol (SEM 1812, 1824-1827, 1832-1834), USNM 87621. Paratypes: Eltanin-1343, many large branches and smaller fragments, all paratypes preserved in alcohol (SEM 177, 187, 290, 1392-1393, 1400, 1470), USNM 58169-58172; young variant form (SEM 2558-2559), USNM 87623; Eltanin-1345, one branch (paratype) in alcohol, USNM 98264; Eltanin-1346, one colony devoid of polyps but with many individual detached polyps, in alcohol, USNM 87624, and a massive dry calcified basal branch without polyps USNM 87625, and one large colony and many smaller branches (most in alcohol, some branched dried) (SEM C1113-C1116), USNM 87627, and one small variant colony attached to Solenosmilia variabilis (Duncan, 1873) (SEM 1394-1397, 2557), USNM 87622.

 

Type Locality.—54º49’S, 129º48’W (Subantarctic seamount on the Heezen Fracture Zone of the Eltanin Fracture Zone System), 549 m.

 

Diagnosis.—Primnoa with basal body scales not strongly developed, without conspicuous projecting marginal processes or spines; medial body wall scales irregularly arranged; 4–5 large marginal scales, the remaining marginals much smaller.

 

Description.—The growth form of the colonies is similar to that of typical resedaeformis. The largest fragments are about 40 cm tall, indicating that complete colonies would be much larger, possibly a meter or more in height; the holotype is a branch fragment 23 cm in length. The stoutest main stem is about 15 mm in diameter, hence much smaller than the trunk of fully developed colonies from the North Pacific. A main stem with holdfast (USNM 87624) has a calcareous basal thickening like that of P. resedaeformis, and another massive calcareous holdfast from Eltanin-1346 (USNM 87625) gives rise to a very large stout main trunk axis 23.5 mm in diameter, spreading over the substrate to a radius of 15 cm and to a thickness of 13 mm in places. Although this specimen is devoid of polyps, the axial material is identical with that of the other specimens and could hardly by anything but P. notialis. In thinner branches and twigs the axis has a brilliant golden sheen but in most places is brown with a dull metallic luster; in some places it may be very dark brown, almost black, with no gloss. The axial surface is longitudinally grooved. Branching is irregularly dichotomous and roughly in the same plane; the terminal branchlets curve upward and often are rather sinuous, some of them with a prominent apex devoid of polyps, others with a blunt tip about 9 mm in diameter formed by the bases of the uppermost polyps. Branchlets originating from the lower side of more or less horizontal branches turn upward through as much as 180°.

 

The polyps are densely crowded all around the branches, most of them bent downward, but individuals directed upward and obliquely in various directions are not uncommon. They are so closely and irregularly placed that usually no verticillate arrangement is obvious, but areas showing a tendency toward arrangement in whorls can be found here and there throughout the colonies (see “variation”). Depending upon girth, the circumference of the axis accommodates from five or six to up to ten or more polyps. For the most part the polyps are only slightly flared distally (mid-to distal ratio of polyp diameter 0.5–0.6), having a campanulate aspect. They are 3–5 mm in length, 1.5–2.0 mm in diameter near the middle, and 2–3 mm across the marginal scales.

 

Sclerites are fully developed only on the abaxial side of the polyp, usually only indistinctly arranged in two rows if at all. The unpaired basal scales are slightly or not at all larger than the medials and do not have marginal projections. In by far the vast majority of polyps, the medial abaxial scales, which occur in 3–6 indistinct tiers, are irregularly disposed. They consist of larger elliptical to rhomboidal-shaped scales 0.8–1.1 mm in width and numerous tiny supernumerary irregularly-shaped sclerites 0.15–0.40 mm in width arranged around the edges of the larger scales. The larger medial scales are rather thick and slightly convex above, often with irregular digitiform edges. The marginal scales differ in size, each polyp usually having five large, slightly convex, rectangular marginal scales in the abaxial and outer lateral positions, these scales up to 2.3 mm in height and 1.7 mm in width, their distal edges projecting well above (0.50–0.75 mm) the insertion of the proximal edges of the opercular scales, together forming a prominent hood for the operculum. Their distal and lateral edges are finely serrate, their proximal edges digitiform. The lower two-thirds of the inner surface is tuberculate, the upper third striate; the outer surface is granular. Two pairs of smaller (0.75–1.0 mm in width), squarish marginal scales occur in the inner lateral position and 2–3 pairs of slightly smaller marginal scales also occur in the adaxial position (Fig. 12D). The opercular scales curve slightly to mold to the curvature of the polyp, forming an operculum consisting of eight isosceles-triangular shaped scales with a rounded apex, when folded together forming a compact, prominent blunt cone. The abaxial operculars of fully developed polyps are 1.8–1.9 mm in height and 0.8–1.0 mm wide at the base; the adaxial operculars are 1.2–1.4 mm in height and 0.6–0.7 mm wide at the base. The operculars have a low, blunt longitudinal keel on their inner surface as well as being covered with tubercles on the proximal portion and striate towards the tip. The outer opercular surfaces are covered with granules, which are developed into small spines toward the tip. The outer and lateral edges of the operculars are finely serrate, the proximal edge digitiform. Often a small, rounded scale lies beneath each of the operculars, as was noted also in P. pacifica by Kinoshita (1908a: 44, pl. 6, fig. 49). The outer surfaces of all body wall and opercular scales are covered with a low, fine granulation, the granules measuring 15–20 μm in diameter, and arranged in radiating lines from an origin point about one-third up from the base of each sclerite. Tentacular rods are straight, rotund and up to 0.17 mm in length and 0.035–0.045 in diameter. Coenenchymal sclerites are thick, elongate rods, irregularly rounded plates, and scales with lobed margins, varying from about 0.5 to a little more than 1 mm in greatest length. Their outer surfaces are covered with granules 25–28 μm in diameter whereas their inner surfaces are covered with complex tubercles, some of which are as large as 35 μm in diameter.

 

Many polyps contain several dozen small yellow eggs, each about 0.45 mm in diameter.

 

Variation.—In a few specimens (USNM 87622, 87623), unfortunately in damaged condition, the body scales of the polyps are larger, thinner, and more regularly arranged, and the opercular scales are more sharply pointed. As these specimens are small colonies attached by their holdfasts to branches of scleractinian coral, it is possible that their polyps retain the basic arrangement of body scales that is disrupted on large colonies, as was noted in the young colony of P. pacifica. The arrangement of body scales is similar to that of some specimens of typical North Atlantic resedaeformis.

 

Although the predominant arrangement of polyps is random, in fact, in small colonies the polyps are often arranged in whorls, but these become disrupted almost at once by asymmetrical growth and the production of young polyps between older ones. The polyps on the branch tip illustrated on Figure 13B clearly shows the polyps arranged in a somewhat oblique whorl. But, in most cases, the polyps are much more crowded near the branch tips where the whorls are completely obscured and the branches are distinctly clavate.

 

Comparisons.—Primnoa notialis most closely resembles P. pacifica in the irregular size and arrangement of the medial body scales, but no polyps with large, Narella-like basal scales have been found in the present material. In this respect, P. notialis is more like typical resedaeformis of the North Atlantic (Table 1).

 

Etymology.—The species is named notialis (Latin: southern) for the only known species of Primnoa south of the equator.

 

Distribution.—Known only from a Subantarctic seamount on the Heezen Fracture Zone of the Eltanin Fracture Zone System at depths of 549–915 m, the site of a deep-water coral bank composed primarily of the scleractinian coral S. variabilis (see Cairns, 1982).”

 

(Cairns & Bayer 2005)

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Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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