Narella ambigua (Studer, 1894)

Cairns, Stephen D., 2018, Deep-Water Octocorals (Cnidaria, Anthozoa) from the Galapagos and Cocos Islands. Part 1: Suborder Calcaxonia, ZooKeys 729, pp. 1-46 : 12-15

Narella ambigua (Studer, 1894) Figures 2e, 9

Stachyodes ambigua Studer 1894: 63-64; Menneking 1905: 248-251, pl. 8, figs 1-2, pl. 9, figs 11-12; Versluys 1906: 103-104; Kükenthal 1919: 464 (key to species); 1924: 314.

Narella ambigua Cairns and Bayer 2007 (not 2008): 86 (listed); Cairns 2007b: 512 (listed); Cairns and Bayer 2009: 30 (listed).

Material examined.

Branch fragments and detached polyps from Alb-3404, MCZ 79048, and USNM 1405230 (topotypic: possible syntypes); Alb-2818, 1 colony and SEM stubs 2312-2315, USNM 44165; Gilliss-21, 1 branch, USNM 57576; JSL-I-1927, 1 colony, USNM 1297223.

Types.

As mentioned in the account of Calyptrophora agassizii , about 65% of the type lot (branches and detached polyps) of that species consisted of Narella ambigua . Narella ambigua was collected at the previous station (Alb-3403) to that of C. agassizii (Alb-3404), approximately 20 km to the northeast and bathymetrically 2 m shallower, both stations from off the southern coast of San Cristóbal. The Narella specimens were separated from the type lot of C. agassizii in 2008 and cataloged as MCZ 79048. Since the type of S. ambigua could not be found at the MCZ in 2008, the specimens cataloged as MCZ 79048 may serve as representative topotypic specimens, and may in fact be type material. A fragment of this colony is also deposited at the NMNH (USNM 1405230).

Type locality.

Alb-3403: 0°58'30"S, 89°17'W (south of San Cristóbal, Galápagos), 702 m depth.

Distribution.

Galápagos: off Santiago, Santa Cruz, and San Cristóbal), 702-741 m deep. Elsewhere: off Panama, 1463 m depth (herein, GS-21).

Description.

The colony is uniplanar, and dichotomously (laterally) and sparsely branched (Figure 2e), large colonies being up to 28 cm in height and up to 1 cm in basal branch diameter. Terminal branches may be quite long, up to 15 cm. The axis is pale yellow. The polyps are arranged in whorls of five to seven (Figure 9e); whorls are not directly adjacent to one another and thus there are only approximately 2.5 whorls per cm branch length; the whorl diameter of terminal branchlets is about 6-7 mm. The horizontal length of a polyp is 2.5-3.0 mm.

The basal scales (Figure 9c, f) stand perpendicular to the branch and extend up to 2.8 mm in height, the distal 0.6-0.7 mm portion projecting beyond the junction with the medial scales as a broad lobate extension (Figure 9b). The lateral edge of one of the basal scales of a polyp will often enlarge and curve toward the corresponding enlarged basal scale of the adjacent polyp, forming a solid tube up to 3.5 mm in diameter that houses a commensal polychaete worm (Figure 9e). The dorso- and anterolateral faces of the basal scales are gently curved, not ridged. The medial scales (Figure 9g) are narrow, 0.9-1.1 mm in length, and have upturned edges proximally and distally (saddle-shaped). The buccal scales (Figure 9b, c, h) are longer (up to 1.6 mm) and about twice as wide as the medials, their distal edges rounded and smooth, forming a cowl (Figure 9a) up to 0.6 mm that encircles the operculum; the distal edges of the two buccal scales form a bilobate shape for the tip of each polyp, not unlike the distal edges of the basal scales. The ratio of the major body wall scales is about: 1:0.6:0.7. There are four pairs of small elliptical adaxial body wall scales (Figure 9d, j), ranging from 0.26 to 0.42 mm in greater diameter. The outer faces of all body wall scales are covered with small granules and thus look rather smooth. All of the opercular scales (Figure 9i) are roughly the same length, ranging from 1.0-1.3 mm in length, but the single abaxial opercular is quite broad (e.g., L:W = 1.2), whereas the single adaxial is quite slender (e.g., L:W = 3.0). The other six lateral operculars usually have a basal shoulder on their adaxial edges and thus have an intermediate L:W ratio. The outer surface of the operculars is granular like the body wall scales, whereas the inner surface bears a rounded keel. The coenenchymal scales (Figure 9k) are irregular to polygonal in shape, up to 1.4 mm in length, and have a flat to slightly concave outer surface.

Comparisons.

Narella ambigua is easily distinguished from the somewhat similar Paracalyptrophora enigma by its long terminal branches, polychaete commensalism that causes highly modified basal scales, fewer polyp whorls per cm, non-toothed basal scales, lack of an articular ridge, and granular (not ridged) coenenchymal scales.

Remarks.

Although discussed by several authors through the years (see synonymy), this is the first subsequent report of this species since its original description.