Narella aurantiaca, Cairns, 2018

Cairns, Stephen D., 2018, Primnoidae (Cnidaria: Octocorallia: Calcaxonia) of the Okeanos Explorer expeditions (CAPSTONE) to the central Pacific, Zootaxa 4532 (1), pp. 1-43 : 31-34

Narella aurantiaca , n. sp.

Figs. 1 K–L, 16A–K

Etymology. Named aurantiaca (Latin for orange colored), in allusion to the orange color of the colony and its commensal ophiuroids.

Types and Type Locality. The holotype, now in three parts, and SEM stubs 2411-2415, USNM 1424215. Paratype: EX 1708-12-05, 30.440˚N, 164.01˚W (Mussorgsky Seamount, Musicians Seamounts), 1983 m, fragments of a colony, USNM 1467597 ; FK 17-358, 3˚35.702’S, 174˚9.265’W (off Nikumaroro , Phoenix Islands), 1112 m , 27

October 2017, 1 colony, Temple University. Type Locality: EX 1606-8-01: 19.3304˚N, 166.6038˚E (northwest of Wake Island), 745 m , 10 August 2016.

Material Examined. Types.

Description. The holotype was collected intact, measuring 21 cm in height and 11 cm in width, with a calcified basal stem 3.9 mm in diameter; the colony is uniplanar. Branching is sparse and equal-dichotomous, with quite long terminal branches up to 18 cm in length; most branching occurs near the base of the colony ( Fig. 1L ). The color of the colony is white to pale orange. The polyps are arranged in moderately closely spaced (3–3.5/cm) whorls of four to six polyps; the whorl diameter ranges from 6.5–7.0 mm. The horizontal length of mature polyps is 2.8–3.2 mm in their contracted position.

The basal scales ( Fig. 16B, E ) stand perpendicular to the branch and are up to 2.9 mm in height, the distalmost 0.65–0.70 mm projecting as a cowl encircling its attachment to the proximal edge of the medial scales ( Fig. 16C ), their edge being smooth (i.e., not serrate or spinose). The dorsolateral edge of the basal scale is rounded and does not bear ridges; none of the body wall scales are ridged, but all are covered with a low granulation. The adaxial edges of the basal scales do not meet (open position, Fig. 16D ). When a polychaete commensal is present (usually only near the base of the colony), the basolateral edges of adjacent buccal scales are modified (reflected) to form a circular worm tube about 1.1 mm in diameter. The medial scales are much shorter (1.2–1.3 mm in length) and narrower, having a highly concave outer surface. The broad buccal scales are up to 1.9 mm in length, forming a cowl around the opercular scales. The distal edges of all body wall scales are rounded (not serrate or spinose). The ratio of the major body wall scales is approximately: 1: 0.44: 0.65.There is one pair of elliptical adaxial buccal scales ( Figs. 16D, H ), measuring 0.4–0.6 mm in greater diameter, the lower adaxial portion of the polyp being naked.

The abaxial opercular scales are symmetrical, 1.6–1.8 mm in length, and have an L:W of about 1.4. The outer and inner lateral operculars are similar in size and shape, 1.3–1.7 mm in length, slightly asymmetrical, and have an L:W of about 2.1. The adaxial operculars are the smallest, only 1.1–1.3 mm in length, symmetrical, and have an L: W of about 2.3.

There are two types of coenenchymal scales. Some are roughly rectangular, up to 1.5 mm in greater width, thin, and flat (unridged), having several thin, shallow notches or indentations on their edges, which gives them an irregular outline ( Fig. 16J ). The second type is roughly the same size and shape but bears tall vertical ridges that fit into the peripheral notches of the other type of scale ( Fig. 16K ) thus forming an interlocking structure that inhibits lateral movement of the scales.

Pinnular scales are about 0.17 mm in length and 0.03 mm in width, flat, and slightly curved ( Fig. 16L ).

Comparisons. Among the 27 species of Narella that lack dorsolateral ridges on the basal scale, N. aurantiaca is morphologically most similar to N. ambigua ( Studer, 1894) , a species known only from the Galápagos and off Panama at 702–1463 m (Cairns 2018). It differs in having only one pair (not four) of adaxial body wall scales, and in having ridged interlocking coenenchymal scales, the latter character unique to this species. Narella aurantiaca is also similar to N. leilae Bayer, 1951 , known from Indonesia at 740 m, but differs by having larger polyps, rounded (not serrate) buccal and basal scales, and in having interlocking coenenchymal scales.

Remarks. Two orange ophiuroids were attached to the holotype.

Distribution. Off Wake Island, Phoenix Islands, and Mussorgsky Seamount, 745–1983 m.

Figures

FIGURE 1. In situ images of various species: A, Callogorgia cracentis, holotype. B, Calyptrophora lyra, holotype (not in situ). C, C. diaphana, EX1606-9-1. D, C. carinata, holotype. E, C. clarki, EX1605-L3-6. F, C. pourtalesi, holotype. G, C. distolos, holotype. H, Candidella gigantea, EX1606-6. I, Macroprimnoa ornata, holotype. J, Narella virgosa, holotype. K-L, N. aurantiaca, holotype. M, N. merga, holotype. N, N. horrida, EX1703-2-3. O, N. fordi, holotype. P, N. calamus, holotype. Q, N. virgosa, paratype, EX1504-L4-9-4. R, N. macrocalyx, EX1606-7. S, N. hawaiiensis, EX1504-9-2. T, Paracalyotrophora hawaiiensis, EX1703-2-1. U, P. echinata, EX1703-10-1. V, P. spiralis, holotype. W, Plumarella circumoperculum, EX1603-2-3. X, Thouarella hilgendorfi, EX1605-L1-17.

FIGURE 16. Narella aurantiaca, holotype: A, stereo view of two polyp whorls. B–D, stereo views of lateral, oblique abaxial, and adaxial sides of a polyp. E, basal scales. F, medial scale. G, buccal scales. H, adaxial buccal scales. I, opercular scales. J, coenenchymal scales. K, stereo view of interlocking coenenchymal scales. Scale bars in mm.