Narella virgosa, 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 : 27-29

Narella virgosa , n. sp.

Figs. 1J, Q , 13 A–J

Etymology. Named virgosa (Latin for bushy), in allusion to the bushy nature of the large colony.

Type and Type Locality. Holotype: over a dozen branches and many detached polyps from the same colony, the largest branch 18 cm in length, and SEM stubs 2406-2408, USNM 1424064 . Paratypes: EX 1504-L 4-9-04, 16.14˚N, 167.85˚W ( South Karin Ridge , southeast of Johnston Atoll), 1931 m, a colony, now in eight branch fragments, and SEM stubs 2522-2526, 2528-2529 . USNM 1297747 ; EX 1708-17-05, 26.6˚N, 160.67˚W ( Rapano Seamount , Musi- cians Seamounts), 1901 m, distal branches of a colony, USNM 1467640 . Type Locality: EX 1603-7-02 : 26.43˚N, 177.80˚W ( Castellano Seamount , approximately 370 km south of Midway Islands, Hawaiian Islands), 1985 m, 10 March 2016 .

Material Examined. Holotype.

Description. The holotype colony is roughly uniplanar but also slightly bushy, abundantly branched and thus having many distal branches. Only a small portion of the holotype was collected, but photographs of the living colony ( Fig. 1J ) show it to be about 70 cm in height and 85 cm in width. Branching is initially lyrate, followed by equal dichotomous branching, resulting in long unbranched terminal branches up to 60 cm in length. The color of the colony is a very pale orange. The polyps are arranged in moderately closely spaced whorls (about 3/cm) of three or four polyps; the whorl diameter ranges from 3.3–4.5 mm. The horizontal length of the polyps is 2.6–3.6 mm in their contacted position, although the living polyps appear to be straight and stand perpendicular to the branch and are thus taller. Polychaete commensalism was not noted.

The basal scales ( Figs. 13 B, E ) stand perpendicular to the branch and extend up to 1.65 mm in height, their distal edges smooth (not serrate or spinose), forming a relative short cowl (0.3 mm) around the proximal portion of the medial scales. The dorsolateral edge of the basal scale is rounded but bears multiple thin longitudinal ridges, some as tall as 0.1 mm. Otherwise, the outer face is covered with small granules. The adaxial edges of the basal scales do not meet (open position, Fig. 13C ). The medial scales ( Fig. 13F ) are much shorter (1.10–1.15 mm in length), and do not wrap around the polyp as the basal and buccal scales do. Each medial scales usually bears a single longitudinal ridge. It is not unusual for there to be two pairs of medial body wall scales. The buccal scales ( Figs. 13B, G ) are 1.1–1.35 mm in length and quite broad, wrapping around most of the polyp; they also bear a series of low radiating longitudinal ridges, and their distal edge is rounded, forming a short cowl of about 0.4 mm over the opercular crown. The ratio of the major body wall scales is thus: 1: 0.7: 0.85. There is one pair of large (each up to 0.7 mm in width), roughly rectangular adaxial buccal scales ( Fig. 13H ), below which the polyp is naked, probably to facilitate bending of the polyp toward the branch.

The abaxial opercular scales are symmetrical, 1.2–1.35 mm in length, and have an L:W of about 1.4. The outer and inner lateral operculars are similar in size and shape, 1.2–1.3 mm in length, slightly asymmetrical (having a small adaxial lateral lobe), and an L:W of about 1.7. The adaxial operculars are small (0.8–1.0 mm in length), symmetrical, and have an L:W of about 2.0. All opercular scales ( Fig. 13I ) bear a short longitudinal keel on the distal third of their inner surface; their outer surface is granular.

The coenenchymal scales ( Fig. 13J ) are flat and elongate (up to 1.8 mm in length, with an L:W = 3–6), each usually bearing one of more longitudinal ridges, these ridges sometimes up to 0.15 mm in height and thus resembling sail scales.

Comparisons. When compared to other Narella found in the closely adjacent Hawaiian Islands (see Cairns & Bayer 2007), Narella virgosa most closely resembles N. muzikae Cairns & Bayer, 2007 , particularly in the ridging of the basal and coenenchymal scales. However, N. virgosa differs from that species in having non-ridged adaxial buccal scales, fewer polyps per whorl, non-ridged outer surface of opercular scales, larger polyps, and by occurring in much deeper water. Within the larger Indo-Pacific region, N. virgosa is most similar to N. parva ( Versluys, 1906) , known from Indonesia and New Zealand at 920–2400 m (see Cairns 2012), but differs in having lyrate branching, fewer polyps per whorl, and small polyps. The lyrate nature of the branching of Narella virgosa is shared with only four other species in the genus ( Taylor & Rogers 2017), but that of Narella virgosa is so profusely branched as to considered bushy, and may be unique for the genus.

Remarks. The holotype was host to several large, orange-red ophiocanthid ophiuroids ( Fig. 1J ).

Distribution. Midway Island, off Johnston Atoll and Musician Seamounts north of Hawaiian Islands, 1901– 1985 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 13. Narella virgosa, holotype: A, stereo view of a whorl. B–D, stereo views of lateral, adaxial, and opercular aspects of a polyp. E, outer surface of basal scale. F, medial scales. G, buccal scales. H, adaxial buccal scale. I, opercular scales. J, coenenchymal scales. Scale bars in mm.