Narella merga, 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 : 23-25

Narella merga , n. sp.

Figs. 1M, 11 A –J

Etymology. Named merga (Latin for a two-pronged pitchfork), in allusion to the growth form of the colony. The name is considered as a noun in apposition.

Type and Type Locality. Holotype and SEM stubs 2436-2440, USNM 1424202 . Type Locality: EX 1606-502,

19.15048˚N, 164.5587˚ E ( McDonald Guyot, Mid-Pacific Mountains Range west of Wake Island), 2575 m.

Material Examined. The holotype.

Description. Only the distal 9.5 cm (19 whorls) of the holotype was collected, representing just part of one of the two branches, but in situ photographs ( Fig. 1M) show the colony to have a short, stout stem about 2 cm in height that bifurcates into two long branches, each about 20 cm long. The color of the colony is white. The whorls are relatively closely spaced (about 2 whorls/cm), each whorl having three polyps; the whorl diameter is about 4.4 mm. The horizontal length of a contracted polyp is about 4.0 mm. Polychaete commensalism was not noted.

The basal body wall scales ( Fig. 11D) are 1.8–2.2 mm in height, their distal margin rounded (not spinose, serrate or undulate), forming a short cowl around the medial scales. The dorsolateral edge of the basal scale is rounded but on its lower half bears one or two short but tall (up to 0.5 mm) thin ridges. The basal scales are open on the adaxial side. The medials ( Fig. 11E) are short (1.3–1.5 mm), narrow, and upturned at their distal edge. The buccal scales ( Fig. 11F) range from 1.6–2.2 mm in length and are quite wide, also having a rounded distal edge. All body wall scales bear a low granulation and are not ridged except for the dorsolateral edge of the basals. The ratio of the lengths of the major body wall scales is: 1: 0.7: 0.95. There is one pair of flat adaxial buccal scales, shaped as rectangles or ellipses, measuring 0.6–0.7 mm in greater diameter. The adaxial polyp side is also covered with numerous smaller elliptical scales ( Fig. 11G) measuring 0.25–0.35 in diameter.

The abaxial opercular scales ( Fig. 11, top) are symmetrical, each bearing broad lateral lobes and measuring 1.8–1.9 mm in length (L:W = 1.2). The lateral opercular scales are asymmetrical, having only one lateral lobe, and measure 1.8–1.9 mm in length (L:W = 1.5–2.0). The symmetrical (no lateral lobes) adaxial opercular scales are the smallest ( Fig. 11H, lower), measuring 1.2–1.4 mm in length (L:W = 1.9–2.0). The adaxial operculars are flat, whereas the other operculars have highly concave outer surfaces. The pinnular scales are about 0.11 mm in length, flat, and slightly curved ( Fig. 11J).

The coenenchymal scales ( Fig. 11I) are a mixture of elongate (L:W = 3.1) to elliptical (L:W = 1.4) in shape and up to 2.2 mm in length. They are thin and imbricate, most bearing a short and relatively low ridge on their outer surface.

Comparisons. The single bifurcation growth mode of N. merga appears to be unique within the genus. Among those species that have sparse dichotomous branching and a basal scale dorsolateral ridge, N. merga is most similar to N. alaskensis Cairns & Baco, 2007 (Gulf of Alaska, 2377–3075 m) and even shares an overlapping depth range. But, N. alaskensis differs in having more polyps per whorl (4–9), smaller polyps, and much longer medial body wall scales that sometimes bear a longitudinal ridge.

Distribution. Known only from the type locality.