Plumarella longispina Kinoshita, 1908

Figs. 1B, 4A–I

Plumarella longispina Kinoshita, 1908: 14–15, pl. 1, fig. 5, pl. 5, fig. 39a–e.— Kükenthal, 1919: 349–350; 1924: 255 (key), 260–261, fig. 149.— Cairns, 2007: 512 (in part: listing from Japan)

Material Examined. fragment of holotype, USNM 50117; Albatross 3747, Sagami Bay, 82–88 m, 19 May 1900, 2 colonies in alcohol and SEM stubs 2845–2847, USNM 49344.

Types and Type Locality. The holotype is presumed to be deposited at the Zoological Institute, University of Tokyo. A fragment of the holotype is also deposited at the NMNH (USNM 50117). Type Locality: Sagami Bay, Japan, 604 m.

Description. Colonies branch in a uniplanar fashion, the largest specimen known (type) is 16 cm in height. Branching occurs in a regular alternate-pinnate manner (Fig. 1B), the branchlets are of fairly uniform length (13–20 mm), producing a regular comb-like pattern.

Polyps are densely arranged (i.e., 16–20 polyps per cm - not 10/cm as stated by Kinoshita, 1908) in an alternating arrangement (never in pairs, Fig. 4A), and always in the plane of the flabellum. The polyps are cylindrical, curved distally (somewhat adnate), and quite short, measuring 0.50–0.75 mm in length (Figs. 4B–C).

Each polyp is encased in eight triangular opercular scales and eight rows of body wall scales. The opercular scales are isosceles triangular in shape (Fig. 4F), ranging from 0.29–0.49 mm in length and having a L:W of 1.6-2.1; their size gradually decreases from the ab- to the adaxial margin. The outer face of each opercular is covered with small granules arranged in a radiating pattern from a center located near the base of the scale; their proximal inner face is tuberculate, whereas the distal inner face is smooth. The marginal scales (Figs. 4B–E) are polymorphic in shape and size. The abaxial and outer-lateral pairs of marginals (Fig. 4B) range from 0.50 to 0.65 mm in height and are often broken during collection. Each marginal has a massive rectangular base up to 0.35 mm in width, which supports an elongate, cylindrical, pointed spine that can be up to 0.35 mm in length, thus composing about half the length of the scale. The inner-lateral marginals (Fig. 4C) are shorter, about 0.4 mm in length, but also bear a terminal spine. The adaxial marginals are rectangular (Fig. 4D), about 0.23 mm in width, thin, non-spinose scales. Proximal to the marginal scales are the curved body wall scales (Figs. 4B–C, G), which are somewhat rectangular in shape (the greater width 0.30 mm), and often with a rounded, finely serrate margin. The body wall scales are arranged in eight longitudinal rows. Including the marginals, each of the two abaxial rows includes 4 scales, each outer- and inner-lateral row has 3–4 scales, and the adaxial rows have 3 scales plus an irregular scattering of smaller scales on the proximal adaxial body region. The body wall scale formula is thus: 4:3-4:3-4:3+. Wide, strongly curved infrabasal scales (Fig. 4H) may also be present proximally. The outer face of the marginal scale is smooth, whereas the outer surface of the body wall scale is granular, at least on its proximal edges.

The coenenchymal scales (Figs. 4B, I) are elongate (L:W = 3.3–3.9) or polygonal, rarely exceeding 0.35 mm in length; their outer surface is covered with robust granules.

Remarks. Of the 33 species of Plumarella, 15 of them have prominent marginal spines, like those of P. longispina. But of those, five species have polyps on all sides of branchlets (vs alternating or paired), which at one time formed the basis for the subgenus of Plumarella (Dicholapis) Kinoshita, 1907 and thus cannot be confused with P. longispina. As discussed above, P. longispina is quite similar to but distinct from P. williamsi, but of the eight other species with prominent marginal spines, five occur off Japan, the type locality of P. longispina. They are: P. spinosa Kinoshita, 1907, P. rigida Kükenthal & Gorzawsky, 1908, P. adhaerans Nutting, 1912, P. recta (Nutting, 1912), and P. alternata (Nutting, 1912). Kükenthal (1924) provides a dichotomous key to all species of Plumarella described before 1924, the first couplet being whether the marginals are pointed/spined or not. He concluded that P. longispina is distinctive by having a relatively small number of abaxial body wall scales (i.e., 4), a high number of adaxial body wall scales (i.e., 3+), and small polyps less than 1 mm in length.

Distribution. Known only from Sagami Bay, 88– 604 m.