Isidella tenuis, Cairns, Stephen D., 2018

Cairns, Stephen D., 2018, Deep-Water Octocorals (Cnidaria, Anthozoa) from the Galapagos and Cocos Islands. Part 1: Suborder Calcaxonia, ZooKeys 729, pp. 1-46 : 27-29

Isidella tenuis sp. n. Figures 3g, 16

Isidella sp. Breedy and Cortés 2008: 73, 76.

Material examined.

Types. Holotype: colony and SEM stubs 2355-2358, JSL-I-1942, USNM 89382. Paratypes: JSL-I-1942 4 colonies, USNM 1423001.

Type locality.

5°34.6'N, 87°04.25'W (off Cocos Island), 606-628 m deep.

Distribution.

Known only form the type locality.

Description.

The colony is uniplanar, the largest specimen (the holotype, Figure 3g) measuring 18 cm in height and 7 cm in width, with a basal branch diameter of 1.7 mm. The holotype shares a thin basal encrustation with another specimen (a paratype). Branching is always dichotomous from nodes, the internodes ranging from 9-14 mm in length. The internodes are white, not longitudinally grooved, and hollow, the central canal (Figure 16b) constituting about 35-40% of the branch diameter.

The polyps are uniserially placed (Figure 16a), their bases about 4-6 mm apart, but because of the length of the upturned polyps there is only 1-3 mm between adjacent polyps. The polyps are cylindrical and slender (Figure 16a), up to 3.3 mm in length and about 0.5 mm in diameter. Most of each polyp consists of eight elongate (up to 2.9 mm, L:W = 26-31), straight, cylindrical needles (Figure 16d), their pointed tips projecting beyond the tentacles. The sclerites bear numerous short (22-26 µm in length) ridges about 5 µm in height, which are arranged longitudinally on the sclerite (Figure 16e). Toward the base of the polyp are several shorter needles 0.95-1.0 mm in length (L:W = 17-19), these needles (Figure 16f) also being cylindrical but having blunt, flattened tips. Directly adjacent to the coenenchyme are also several even shorter needles (0.5 mm in length, L:W = about 13), also with flattened, blunt tips (Figure 16i). These two smaller size classes of needles allow for some flexibility of the polyp where it attached to the branch. The tentacular platelets (Figure 16h) are numerous, consisting of flat, blunt-tipped sclerites 0.095-0.1 mm in length and having a L:W of about 7. Their flat surfaces are fairly smooth, covered by small granules and low ridges. The pharyngeal sclerites (Figure 16j) are small (0.072-0.10 mm in length) rodlets that bear relatively tall spines. The coenenchymal sclerites (Figure 16g) are quite rare, consisting of flat, blunt-tipped scales (like those of the tentacles), but larger: 0.15-0.18 mm in length (L:W = 4-5).

Comparisons.

Isidella tenuis differs from I. trichotoma Bayer, 1990 (Hawaii, 1920 m) in having dichotomous branching, much smaller coenenchymal and body wall sclerites, and differently shaped pharyngeal sclerites. Isidella tenuis differs from I. tentaculatum Etnoyer, 2008 (California to Alaska, 720-1050 m) in having needle-shaped body wall scales, differently shaped pharyngeal scales, smaller polyps, uniserial polyps, and blunt-tipped body wall sclerites.

Etymology.

Named “tenuis” (Latin for thin) in reference to the slender polyps of the species.