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- Errinopora dichotoma Lindner, 2005: 93-96, figs 4.2H, 4.7A, 4.12 (unpublished name).
Holotype: Dominator 971–73, 1 alcohol-preserved male colony 11.5 cm in height, USNM 1123508 (Fig. 11D). Paratypes: Alaskan Leader, 53°01'42"N, 170°05.99'W, 200–400 m, 4 Jun 2000, 1 male, USNM 1123507; Alaskan Leader 35, 53°01'48"N, 170°06'12"W, 172–178 m, 4 Jun 2002, 1 female, 1 male, USNM 1137600; Dominator 971–73, topotypic, 1 dry branch, male, USNM 1148143. Type locality. Dominator 971–73, 52°33'10"N, 179°25'18"E (off northwestern Petrel Bank), 217 m, 26 Jun 1997.
The specific name dichotoma, meaning “in two parts" (from the Greek dicha, meaning “in two" and tomos, meaning “part" or “slice"), referring to the dichotomous branching mode of this species.
Colonies three dimensional, robust, and sparsely branched, branching equally and widely dichotomously, resulting in broad U-shaped axils; branch anastomosis absent. Largest colony (holotype, Fig. 11D) 11.5 cm in height, with a basal branch diameter of 16 × 20 mm. Branches circular to elliptical in cross section, attenuating to thick (7–8 mm in diameter), blunt tips; tips of most branches missing (broken) from type material. As in most species of Errinopora, coenosteum quite porous (Fig. 12F–I), composed of a reticulum of thin, spinose strips separated by wide slits or series of pores, the spines being up to 55 µm in height and 15–24 µm in diameter. Coenosteum orange, branch cores being white.
Dactylopore spines occur on all branch surfaces and quite variable in orientation (Fig. 12B), sometimes forming transverse or longitudinal rows of up to 7 laterally fused spines, spines sharing the same laterally fused row sometimes oriented in opposite directions, their dactylotomes facing in opposite directions. Isolated dactylopore spines also present. Dactylopore spines of moderate size and thick-walled, up to 1.2 mm in height and 1.1 mm in width, the dactylotome occupying one-fourth to one-third width of spine. Small (80 µm diameter), circular secondary dactylopores common. Dactylostyles robust (Fig. 12C, L–M), each about 0.125 mm in width, composed of elements up to 40 µm in height and 10-12 µm in diameter.
Gastropores circular, sometimes arranged in rows, otherwise randomly arranged, 0.3-0.5 mm in diameter; pores lack a ring palisade. Secondary gastropores (Fig. 12C, lower) 0.22–0.30 mm in diameter. Gastrostyle occupies most of gastropore cavity. Gastrostyles lanceolate, up to 0.5 mm in height, bearing longitudinal, anastomosing, spinose ridges.
Intact female ampullae never observed, but coenosteal depressions 1.0–1.1 mm in diameter are common in one specimen, these presumed to be spent female ampullae. Male ampullae small, porous hemispheres 0.5–0.6 mm in diameter.
Errinopora dichotoma is one of three species in the genus having a predominantly unilateral arrangement of dactylopore spines in which only one row of laterally fused spines (usually proximal to gastropores) have their dactylotomes facing a gastropore or gastropore row, the other species being Errinopora nanneca and Errinopora zarhyncha. Errinopora dichotoma is compared to those species in their respective accounts and in the Dichotomous Key and Table 1. Of the five specimens examined, 1 was presumed to be female and 4 male.
- Cairns, S; Lindner, A; 2011: A Revision of the Stylasteridae (Cnidaria, Hydrozoa, Filifera) from Alaska and Adjacent Waters ZooKeys, 158: 1-88. doi
- Cairns S (1992) A generic revision of the Stylasteridae (Coelenterata: Hydrozoa). Part 3. Keys to the genera. Bulletin of Marine Science 49(1–2): 538-545.
- Appeltans W, Bouchet P, Boxshall G, Fauchald K, Gordon D, Hoeksama B, Poore G, van Soest R, Stohr S, Walter T, Costello M (2001) World Register of Marine Species. www.marinespecies.org [Accessed on 2011.09.19]