Chromoplexaura, Williams, Gary C., 2013

Williams, Gary C., 2013, New taxa and revisionary systematics of alcyonacean octocorals from the Pacific coast of North America (Cnidaria, Anthozoa), ZooKeys 283, pp. 15-42 : 28-30

Genus Chromoplexaura gen. n. Figures 12-17, 19

Generic diagnosis.

Plexaurid gorgonians. Colonies tall, erect, planar. Branching lateral from single basal stem. Upper branches relatively sparse, slender, elongate, mostly slightly curved. Retracted polyps as numerous low rounded protuberances all round surfaces of branches and stem. Sclerites mostly robust spindles and radiates, some ellipsoid to sub-spherical in shape.

Type species.

Euplexaura marki Kükenthal, 1913.

Etymology.

The generic name is derived from the Greek chroma (color), and the gorgonian generic name Plexaura , in reference to the vivid color of the colonies.

Systematics and phylogenetic assessment.

The genus Euplexaura (Figures 12D, 18) is an Indo-Pacific genus (eastern Africa to the central Pacific) of 37 named species ( Ofwegen 2012a), with the number of valid species not determined. The surface coenenchyme contains numerous robust ovoid to subspherical sclerites ( Fabricius and Alderslade 2001). All sclerites are colorless. Since Euplexaura marki differs in these several respects to the genus to which is was originally described, a new genus is here named to accommodate it.

A comparison is also warranted between Chromoplexaura and two plexaurid genera that share some superficial similarities - Thesea with 31 described species from the Atlantic Ocean ( Deichmann 1936: 110; Humann and DeLoach 2002: 78; Ofwegen 2012d), and Swiftia with 14 described species from the Atlantic and eastern Pacific ( Deichmann 1936: 185; Goldberg 2001: 100; Humann and DeLoach 2002: 65; Ofwegen 2012c). It is yet to be determined if the Pacific species presently allocated to Swiftia do indeed belong to that genus or another one. The polyps of Swiftia emanate from calyx-like protuberances, and both Thesea and Swiftia have a preponderance of narrow/elongate to robust spindles. The sclerite complements of both genera are composed mostly of spindles with few to no radiates present. On the other hand, the sclerite complement of Chromoplexaura is comprised primarily of radiates and variably-shaped spindles.

Forty five genera of the holaxonian family Plexauridae are currently considered valid ( Williams and Cairns 2011). Molecular phylogenetic studies have shown that the resolution necessary to produce a molecular phylogeny of the octocorals is lacking at present, due to slow rate of mitochondrial gene changes and a paucity of markers necessary to distinguish some taxa. Regarding future research, it is anticipated that ITS2 sequence data will produce improvements regarding better resolution and more credible results ( McFadden et al. 2006, McFadden et al. 2010, Wirshing et al. 2005).

Currently, the evidence based on molecular data does not support the family as being a monophyletic one, but rather has shown many genera dispersed throughout richly-populated phylogenetic trees, and do not exhibit close affinities as a group. In some cases, plexaurid genera have even appeared associated with genera in other families ( McFadden et al. 2006; Wirshing et al. 2005). At present, it is therefore not possible to produce a plausible topology of phylogenetic relationships for such genera as Euplexaura , Swiftia , Thesea and Chromoplexaura gen. n.

Key to the genera Chromoplexaua and Euplexaura