Euplexaura plana, Namin, Samimi & Ofwegen, Van, 2009

Namin, Samimi & Ofwegen, Van, 2009, Some shallow water octocorals (Coelenterata: Anthozoa) of the Persian Gulf, Zootaxa 2058, pp. 1-52 : 25-28

Euplexaura plana n. sp.

( Figs. 2 d, 17)

Material: Holotype, RMNH Coel. 38778, Farur Island, coll. S.A. Mohtarami, 2006.

Description. The holotype is 15.5 cm high and 27 cm wide ( Fig. 2 d). The colony is branched in one plane and the end branches especially are flattened in the plane of branching. On large parts of the colony the coenenchyme is lacking; the calyces are low, dome-shaped.

The polyps have points with flattened spindles, up to 0.30 mm long ( Fig. 17 a). A collaret is not present.

The surface layer of the branch has blunt ellipsoids and spindles, up to 0.35 mm long, with complex tubercles ( Fig 17 b). Several of them with one side less tuberculate.

The lower layer has sclerites similar to those of the surface layer, but they are less tuberculate, and smaller, up to 0.25 mm long ( Fig. 17 c).

Colour. Alive, the colony was pinkish in colour, preserved it is white. Sclerites are colourless.

Etymology. The species name is from the Latin planus, flat, referring to the flattened branches.

Remarks. Most Euplexaura species have rather small sclerites. Kükenthal (1924: 91–98) mentioned only four species with coenenchymal sclerites 0.25 mm long, or more: E. aruensis Kükenthal, 1911 , described from the Aru Islands, Indonesia, with sclerites up to 0.25 mm long; E. erecta Kükenthal, 1908 , from Japan, with sclerites up to 0.30 mm long; E. robusta Kükenthal, 1908 from Japan, with sclerites up to 0.32 mm long; E. kukenthali Broch, 1916 from NW Australia, with spindles up to 0.50 mm long. All these four species show no flattened branches and are therefore considered to be different species.

E. rhipidalis Studer, 1894 , originally described from Singapore, does have flattened branches, and was recorded to occur in the nearby Red Sea ( Grasshoff 2000: 59). Grasshoff re-examined the type specimen of E. rhipidalis and observed this species actually has sclerites with a wide range of size, up to 0.30 mm long, instead of the 0.15 mm long measured by Studer, and being close to the 0.35 mm reported for E. plana .

Because of the similarities in colony shape and sclerite size between E. plana and E. rhipidalis , and because the drawings of sclerites presented by Grasshoff are rather schematic, we decided to make extra SEM photographs of RMNH Coel. 6040, a specimen identified by Stiasny (1959: 47) as Muricella tenera , but synonymized with E. rhipidalis by Grasshoff (2000). RMNH Coel. 6040 showed even longer blunt ellipsoids and spindles than recorded by Grasshoff for E. rhipidalis , viz. up to 0.40 mm long ( Fig. 18 c); like in E. plana several of them with one side less tuberculate. However, the interior sclerites of RMNH Coel. 6040 ( Fig. 18 d) are different from those of E. plana ( Fig. 17 c), they have less developed tubercles, and quite some sclerites have pointed ends. Strangely, sclerites like that were not at all depicted by Grasshoff. Because of the differently shaped interior sclerites, a character also present in the below described Euplexaura spp. and the much more flattened branches than in E. rhipidalis we decided to describe the present material as a new species.

Figures

FIGURE 17. RMNH Coel. 38778, holotype of Euplexaura plana n. sp.: a, polyp spindles; b, ellipsoids and spindles of surface layer; c, spindles of the subsurface layer. Scale at b only applies to b.

FIGURE 18. RMNH Coel. 6040, Euplexaura rhipidalis Studer, 1894: a, tentacle rods; b, collaret and point spindles; c, ellipsoids and spindles of surface layer; d, spindles of the subsurface layer. Scale at d also applies to a.

FIGURE 2. a – b, RMNH Coel. 38756, holotype of Sarcophyton minusculum n. sp.; a, lateral view, b, view from above; c, RMNH Coel. 38767, Muricella sp.; d, RMNH Coel. 38778, holotype of Euplexaura plana n. sp.; e, RMNH Coel. 38779, Euplexaura sp. a; f, RMNH Coel. 38780, Euplexaura sp. b. Scales 1 cm.