Trimuricea Gordon, 1926

Samimi-Namin, Kaveh & Van Ofwegen, Leen P., 2016, A revision of Trimuricea Gordon, 1926 (Cnidaria: Octocorallia: Plexauridae) with the description of six new species, Zootaxa 4105 (1), pp. 1-44 : 3-4

Genus Trimuricea Gordon, 1926

Trimuricea Gordon, 1926: 515 ; Bayer 1981: 945 “= Echinogorgia ?”; Grasshoff 1999: 48; Samimi-Namin & van Ofwegen 2009a: 43, 2009b: 517.

Diagnosis. Plexaurids with colonies irregularly, laterally branched more or less in one plane or forming net-like fans. Polyps retractile, situated all around the branches, having flattened triradiate sclerites, commonly along with curved, hockeystick or boot-shaped, flattened point sclerites and flattened collaret spindles ( Fig. 30a ). Sometimes the uppermost collaret sclerite can have a more or less medially situated branch that is angled distad and becomes incorporated into the points. Tentacles with a few curved or bootshaped scales. Calyces well developed, with thornscales. Coenenchyme between the calyces with spindles, and sometimes additional thornspindles or derivatives of radiates. Sclerites are colourless or yellowish.

Type species. Trimuricea reticulata ( Thomson & Simpson, 1909) by original designation.

Remarks. Gordon included Echinomuricea andamanensis Thomson & Simpson, 1909 in the genus Trimuricea . According to us it should be considered as a species of Echinogorgia . Both Gordon’s pictures of the sclerites (1926: Fig. 6 ) and Thomson & Simpson’s (1909: Pl. 8, Fig. 2 ) show typical Echinogorgia thornscales.

We examined the sclerite arrangement in the polyps of all Trimuricea species except for T. africana , T . caledonica and T. reticulata , but because of the small size of fragments available and all polyps were tightly retracted, the arrangement of polyp sclerites could not be studied satisfactory. The removal of calyx thornscales for a better view resulted in breakage of the polyps, even with material kept in alcohol. However, we were able to establish that the collaret generally had one or two rows of spindles and the points were made up of two triradiates, or a triradiate and a few curved, hockeystick or boot-shaped, flattened spindles; sometimes two triradiates and a small spindle formed a point. Due to the variation and inconsistency of the sclerite arrangement between and within the polyps, counting number of rows in the collaret and number of point sclerites did not provide any meaningful information. Also in previously described species this arrangement was often not mentioned in detail, probably because of the same problem. As a result of these observations and uncertainty about the arrangement of the polyp sclerites we exclude it from the descriptions of all but one species. However, we do schematically show the arrangement of the triradiates in the points as this has never been published before ( Fig. 30a ).

Noteworthy, in addition to the sclerites in the top of the colony, usually used for identification of gorgonians, we also checked other parts of the colonies and we noticed additional types of sclerites, irregular radiates and derivative of radiates up to 0.05 mm long. These sclerites occur in the interior layer of the coenenchyme of the main stem, and some of the main branches where the axis is relatively solid. These sclerites do not normally occur at the tip of the branches. We assume this is a generic feature and occurs in all Trimuricea species.

The genus resembles Echinomuricea and Echinogorgia in the structure of the calyces and coenenchyme and the presence of thornscales. However, it differs from Echinomuricea in growth form, having tripartite sclerites in the polyps, and shape of the thornscales. Echinogorgia differs in the shape of the thornscales, with more development of the thorns and the base than in Trimuricea , and the presence of capstans in the interior of the coenenchyme.

Distribution. The genus Trimuricea has been recorded in the NW Indian Ocean including the Persian Gulf, Oman Sea (Samimi-Namin & van Ofwegen 2009a & b and this paper), the Arabian Sea, east Africa and the central Indo-Pacific ( Fig. 1). No species have yet been recorded from the central Indian Ocean and most of the Pacific.

Figures

FIGURE 2. Sclerites of T. africana Gordon, 1926, holotype, BMNH 1933.5.3.102: a, point triradiates; b, point spindles; c, collaret spindles; d, tentacle scale; e, spindle and unilateral spinose spindles of coenenchyme.

FIGURE 6. Sclerites of T. bicolor n. sp., RMNH Coel. 39860: a, calicular thornscales; b, coenenchymal spindles.

FIGURE 30. a, schematic arrangement of sclerites in a Trimuricea polyp: a, tentacle scales,; b, triradiates; c, collaret spindles; d, calicular thornscale: b, live colony of T. bicolor n. sp. holotype, RMNH Coel. 39860 (photo: B. W. Hoeksema).