Sympodium hexagonotus, Benayahu & Ekins & Mcfadden, 2021

Benayahu, Yehuda, Ekins, Merrick & Mcfadden, Catherine S., 2021, Overview of the genus Sympodium Ehrenberg, 1834 (Octocorallia, Alcyonacea, Xeniidae), with the description of new species, revealing regional endemism, Zootaxa 5072 (4), pp. 324-350 : 338

Sympodium hexagonotus sp. n.

Figs. 3F , 10 , 11 .

Material. Australia. Holotype : QM G330076 , Ningaloo Reef , inside Norwegian Bommies, Western Australia, Australia (22°37’17.6”S, 113°38’32.6”E), Lagoon (Patch Reef), 5–6 m, 19 May 2009, coll. M. Ekins & M. Bryce ; Paratypes: QM G339750 , four fragments same details as the holotype .

WAM Z29359, same details as the holotype .

Description. The holotype measures 25 x 33 mm ( Fig. 10A ), and features mounds covered with densely packed polyps. The spreading membrane is about 1 mm thick and the mounds are about 10 mm high. Only a few polyps are significantly expanded while the majority are in various states of retraction. The expanded polyps are up to 1.5 mm long and their tentacles are approximately 0.5 mm long with a single row of 7–8 pinnules on either side of the tentacle.

The sclerites of the holotype are ellipsoid platelets, mostly hexagonal in shape. They are opalescent and abundant throughout the colony, measuring 0.010 –0.028 x 0.008 –0.023 mm in diameter ( Fig. 11A ). The sclerites are composed of calcite rods whose tips provide a uniform granular appearance to the sclerite surface. They are arranged in dense patches with some space in between ( Fig. 11B ).

Color. The ethanol-preserved holotype is cream.

Etymology. The species’ name, hexagonotus in Greek, means a six-sided polygon, referring to the unique shape of the sclerites.

Remarks. The paratypes resemble the holotype except for their size. The morphology of the colonies is characterized by both mounds and the hexagonal sclerites whose diameter is the largest recorded to date among the congeners (0.028 mm). The ethanol-preserved holotype (QM G330076) was sequenced and subsequently assigned to MOTU44 ( McFadden et al. 2019).

Living features. The live colonies feature distinct mounds and are bluish/cream in color ( Fig. 3F )

Distribution. Western Australia

Figures

FIGURE 3. Live colonies of Sympodium species on the reef. (A) S. arbusculum sp. n.: colonies with clusters of expanded polyps. (B, C) S. caeruleum Ehrenberg, 1834; membrane-like colonies with expanded polyps. (D, E) Patches of Sympodium gibbaeum sp. n. colonies with expanded polyps over the mounds. (F) S. hexagonotus sp. n. holotype colony featuring distinct mounds with expanded polyps.

FIGURE 10. Sympodium hexagonotus sp. n.: morphology of type material colonies. (A) Holotype (QM G330076) featuring mounds with mostly retracted polyps. (B) Paratype fragments (QM G339750).

FIGURE 11. Scanning electron micrographs of sclerites of Sympodium hexagonotus sp. n. Holotype (QM G330076): (A) Ellipsoid platelets with hexagonal outline. (B) Tips of calcite rods provide a granular appearance to the sclerite surface but organized in patches with space in between.