Xenia sansibariana May, 1899

Xenia sansibariana May, 1899: 87

Xenia sansibariana; Kükenthal 1902: 655

Xenia actuosa Verseveldt & Tursch, 1979: 145 –146 —new synonym

Xenia actuosa Haverkort-Yeh et al. 2013

Material. Syntype: ZMB 3828, Indian Ocean, Zanzibar, 1885, coll. Sander. Holotype of X. actuosa: RMNH 12866, South-Western Pacific Ocean, Bismarck Sea, Boëso I., South reef flat, 5 m, 1975–1977, King Leopold III Biological Station at Laing Island, coll. A. Tursch.

Description. The syntype is 38 mm high; its stalk is 16–20 mm long, 15 mm wide at its base and 25–27 mm wide at the uppermost part. The polyp body is up to 10 mm long, and the tentacles are up to 6 mm long, featuring four rows of pinnules on each side. The pinnules are relatively short and slender, up to 0.7 mm long and 0.1 mm wide, 26–33 in the outermost row with a space of 0.5–1.5 pinnule-width between adjacent pinnules. No sclerites could be found in the syntype. Zooxanthellae can be seen in the stalk and also a few small gonads. The ethanolpreserved holotype is dark grey in color.

The holotype of X. actuosa is 40 mm high; its stalk splits at the base into three branches, two of which split again into two, the latter branches are 8 and 10 mm long, 15 and 20 mm wide at their base, 20 and 23 mm wide at their uppermost part, respectively. The third branch does not split; it is 30 mm long, 18 mm wide at its base and 40 mm at the uppermost part. The polyp body is up to 6 mm long, and the tentacles up to 11 mm long, featuring four rows of pinnules on each side. The pinnules are relatively short and stout, up to 0.80 mm long and 0.24 mm wide, 25–29 in the outermost row with a space of up to a half pinnule-width between adjacent pinnules. No sclerites could be found in any part of the colony. The original description indicated pulsating polyps for the live colonies. The ethanol-preserved holotype is yellow to dark beige in color.

Similar species and conclusion. The original description of Xenia sansibariana and Kükenthal's (1902) revision referred to five rows of pinnules, in comparison to four rows recorded in the current study. Verseveldt & Tursch (1979) described X. actuosa with four rows of pinnules with 21–28 pinnules and no sclerites, in full correspondence to the current findings. The two species overlap in the number of pinnule rows, number of pinnules on the outermost row, and both lack sclerites. Therefore, based on their morphological features X. actuosa should be considered a junior synonym of X. sansibariana, given the priority of the earlier description. However, while considering the geographical distance between the type localities of X. sansibariana and X. actuosa (West Indian Ocean and South-Western Pacific Ocean, respectively), genetic data should be obtained to verify the synonymy.

Xenia mucosa and X. sansibariana both feature four rows of pinnules, but differ in the number of pinnules in the outermost row (25–29 and 30–42 respectively), and, therefore, the two species should be considered as separate.

Distribution. South-Western Pacific Ocean: Bismarck Sea, Indian Ocean: Zanzibar, Red Sea.