Xenia fusca Schenk, 1896

Halász, Anna, Mcfadden, Catherine S., Toonen, Robert & Benayahu, Yehuda, 2019, Re-description of type material of Xenia Lamarck, 1816 (Octocorallia: Xeniidae), Zootaxa 4652 (2), pp. 201-239 : 211-212

Xenia fusca Schenk, 1896

Fig. 6

Xenia fusca Schenk, 1896: 59

Material. Syntype: SMF 40 , Indonesia, Ternate Island, 1894, coll. W. Kükenthal.

Description. The syntype is 38 mm high; its stalk is 32 mm long and 18 mm wide at its base, 25 mm wide at its uppermost part. The polyp body is up to 3 mm long, and the tentacles are up to 2.5–3 mm long, featuring mostly four rows of pinnules along each of the tentacle margins. Occasionally 3 and even 5 rows are present. The pinnules are relatively short and stout, up to 0.25 mm long and 0.10 mm wide, 14–22 in the outermost row, spacing ranging from no gap to up to a half pinnule-wide space between adjacent pinnules.

Sclerites are abundant in all parts of the colony; they are ellipsoid platelets, 0.006 –0.014 X 0.013 –0.019 mm in diameter ( Fig. 6a, n =20). The sclerites are composed of dendritic rods assembled within the sclerite interior ( Fig. 6b ), providing a granular appearance to the sclerite surface. Few fractured sclerites were observed, and they remained intact after preparation ( Fig. 6c ). The ethanol-preserved holotype is dark gray in color.

Remarks. In the original description of X. fusca, Schenk (1896) indicated that the species has 6–7 irregular rows of pinnules and 13–14 pinnules in each row, as opposed to the current findings that revealed mostly four rows and 14–22 pinnules in the outermost row. The dimensions of the sclerites obtained in the current study correspond to the original description. The sclerites of the type of Xenia fusca differ from those commonly occurring among other Xenia species (e.g., X. bauiana : Fig. 2 , X. blumi : Fig. 3 , X. garciae Bourne, 1894 : Fig.7 ), feature a densely packed granular surface, and do not exhibit the typical radial cracks under SEM (e.g. X. blumi : Fig. 3 , X. plicata : Fig. 4 ).

Similar species and conclusion. X. fusca and Xenia rubens Schenk, 1896 feature mostly four rows of pinnules and a similar number of pinnules in the outermost row. They also share the same type of sclerite surface but the internal structure of their sclerites differs: the latter with wide rods and a void in the interior and the former with randomly arranged calcite rods ( Figs. 13 and 6 , respectively). Therefore, it is concluded that the two species should be considered as separate until further data on freshly collected colonies and their sclerite microstructure become available.

Distribution. Indonesia: Ternate Island.

Figures

FIGURE 2. Scanning electron micrographs of polyp sclerites of Xenia bauiana May, 1899 syntype (ZMB 3673). a. Ellipsoid platelets, mostly fractured; b. Fractured sclerite composed of dendritic rods, more or less radially arranged in the peripheral region; Scale bar at a 0.010 mm, at b 0.005 mm.

FIGURE 3. Scanning electron micrographs of polyp sclerites of Xenia blumi Schenk, 1896 holotype (SMF 44). a. Ellipsoid platelets, fractured; b. Fractured sclerite enlarged; c. Fractured sclerite composed of dendritic rods; d. Overview of sclerites. Scale bar at a, c and d 0.010 mm, at b 0.002 mm.

FIGURE 4. Scanning electron micrographs of polyp sclerites of Xenia plicata Schenk, 1896 holotype (SMF 45). a. Ellipsoid platelets, most fractured; b. Fractured sclerite; c. Fractured sclerite, enlarged, composed of calcite rods, often dendritic and sinuous, and more or less radially arranged in the peripheral region. Scale bar at a and b 0.010 mm, at c 0.001 mm.

FIGURE 6. Scanning electron micrographs of polyp sclerites of Xenia fusca Schenk, 1896 syntype (SMF 40). a. Ellipsoid platelets; b. Fractured sclerites composed of a latticework matrix of dendritic calcite rods and more or less radially arranged in the peripheral region; c. Overview of sclerites. Scale at a and c 0.010 mm, at b 0.002 mm.

FIGURE 7. Scanning electron micrographs of polyp sclerites of Xenia garciae Bourne, 1894 type (BML 1921.11.18.1). a. Sclerite with a surface crest, fractured; b. Ellipsoid sclerites, fractured c. Fractured sclerite composed of a latticework matrix of calcite rods, dendritic and sinuous and radially arranged in the peripheral region; d. Overview of sclerites, fractured. Scale bar at a, b and d 0.010 mm, at c 0.002 mm.

FIGURE 13. Scanning electron micrographs of polyp sclerites of Xenia rubens Schenk, 1896 type (SMF 46). a. Ellipsoid platelets; b. Fractured sclerites revealing internal void; c. Overview of sclerites. Scale bar at a 0.010 mm, at b 0.002 mm, at c 0.020 mm.