Xenia membranacea 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 : 217-218

Xenia membranacea Schenk, 1896

Fig. 9

Xenia membranacea Schenk, 1896: 60 , plate 3, Fig 15

Xenia membranacea ; Ashworth 1900: 512; Kükenthal 1902: 654–655; Ashworth 1900: 512; May 1899: 86; Thomson & Dean 1931: 31; Roxas 1933: 90, plate 2, Fig 7 ; Verseveldt 1960: 244–246; Utinomi 1977: 5–6; Benayahu 1990: 118, table 1, listed only; Reinicke 1997: 50–51; Janes 2013; McFadden et al. 2014a.

Material. Syntype: SMF 41 , Indonesia, Ternate Island, Moluccas, 1894, coll. W. Kükenthal.

Description. The syntype is 25 mm high; its stalk is 9 mm long and it splits 2–3 mm above its base into eight short branches, two of which split again into two; the length of each branch is 8–10 mm and their width is about 5 mm at the base and 5–6 mm at the uppermost part. The polyp body is up to 3 mm long, and the tentacles up to 4 mm long, featuring three and occasionally a partial fourth row of pinnules on each side. The pinnules are relatively slender, up to 0.75 mm long and 0.25 mm wide, 20–25 in the outermost row with no gap between adjacent pinnules.

Sclerites are present in all parts of the colony; most of them are ellipsoid platelets, 0.010 –0.019 X 0.015 –0.025 mm in diameter ( Fig. 9 , n=26). Their surface outline ranges from almost smooth to irregular ( Fig. 9a, b ). Some of the sclerites feature a crest, or surface depressions ( Fig 9c, e ). Others are almost round ( Fig. 9f ) or feature a longitudinal furrow ( Fig. 9g ). The sclerites are composed of calcite rods arranged radially, at least on the surface of the sclerite ( Fig. 9d ), providing a granular appearance to all the various morphologies. The ethanol-preserved holotype is light gray in color.

Remarks. The original description of Xenia membranacea indicated 3–4 irregular rows of pinnules, 20–25 pinnules in each one. The sclerites were referred to as round discs, long ovals, or rod-like, 0.015 –0.020 mm, 0.02– 0.025 X 0.010 –0.015 mm and 0.020 –0.030 X 0.006 –0.010 mm, respectively. Except for the latter, their measurements match our re-description of the type. Verseveldt (1960) identified material from Obi Latu ( Indonesia) and from the Bay of Djakarta, Malay Archipelago. For the former he described four rows of pinnules, 20–24 in a row, and "numerous oval" sclerites measuring 0.018 –0.022 X 0.013 –0.015 mm; while for the one from the Malay Archipelago he described five rows of pinnules, referring to Thomson & Dean (1931: 31) who also described five rows for specimens from the same location. The material from Obi Latu corresponds to the X. membranacea type while the Malay material might belong to X. fusca . X. membranacea was reported from the Red Sea by Benayahu (1990) and Reinicke (1997).

Similar species and conclusion. Roxas (1933) identified two specimens from the Philippines as Xenia membranacea and noted that it had been synonymized by Hickson (1931a: 152) with X. crassa . X enia membranacea and X. crassa feature three and sometimes four rows of pinnules, but differ in the number of pinnules. Their sclerite microstructure also differs ( Figs. 9 and 5 , respectively), and thus they should be considered as separate. Although features of X. membranacea also resemble those of X. grasshoffi , the former possesses sclerites with sinuous rods lacking in the latter, thus the two should be considered as separate species.

Distribution. Indonesia: Ternate Island, Moluccas, Philippines, Japan, Malay Archipelago, Red Sea.

Figures

FIGURE 5. Scanning electron micrographs of polyp sclerites of Xenia crassa Schenk, 1896 holotype (SMF 39). a. Sclerites with a surface crest, fractured; b. Ellipsoid platelet, mostly fractured; c. Fractured sclerite composed of a latticework matrix of dendritic calcite rods and more or less radially arranged in the peripheral region. Arrows at b, c indicate surface furrow. Scale bar 0.010 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 9. Scanning electron micrographs of polyp sclerites of Xenia membranacea Schenk, 1896 syntype (SMF 41). a. Irregular sclerites with rough surface texture; b. Irregular sclerites with granular surface texture; c. Sclerites with surface crest, some fractured; d. Fractured sclerites composed of dendritic rods (enlarged). e. Ellipsoid platelets; f. Round sclerite; g. Fractured sclerite. Scale bar at a, b, c, e, f, g 0.010 mm, at d 0.002 mm.

FIGURE 15. Scanning electron micrographs of polyp sclerites of Xenia viridis Schenk, 1896 holotype (SMF 42). a. Ellipsoid platelets featuring rough granulated surface, arrow indicates surface furrow; b. Sclerites with surface crest, fractured; c. Fractured sclerites composed of a latticework matrix of calcite rods, dendritic and sinuous, and radially arranged in peripheral region. Scale bar at a and b 0.010 mm, at c 0.002 mm.