Margaretta gracilior (Ortmann, 1892)

Margaretta gracilior (Ortmann, 1892) View in CoL

Figure 37 View FIGURE 37

v. 1892 Tubucellaria gracilior Ortmann , p. 699.

v. 1957 Margaretta gracilior (Ortmann) ; Harmer,

p. 835, pl. 55, figs. 23–28.

v. 2006 Margaretta gracilior (Ortmann) ; Tilbrook,

p. 234, pl. 51D.

Figured material. PMC EDM-Collection J.H.B.136a, sample 19200 ( Figure 37A–C View FIGURE 37 ) and sample 19195 ( Figure 37D–F View FIGURE 37 ); Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Description. Colony erect, articulated with cylindrical, quadriserial internodes, either straight or slightly curved, narrow, measuring c. 100 µm in width at the undivided base of the rami, expanding to 335–600 µm; internode attachment base circular, 65–95 µm in diameter, undivided, located laterally on the autozooid frontal midway between the secondary orifice/peristome and ascopore. Autozooids arranged in whorls of back to back pairs, with each pair rotated 90º relative to the next, flask-shaped, elongate (mean ZL/ZW 2.56), with indistinct lateral boundaries. Frontal shield convex, smooth, regularly and evenly perforated by small, sunken, circular pseudopores (5–13 µm in diameter), centred in an elliptical to polygonal mesh (35– 50 µm in maximum dimension), overall appearance reminiscent of a peanut shell; ascopore circular to transversely elliptical, measuring 28–56 × 41–51 µm, surrounded by a raised rim slightly crenulated distally, placed distomedially, 250–370 µm from the proximal margin of the secondary orifice. Secondary orifice transversely elliptical; peristome relatively short, projecting from the frontal plane of the branch by about 100–130 µm, at an angle of approximately 45°, not bordered by a basal ridge; peristome of brooding autozooids swollen at the base, longer and curved upward; brooding autozooids grouped in whorls.

Measurements (µm). ZL 909±120, 747–1205 (3, 13); ZW 354±39, 286–435 (3, 13); OL (secondary) 94±7, 85–108 (3, 7); OW (secondary) 141±11, 130–157 (3, 7).

Remarks. Key characters for distinguishing species of Margaretta include the number of autozooids in each whorl, the number of partitions at the base of the rami, the shape and development of the peristome, the position of the ascopore relative to the orifice, the patterning of the frontal shield, and the shape and arrangement of pseudopores. Our specimens align closely with the description of M. gracilior as provided by Harmer (1957) and Tilbrook (2006) in all these aspects. Margaretta gracilior was first described from the Red Sea and has since been widely reported across the Indo-Pacific region ( Tilbrook, 2006).