Margaretta cf. tenuis Harmer, 1957

Margaretta cf. tenuis Harmer, 1957 View in CoL

Figure 38 View FIGURE 38

cf. 1957 Margaretta tenuis Harmer , p. 840, pl. 55,

figs. 13–18.

Figured material. PMC EDM-Collection J.H.B.137a, sample 19047 ( Figure 38A–F View FIGURE 38 ) and sample 19185 ( Figure 38G View FIGURE 38 ); Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Description. Colony erect, articulated with straight or slightly curved internodes, cylindrical, measuring c. 180 µm in width at the bipartite base of the rami, expanding to 330–660 µm; internode attachment base not observed. Autozooids arranged back to back in alternating whorls of two, but mainly in whorls of three, flask-shaped, elongate (mean ZL/ ZW 3.15), distinct, separated by shallow grooves. Frontal shield convex, sculptured, regularly perforated by small, sunken, circular pseudopores (7–20 µm in diameter), centred in an oval to polygonal mesh (40–80 µm in maximum dimension), with larger mesh size proximally on the frontal shield and finer on the peristome; ascopore circular, measuring 30–45 µm, positioned at the same level as the frontal shield, though not very noticeable, placed distomedially, 340–480 µm from the proximal margin of the secondary orifice, adjacent to or very close (28–46 µm below) to the basal ridge of the peristome. Secondary orifice transversely elliptical with the oral rim appearing slightly denticulate due to the frontal projection of the peristomial ridges. Peristome 250–520 µm long, with marked, broadly V-shaped, basal ridge; in standard autozooid, almost parallel to the frontal plane, causing the secondary orifice to face upwards with no distance between the distal margin of the secondary orifice and the distal margin of the autozooid; in brooding zooids, projecting from the frontal plane at an angle of almost 90°, swollen at the base, expanding the distance between the distal margin of the peristome and the distal margin of the autozooid, curved upwards, with marked longitudinal ridges and pseudopores, much larger than those on the frontal, measuring 20–40 µm in diameter, in valleys between ridges. Brooding autozooids grouped in whorls.

Measurements (µm). ZL 1408±211, 1083–1671 (3, 10); ZW 447±73, 330–569 (3, 10); OL (secondary) 131±22, 98–147 (3, 4); OW (secondary) 182±18, 163–201 (3, 4).

Remarks. The Recent Indo-Pacific M. tenuis Harmer, 1957 closely resembles the Holocene Japanese species, sharing features such as the number of autozooids in a whorl, distinct boundaries of autozooids, a long tubular peristome with a prominent basal ridge projecting at right angle or obliquely, and an ascopore adjacent to the basal ridge. However, it differs in having a tripartite rather than bipartite base of the rami, a circular rather than elliptical secondary orifice, and a peristome basal ridge much closer to the proximal margin of the orifice (Harmer, 1957).