Triphyllozoon cf. benemunitum ( Hastings, 1932 )

Martino, Emanuela Di & Taylor, Paul D., 2018, Early Pleistocene and Holocene bryozoans from Indonesia, Zootaxa 4419 (1), pp. 1-70 : 57-59

Triphyllozoon cf. benemunitum ( Hastings, 1932)

( Figs 171–176 ; Table 38)

cf. Retepora tubulata: Busk, 1884: 121 , pl. 28, figs 2, 2b. cf. Retepora monilifera var. benemunita Hastings, 1932: 441 , pl. 1, fig. E.

cf. Triphyllozoon benemunitum: Harmer, 1934: 605 , pl. 35, figs 25, 26, pl. 39, figs 20–26; Hayward, 2000: 110, fig. 1.

Figured material. RGM.1350593, RGM.1350594, RGM.1350595, Holocene, UPGG 041, off South Sulawesi.

Description. Colony erect, rigid, fenestrate. Fenestrulae oval, on average 1 mm long by 0.5 mm wide, often with an undulose outline because of protruding large avicularia and ovicells. Trabeculae stout, consisting of 2–4 alternating series of autozooids. Autozooids distinct, bordered by a thin, raised rim of smooth calcification, rhomboidal to hexagonal, longer than wide (mean L/W = 1.46). Frontal shield flat to gently convex, smooth but becoming coarsely granular with ontogeny, imperforate except for a few, sparse, marginal areolar pores, circular, 15–20 µm in diameter. Primary orifice slightly wider than long, about 120 µm wide by 115 µm long (including notch), distal border denticulate, proximal edge asymmetrical with a small U-shaped notch on one corner; secondary orifice subcircular with a drop-shaped pseudosinus formed by the fusion of the two lobes of the short, flared peristome. Two oral spine bases, about 15 µm in diameter, are present in early ontogeny, later obscured by the development of the peristome. A small, adventitious avicularium frequently present on the peristome rim to one side of the drop-shaped pseudosinus, oblique to the frontal plane, directed laterally; rostrum up-curved, triangular, denticulate; crossbar complete. Avicularia on the frontal shield of two types, small and subcircular to oval (Av1) or slightly larger and elliptical to eight-shaped (Av2), both types with complete crossbar and rostrum tip either flat and smooth or up-curved and denticulate. A large, spatulate avicularium, with the distal end upturned and divided in two sharp cusps, is present proximolaterally within some fenestrulae. Ooecia globular, broader than long, bearing the characteristic tri-lobed, sieve-like, frontal suture, the median suture commonly as long as the lateral sutures, rarely longer or even shorter; lateral sutures diverging at almost 180˚. Abfrontal surface granular, divided into irregular polygonal sectors by vibices; within each sector sparse, small circular pores, and numerous, polymorphic avicularia; smaller avicularia similar to those seen on the frontal shield, larger avicularia with parallel-sided rostra channelled and bicuspate distally, distolaterally directed, crossbar complete.

Remarks. Represented by 734 fragments, Triphyllozoon cf. benemunitum is the most abundant species found in our samples. The nominal species was first recognized and described by Busk in an unpublished manuscript, and subsequently validated by Hastings (1932), who selected the type specimen from an unknown Australian locality. Specimens from Busk’s collection, reported by Harmer (1934), are all from Torres Strait. Hayward (2000, p. 110, fig. 1a–c) described and imaged the holotype, which mainly differs from the fossil material in having enlarged, oval avicularia supported by a tumid cystid distal in many fenestrulae.

N, Number of colonies and number of zooids measured; SD, standard deviation; Av, avicularium; Abfr, abfrontal.

Figures

FIGURES 171–176. Triphyllozoon cf. benemunitum (Hastings, 1932), Holocene, UPGG041, off South Sulawesi. 171–173. RGM.1350593. 171. General view of a colony fragment. 172. Close-up of an autozooid and cuspate fenestral avicularium. 173. Close-up of a broken ooecium, showing the trilobate sutures with the lateral branches diverging at 180˚, and the primary orifice with notch. 174, 175. RGM.1350594. 174. Group of zooids with numerous frontal avicularia. 175. Abfrontal surface with numerous, polymorphic avicularia. 176. RGM.1350595, close-up of an ooecium with the median suture shorter than the lateral ones. Scale bars: Figs 171, 174, 175 = 200 µm; Figs 172, 173, 176 = 50 µm.