Triphyllozoon hirsutum ( Busk, 1884 )

Martino, Emanuela Di & Taylor, Paul D., 2018, Early Pleistocene and Holocene bryozoans from Indonesia, Zootaxa 4419 (1), pp. 1-70 : 59-61

Triphyllozoon hirsutum ( Busk, 1884)

( Figs 177–183 ; Table 39)

Retepora hirsuta Busk, 1884: 119 , pl. 26, fig. 4a–g.

Triphyllozoon hirsutum: Harmer, 1934: 594 , pl. 35, fig. 24, pl. 36, fig. 1, pl. 39, figs 1–4; Hayward, 2000: 112, fig. 2a–c.

Figured material. RGM.1350596, RGM.1350597, Holocene, UPGG 041, off South Sulawesi.

Description. Colony erect, rigid, fenestrate. Fenestrulae oval, on average 0.65 mm long by 0.35 mm wide, often with an undulate outline because of protruding ovicells and avicularia. Trabeculae stout, consisting of 3–5 alternating series of autozooids. Autozooids distinct, bordered by a thin, raised rim of smooth calcification, rhomboidal to hexagonal, slightly longer than wide (mean L/W = 1.26). Frontal shield flat to gently convex, nodular, imperforate except for a few, scattered, marginal areolar pores, circular, 10–20 µm in diameter. Primary orifice slightly longer than wide, about 90–95 µm long (including sinus) by 75–85 µm wide, distal border denticulate, proximal edge straight with a median, small, U-shaped sinus; secondary orifice subcircular with a median, drop-shaped pseudosinus formed by the fusion of the two lobes of the short, flared peristome. Up to five oral spine bases are present in early ontogeny, the two lateral pairs often coalescent; commonly two spine bases persist later in ontogeny, but sometimes they are completely obscured by the development of the peristome. No avicularium on the peristome. Adventitious frontal avicularia of two types, smaller and oval (Av1), often associated with the ooecium, or slightly larger and elliptical (Av2), both types with complete crossbar. Rarely a large, lanceolate avicularium, with raised, channeled rostrum is present within the fenestrulae. Ooecia globular, broader than long, bearing the characteristic tri-lobed, sieve-like, frontal suture, the median suture commonly as long as or shorter than lateral sutures, which diverge at about 180 ˚ and curve medially. Abfrontal surface granular, divided into irregular polygonal sectors by vibices; within each sector sparse, small circular pores, and numerous, polymorphic avicularia; small elliptical avicularia similar to those seen on the frontal shield but sometimes with a more spatulate rostrum, and larger lanceolate avicularia similar to those seen within the fenestrulae.

Remarks. Triphyllozoon hirsutum is very abundant in our samples, with 25 and 405 fragments in the early Pleistocene and Holocene sample, respectively. This species, originally described from the Torres Strait at about 15 m depth, was subsequently recorded by Harmer (1934) from several localities in the Indo-West Pacific, including stations in the Makassar Strait, the western end of New Guinea, and East Timor, at 0–94 m depth. Two main diagnostic characters distinguish Triphyllozoon hirsutum from T. cf. benemunitum : the thick, coalescent spines seen in early astogeny, and defined as antenniform by Harmer (1934), and the trilobate suture with curved lateral branches.

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

Figures

FIGURES 177–183. Triphyllozoon hirsutum (Busk, 1884), Holocene, UPGG041, off South Sulawesi. 177–180. RGM.1350596. 177. General view of a colony fragment. 178. Group of zooids some of which are ovicellate. 179. Abfrontal surface with elliptical and spatulate avicularia. 180. Close-up of a lanceolate avicularium on the abfrontal surface. 181–183. RGM.1350597. 181. Close-up of autozooids showing the primary orifice and the robust, coalescent oral spine bases. 182. Close-up of a large, lanceolate avicularium placed within the fenestrula. 183. View of the abfrontal surface with spatulate and lanceolate avicularia. Scale bars: Fig. 177 = 300 µm; Figs 178, 180 = 100 µm; Figs 179, 183 = 200 µm; Figs 181, 182 = 50 µm.