Actisecos regularis Canu & Bassler, 1927

Martino, Emanuela Di & Taylor, Paul D., 2018, Early Pleistocene and Holocene bryozoans from Indonesia, Zootaxa 4419 (1), pp. 1-70 : 43-44

Actisecos regularis Canu & Bassler, 1927

( Figs 128–129 ; Table 28)

Actisecos regularis Canu & Bassler, 1927: 11 , pl. 1, fig. 13; Canu & Bassler, 1929: 517, pl. 66, figs 1–4; Harmer, 1957: 856, pl. 60, figs 12–16; Cook, 1966: 208; Cáceres-Chamizo et al., 2017: 65 , fig. 27.

Figured material. RGM.1350576, RGM.1350577, Holocene, UPGG 041, off South Sulawesi.

Description. Colony rooted, presumably discoidal when complete, small, the maximum diameter of the examined colony fragments measuring 2.2–2.3 mm, slightly convex frontally and slightly concave basally. Autozooids distinct with shallow interzooidal furrows, arranged regularly in alternating circlets, oval to rhomboidal, longer than broad (mean L/W = 1.56). Frontal shield convex, granular, perforated centrally by 12–15 large, funnel-shaped pseudopores encircled by a raised rim and arranged in alternating rows; the external diameter of pseudopores about 40 µm, the internal diameter about 20 µm. Peristome raised, tubular, about 140–160 µm long, coarsely tuberculate, imperforate. Secondary orifice subcircular. Ooecium globular, small, peristomial, placed on the basal side of peristomes of marginal and submarginal zooids, as wide as the peristome, barely visible in frontal view as a small semicircular cap, coarsely tubercular and porous. Basal surface showing rounded, up-side down triangular depressions on the distal portion of marginal zooids, just below the ooecium, allocating two small rootlet pores.

Remarks. Eight fragments of Actisecos regularis have been found in our samples. Actisecos is an Indo-Pacific genus characteristic of muddy-sandy sea-bottoms at 59–201 m depth. It includes three Recent species A. regularis Canu & Bassler, 1927 , A. pulcher Harmer, 1957 and A. discoidea ( Canu & Bassler, 1929) . Two further species, left in open nomenclature, are known from the middle Miocene of East Kalimantan (Di Martino & Taylor 2015). Actisecos regularis has ooecia as wide as the peristome. This feature distinguishes this species from A. pulcher , characterized instead by ooecia much wider than the peristomes. Actisecos discoidea differs in having ooecial pseudopores with a raised rim and a single rootlet pore at the distalmost depression on the basal surface. Cáceres- Chamizo et al. (2017) considered Actisecos as a completely free-living genus, and interpreted the distalmost depressions on the basal surface as basal pore-chambers with communication pores. However, the general aspect of the colony and the lack of vibracula suggests it was rooted ( Harmer 1957; Cook & Chimonides 1981; Cook & Bock 2002).

N, Number of colonies and number of zooids measured; SD, standard deviation.

Figures

FIGURES 128, 129. Actisecos regularis Canu & Bassler, 1927, Holocene, UPGG041, off South Sulawesi. 128. RGM.1350576, frontal view of a colony fragment. 129. RGM.1350577, close-up of the basal side of two autozooids with ooecium and rootlet pores. Scale bars: Fig. 128 = 500 µm; Fig. 129 = 200 µm.