Actisecos regularis

(Figs 128 – 129; Table 28)

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.

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

Description. Colonies free, discoidal, small (no more than four zooidal generations have been observed). Frontal surface convex, basal surface concave, giving to the colony a flat conical form. Autozooids small, oval in shape, separated by shallow grooves. Primary orifice subcircular. Peristome tubular, often slightly swollen in the base which external surface bears pointed, uniformly distributed tubercles. Distal part of the peristome smooth. Frontal shield perforated by 9 – 20 well-spaced, rounded or oval foramina that occupy the most of the frontal shield. Majority of foramina with low rim. Walls of the foraminal lumen vertical or inclined with a lower opening smaller than the upper. Frontal shield between foramina with sporadic pointed tubercles, the most observed in the peripheral area of the zooid. Marginal pores (areolae) not present. Peripheral autozooids display basal pore chambers with 1 – 2 communication pores. The distalmost chambers predominantly have two such pores, distolateral just one. Basal part of the colony covered by flat, often irregularly shaped kenozooids with gymnocystal periphery and large central ' membranous' area. Ovicell peristomial (ooecium fused with and opened into the peristome), terminal, only developed by peripheral autozooids. Kenozooidal ooecium globose, budded by the maternal zooid. Ectooecium membranous, entooecium calcified with numerous pointed tubercules and small pseudopores predominantly without a raised rim. Ancestrula autozooidal, smaller than the rest of zooids, always having a central position in the colony, surrounded by six autozooids. Philippines Remarks. Among three specimens kept at the USNM only one (USNM 8325) was mentioned as cotype having a catalogue number (Canu & Bassler 1929). We selected it as lectotype. It was collected at the Station D. 5335 (Canu & Bassler 1927, 1929), whereas two other colonies (selected here as paralectotypes) were collected at the Stations D. 5336 and D. 5478. Communication pores are not seen within ‘ membranous windows’ in basal kenozooids that suggests that they were secondarily closed. Instead, few tiny pits (pores?) were detected on the gymnocystal areas of kenozooids. External morphology of ooecia corresponds to both, “ escharelliform ” and “ microporelliform ” type (Ostrovsky 2013 a), and more precise attribution will be possible when colonies with developing ooecia will be found and anatomical sections of the fresh material will be made (for methodology, see Ostrovsky & Schäfer 2003; Ostrovsky et al. 2003). We suggest, however, that Actisecos has an escharelliform ooecium since no cheilostome with an umbonulomorph frontal shield is known having microporelliform ooecium. On the other hand, no escharelliform ooecia with pseudopores has been ever described.

Distribution. Actisecos regularis was found in Philippines, Indonesia, and New Guinea.

Material examined. Lectotype: USNM 8325. Philippines, Linapacan Strait, Observatory Island, 11 ° 37´15 ´´ N, 119 ° 48´45 ´´ E, Albatross Station D. 5335, depth 46 fathoms, 18 December 1908. Paralectotypes: USNM 545928. Philippines, Linapacan Strait, Observatory Island, 11 ° 37´45 ´´ N, 119 ° 46´E, Albatross Station D. 5336, depth 46 fathoms, 18 December 1908. USNM 545929. Tacbuc Point, Leyte Island, 10 ° 46´24 ´´ N, 125 ° 16´30 ´´ E, Albatross Station D. 5478, depth 57 fathoms, 29 July 1909.