Actisecos discoidea ( Canu & Bassler, 1929 )

Cáceres-Chamizo, Julia P., Sanner, Joann, Tilbrook, Kevin J. & Ostrovsky, Andrew N., 2017, Revision of the Recent species of Exechonella Canu & Bassler in Duvergier, 1924 and Actisecos Canu & Bassler, 1927 (Bryozoa, Cheilostomata): systematics, biogeography and evolutionary trends in skeletal morphology, Zootaxa 4305 (1), pp. 1-79 : 67-68

Actisecos discoidea ( Canu & Bassler, 1929)

( Fig. 28 , Table 27)

Exechonella discoidea: Canu & Bassler 1929 , p. 123, pl. 20, figs 5–6.? Exechonella discoidea: Gordon 2016 , p. 609.

Not Exechonella sp. cf. discoidea: Cook & Bock 2004 , p. 276, figs 4a–d.

Material examined. Lectotype: USNM 5 45923. Philippines, east coast Mindanao , Nagubat Island, 9° 43´N, 125° 48´15´´ E, Albatross Station D. 5235, depth 44 fathoms, 9 May 1908 . Paralectotypes: USNM 545924 , USNM 545925 , USNM 545926 , USNM 545927 . Philippines, east coast Mindanao , Nagubat Island, 9° 43´N, 125° 48´15´´ E, Albatross Station D. 5235, depth 44 fathoms, 9 May 1908 .

Description. Colonies free, discoidal. Frontal surface convex, basal surface slightly concave, especially in the centre (ancestrular area). Autozooids small, oval in shape, separated by shallow grooves. Orifice subcircular, slightly wider than long, condyles not observed. Peristome tubular, with slightly swollen base, external surface with pointed tubercles. Frontal shield perforated by 9–19 well-spaced, rounded or oval foramina that occupy the most of the frontal shield. Each foramen with a slightly raised rim. Frontal shield between foramina with sporadic pointed tubercles, mostly observed in the peripheral area. Marginal pores not present, only two small pores located one on each side of peristome were seen in some autozooids. Peripheral autozooids display basal pore chambers with a single communication pore. Basal part of the colony covered by flat, often irregularly shaped kenozooids with gymnocystal periphery and large central 'membranous' area. Ovicell peristomial, only developed by peripheral autozooids. Kenozooidal ooecium globose, budded by the maternal zooid. Ectooecium membranous, entooecium calcified with numerous pointed tubercules and small pseudopores often surrounded by a raised rim. Ancestrula autozooidal, smaller than the rest of zooids and having central position in the colony, surrounded by six autozooids.

Remarks. Harmer (1957) introduced the family Exechonellidae based on the umbonuloid nature of the frontal shield. From that time several genera and species have been assigned to the family, either fossil or recent, some of which have been questioned or reassigned to other families. Among them is “ Exechonella ” discoidea that form small free-living colonies with radiating budding pattern and peristomial ovicells. Despite an obvious similarity in colony form and zooidal appearance Canu and Bassler (1929) assigned this species to Exechonella , not to Actisecos , although A. regularis was described in the same Philippine volume.

There are five specimens of this species kept in the USNM collection. All originate from the same sample. The specimen USNM 545923 was selected as lectotype whereas the rest as paralectotypes.

Actisecos discoidea strongly resembles A. regularis . The recognized differences are that (1) colony conical in A. regularis and almost flat in A. discoidea ; (2) ooecial pseudopores are normally without a rim around them in the former species and with a raised rim in the second; (3) distal part of the peristome is smooth in A. regularis and tuberculate or uneven in A. discoidea ; (4) there are mostly two communication pores at the distalmost basal pore chambers in A. regularis and one in A. discoidea .

Dumont (1981) and Winston (1986) [based on Dumont’s paper] mentioned this species in the Red Sea, but it is probably confusion resulted from a general similarity of the frontal wall in Actisecos and Exechonella .

Gordon and d’Hondt (1997) described one colony from New Caledonia under the name of Actisecos regularis . This specimen represents a new Actisecos species.

Finally, Cook and Bock (2004, p. 267) described as Exechonella sp. cf. discoidea a specimen that is undoubtedly belongs to E. ampullacea species-complex (see above).

Distribution. Actisecos discoidea is only known from the Philippines.

Figures

FIGURE 28. Actisecos discoidea (Canu & Bassler, 1929). Philippines (A, B: lectotype USNM 545923; C, D, F, paralectotype USNM 545924; E, G, paralectotype USNM 545925; H, paralectotype USNM 545927). A, B, general view of lectotype (A) and paralectotype (C) from above. B, central part of lectotype from above (ancestrula shown by arrowhead). D, F, peripheral part of colony showing peristomes (mostly broken in F) and ooecia. E, general view of paralectotype from below. G, close-up of the peripheral part of colony from below showing details of partial ooecium, basal pore chambers (some shown by arrows) with communication pores and flat kenozooids. H, details of primary orifice and frontal shield. Scale bars: A, C, E = 500 µm; B, D, F, G = 200 µm; H = 100 µm.