Metroperiella cotoensis n. sp., 2020

Dick, Matthew H., Ngai, Nguyen Danh & Doan, Hung Dinh, 2020, Taxonomy and diversity of coelobite bryozoans from drift coral cobbles on Co To Island, northern Vietnam, Zootaxa 4747 (2), pp. 201-252 : 221-223

Metroperiella cotoensis n. sp.

( Figs 9 D–F; 20H)

urn:lsid:zoobank.org:act:DEB38710-D95B-472C-8E28-83627EA25362

Etymology. The specific name comes from Co To Island, the type locality.

Material examined. Holotype, VNMN-0238 (CT-39), on SEM stub.

Measurements. AzL, 0.64–0.85 (0.709 ± 0.054); AzW, 0.37–0.49 (0.416 ± 0.035) (n = 15, 1). OrL, 0.16–0.19 (0.167 ± 0.012); OrW, 0.14–0.17 (0.154 ± 0.012) (n = 7, 1). OvL, 0.228 –0.268 (0.249 ± 0.020); OvW, 0.281 –0.344 (0.308 ± 0.033) (n = 3, 1). AvRL, 0.11–0.16 (0.138 ± 0.017); AvRW, 0.06–0.09 (0.071 ± 0.011) (n = 15, 1).

Diagnosis. Frontal shield rugose, with numerous small psuedopores. Primary orifice longer than broad; proximal sinus broad and deep between small condyles. Rounded orificial collar proximolaterally and laterally, with slight lateral lappets. Single small avicularium in midline proximal to orifice, slightly shorter than orifice width; di- rected proximally, mandible long-triangular. Ooecium ininially smooth, hyperstomial, with numerous pseudopores, becoming rugose, immersed with age, but retaining pseudopores.

Description. Colony encrusting, unilaminar, sheet-like.

Zooids irregularly hexagonal or long-oval, distinct, delineated by groove. Frontal shield convex, evenly perforated by small pseudopores, surface between pores irregular. Orifice terminal, ovoid in overall shape, with anter horseshoeshaped, poster deeply and broadly U-shaped, sometimes flattened at bottom, separated from anter by small, rounded condyles. Dimorphism of primary orifice unclear; that of ooecium-bearing zooids possibly slightly larger, broader than that of zooids lacking ooecia. Orifice with smooth, blunt rim proximally and laterally, often raised laterally to form low lappet on each side; rim confluent distally with sharp, raised distal margin of orifice. Oral spines lacking.

Each zooid bearing avicularium proximal to orifice; very close to orificial rim, usually in midline and directed proximally, occasionally slightly offset from midline and directed proximally or proximolaterally. Rostrum raised from frontal surface, face slightly convex rather than parallel to frontal plane; proximal end of rostrum semicircular, mandibular part long-triangular, acute; rostral opesia oval, crossbar complete; average avicularium length about equal to orifice width. No spatulate avicularia observed, either in place of suboral avicularium or as enlarged frontal avicularia; no interzooidal avicularia.

Ooecium prominent, closed by operculum, slightly broader than long, proximal margin confluent with lateral oral lappets; surface smooth, evenly perforated by pseudopores except in proximocentral area; pseudopores about same size as frontal pores. With age, ooecium becomes completely immersed in thick, pseudoporous frontal calcification from next-distal zooid.

Remarks. Most species of Metroperiella have a suboral avicularium that lies in the midline or can be somewhat offset from it, and that bears an acute or rounded mandible; in some species, it can be replaced by a more-or-less spatulate, sometimes enlarged median avicularium. In addition, in some species, zooids can additionally or exclusively produce an enlarged, markedly spatulate frontal avicularium proximolateral or lateral to the orifice, directed proximally or distally. In species that have an acute, usually median suboral avicularium, spatulate avicularia can be uncommon. Only a single size of acute, more-or-less median suboral avicularium was seen in the Co To specimen, although in this single, small colony, enlarged spatulate avicularia might simply be absent. However, two additional features distinguish it from congeners. One is the unusually deep, broad poster. The other is the immersed ooecium; while the ooecium in young stages is typical of the genus, few other Metroperiella have been reported to have an immersed ooecium in later stages.

Metroperiella ovoidea ( Canu & Bassler, 1929) , described from the Philippines, has the ooecium similarly immersed, covered with the same frontal calcification as the autozooids, but the poster is shallower and narrower in that species, and the zooids smaller (ZL, 0.44–0.54 mm) ( Canu & Bassler 1929). The median suboral avicularia are much smaller and, while there is no mention in the original description of large, spatulate adventitious avicularia, large vicarious avicularia occur. Metroperiella montferrandii ( Audouin, 1826) is a common species supposedly distributed almost circumtropically, with previous records from the region of Vietnam ( Tilbrook 2006); the median suboral avicularia are quite similar to those in M. cotoensis n. sp., but some zooids in M. montferrandii have the smaller, median avicularium replaced by an enlarged, spatulate avicularium proximolateral to the orifice, the poster is much shallower, and there has been no report of immersed ooecia. Metroperiella agassizi Winston & Woollacott, 2009 , reported from Barbados in the eastern Caribbean, has monomorphic suboral avicularia similar in size, shape, and position to those in M. cotoensis n. sp., and zooid size is similar, but the poster is shallower and the ooecia in mature colonies are not immersed. Metroperiella anatina ( Canu & Bassler, 1927) , described from Hawaii, and M. hastingsi ( Soule, Soule & Chaney, 1995) , described from the Galapagos, may be conspecific with one another. In both species, some zooids have a relatively broad, deep poster, and many zooids have an acute suboral avicularium like that in M. cotoensis n. sp.; however, some zooids have the acute suboral avicularium replaced by an enlarged, spatulate avicularium in the same position.

Distribution. Co To Island is the only known locality.

Figures

FIGURE 9. A–C. Parasmittina acondylata n. sp., holotype, VNMN-0236. A. Colony. B. Autozooids with and without ooecia, and primary orifices. C. Zooids forming ooecia, and primary orifices, some with alate lyrulae; arrowheads, adventitious avicularia. D–F. Metroperiella cotoensis n. sp., holotype, VNMN-0238. D. Autozooids, showing primary orifice. E. Young, perforated ooecia, before being covered by secondary calcification. F. Autozooid with semi-immersed ooecium (arrow). Scale bars: A, 500 µm; B, 150 µm; C–F, 250 µm.