Microporella tonkinensis, Dick & Ngai & Doan, 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 : 227-228

Microporella tonkinensis n. sp.

( Fig. 12 A–D)

urn:lsid:zoobank.org:act:D8480B51-CC0D-4B7B-B038-581C87933ADC

Etymology. The specific name comes from the Gulf of Tonkin, wherein lies the Co To island group.

Material examined. Holotype, VNMN-0248 (CT-6); paratype, VNMN-0249 (CT-41); both on SEM stubs.

Measurements. Holotype, VNMN-0248: AzL, 0.43–0.59 (0.513 ± 0.050); AzW, 0.28–0.48 (0.357 ± 0.051); OrL, 0.062 –0.074 (0.068 ± 0.003); OrW, 0.106 –0.124 (0.113 ± 0.005); OvL, 0.19–0.23 (0.207 ± 0.011); OvW, 0.23–0.27 (0.260 ± 0.011); AvRL, 0.090 –0.114 (0.102 ± 0.007); AvRW, 0.046 –0.063 (0.053 ± 0.006) (n = 15, 1). Paratype, VNMN-0249: AzL, 0.34–0.49 (0.428 ± 0.039); AzW, 0.23–0.38 (0.294 ± 0.043); OrL, 0.056 –0.072 (0.066 ± 0.004); OrW, 0.087 –0.104 (0.098 ± 0.005); AvRL, 0.068 –0.092 (0.082 ± 0.007); AvRW, 0.038 –0.057 (0.046 ± 0.005) (n = 15, 1).

Diagnosis. Orifice with straight, weakly denticulate proximal margin; small condyles mediad to proximolateral corners of orifice. Modal number of oral spines four or five; spine bases often evident in zooids away from colony margin. Ascopore non-cribriform, without conspicuous umbo; pustulation between ascopore and orifice. Avicularia lateral or proximolateral to ascopore, one per zooid, small relative to orifice size. Non-personate, non-ribbed ooecium retaining pair of spines at proximolateral corners.

Description. Colony unilaminar, encrusting, sheet-like.

Zooids irregularly hexagonal, distinct, delineated by groove. Frontal wall markedly convex, with two to five small, inconspicuous areolae along each lateral margin; perforated over entire surface by small pseudopores, except in zone between ascopore and orifice; texture uniformly coarsely pustulose between pores; pustules usually present between ascopore and orifice, sometimes in discrete row. Orifice broader than long, broadly D-shaped, surrounded by low, smooth rim; proximal margin straight or slightly concave between conspicuous triangular condyles; condyles positioned slightly mediad to proximolateral corners of orifice; proximal margin weakly denticulate. Oral spines short, articulated; three (n = 5) or four (n = 27) in colony CT-6; three (n = 1), four (n = 13), five (n = 17), or six (n = 4) in colony CT-41; spines retained even in older parts of colony. Ascopore small, broader than long, encircled by smooth, raised rim, separated from proximal orificial margin by 1–1.5 times height of ascopore plus rim; with small lingula projecting proximally, leaving C-shaped opening; margin of opening finely denticulate all around. Sometimes proximal part of ascopore rim widened and raised as low, smooth tubercle.

One avicularium per zooid, lateral to ascopore and directed distolaterally or sometimes laterally, or along zooidal margin proximolateral to ascopore, sometimes at lateral corner of zooid or even more proximally, directed distolaterally or laterally. Frontal avicularia moderately small, rostrum raised, sides and edges smooth, crossbar complete, area proximal to crossbar semicircular, mandibular area triangular, slightly longer than broad, guttered distally to allow for setiform mandible; setiform portion of mandible as long as or shorter than triangular rostral portion.

Ooecium prominent, resting on frontal wall of next-distal zooid, broader than long, closed by operculum, with narrow, smooth, flat zone around proximal margin where operculum meets ooecium; with many small pseudopores around steep periphery, few in central-proximal area; top more finely pustulose than frontal wall, coarsely pustulose around periphery, with some moderately large marginal openings at base around distal margin; ooecium appearing peripherally ribbed at low magnification. Most-proximal pair of spines lateral to orifice retained in ooecium-bearing zooids, abutting proximolateral corners of ooecium.

Remarks. Microporella is a speciose genus, with roughly 140 mostly Recent species described worldwide, from polar regions to the tropics ( Bock 2018). The generic features are rather stereotyped, simplifying identification to genus but complicating identification to species. Until relatively recently, taxonomists viewed the European species M. ciliata ( Pallas, 1766) as having a cosmopolitan distribution that essentially mirrored the range of the genus. While many species worldwide were correctly delineated from M. ciliata on the basis of unique apomorphies or combinations of characters, in the older literature many specimens from the tropical Pacific and elsewhere more or less similar to M. ciliata were attributed to that species, without description; for example, Canu & Bassler (1929) list M. ciliata from Hong Kong and the Philippines.

Some of the characters utilized in the taxonomy of this genus are variable rather than discrete. For example, M. germana Dick & Ross, 1988 at Kodiak, Alaska, had three to five oral spines, with the modal number four, but at Ketchikan had four to six spines, with the modal number five (Dick et al. 2005). Similar interpopulation variation is seen in the frequencies of zooids having single, paired, or no avicularia per zooid, and in the shape of the ascopore (e.g., Harmelin et al. 2011, p. 18, fig. 9). One useful character that distinguishes one large group of species from another is the presence or absence of a personate ooecium (ooecium-bearing zooids have a raised peristomial rim, proximal and lateral to the orifice, that meets the ooecium distally) ( Harmelin et al. 2011); M. dentilingua above has a personate ooecium, whereas M. tonkinensis n. sp. does not.

Several similar species in the northwestern Pacific differ from M. tonkinensis n. sp. in the following ways. Microporella formosa Suwa & Mawatari, 1998 from Hokkaido, Japan, has larger avicularia relative to orifice size; the proximal orificial margin is smooth, with the condyles larger and occupying the proximolateral corners of the orifice. The orifice in Microporella antiborealis Liu & Liu, 2001 [listed in Liu et al. (2001) as previously described rather than as a new species, but we could find no reference for Liu & Liu (2001)] from China has a similarly finely denticulate proximal margin, but has larger avicularia relative to orifice size, a larger ascopore, and modal spine number six, and lacks the pair of lateral oral spines remaining at the proximolateral corners of the ooecium. Like M. tonkinensis n. sp., Microporella borealis Suwa & Mawatari, 1998 from Hokkaido, Japan, has a finely denticulate proximal orificial margin, and has four or five oral spines, retaining one pair at the proximolateral corners of the ooecium, but the condyles are larger and in the proximolateral corners of the orifice, the avicularia are much larger relative to orifice size, and there is no pustulation between the ascopore and orifice.

Only two specimens of M. tonkinensis were found; these differed markedly in zooid size, with CT-6 having larger zooids than CT-41. This sort of variation seems to be common in tropical to subtropical cheilostomes, both within and between colonies; a similar case was observed in Rhynchozoon lunifrons Dick & Grischenko, 2017 at Okinawa. While some of this variation may be due to differences in temperature at time of growth ( O’Dea & Okamura 1999, 2000), the degree of variation seems greater than occurs in cold-temperate faunas, and intercolony variation may require additional explanation. In any case, bryozoan taxonomists working in the tropics and subtropics should be aware that zooid size should be treated with caution as a taxonomic character.

Distribution. Co To Island is the only known locality.

Figures

FIGURE 12. A–D. Microporella tonkinensis n. sp., holotype, VNMN-0248. A. Colony. B. Autozooids with and without ooecium. C. Enlargement showing orifice and ascopore. D. Proximofrontal view of autozooids with ooecia. E, F. Bryopesanser tonsillorum Tilbrook, 2012, VNMN-0250. E. Autozooids with and without ooecium. F. Enlargement showing orifice. Scale bars: A, 1 mm; B, D, 250 µm; C, 50 µm; E, 500 µm; F, 200 µm.