Disporella phaohoa Dick & Ngai & Doan 2020, n. sp.

Disporella phaohoa n. sp.

(Figs 18, 20F)

urn:lsid:zoobank.org:act: 6C16A5DC-2688-4DBD-AF0D-25CC88754823

Etymology. The specific name comes from the Vietnamese pháo hoa (firework), referring to the starburst pattern of the radiating connate series of zooids.

Material examined. VNMN-0268 (CT-35), three colonies on SEM stub; largest colony, with broken brood chamber, is the holotype; the others are paratypes. Paratypes, VNMN-0268 (two of three colonies), VNMN-0269 (CT-36), on SEM stubs. Other material: VNMN-0256, one colony with Plesiocleidochasma porcellaniforme; VNMN-0270, seven dried specimens.

Measurements.Az inside diameter, 0.055 –0.080 (0.068 ±0.007); alveoli inside diameter, 0.069 –0.115 (0.085 ± 0.012) (n = 15, 1). Diameter of largest colony observed 5.5 mm; most colonies 4.0– 4.5 mm.

Diagnosis. Mature colony typically ca. 5 mm in diameter. Colony with smooth (non-spinous) marginal lamina; with single macula. Zooids in radiating connate series, two to three zooids wide in widest portion. Peristomes erect at margin, each with acute tip distal to orifice. Alveolus inside diameter up to twice peristome inside diameter; alveolar spinules lacking. Brood chamber smooth-walled, in macular center; ooeciostome angled to frontal surface, not flared.

Description. Colony disk-like, circular or elliptical in outline; surrounded by narrow marginal lamina traversed by radiating lines indicating newly forming zooidal boundaries; comprising single circular or irregularly elongate macula.

Zooids arranged in connate series radiating from center; series initially one zooid wide toward center but two (occasionally three) zooids wide in alternating arrangement toward margin. As colony size increases, space between adjacent radiating connate series widening, with new, secondary connate series not reaching center of macula becoming intercalated between them. Peristomes in radiating series shorter toward center, becoming increasingly longer and sometimes erect toward margin; end of peristome with acute tip distal to orifice. Alveoli (= kenozooids) irregularly polygonal; inside diameter up to twice that of autozooids; becoming constricted by centripetally deposited calcification; no spinules observed inside alveoli.

Brood chamber evident as smooth area in macular center, sometimes extending as interradial lobes; with distinct, smooth roof; presumed ooeciopore appears to open at end of tube angled to frontal surface; opening terminally or frontally directed, not flared.

Remarks. Disporella is a speciose genus, with close to 60 nominal species described worldwide (Bock 2018). The name Lichenopora Defrance, 1823 was mistakenly applied to this genus for over a century, until Gordon & Taylor (1997, 2001) clarified that it applies to Cretaceous to Miocene species having conical-pedunculate colonies, with the names Disporella Gray, 1848 and Patinella Gray, 1848 applying to Cenozoic and Recent species having adnate, discoid colonies.

Among several nominal Disporella species previously reported in East Asia (as Lichenopora), the species most similar to D. phaohoa n. sp. is D. wanganuiensis (Waters, 1887), as redescribed by Gordon & Taylor (2001). The two species have in common a smooth marginal lamina; large alveoli lacking pinhead spinules; zooids arranged in connate series one to three zooids wide; and the brood chamber located in the macular center, with or without interradial lobes. Disporella wanganuiensis differs in having alveolar walls extending over the surface the brood chamber roof, which also bears numerous, minute pseudopores that are nearly closed by fine radial spokes (Gordon & Taylor 2001: fig. 34); in D. phaohoa n. sp., the roof of the brood chamber is smooth, without the alveolar covering or pseudopores. In D. wanganuiensis, the ooeciostome is flared and distinctively composed of stacked, concentric layers. While it is not clear whether the arrowed structure in Fig. 18F represents the ooeciostome in D. phaohoa n. sp., as opposed to the terminal end of an isolated autozooid, a structure like this was seen in the macular center in several colonies. Finally, Disporella wanganuiensis can produce daughter colonies by frontal budding, leading to stacked colonies, a feature not observed in D. phaohoa n. sp.

Disporella wanganuiensis was originally described from New Zealand, where it is a shelf species typically found on calcareous substrata, with a known depth range of 107–419 m (Gordon & Taylor 2001). It is unlikely from an ecological standpoint that the same species also occurs in the shallow, subtropical, reef-rubble habitat at Co To. It is noteworthy that many of the synonyms Gordon & Taylor (2001) present for D. wanganuiensis are uncertain and prefaced by a question mark; records of that species from outside the New Zealand region need to be reexamined.

Distribution. Co To Island is the only known locality.