Microeciella argentina López-Gappa and Liuzzi, 2022

López-Gappa, Juan, Liuzzi, María G., Castro, Karen L., Bobinac, Magalí & Schwindt, Evangelina, 2022, Fouling bryozoans in Argentine harbours (Southwest Atlantic): new records and the description of a new species, Zootaxa 5205 (4), pp. 374-400 : 391-392

Microeciella argentina López-Gappa and Liuzzi n. sp.

( Figs 37–40 )

Holotype. MACN-In 43885, sublittoral Mytilus bank off Mar del Plata , depth unknown (35–50 m according to Penchaszadeh 1974), January 15, 1971.

Paratypes. MACN-In 43886, Punta Pardelas , Chubut, on Aulacomya atra , collected by SCUBA diving by J. Callebaut, September 13, 1978 .

Additional material. MACN-In 20570, mouth of Río Negro, A. R.A. “ San Luis ”, July 6, 1932 . MACN-In 43887, Storni pier, Puerto Madryn , October 27, 2016, collected by Karen Castro.

Description. Colony encrusting, multiserial, thin, flat, initially fan-shaped, soon expanding by peripheral budding around its margin to attain an irregularly subcircular shape, maximum observed diameter 8 mm. Colour white when dried. Growing margin narrow, usually one generation of zooids visible at budding zone. Ancestrula only visible in young colonies, usually completely overgrown during astogeny; protoecium rounded, about 102 µm in diameter, with sparse, scattered pseudopores; distal tube elongate, strongly curved, about 344 µm long by 82 µm wide, aperture longitudinally elliptical, 83 by 48 µm, tilted to one side. Two distal zooids strongly curved to right and left budded from the ancestrula. Autozooids elongate, proximally indistinct; pseudopores scattered, teardrop-shaped, pointed distally, 5–6 µm wide. Apertures circular to longitudinally elliptical, 84–124 µm long by 65–80 µm wide, sometimes closed by pseudoporous diaphragms; peristomes low. One or more gonozooids near or at a certain distance from the margin of each colony; brood-chamber ovoidal to subcircular, elongate to wider than long (L/W 0.70–2.5), outline indented (but roof not crossed) by apertures of neighbouring autozooids; roof densely pseudoporous, with parallel wrinkles on its surface. Ooeciopore terminal, smaller than an autozooidal aperture, subcircular to transversely elliptical, 58 × 87 µm, erect or curved proximally.

Remarks. A closely related species, M. suborbicularis ( Hincks, 1880) , has been recorded as a cenozoic fossil in Argentina. It has been mentioned for the early Paleocene (Danian, Roca Formation, Río Negro Province; Canu 1911), the late Oligocene (San Julián Formation, Santa Cruz Province; Canu 1904), and the early Miocene (Punta Borja, Comodoro Rivadavia, Chenque Formation, Chubut Province; Canu 1908) of Patagonia. The examination of the material from the Roca Formation identified by Canu (1911) as Diastopora (Berenicea) suborbiculari s (MACNPi 1885), however, shows that it is not conspecific with M. suborbicularis . One of the two colonies deposited in the MACN-Pi collection was reproductive. Its gonozooid differs from that of the Recent M. suborbicularis by being twice as wide as long, with its roof penetrated by autozooidal peristomes, as has been recently described for Platonea sp. from the Roca Formation ( Brezina et al. 2021). A re-examination of the Oligocene and Miocene materials ( Canu 1904, 1908) from Patagonia would be necessary to confirm their identity.

Microeciella argentina n. sp. differs from M. suborbicularis , a well-known European species (see Harmelin 1976, as Microecia suborbicularis ; Hayward & Ryland 1985a, b; De Blauwe 2009, as Eurystrotos compacta ; Taylor & Zaton 2008), in the L/W ratio of the gonozooid (longer than wide in M. suborbicularis , longer than wide to wider than long in M. argentina n. sp.), in the shape of the brood chamber roof (draped back over the proximal frontal wall in M. suborbicularis , crossed by wrinkles in M. argentina n. sp.), and in the shape of the ancestrula (distal tube of the ancestrula straight in M. suborbicularis , strongly curved in M. argentina n. sp.). Genetic studies would help to better distinguish the two species.

According to the material examined, M. argentina n. sp. is present in coastal localities of Río Negro and Chubut provinces at least since 1932, and in a sublittoral mussel bank off Buenos Aires Province since 1971.

Distribution. Buenos Aires, Río Negro and Chubut provinces, Argentina (this study).

Figures

FIGURES 37–40. Microeciella argentina n. sp.; 37, general aspect (Holotype, MACN-In 43885). The likely location of the overgrown ancestrula is marked with an asterisk; 38, colony margin and developing gonozooid (Paratype, MACN-In 43886); 39, close-up of gonozooid (Holotype, MACN-In 43885); 40, ancestrula and early astogeny (Paratype, MACN-In 43886). Scale bars. 37: 1000 µm; 38–40: 200 µm.