Adeonella adae ( Neviani, 1891 )

Rosso, Antonietta & Novosel, Maja, 2010, The genus Adeonella (Bryozoa, Ascophora) in the Mediterranean, with description of two new living species and rediscovery of a fossil one, Journal of Natural History 44 (25 - 28), pp. 1697-1727 : 1714-1716

Adeonella adae ( Neviani, 1891)

( Figures 3C , 8 )

Smittia Adae Neviani, 1891: 127 , pl. 4, fig. 7

Microporella (Diporula) Adae (Smittia) : Neviani, 1896a: 118; 1896b: 25, fig. 8; 1900a: 364; 1900b: 181, pl. 2, fig. 8.

Adeonella polystomella: Rosso, 1989b: 178 , pl. 2, figs. 1,2.

Examined material

Early Pleistocene: Monte dell’Apa (central Sicily): five fragments from sample 2b, C concretions on shelf soft-bottoms. PMC. R.I.Ps.B6a; Furnari Unit in the Barcellona Pozzo di Gotto Basin (north-east Sicily), presumably deposited in mid-to-deep circalittoral environments: a total of five fragments from samples MCE 4 and MCE 134. PMC. R.I.Ps.B6b.

Description

Branches ribbon-like, 2 mm wide with nine or ten zooidal rows on each side; wider (3 mm and about 15 zooidal rows) proximally to bifurcations. Autozooids usually elongate hexagonal to rhomboidal ( Figure 8B–E ), with a rounded distal portion and a narrow, proximal termination; marginal rows consisting of larger subrectangular zooids. Frontal shield finely granular and flat but intumescent in the best-preserved specimens, pierced by large pores, the peripheral ones often elongated and aligned along a row. Primary orifice with a narrow sinus sometimes visible through the spiramen ( Figure 8D ). Secondary orifice semicircular to transversely elliptical, rarely with a blunt proximal process. Spiramen orbicular but variable in size; separated from the secondary orifice by a stout bridge, usually flanked by two pores ( Figure 8D ). A single, small peristomial avicularium presumably present on a few zooids situated just distolaterally to the spiramen and proximally directed. A large frontal avicularium is usually present in the proximal third of each zooid, except for the marginal rows, the rostrum blunt triangular, rarely somewhat spathulate ( Figures 8C,F ), distally or distolaterally directed. Smaller round-to-triangular, variably oriented frontal avicularia, usually located at the lateral and/or proximal angles in the markedly diamond-shaped zooids, seem to develop on senescent zooids, whose orifices are becoming occluded by calcification ( Figure 8E,F ). Vicarious avicularia and gonozooids seemingly absent.

Measurements

ZL: 571 ± 31.11, 500–625 (2, 17); ZW: 370 ± 52.77, 294–469 (2, 17); sOL: 69 ± 9.23, 56–82, (2, 14); sOW: 115 ± 6.73, 106–128 (2,14); fAL: 121 ± 16.94, 88–147 (2, 13); fAW: 84 ± 9.01, 77–100 (2, 6).

Remarks

Although examination of Neviani’s type material was hampered, Adeonella adae features are well depicted in fig. 8 by Neviani (1891), reproduced on Figure 8A . The species is well characterized by the presence of its proximally located and distally directed frontal avicularium. This feature is unique within the Mediterranean species, and is reminiscent only of the Recent A. gibba Hayward and Cook, 1983 from South Africa. Nevertheless, in this latter species, which differs also in several other characters, the proximal avicularium is located distally to the spiramen. A relatively long frontal avicularium has been figured also for some specimens ascribed to A. polystomella from Messinian layers cored in the Gulf of Gabes by Moissette (1997: pl. 3, fig. 3) but, although variably inclined, it is always proximally directed.

Distribution

Adeonella adae seems to be restricted to the Pleistocene of Italy. It is known from northern localities, in the “clays” cropping out near Livorno (Tuscany: Neviani 1891; 1896 a, 1900a), and from some southern sites, including Spilinga ( Neviani 1896b; 1900b) in Calabria, and Furnari (near Messina: Messina 2003; Di Geronimo et al. 2005) and Gela ( Rosso, 1989b), in Sicily. Specimens are always rare and originate from sandy sediments, carbonate to silici-bioclastic in composition, which were presumably deposited in shallow circalittoral environments.

Figures

Figure 3. Adeonella calveti Canu and Bassler, 1930. All figures from the same colony, from an overhang, off Acitrezza (near the Ciclopi Islands), about 40 m. (A) Some zooids from a newly formed branch, just behind the growing tip. Note the morphology and the distribution of frontal avicularia. Scale bar: 500 µm. (B) Detail of (A) to show the drop-shaped notch left by the convergent growth of the proximal peristomial wings. Scale bar: 50 µm. (C) The primary orifice covered by the operculum. Scale bar: 20 µm. (D) A colony branch showing dimorphic diamond-shaped central zooids and subrectangular marginal zooids. Scale bar: 1 mm. (E) Young zooids with protruding peristomes and transversely elliptical secondary orifices. Scale bar: 200 µm. (F) Zooids from the branch sides with their subtriangular avicularia located lateral to the spiramen, medially and distally directed. Scale bar: 500 µm. (G) Developing zooids from the growing tip. Note the early

Figure 8. Adeonella adae (Neviani, 1891). (A) Original fig. 8 from the paper of Neviani (1891). (B–D) Furnari, Early Pleistocene. (B) Fragment of a presumed juvenile branch. Scale bar: 500 µm. (C) Detail of the proximal part of (B) showing elongated, distally directed avicularia on all zooids except those from the marginal rows. Scale bar: 500 µm. (D) A single zooid with a slightly spatulate frontal avicularium. Note the narrow U-shaped sinus visible through the spiramen. Scale bar: 200 µm. (E,F) Monte dell’Apa, Early Pleistocene. (E) Fragment of the presumed proximal portion of a colony, just before its bifurcation. Orifices and large proximal avicularia are locally obliterated by secondary calcification and small variably located avicularia develop. Scale bar: 500 µm. (F) Close-up of some zooids in (E), some with small frontal avicularia, resulting from the regeneration of larger ones. Scale bar: 200 µm.