Adeonella pozarae, Rosso & Novosel, 2010

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 : 1716-1719

Adeonella pozarae sp. nov.

( Figures 3C , 9 )

Etymology

Named in honour of Professor Antonieta Požar-Domac.

Holotype

CNHM Inv. br. 32a, a young colony, off Lastovo Island (Vrhovine), Adriatic Sea, 30–40 m, among Cellaria fistulosa (Linnaeus, 1758) meadows. Paratype: CNHM Inv. br. 32b, small colony fragment from the same locality.

Description

Colony whitish in colour, small, erect, seemingly non-branching, and rod-like, in the available material, round in cross-section, up to 3 mm high and 500 µm in diameter ( Figures 9A,B ).

Zooids arranged in four alternating longitudinal rows ( Figure 9A,D ) in the available material, separated by distinct grooves and a thin raised sutura. Zooids monomorphic, elongate-cylindrical and prominent ( Figure 9E ). Frontal wall finely granular with a single row of widely spaced, relatively small marginal areolar pores. Primary orifice orbicular, with a semicircular distal rim and a straight proximal lip; sinus U-shaped, large and shallow ( Figure 9F,G ); condyles small. Peristome thin and distally raised; secondary orifice from subcircular to semicircular, the proximal border sometimes slightly convex. Spiramen subcircular, located just proximal to the peristome usually concealing the orificial sinus tending to be occluded in ontogeny by secondary calcification. Avicularia above the spiramen, single or paired, occasionally lacking; typically subtriangular, small and distomedially directed ( Figure 9I–M ), straight to slightly curved and slightly pedunculate, often projecting above the orifice. Vicarious avicularia and gonozooids absent. Encrusting base, only partly preserved in the available material, formed by zooids similar, in shape and size, to those from the erect branches.

Measurements

ZL: 479 ± 78, 339–593 (2, 20); ZW: 215 ± 21, 186–254 (2, 20); sOL: 114 ± 15, 85–136 (2, 20); sOW: 127 ± 41, 102–287 (2, 20); AL: 62 ± 8, 51–68 (2, 20); AW: 38 ± 9, 25–51 (2, 20).

Remarks

Adeonella pozarae sp. nov. is morphologically distinguishable from all other Adeonella species presented here by several features. Zooids are extremely elongated and the secondary orifices are comparatively larger and particularly longer in comparison to all other Adeonella species from the Mediterranean, as pointed out by the Z-SI and O-SI indexes values ( Table 1). The frontal surface shows a single row of peripheral pores, and the peristomial avicularia, either single or paired, are distomedially directed, their rostra usually protruding above the secondary orifice. Last but not least, the hardly visible primary orifice exhibits an orificial sinus larger and shallower than that of all other species. These features induce the erection of A. pozarae sp. nov. for the small, unbranched colonies here described, which, although roughly recalling A. pallasii , cannot be considered as juveniles of this species, as demonstrated by the pronounced secondary calcification of the paratype specimen. Actually, the common A. pallasii , coexisting in the same area and habitat, exhibits rhomboidal zooids with a narrower and deeper sinus, round to transversely elliptical secondary orifices and peristomial avicularia, which are proximally inclined or coaxial with the peristomial bridge. Moreover, zooids of this species have a decidedly larger spiramen. Finally, A. pozarae shows a budding pattern leading to the construction of cylindrical branches whose cross-sections clearly show as each zooid is completely bounded by its own walls. In contrast, in other Adeonella species forming ribbon-like branches, zooids are arranged into two back-to-back layers separated by a median lamina serving as a basal surface for zooids from both layers. Adeonella pozarae sp. nov. superficially recalls A. falcicula Hayward, 1981 , from the tropical east Africa continental slope, because of its growth habit and colony size, although it sharply differs in orifice morphology, frontal shield ornamentation and number, morphology and position of peristomial avicularia (see Hayward 1981, 1988), which are lateral to the spiramen.

Variability and ecology

Variability on the scant available material mostly relates to the presence and number of the peristomial avicularia, which can develop from one or both of the two large suboral pores. Specimens were found among numerous colonies of the erect flexible bryozoan Cellaria fistulosa that form a dense “meadow” on a steep rocky bottom between depths of 30 and 40 m.

Distribution

Adeonella pozarae is presently known only from its type locality, in the mid-eastern part of the Adriatic Sea, off Lastovo Island.

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 9. Adeonella pozarae sp. nov. Holotype (A, C, E, G, I–M) and Paratype (B, D, F, H): off Lastovo Island (Vrhovine), Adriatic Sea, Recent. (A) The holotype. Scale bar: 500 µm. (B) The paratype. Scale bar: 500 µm. (C) Growing tip from the holotype with developing zooidal walls. Scale bar: 200 µm. (D) Cross-section of the paratype with evident layers of primary and secondary calcification in the frontal walls. Scale bar: 100 µm. (E) A zooid from the holotype. Scale bar: 200 µm. (F) Primary orifice. Scale bar: 100 µm. (G) Primary orifice with the operculum. Scale bar: 100 µm (H) Orifice of a proximal zooid from the paratype being occluded by proceeding calcification. Scale bar: 100 µm. (I) Secondary orifice with paired peristomial avicularia. Scale bar: 100 µm. (L) Secondary orifice with a single peristomial avicularium. Scale bar: 100 µm. (M) Deatail of an avicularium. Scale bar: 50 µm.