Adeonella flabellata, 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 : 1719-1721

Adeonella flabellata sp. nov.

( Figures 1F,G , 3C , 10 )

Etymology

Referring to the fan morphology of the colony and the colony branches.

Holotype

CNHM Inv. br. 33, a single colony from Kornati (Mana), 20–40 m. Novosel, 10 July 2003.

Description

Colony 18 mm high and 15 mm wide, formed by a 5 mm long subcylindrical stalk from which two angulated, fan-shaped irregularly outlined, bilaminar blades about 1 mm thick and nearly 8 mm wide, develop ( Figure 1F ).

Autozooids decidedly diamond-shaped ( Figure 10C,G ); elongate rhomboidal, with a rounded enlarged distal portion only in early ontogeny and along exposed marginal rows, where they form the blade edges in back-to-back couples ( Figure 10E ). Margins marked by deep grooves and thin raised characteristically undulate sutures. Frontal shield finely granular and swollen, mostly in the distal half, pierced by a peripheral row of round marginal areolar pores plus a few others near the orifice and proximally to the spiramen ( Figure 10A ). Primary orifice slightly longer than wide ( Figure 10B ) with a bluntly V-shaped sinus occupying about half of the proximal border. Condyles small lateral and squared, hardly visible from frontal view. Secondary orifice developing suddenly ( Figure 10D ), bean-shaped to transversely elliptical in early ontogeny with a convex proximal lip, becoming circular and slightly smaller in late ontogeny. Spiramen large, subcircular to longitudinally elliptical with increasing frontal calcification, leaving the oral sinus partly visible at least during the early ontogenetic stages; separated from the secondary orifice by a stout bridge of calcification, typically marked by a couple of large pores, one on each side ( Figure 10A,C,E ). Peristomial avicularium absent ( Figure 10A,C,D ), except for a few zooids from the marginal rows ( Figure 10E ). When present, single and small, situated on the spiraminal bridge, distally or medially pointing; rostrum bluntly triangular. A very few zooids exhibit paired converging avicularia, pointing just slightly proximally ( Figure 10F ). Frontal shield rapidly becoming swollen with ontogeny, developing two lateral and one proximal tubercles, later sinking in frontal calcification together with secondary orifices ( Figure 10G ). In latest ontogenic stages, orifice and spiramen become completely occluded and frontal shield evolves in a flat polygonal surface outlined by undulating sutures and sculptured with a marginal row and a central cluster of small round pores ( Figure 10G ). Frontal avicularia raised and variably oriented, similar in shape and size to the peristomial ones develop on some zooids from the marginal rows ( Figure 10G ). Vicarious avicularia and gonozooids not observed and seemingly absent. Small swollen kenozooids with a dozen pores fill spaces between zooids at distal blade edges where growth stops ( Figure 10H ) and occasionally along lateral margins. Encrusting base not observed.

Measurements of the holotype

ZL: 574 ± 35.55, 510–649 (1, 20); ZW: 470 ± 28.28, 419–529 (1, 20); sOL: 96 ± 7.67, 80–112, (1, 20); sOW: 115 ± 5.70, 104–122, (1, 20); pOL: 117 ± 5.59, 109–124, (1, 6); pOW: 107 ± 7.31, 100–118, (1, 6); sOL: 91± 5.05, 87–100, (1, 6); sOW: 112 ± 5.43, 105–118, (1, 6); mAL: 55 ± 4.43, 50–60 (1, 4); mAW: 43 ± 2.87, 40–47 (1, 4).

Remarks

Adeonella flabellata sp. nov. shows close affinities to A. pallasii , as also indicated by the SI index ( Table 1). Nevertheless, it is easily distinguishable from that species and all other congeners from the Mediterranean for both colony and zooidal morphology. Zooids are mostly lacking in frontal and even in peristomial avicularia, and the primary orifice is high and has a conspicuous sinus. Furthermore, this species is unique within the Mediterranean area in forming bladed, instead of narrowly branched, colonies. Lobate growth morphology is shared with a group of species all originating from South Africa, namely A. lobata Hayward, 1988 , A. spathulata Hayward, 1988 and A. alia Hayward and Cook, 1983 . Nevertheless, they exhibit completely different zooidal morphology, including the shape of the primary orifice, an evenly porous frontal wall, the presence of gonozooids and/or vicarious avicularia and a different position of the peristomial avicularia, not located on the peristomial bridge.

Variability and ecology

Zooidal variability is mostly related to ontogeny and the development of frontal calcification. The unique colony, originating from coralligenous bottoms, constitutes the substratum for spirorbids, which colonize non-functional zooids of the basal stalk.

Distribution

The species is presently known only from the type locality, Kornati, in the eastern Adriatic Sea and is unknown as a fossil.

Figures

Figure 1. Colony morphology of some Adeonella species from the Mediterranean area. (A–C) Adeonella calveti from an overhang, off Acitrezza, about 40 m: basal (A) and top (B) views of the same colony, formed by a set of contiguous fans, each consisting of branches dichotomizing in the same plane. (C) Detail: note how anastomoses are avoided through changes in the growth direction of branches and their tilting and twisting. (D) Adeonella calveti: a colony from the roof of Galatea cave near Alghero, north-west Sardinia, 7 m. (E) Adeonella pallasii: an almost complete (?) colony from coralligenous bottoms of Prvić Island, about 10 m. (F,G) Adeonella flabellata: the unique colony consisting of a stalk-like proximal part and distal enlarged blades. Coralligenous bottoms from Mana, 20–40 m. Scale bar: 1 mm for all 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 10. Adeonella flabellata sp. nov. Holotype. Mana 20–40 m, Adriatic Sea. Recent. (A) Zooid from near the growing edge. Note the absence of avicularia and the similar secondary orifice and ascopore. Scale bar: 200 µm. (B) Primary orifice with straight proximal border with large U-shaped sinus. Scale bar: 50 µm. (C) Some diamond-shaped zooids with developing frontal tubercles. Scale bar: 200 µm. (D) Zooids from the growing margin, one with peristomial wings converging to form the orificial bridge. Scale bar: 200 µm. (E) Lateral margin of the main colony blade, formed by large zooids, less rhomboidal than the others. Scale bar: 500 µm. (F) Zooids from the margin of a narrow notch in the colony blade. Note the small proximalinward directed avicularia associated with the peristomial bridge. Scale bar: 200 µm. (G) Basal portion of the colony showing the downward increase in secondary calcification and the formation of small prominent frontal avicularia on marginal zooids. Scale bar: 500 µm. (H) Colony margin with kenozooids filling interzooidal spaces. Scale bar: 500 µm.