Pirabasoporella atalaiaensis, Zágoršek, Kamil, Ramalho, Laís V., Berning, Björn & Távora, Vladimir De Araújo, 2014

Zágoršek, Kamil, Ramalho, Laís V., Berning, Björn & Távora, Vladimir De Araújo, 2014, A new genus of the family Jaculinidae (Cheilostomata, Bryozoa) from the Miocene of the tropical western Atlantic, Zootaxa 3838 (1), pp. 98-112 : 102-105

Pirabasoporella atalaiaensis n. sp.

( Figs 3–4 )

Etymology. Alluding to the type locality at Atalaia Beach (Salinopolis city, Pará State).

Material examined. Holotype: MG-UFPA 6200-I, a colony fragment from the type locality at Atalaia Beach (Salinopolis city, Pará State); type stratum, Pirabas Formation, Miocene. Paratype: 10 separate colony fragments labelled as MG-UFPA 6201-I to 6211-I. Additional material: More than 100 colony fragments, MG-UFPA 6212-I to 6300-I from sections Atalaia, B-17 Capanema and Aricuru.

Diagnosis. Pirabasoporella with relatively large zooids and few pores in the frontal shield. Oral spines absent. Adventitious avicularia of two types: a small suboral one associated with an umbo, and a larger one occasionally developing on the frontal shield during ontogeny. Ovicell terminal, hyperstomial with uncalcified ectooecium and a pitted endooecial surface, not closed by the operculum. Abfrontal rhizoidal foramen relatively small and proximally situated.

Description. Colony rigid, reticulate with bifurcating branches connected by kenozooidal struts at regular intervals, branches growing more or less parallel to each other ( Figs. 3 A-C). The struts usually developing at every second autozooid, jointly budded laterally from the distolateral and proximolateral corners of two zooids ( Fig. 3 B), slightly curved or straight, thick but hollow with microstructures indicating the same origin as autozooidal skeleton, surface smooth or with faint ridges and a row of slit-like areolar pores near each branch contact ( Fig. 3 D), struts delimiting elongate rounded-rectangular to lozenge-shaped fenestrules indented by slightly bulging peristomial rim of the interjacent zooids.

Autozooids rectangular but slightly curved, arranged in two alternating longitudinal series initially separated by thin raised ridges that gradually thicken during ontogeny ( Fig. 3 F), frontal shield mixed umbonuloid and lepralioid, the short umbonuloid part restricted to the distal shield ( Fig. 4 F, G), the interior surface smooth and often with concentric growth lines, the lepralioid frontal shield perforated by 15–25 pores, some pores not penetrating the shield entirely ( Fig. 4 E, F). Primary orifice immersed, ill-defined, secondary aperture not well preserved, relatively large, suborbicular with a variably broad U-shaped pseudosinus ( Fig. 3 E), surrounded by a short, wide peristome that becomes thickened during ontogeny, proximolaterally carrying two protuberances, the prominent one towards the neighbouring zooid produced by a suboral avicularium ( Fig. 3 D, E).

Avicularia polymorphic, of two different types: a single, small, suboral avicularium on each autozooid ( Fig. 3 E), cystid slightly raised, situated proximolateral to aperture, rostrum subtriangular, directing laterally to proximolaterally, pivotal bar complete. Large adventitious frontal avicularia forming anywhere on the frontal shield in elder zooids ( Fig. 3 D); rostrum elongate-triangular, directed proximolaterally.

Ovicells large, terminal, globular but flattened frontally, hyperstomial, recumbent on proximal part of distal zooid ( Fig. 4 A–D); ectooecium uncalcified, endooecium densely sculptured with numerous tiny pits or pores apart from a broad, smooth, prominent rim surrounding ovicell opening that arches above aperture ( Fig. 4 D), not closed by the operculum of the maternal zooid in life ( Fig. 4 B).

Abfrontal side of colony smooth, zooidal borders marked by thin raised ridges ( Fig. 3 G), each zooid with large, deep, round to elongate rhizoid pore, occasionally surrounded by a thick prominent rim during ontogeny, sealed at its base by a multiporous pore plate with the pores situated along the margin ( Fig. 4 E). An additional pore of the same type present at distal edge of lateral walls of zooids that do not produce a kenozooidal strut.

Ancestrula not observed.

Remarks. Although more than 100 colony fragments of Pirabasoporella atalaiaensis n. sp. were found, all of them are very small, which complicates assessing the presence and extent of morphological change during ontogeny within a colony, and distinguishing it from interspecific differences. The fragments do vary to quite an extent with respect to strut thickness, presence/absence of large frontal avicularia, and size of the frontal shield pores, for example (compare Figs 3 B, 3D, 4A). Morphometric analyses show overlapping ranges of strut thickness in the various fragments, with thin struts appearing in colonies that can be regarded as ontogenetically young colonies ( Fig. 4 A), and thick struts in older colonies ( Fig. 3 B). Large frontal avicularia were exclusively found in colonies that were composed of older or even ephebic (gerontic) zooids, some orifices of which were sealed off by frontal calcification ( Fig. 3 D, zooid at lower left). Thus, we consider intercolonial morphological variability to be the result of ontogenetic change, not of interspecific differences. Frontal thickening of zooids and an increase in strut diameter is likely to be explained by the necessity to reinforce an expanding colony.

Figures

FIGURE 3. Pirabasoporella atalaiaensis n. sp. A, general view of the holotype (collection number MG-UFPA 6200 - I). B, detail of holotype showing arrangement of the autozooids and struts. C, detail of paratype (collection number MG-UFPA 6201 - I) showing well-pronounced apertural pseudosinus and suboral avicularium. D, detail of paratype (collection number MG- UFPA 6202 - I) showing larger frontal avicularia. E, close-up of aperture with small suboral avicularium and well-pronounced pseudosinus (collection number MG-UFPA 6203 - I). F, paratype (collection number MG-UFPA 6203 - I) showing frontal avicularia and pseudopores on frontal shield. G, abfrontal view of paratype (collection number MG-UFPA 6204 - I) showing arrangement of rhizoid pores. Scale bars: A, 1 mm; B – G, 100 µm.

FIGURE 4. Pirabasoporella atalaiaensis n. sp. A, two well-developed ovicells facing the same fenestrule (collection number MG-UFPA 6205 - I). B, four ovicells, showing the thickened imperforate lip around the ooecial opening (collection number MG-UFPA 6206 - I). C, close-up of ovicell showing its shape and contact with the distal autozooid (collection number MG- UFPA 6207 - I). D, close-up of ovicell showing opening and contact with the distal autozooid (collection number same as A). E, interior view showing communication pores of rhizoidal pore plates (collection number MG-UFPA 6208 - I). F, interior view showing orifices and pores in proximal frontal shield (collection number MG-UFPA 6209 - I). G, close-up of the interior of an autozooid showing the umbonuloid part of the frontal shield arrow (collection number same as F). Scale bars all 100 µm.