Pirabasoporella, 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 : 101-102

Genus Pirabasoporella gen. nov.

Type species. Pirabasoporella atalaiaensis n. sp.

Other species included. Pirabasoporella baitoae n. sp. and Pirabasoporella chipolae n. sp.

Etymology. Alluding to the type formation (Pirabas Formation) of Miocene strata in Brazil ( Maury 1925).

Diagnosis. Colony rigid, dichotomously branching, reticulate, subparallel neighbouring branches connected by tubular horizontal struts; branches with autozooids arranged in two alternating longitudinal series and opening on one side only, colony attached by rhizoids. Autozooids with a pseudoporous, mixed umbonuloid and lepralioid frontal shield, orifice with proximal pseudosinus, condyles indistinct if present, oral spines present or absent. Struts formed by hollow kenozooids budded from and communicating with large pore plates at the distolateral and proximolateral walls of two zooids on either side. Adventitious avicularia of two types: suboral (always present) and frontal or abfrontal (occasionally present). Ovicell terminal, hyperstomial with uncalcified ectooecium and a pitted endooecial surface, not closed by the operculum in life. The dorsal (abfrontal) side of each zooid with a large circular foramen that is sealed by a multiporous pore plate and from which the rhizoid is produced.

Remarks. Owing to its peculiar reticulate colony growth, with kenozooidal struts connecting neighbouring branches, and because of strong similarities in orifice and ovicell shape as well as its mode of attachment via abfrontal rhizoids, Pirabasoporella gen. nov. is classified in the family Jaculinidae Zabala, 1986 . This poorly known family, which is presently being revised by Rosso and Berning (in prep.), today occurs in the bathyal eastern Atlantic and Mediterranean Sea. Recent species assigned to the eponymous genus Jaculina Jullien in Jullien and Calvet, 1903 include the genotype J. blanchardi Jullien in Jullien and Calvet, 1903 as well as J. parallelata ( Waters, 1895) and J. tessellata Hayward, 1979 . However, the Mediterranean fossil species Vibraculina conti Neviani, 1895, which is the genotype of Vibraculina Neviani, 1895 and which is currently provisionally classified in the family Vicidae Gordon, 1988 (D.P. Gordon, pers. comm. 2013), can probably be regarded as congeneric. Vibraculina is thus likely to be a senior synonym of Jaculina , and Pirabasoporella would be the only other genus in the Jaculinidae .

Besides the kenozooidal struts that connect neighbouring branches, which are composed of one or two series of autozooids, species hitherto classified with the Jaculinidae are characterized by hyperstomial ovicells with a smooth or deeply pitted surface, by a sinusoidal orifice with or without oral spines, by the presence of adventitious avicularia, by abfrontal pore plates from which rhizoids are produced, and by frontal shields that are imperforate except for a single marginal row of pores. Everything else being principally the same, the major morphological difference justifying the introduction of the new jaculinid genus Pirabasoporella is the pseudoporous frontal shield in these western Atlantic species (see Discussion). Moreover, the mostly oval abfrontal rhizoidal pore plates, as well as their communication pores, are distinctly larger and situated towards the zooid centre, whereas those in the eastern Atlantic/Mediterranean taxa are comparatively small, round, and positioned directly at the distal zooidal margin. Adventitious (spatulate) avicularia on the frontal and abfrontal zooidal surface, in addition to the small suboral one, are also known only in Pirabasoporella .

The Jaculinidae has been classified in the lepraliomorph superfamily Schizoporelloidea Jullien, 1883 (D.P. Gordon, pers. comm. 2013). The discovery of an umbonuloid component in the frontal shield in Pirabasoporella ( Fig. 4 F, G), and the fact that the jaculinid ovicell is not of the schizoporelloid type, suggests placing the family among umbonulomorph taxa. For lack of a better alternative, we here classify the Jaculinidae within superfamily Lepralielloidea. The jaculinid ooecium consists of a mostly membranous ectooecium, only the most basal part of which is calcified, and an entirely calcified and imperforate endooecium. The endooecial surface is smooth ( Jaculina blanchardi ), or more or less deeply but superficially pitted ( Jaculina parallelata , Pirabasoporella atalaiaensis n. sp.). A similar type of ovicell is found in the Petraliidae Levinsen, 1909 and Petraliellidae Harmer, 1957 , which are also grouped in the Schizoporelloidea at present. Moreover, orificial structure, including the presence of a suboral avicularium, and the formation of reticulate colonies in some petraliid species (see below) argue for a closer relationship among these taxa. However, it is unknown to us whether the Petraliidae and Petraliellidae have a lepralioid or (partly) umbonuloid frontal shield. A thorough phylogenetic analysis will therefore be dealt with in a future revision of the Jaculinidae (Rosso & Berning, in prep.).

Similarities between the reticulate colonies of jaculinid species and those of other bryozoan taxa are only superficial and not indicative of any phylogenetic relationship. Fenestrate, or reteporiform, colonial growth habits have repeatedly evolved in a number of unrelated taxa ( McKinney & Jackson 1989). Although differing significantly in origin and structure, kenozooidal struts also characterize the well-known Paleozoic order Fenestrata as well as some Recent cyclostome bryozoan genera such as Fenestulipora Taylor & Gordon, 1997 . In contrast, the connections between branches in all modern Cheilostomata with reteporiform colonies (termed trabeculae) are composed of autozooids. Reticulate colonies sensu lato appear in distantly related cheilostome genera such as, among others, Retiflustra Levinsen, 1909 (Flustridae) , Smittipora Jullien, 1882 (Onychocellidae) , Petralia MacGillivray, 1869 (Petraliidae) , Galeopsis Jullien in Jullien and Calvet 1903 ( Celleporidae ), Reteporella Busk, 1884 (Phidoloporidae) , or Julianca Gordon, 1989 (incertae sedis).

Apart from species of Retiflustra , the colony bases in all other above-mentioned taxa are attached to more or less hard, stable substrata, and are heavily calcified in order to provide maximum resistance to wave action for these erect, rigid colonies. As a colony base or excessive ontogenetic frontal thickening of proximal branches have never been observed in any jaculinid species, it is likely that early astogeny does not involve fixation to a stable substratum. Instead, in Recent species the cuticular rhizoids, which derive from the large abfrontal pore plates, have a relatively large diameter and very thin walls, and are presumably the only means of attachment on soft substrata in Jaculinidae (see Discussion). As a consequence of these differences in habitat and attachment mode, we here refrain from classifying these rooted reticulate colonies in the Jaculinidae as ‘fenestrate’ or ‘reteporiform’.

Figures

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.