Pirabasoporella baitoae, 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 : 105-107

Pirabasoporella baitoae n. sp.

( Figure 5 )

Etymology. Alluding to the Early Miocene type Baitoa Formation in the Dominican Republic.

Material examined. Holotype: USNM 595120, the colony fragment depicted in Fig. 5 A, B, from the type locality at Rio Yaque del Norte; type stratum Baitoa Formation, Early Miocene, (sensu Saunders et al. 1986), Dominican Republic. Paratypes: USNM 595121 to 595125, 5 separate colony fragments. Additional material: More than 100 colony fragments in USNM, numbers NMB 17285–17289 and NMB 16935, NMB 17184 and Olsson 179.

Diagnosis. Pirabasoporella with relatively few frontal-shield pores that become progressively closed during ontogeny, surface often nodular. Apertural pseudosinus relatively wide. Abfrontal rhizoidal pores large and encircled by an elevated rim, strut pores very large. Adventitious avicularia present on abfrontal side of some zooids; apart from the suboral avicularium additional frontal avicularia are lacking. Ovicells unknown.

Description. Colony rigid, reticulate, with bifurcating branches connected by kenozooidal struts, branches growing more or less parallel to each other ( Fig. 5 A, C); struts irregularly developed, jointly budded laterally from strut pore-plate, rarely one strut budded from two adjacent plates ( Fig. 5 G), slightly curved or straight, surface smooth or with faint ridges and a row of slit-like areolar pores near each branch contact. No fenestrules preserved.

Autozooids elongate-pentagonal, widest at about mid-distance, arranged in two alternating longitudinal series, separated by thin raised ridges that are especially prominent on the abfrontal side, the lepralioid part of the frontal shield perforated by up to 40 pores, many of which are closed during ontogeny while the lateral areolar pores remain open, surface occasionally nodular; umbonuloid part confined to distalmost frontal shield. Interzooidal communication via multiporous pore plates. Primary orifice immersed and ill-defined, with inconspicuous condyles, secondary orifice relatively large ( Fig. 5 B), suborbicular, about as wide as long, with a broadly U-shaped pseudosinus comprising 1/5 of total orifice length, formed by two extremely short pointed lateral denticles.

Two types of avicularia present: each autozooid on frontal side with a single, small, suboral avicularium situated directly proximolateral to pseudosinus ( Fig. 5 B), oblique to frontal plane, rising distally, rostrum semielliptical, directed laterally towards median line, cystid raised distally to produce a suboral umbo, crossbar complete, without columella. Some zooids have an additional, slightly larger (see Table 2 for measurements) adventitious avicularium on abfrontal side, situated proximal to rhizoidal pore on a somewhat elevated cystid, elongate- oval with complete crossbar ( Fig. 5 F, G)

Abfrontal side of colony relatively smooth to distinctly nodular, zooidal borders marked by prominent ridges with a deep central suture, each zooid with an extremely large oval to circular rhizoid pore (up to 268 µm diameter) positioned relatively distal, surrounded by a thick prominent rim and sealed at its base by a multiporous pore plate with the large pores situated along the margin ( Fig. 5 F). Rhizoid pores of a similar type, but prominently oval ( Fig 5 G), present at distal edge of lateral walls of zooids that do not produce a kenozooidal strut, the pores in these usually smaller, not limited to pore-plate margin.

Ovicells and ancestrula not observed.

Remarks. Pirabasoporella baitoae n. sp. differs from P. atalaiaensis n. sp. and P. chipolae n. sp. in having generally fewer pores in the frontal shield (which occasionally displays a nodular surface), a broader apertural pseudosinus and the occasional presence of abfrontal avicularia while large frontal avicularia are absent. Further differences from P. atalaiaensis are the shorter but broader autozooids, and distinctly larger abfrontal rhizoidal pore plates that are circled by an elevated rim. In contrast to P. c hi po l ae, P. baitoae does not have oral spines.

Among the approximately 100 colony fragments studied, none contained ovicells or indications of their presence. Insofar as P. atalaiaensis , like all other jaculinid species, produces hyperstomial ovicells, we do not interpret their lack in P. ba i t o ae as an indication of internal brooding but perhaps reflecting a response or adaptation to environmental conditions, in which asexual colony growth may prevail over sexual reproduction. A similar strategy is found in Metrarabdotos , for example, in which several hundred autozooids may be formed for every gonozooid ( Cheetham et al. 2001). However, we have no evidence (e.g. repair of broken zooids) that propagation in P. baitoae took place predominantly via fragmentation of colonies. On the other hand, neither ancestrulae nor early astogenetic colonies have ever been reported in any living or fossil jaculinid.

In one instance ( Fig. 5 E) a connecting strut was observed that originated from two different pore plates (i.e. zooids) on one side of the branch while fusing towards, and connecting to, a single pore plate on the opposite branch.

Figures

FIGURE 5. Pirabasoporella baitoae n. sp. A, holotype, general view (collection number USNM 595120). B, detail of aperture of holotype, with suboral avicularium. C, paratype (collection number USNM 595121) showing late ontogenetic stage with several closed frontal pores. D, paratype (collection number USNM 595122) with partly preserved struts. E, strut initiated from two different pore plates (i. e. zooids) on one side of branch while fusing towards, and connecting with, a single pore plate on the opposite branch (collection number USNM 595123). F, paratype (collection number USNM 595124) showing strutproducing pore plates (right margin), rhizoid-producing pore plates (left margin and central part), and small oval avicularia in the bifurcation and on zooids in the branch centre (arrow). G, lateral view of paratype (collection number USNM 595125) showing three round, strut-producing pore plates (black arrows on two of them), two oval rhizoid pore plates (centre), and two small avicularia (white arrows). Scale bars all 100 µm.

Tables

TABLE 2. Measurements for Pirabasoporella baitoae n. sp.

	BW	SD	AL	AW	AD	SPL	SDW	PRL	RPW	AAL	SAL
mean	458	183	500	236	151	245	233	186	97	93	57
min	403	153	443	200	142	181	179	128	85	64	44
max	514	202	543	28	158	302	268	219	113	113	81
#	37	18	32	32	64	12	12	24	24	6	5