Petrascula piai Bachmayer, 1944

Bucur, Ioan I. & Săsăran, Emanoil, 2012, Large dasycladalean algae from Upper Jurassic limestone deposits of the Apuseni Mountains (Romania) - habitat and depositional environment, Geodiversitas 34 (1), pp. 219-239 : 219-239

publication ID	https://doi.org/ 10.5252/g2012n1a12
DOI	https://doi.org/10.5281/zenodo.4610241
persistent identifier	https://treatment.plazi.org/id/D6130250-FFD4-891A-5FCD-FE2EB07D53A0
treatment provided by	Felipe
scientific name	Petrascula piai Bachmayer, 1944
status

Treatment

Petrascula piai Bachmayer, 1944 ( Figs 5-8 View FIG View FIG View FIG View FIG )

Petrascula piai Bachmayer, 1944: 238 , figs 3-6 (emend. Bernier 1979: 845, pls 3, 4). — Bernier 1984: 478, pl. 11, figs 1, 2. — Moshammer & Schlagintweit 1999: 557, pl. 1, figs 4, 5. — Bucur & Săsăran 2005: 28, pl. 3, fig. 1.

Non Petrascula cf. piai – Okla 1991: 92, pl. 2, figs 3-5.

Montenegrella sp. – Bodeur 1992: pl. 16, figs 5, 7-9, 12.

? Suppiluliumaella tuberifera (Sokač & Nikler) – Dya 1992: 81, pl. 8, figs 1, 2, 6, 7.

?Dasycladale indet. – Carras 1995: pl. 22, fig. 2.

REMARKS

Petrascula piai was firstly described by Bachmayer (1944) from Jurassic limestones at Dörfless ( Austria). The species was based on four fragments partly detached from the matrix, with two head fragments and two stalk fragments.No specimen was illustrated in thin section. Bachmayer’s description (translated from the German) is as follows: “This form is characterized by a sharp difference between head and stalk. The head is almost spherical. Head and stalk were found separately. However, it is likely that the fragments illustrated in figs. 5 and 6 belong to the same species. The head consists of densely arranged secondary veriticilated branches, so that little space is left for the calcareous deposit.Within the skeleton, the secondary pore fillings were joined by calcite recrystalisation, and made a rigid sphere. The outer ends of the pore fillings give the exterior very regular, hemispherical papillae-like prominences, and very probably the pores were closed to the exterior. In addition, tertiary verticillar branches could not be recognized. Within the stalk the primary verticillar branches are set at a distance from each other, in very well defined verticils. They are set obliquely to the upper part. The branch number in a verticil ranges from 16 to 20. The division of primary ver- ticillar branches into secondaries can be observed in some places, but the number of secondary branches within a bush could not be established due to the poor preservation of the stalk.”

Bachmayer (1944) gives neither details related to the morphology of the primary and secondary laterals, nor remarks on the paleoenvironment.

In his detailed study of the species of the genus Petrascula, Bernier (1979) emended the diagnosis (i.e. description) given by Bachmayer (1944) based on many specimens observed in thin section. Bernier (1979) made the following remarks:

– the primary laterals are spherical to subspherical or ovoid; sometimes, the incomplete calcification around the primary laterals make them communicate in some places;

– the 4 to 5 secondary laterals seem to be vesiculiform, with a proximal filiform portion, and a distal enlarged portion.

Bernier (1979: 846) mentioned that he had the opportunity to examine Bachmayer’s type material, and noted that the “original figurations are of very bad quality”. Bernier (1979) also made some remarks on the paleoenvironment and noted that “Le biotope de P. piai était certainement un milieu calme de plate-forme peu profonde, dans une eau relativement chaude”. However, he noted that he had not found any complete skeleton, only separated head and stalk fragments.

In the section from Şerbota Hill (near Astileu, Pădurea Craiului Mountains; Fig. 2 View FIG ) we identified numerous specimens referable to this species. Most of them are stalk fragments ( Figs 5-7 View FIG View FIG View FIG ; 8A, B, D View FIG ), but some rare fragments could belong to the head ( Fig. 8C View FIG , E-G).

MORPHOLOGY OF THE STALK

The stalk fragments are cylindrical ( Figs 5-7 View FIG View FIG View FIG ), with a slight enlargement in the upper part where the passage from stalk to the head begins ( Figs 5D View FIG ; 8A View FIG ). The longitudinal and longitudinal-oblique sections ( Fig. 5 View FIG ) allow the morphology of the laterals to be well observed. The first-order laterals are spheroidal to ovoidal in shape ( Fig. 5A, B View FIG , D-F). In some longitudinal sections ( Fig. 5C View FIG ) the first-order subspherical laterals become subquadrangular, being higher than wide (see also the oblique sections in Fig. 6A, B View FIG and the tangential section in Fig. 7H View FIG ). This is due, most probably, to reciprocal pressure between laterals of the same verticil (e.g., Fig. 8B View FIG ). This reciprocal pressure does not operate in the vertical plane because of the spaced out arrangement of the verticils along the stalk. In transverse sections ( Fig. 7 View FIG A-E) the shape of the first-order laterals range from sub-cylindrical to sub-quadrangular.

The relationship between the first-order and second-order laterals is visible in oblique sections ( Fig. 6 View FIG ): each first-order lateral gives rise to a bush of secondaries. The second-order laterals have a proximal narrow tubular part and enlarge distally to the exterior (phloiophorous type). The link between the first-order and second-order laterals is made by a short narrow peduncle ( Figs 7A View FIG [left side]; 8D). The number of second-order laterals in a bush originating from a first-order lateral varies from 4 to 6. This is clearly visible in tangential sections ( Fig. 7G, I View FIG ).

Both Bachayer (1944) and Bernier (1979) emphasized that P. piai has only two orders of laterals. Bachmayer (1944) considered that P. piai differs from P.bursiformis by (translated from the German): “sharp passage from the stalk to the head, and the ending of pores with papillae, and additionally by the lack of calcified tertiary verticillar branches”.The same character (the lack of third-order laterals) was utilised by Bernier (1979) to differentiate P.piai from P.bursiformis and P.guembeli : “Elle se distingue aussi aisément de P. bursiformis et P. guembeli qui presentent trois ordres de ramifications dans la tige et au collet”. However, some rare specimens found in the Şerbota Hill section (Pădurea Craiului Mountains) ( Fig. 2 View FIG ) show that P. piai can also have three orders of laterals ( Fig. 8B, D View FIG [arrows]). The second-order laterals give rise, sometimes, to a bush of third-order phloiophorous short laterals.Very probably, the thirdorder of laterals was present only in some portions of the stalk.The thin calcification of the external part of the thallus, as well as the abrasion of the skeletons due to sedimentary transport, have made preservation of the third-order laterals very rare. On the other hand, it is very unlikely that the second-order laterals were closed to the exterior (as put forward by Bachmayer 1944); more probably the second-order or tertiary laterals formed an external cortex.

A distinctive character observed in the specimens from Apuseni Mountains is the presence, in some cases, of a fissuration at the interverticillar level, visible in tangential sections ( Figs 6B View FIG ; 7H View FIG ).

HEAD FRAGMENTS

Figure 8C View FIG , E-H illustrates fragments considered to represent calcified parts of the head of P. piai . The calcified parts include here, most probably, the terminal part of the second-order laterals and the third-order laterals. Lack of continuity between the head and stalk makes the attribution of these fragments to the head of P. piai problematic. The only specimen in which head and stalk are preserved together is a tangential-longitudinal section illustrated by Moshammer & Schlagintweit (1999: pl. 1, fig. 4).

DIMENSIONS

Table 1 View TABLE gives the dimensions of Petrascula piai measured on 79 specimens.

Petrascula bursiformis ( Etallon, 1859) Pia, 1920 ( Fig. 9 View FIG )

Conodyctium bursiforme Etallon, 1859: 530.

Petrascula bursiformis (Etallon) Pia (emend. Bernier 1979: 843, pl. 2). — Bernier 1984: 477, pl. 10, figs 1-5. — Schlagintweit & Ebli 1999: 394, pl. 9, figs 1, 2. — Rasser & Fenninger 2002: 176, pl. 2, fig. 3 (reproducing the specimen illustrated by Fenninger & Holzer [1972: pl.17, fig. 4]; following Bernier [1979: 844], this specimen does not belong to Petrascula bursiformis ). — Schlagintweit & Gawlick 2009: fig. 2/5.

For more, see synonymy list in Bernier (1979). REMARKS

Some Petrascula View in CoL specimens ( Fig. 9 View FIG ) identified both in the Şerbota Hill (Aştileu) and Sănduleşti areas belong to Petrascula bursiformis . Even in transverse sections through the stalk ( Fig.9 View FIG A-C) and oblique sections at the stalk-head passage level ( Fig. 9D, E, G, H View FIG ), the differences with respect to Petrascula piai are shown by the shape of the first-order laterals: longer in P. bursiformis and with a general club-like shape. They have a narrow proximal part, followed by a sudden and then a gradual enlargement to the distal part ( Fig. 9B, C View FIG ). The presence of three orders of laterals within the stalk and the stalk-head passage is also illustrated in the specimens we identified ( Fig. 9B, F View FIG ). Rare fragments, somewhat similar in shape to the fragments of “ Pseudoepimastopora ” jurassica Endo, 1961 ( Fig. 9I, J View FIG ), could represent fragments of the head of Petrascula bursiformis . Bernier (1979: 848) stressed both in the text and in table 2, the pearl-string shape of the third order laterals of P. bursiformis . Unfortunately, in the absence of close-up views, this character is not visible in the illustration provided ( Bernier 1979: pl. 2).