Prasopora carnica Vinassa de Regny, 1915

Jiménez-Sánchez, Andrea, 2010, New Monticuliporidae (Bryozoa, Trepostomata) from the Cystoid Limestone Formation (Upper Ordovician) of the Iberian Chains (NE Spain), Geodiversitas 32 (2), pp. 177-199 : 188-191

Prasopora carnica Vinassa de Regny, 1915 ( Fig. 5 C-E; Table 3)

Prasopora sp. – Vinassa de Regny, 1914: 205, 206, text-fig. 4.

Prasopora carnica Vinassa de Regny, 1915: 101 , pl. 12, figs 7-9. Conti 1990: 91, pl. 1, figs 1-4.

carnica Vinassa de Regny, 1915 . Abbreviations: see Table 1.

MATERIAL EXAMINED. — One zoarium ( MPZ 2006/113).

STRATIGRAPHIC AND GEOGRAPHIC RANGE. — Upper Katian (Upper Ordovician) of the Carnic Alps: Vinassa de Regny (1914, 1915); Upper Katian (Upper Ordovician) of Sardinia ( Italy): Conti (1990); Cystoid Limestone Formation, La Peña Member, of the Valdelaparra section (Zaragoza, Spain).

DESCRIPTION

General characters

Zoarium incrusting a brachiopod valve and incrusted by Monticuliporidae sp. indet described below. Composed of two layers, with colony thickness 0.9- 1.9 mm, and minimum diameter of 15.0 mm.

Tangential section

Two zones with gradual transition between them:the first one composed by oval or subpolygonal autozooecial apertures, completely surrounded by mesozooecia; and the second one composed by more circular autozooecial apertures, in contact with each other in most of their perimeter, and with scarce mesozooecia located in the space between them.Th e spatial density of autozooecia is almost twice in the second zone than in the first one. Autozooecial sections with an average diameter of 0.20 mm, 7.5 autozooecia per mm2 and 2.2 autozooecia per linear mm on average (measured in the first zone, where they are less numerous). Most autozooecial sections with two or three cystiphragms leaving an oval cavity between them, located either in a central position in the case of two cystiphragms, or on the periphery in the case of three cystiphragms. Shape of mesozooecial cross sections depends on their position in the colony: irregularly hexagonal when surrounding autozooecia and variably shaped when occupying the spaces between autozooecia. Mesozooecia with an average diameter of 0.12 mm, 41.5 mesozooecia per mm2 and six mesozooecia per linear mm on average (measured in first zone where they are more abundant). Both, autozooecial and mesozooecial walls thin (mean of 0.011 mm). Wall microstructure laminated, but zooecial boundaries not observed. Acanthostyles absent.

Longitudinal section

Zoarium composed by two layers of different thickness; lower one with maximum thickness of 1.35 mm; the upper one 0.45 mm, more regular in thickness. Overgrowth marked by development of new basal diaphragms. Th e oblique orientation of the section does not permit measuring the inclination of autozooecia with respect to basal surface. Autozooecia intersect zoarial surface at an angle of 85°. Autozooecia consist of long tubes with cystiphragms and diaphragms. Cystiphragms with an irregular distribution and size, arranged either in single series lining one or both sides of walls, or isolated, also on one or both sides. Isolated cystiphragms can take up three fourths of autozooecial diameter. Nine cystiphragms per linear mm on average. Diaphragms very scarce, always joining the larger isolated cystiphragms to the opposite wall. Mesozooecia are length tubes located between autozooecia or in small groups. Some of them almost as large as autozooecia, distinguish from latter by absence of cystiphragms and by higher density of diaphragms (an average of 16 per mm). Mesozooecial diaphragms straight or slightly oblique. Zooecial walls sinuous, causing narrowing and widening of zooecia, but with constant thickness throughout zoarium.

REMARKS

The specimen from the Iberian Chains is similar to specimens from the Upper Ordovician of Sardinia ( Italy) assigned by Conti (1990) to Prasopora carnica . Th ey have colonies with secondary overgrowths; cystiphragms isolated or in series on one or both sides of the wall, with a similar spatial density in both collections ( Conti 1990 and this one); autozooecia that intersect the upper surface with an angle of about 85°; numerous mesozooecia with closely spaced diaphragms; sinuous walls of constant thickness; as well as absence of acanthostyles. But the Iberian zoarium does not reveal either the cystoidal diaphragms or the macula described by Conti (1990) in Sardinian material.

Two other species of Prasopora are known from the Mediterranean Province, but they can be clearly distinguished. Th e Iberian zoarium is mainly distinguished from Prasopora fistuliporoides ( Vinassa de Regny, 1910) because the former has fewer autozooecial diaphragms, more abundant mesozooecia, and has neither cystoidal diaphragms in overgrown areas nor acanthostyles. From Prasopora grayae the present material is distinguished by less abundant autozooecial cystiphragms and diaphragms as well as by the size of the cystiphragms which occupy less space inside the autozooecial tubes.

Figures

FIG. 5. — A, B, Monticulipora kolaluensis Jaroshinskaja, 1962, MPZ 2006/109, longitudinal thin sections; A, area of the zoarium with large cystiphragms (cy) attached to one side of the autozooecial (az) wall that are joined to the opposite wall by diaphragms (dp); B, an area with smaller cystiphragms (cy) located in both sides of the wall as single rows or isolated; C-E, Prasopora carnica Vinassa de Regny, 1915, MPZ 2006/113; C, longitudinal thin section showing the autozooecia (az), the cystiphragms (cy), and the mesozooecia (mz); D, E, two tangential thin sections separated by less than 3 mm and in the same depth of the colony; D, the autozooecia (az) are completely surrounded by mesozooecia (mz); E, the autozooecia (az) are in contact with other autozooecia in most part of their outline, having two cystiphragms (cy) inside, and scarce mesozooecia (mz); F, Prasopora spjeldnaesi n. sp., MPZ 2006/99, basal surface showing the concentrically wrinkled base and the initial point of growth of the zoarium (ipg). Scale bars: 1 mm.