Prasopora spjeldnaesi, Jiménez-Sánchez, 2010

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 : 191-195

Prasopora spjeldnaesi n. sp. ( Figs 5F ; 6 ; 7 ; Table 4)

Prasopora sp. – Jiménez-Sánchez et al. 2007: 694, fig. 8 (5-6).

TYPE MATERIAL. — Complete zoarium, holotype ( MPZ 2006/99).

ETYMOLOGY. — Th is species is named after Nils Spjeldnaes, who introduced me to the bryozoan world.

MATERIAL EXAMINED. — The holotype.

TYPE HORIZON. — La Peña Member of the Cystoid Limestone Formation, Upper Ordovician.

TYPE LOCALITY. — La Peña del Tormo section (Zaragoza, Spain).

STRATIGRAPHIC AND GEOGRAPHIC RANGE. — It is only known from its type locality, at the La Peña Member of the Cystoid Limestone Formation in La Peña del Tormo section (Zaragoza, Spain).

DIAGNOSIS. — Prasopora species characterized by anomalously large autozooecia and mesozooecia; presence of cystiphragms on one side of the autozooecial wall leaning on lower diaphragms or on other cystiphragms growing from opposite side of wall; autozooecia isolated from each other by mesozooecia; the splitting of largest mesozooecia in two new mesozooecia just above a diaphragm.

DESCRIPTION

External characters

Zoarium lens-shaped with apparent maximum diameter of 27.0 mm, thickness of 6.5 mm in its center and of 5.0 mm in the periphery. Convex upper surface with monticules, surrounded by depressed intermonticular areas. Autozooecial apertures oval, completely surrounded by mesozooecial apertures. Monticular areas composed of slightly smaller and more circular autozooecia than those in intermonticular areas, and by larger mesozooecia. Mean distance between adjacent monticules of 4 mm measured from center to center. Zoarium basal surface concave, with concentrically wrinkled epitheca around ancestrula, with radially arranged autozooecia.

Tangential section

Autozooecial apertures oval, with an average major diameter of 0.51 mm and an average minor diameter of 0.43 mm; these values decrease in deeper sections. Almost two autozooecia per mm 2 and one autozooecia per linear mm on average, always surrounded by mesozooecia. Most autozooecia crossed from side to side by one or two cystiphragms. Intermonticular mesozooecial apertures polygonal (square,rhomboidal, or pentagonal),with an average major diagonal diameter of 0.25 mm, an average of 12 mesozooecia per mm2 and 3 mesozooecia per linear mm. Monticular mesozooecia always surrounding autozooecia, with the shape of apertures in form of irregular polygons and an average major diameter of 0.4 mm. Autozooecialmesozooecial and mesozooecial-mesozooecial walls composed of thin dark lamina; the former with average thickness of 0.01 mm and the latter slightly thinner (0.008 mm on average). Acanthostyles absent.

Longitudinal section

Initial autozooecia originated from the ancestrula and located in the central area of the colony,growing at an angle of 90° to the substrate.Th ese autozooecia form a small convex bulge that breaks the concavity of this surface.Th e other autozooecia growing with an average angle of 54.5° to the basal surface, but bending after a short distance and reaching the zoarial surface with an average angle of 76°. Autozooecia are long tubes, densely tabulated by diaphragms and cystiphragms. Diaphragms very regularly distributed throughout autozooecium length, straight, concave or convex, without a predominance of one type or the other, three per mm of autozooecial length. Cystiphragms grow from one side of wall, and lean on lower diaphragms or on another cystiphragm growing in opposite wall.Th e junction between a cystiphragm and a diaphragm forms a small wedge or semicircular cavity and the junction between two cystiphragms always forms semicircular-shaped cavities.Number of cystiphragms increases towards the zoarial surface, where an average of four cystiphragms per mm have been counted. Mesozooecia are long tubes either isolated separating autozooecia or forming small clusters.They generally have narrower apertures than autozooecia and are densely tabulated by diaphragms (averaging nine per mm). Most mesozooecial diaphragms are straight, but they can also be slightly concave or convex.In continuous mesozooecia tabulated by straight diaphragms, diaphragms develop at the same level, forming a square network. Near zoarial surface the largest mesozooecia split just above the surface of a diaphragm to form two new mesozooecia ( Fig. 7 ).

REMARKS

This Prasopora species shares with most of its congeneric species the presence of monticules on the zoarial surface,the distribution and shape of densely tabulated mesozooecia when they are separating autozooecia, and the presence of diaphragms and cystiphragms in the autozooecia.

It is similar to Prasopora gotlandica Hennig, 1908 . Both species can be distinguished from other Prasopora species (including Prasopora carnica described above) by the form and distribution of their cystiphragms. All the other known species of this genus have cystiphragms either blister-shaped and isolated or forming long series superimposing each other, lining one or both sides of the autozooecial wall; in most cases they are joined to each other or to the opposite wall by one straight diaphragm.In Prasopora spjeldnaesi n. sp. and Prasopora gotlandica the cystiphragms are attached to one side of the wall curving and leaning on the lower diaphragm or on another cystiphragm growing in the opposite wall. Th ey also have in common that the largest mesozooecia divide to form new smaller ones. In spite of these similarities, both species can be clearly distinguished by the different diameters of the autozooecia and mesozooecia (0.25-0.30 mm and 0.10-0.20 mm, respectively, in Prasopora gotlandica vs 0.45-0.55 mm and 0.18-0.34 mm, respectively, in Prasopora spjeldnaesi n. sp.). Th e new species can be also discriminated from Prasopora gotlandica by its higher mesozooecia number/autozooecia number relation (2.5 in Prasopora gotlandica vs 7.0 in Prasopora spjeldnaesi n. sp.).

According to the discussion above, Prasopora spjeldnaesi n. sp. can be clearly discriminated from all the congeneric species. In spite of not being possible, at the moment, to describe the intraspecific variability of the new species, known from a single complete zoarium, it is proposed to erect formally a new species. Th is will facilitate further comparisons within this widespread genus in the Mediterranean Province.

Prasopora spjeldnaesi n. sp. is also similar to Prasopora mesoporosa Fritz, 1957 . Both have numerous mesozooecia forming characteristic rings around autozooecia; but Prasopora mesoporosa has the typical Prasopora cystiphragms and much smaller autozooecia and mesozooecia than Prasopora spjeldnaesi n. sp. (0.24- 0.32mm and 0.05-0.18 mm, respectively,in Prasopora mesoporosa vs 0.45-0.55 mm and 0.18-0.34 mm, respectively, in Prasopora spjeldnaesi n. sp.).

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.

FIG. 6. — Prasopora spjeldnaesi n. sp., holotype (MPZ 2006/99):A, general view of the colony; B, surface of the colony showing autozooecia (az) completely surrounded by mesozooecia (mz), and a cross section of a cystiphragm (cy) inside an autozooecial aperture; C, tangential thin section with abundant mesozooecia (mz) completely isolating autozooecia (az); D, longitudinal thin section showing the autozooecia (az) and mesozooecia (mz) as well as the peculiar cystiphragms (cy); E, a group of mesozooecia (mz) with their diaphragms (dp) at the same level forming a square network. Scale bars: 1 mm.

FIG. 7. — Prasopora spjeldnaesi n. sp., schematic longitudinal section showing the shape and distribution of autozooecial (az) cystiphragms (cy) and diaphragms (dp) and a group of densely tabulate mesozooecia (mz) with diaphragms at the same level. In 1 a large mesozooecium divides to form two smaller mesozooecia. Scale bar: 1 mm.