Monticulipora cystiphragmata, 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 : 185-186

Monticulipora cystiphragmata n. sp. ( Figs 3 A-D; 4; Table 1)

Monticulipora sp. – Jiménez-Sánchez et al. 2007: 694, fig. 8 (3-4).

TYPE MATERIAL. — One colony, holotype ( MPZ 2006/134).

ETYMOLOGY. — Refers to the large globular cystiphragms occurring in all autozooecia.

MATERIAL EXAMINED. — Th ree colonies ( MPZ 2006/132- 134).

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

TYPE LOCALITY. — Valdelaparra section (Zaragoza, Spain).

STRATIGRAPHIC AND GEOGRAPHIC RANGE. — Monticulipora cystiphragmata n. sp. is only know from its type locality, at the La Peña Member of the Cystoid Limestone Formation in the Valdelaparra section (Zaragoza, Spain).

DIAGNOSIS. — Monticulipora characterized by a lensshaped zoarium composed of only one layer, by the presence of large globular cystiphragms in the endozone that tangentially touch the opposite autozooecial wall to which they are attached, and by their centrifugal arrangement, always attached to the farthest autozooecial wall from the center of the colony, and arrangement not related with maculae.

DESCRIPTION

General characters

Zoarium lens-shaped, composed of a single layer. Upper zoarial surface convex and lower one concave. The holotype zoarium is 3.60 mm high in the central part, 2.25 mm high in the extremes, and 6.50 mm in diameter. Specimen MPZ 2006/132 encrusts a zoarium of Ceramopora sp.

Tangential section

Autozooecial apertures regularly or irregularly hexagonal, some of them irregularly pentagonal, with an average diameter of 0.30 mm. Intermacular autozooecia usually separated by a pair of small mesozooecia. Maculae composed of either a small group of mesozooecia surrounded by autozooecia or by a group of densely packed autozooecia with some mesozooecia between them. In monticular area autozooecial apertures have an average diameter of 0.43 mm. In total, including both macular and intermacular areas, nine complete autozooecia are spaced per mm2 and 2.9 autozooecia per mm. In deep tangential sections all autozooecial cross sections have one or two curved cystiphragms inside, changing the form and size of the autozooecial aperture and reducing its space up to 75%. Shape of mesozooecial apertures changes according to the level in the colony. In intermacular areas, one or two pairs of square or triangular-shaped mesozooecia are in contact with one or two autozooecial sides ( Fig. 4 ). In macular areas, mesozooecia form either small groups located in the center of a group of autozooecia or are distributed between several autozooecia. In this area, mesozooecia are more abundant and, when forming small groups, their apertures are more irregular.Their average diameter is 0.11 mm, with seven complete mesozooecia per mm 2 and one complete mesozooecium per linear mm. The difference between the area and linear density is due to differences in the size and shape of the mesozooecia relative to the autozooecia, which result in no mesozooecium per linear mm in the 25%of measures.In specimen MPZ 2006/132 the number of mesozooecia per mm 2 is much smaller than the general average, with only three mesozoecia on average. Acanthostyles have an average diameter of 0.03 mm and a density of four complete acanthostyles per mm 2. Most of them are circular dark masses without a defined microstructure; others are composed of a central light core surrounded by a dark sheath. Both types are located at the junction of three autozooecia. Zooecial walls have a granular microstructure; in distal zone they are 0.014 mm on average thickness and without a zooecial boundary.

Longitudinal section

Autozooecia with an initial growth angle of 32° on average; on the proximal zone they curve sharply and intersect the zoarial surface with an angle of 84° on average. Th ey have a tubular shape divided by cystiphragms and diaphragms. Cystiphragms form single series, starting on a basal diaphragm at the beginning of the autozooecial growth and ending in the first part of the outer exozone; these series are always located on the autozooecial side farthest from the center of the colony (centrifugal arrangement). According to the size of the cystiphragms a lower and an upper zone can be recognized in a longitudinal section of autozooecia. The lower one takes up approximately half of the zoarial length and is characterized by the presence of large cystiphragms that extend across almost the entire autozooecial section. The upper or distal zone is characterized by smaller cystiphragms than in the lower section and by the absence of them in the shallower part of the section. Averaging out the two different zones, there are four cystiphragms per mm. Diaphragms are straight and perpendicular to autozooecial walls. Th ey can be basal diaphragms or diaphragms joining cystiphragms to opposite wall. Two autozooecial diaphragms per mm.Mesozooecia start between autozooecia at the point where they curve to become almost perpendicular to the zoarial surface. Th ey are narrow tubes containing on average six diaphragms per mm of their length, with mesozooecial constrictions where diaphragms join the walls. Most acanthostyles are found in the distal zone of the zoarium, but some can also be found proximally. Th e former are like a thickening of the autozooecial wall and the latter are thin, massive light-coloured carbonate rods. Autozooecial walls are regular in outline and thickness in endozone, but become thicker and more irregular in exozone where acanthostyles are present; in this case the autozooecial walls have a chevron microstructure. Endozone-exozone boundary coincides with a changing of cystiphragms size; their absence marks the inner-outer exozone boundary.

REMARKS

Vinassa de Regny (1910) studied the bryozoan fauna in Upper Ordovician rocks from the Carnic Alps, identifying nine species of Monticulipora , most of them later assigned to other genera. Although these species need a revision, they can be clearly distinguished from the new Monticulipora described here considering its growth habit. Schmidt (1931), in his work on the Paleozoic of the Spanish Pyrenees, identified Monticulipora petropolitana Pander, 1830 , a species that is best placed within Diplotrypa Nicholson, 1879 . Since there is neither a description nor illustrations of Monticulipora petropolitana in Schmidt’s (1931) paper, a comparison of the Iberian specimens with the Pyrenees ones is not possible. Monticulipora cystiphragmata n. sp. is distinguished from all other described Monticulipora species by the size and centrifugal arrangement of the cystiphragms. It is similar to the type species Monticulipora mammulata revised by Boardman & Utgaard (1966), and to Monticulipora parallela , in the structure of maculae. Moreover, with the former it shares the presence of two types of acanthostyles, and with the latter the density and size of them. But Monticulipora cystiphragmata n. sp. can be distinguished from both these species by having fewer mesozooecia; and from Monticulipora mammulata by having a granular microstructure wall.

Figures

FIG. 3. — A-D, Monticulipora cystiphragmata n. sp.; A, C, longitudinal thin sections of the holotype (MPZ 2006/134) and paratype (MPZ 2006/132),respectively,showing the autozooecia (az),the large cystiphragms (cy) joined in some cases to the opposite wall by diaphragms (dp), and the narrow mesozooecia (mz); B, D, tangential thin sections of the holotype and the same paratype as in C showing square and triangular mesozooecia (mz) in B, and the cystiphragms (cy) cross sections inside autozooecial (az) sections in D; E, F, Monticulipora kolaluensis Jaroshinskaja,1962,MPZ 2006/109;E, longitudinal thin section showing the stylolitic contact with another monticuliporid bryozoan; F, tangential thin section showing the macular autozooecia (maz), the mesozooecia (mz), the acanthostyles (ac) in the common vertex of three autozooecia,and a cross section of a cystiphragm (cy) inside an autozooecial (az) section.Scale bars: 1 mm.

FIG. 4.— Monticulipora cystiphragmata n. sp.,schematic tangential section of the holotype (MPZ 2006/134). It shows the disposition of the square- and triangular-shaped mesozooecia (mz), the location of acanthostyles (ac), and the autozooecial aperture shape (az). Scale bar: 0.1 mm.