. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 3. Loosened opercula of Penetrant ia clionoides sp. nov. (A) Dorsal view of operculum. (B) Detail of toothed ridge on anterior sur- face of operculum. (C) Lip on anterior end of operculum. (D) Ventral view of operculum showing the two diametrically opposed protrusions. Figure 5. Borehole apertures and sieves of Penetrantia clionoides sp. nov. (A) Surface view of borehole apertures, sieves and individual holes. (B) Sieve. (C) Sieve over fully formed polypide complete with operculum. Note early stage of bryozoan borehol
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 3. Loosened opercula of Penetrant ia clionoides sp. nov. (A) Dorsal view of operculum. (B) Detail of toothed ridge on anterior sur- face of operculum. (C) Lip on anterior end of operculum. (D) Ventral view of operculum showing the two diametrically opposed protrusions. Figure 5. Borehole apertures and sieves of Penetrantia clionoides sp. nov. (A) Surface view of borehole apertures, sieves and individual holes. (B) Sieve. (C) Sieve over fully formed polypide complete with operculum. Note early stage of bryozoan borehole (arrow). (D) Detail of sieve in 'C. nm and for width vary from nm to nm. The operculum is thinnest at its hind edge and thickest at the rear of the crescent. Examination of the dot distribution maps indicates that the opercula are composed mainly of calcium car-. Figure 4. Unusual borehole apertures of Penetrantia clionoides sp. nov. (A) Calcareous irregular margin around aperture. (B) Raised mar- gin. (C) Plug in calcareous margin. (D) Higher magnification of 'C (ar- row). bonate with traces of sodium, zinc, magnesium, and alu- minum. Burrow apertures occur randomly on the outer surface of the mollusc shell (Fig. 2A). Statistical analyses (G-test of goodness of fit) show that even in colonies in the early stages of development, the pattern is random. The shape of the aperture of the borehole is variable, from approximately circular to keyhole-shaped (Fig. 2A-D). In the latter case, the crescent lies in the narrow region of the aperture (Fig. 2B). These apertures are of the typical ascophoran cheilostome form with an anter and poster (Fig. 2C). On rare occasions, the lining of a borehole is raised above the surrounding substrate (Fig. 4B). In only eight cases, an irregularly shaped calcareous margin was seen around a borehole aperture (Fig. 4A). Three of these margins are plugged in the center (Fig. 4C, 4D), not with an operculum but with a structure that appe
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
