(Pyrgoella sphaera)

Almennt

Pyrgoella sphaera (d'Orbigny, 1839) 

Biloculina sphaeroïdes – Schlumberger, C. 1883. Note sur quelques foraminiféres nouveaux ou peu connus du golfe de Gascogne; Campagne du Travailleur. Feuille Jeunes Nat., année 13 (1882-1883), no.153: p.106, pl.2 figs. 3 and 3a-d.

Planispirina sphaera (d‘Orbigny) – Schlumberger, C. 1891. Révision des Biloculines des grand fonds. Extradit des Mémoires de la Société Zoologique de France, pp.190-191, text. figs. 45-45, pl.12, figs. 87-100. – Cushman, J.A. 1917. A Monograph of the Foraminifera of the North Pacific Ocean. Part VI. Miliolidae. Bull. U.S. Nation. Mus 71, p.37, pl.19, fig. 1.

Pyrgoella sphaera (d‘Orbigny, 1839) – Loeblich and Tappan 1988(1987). Foraminiferal genera and their classification, vol. 1&2, p.343, Pl. 351, figs.1-4. – Jones, R.W., 1994. The Challenger Foraminifera, The Natural History Museum, London, Oxford Univ. Press, p.18, pl.2, fig.4.

Description: Test is spherical; the two last chambers are externally visible; the penultimate chamber covers only a small part of the surface (about 140° of the circumference in axial section). Chambers are hemispherical and strongly embracing, added planispirally in a single plane, where less than two chambers are in one whorl (i.e. each chamber encircles about 220° of a whorl).  The largest tests comprised at least 11 subglobular chambers; walls are rather thin and fragile. Aperture of initial chambers is a simple opening, with a raised and slightly protruding apertural rim, filled with a concave semicircular flap, resulting in a crescentic or V-shaped apertural slit; later chambers have multiple simple apertures, often along with one or more dentritic slits; the largest specimens often have various combinations of circular to irregularly shaped slits; the apertural area is slightly raised above the surrounding surface, always circular to ovate in outline. Walls are relatively thin, sometimes semi-transparent; surface is smooth; sutures distinct but often flush with the surface. The largest specimen is 3,2 mm in diameter, but most are around 1 mm.

Diagnosis: The relatively thin and fragile walls and multiple apertures, distinguishes P. sphaera from Pyrgoella irregularis, which at all stages has a single aperture, with thicker walls and more protruding apertural rim.    

Gudmundur Gudmundsson IINH (gg@ni.is)

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Tegund (Species)
(Pyrgoella sphaera)