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Amphirhopalum virchowii (Haeckel, 1862)

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The shell is bilaterally symmetrical, consisting of two paired arms and an opposite odd one which is a little longer. The angle between the paired arms is smaller than the one between them and the odd arm. Arms are elliptical in cross sections, and arise from a central disc usually composed of two inner spherical shells and two outer annular ones. All are connected by numerous discontinuous radial beams. The upper and the lower calottes of the outer spherical shell are generally poreless and smooth, whereas the annular shells are porous.
Initially from the central disc arise two opposite arms, one corresponding to the odd arm and the other to the proximal part of the paired arm. The latter forks very soon giving rise to the paired arms. Their common, unforked part is, as a rule, composed of only a chamber; most frequently the fifth one. Arms are usually formed from four to six arcuate chambers which gradually expand distally.
In some specimens, the distal ends of one or more arms may taper or become spongy, or even fork. This last case was noticed only in the odd arm of a specimen. A patagium may be sometimes present between the three arms. Finally, the whole shell may be enveloped in a thin-walled lattice-mantle.
Dumitrica 1973


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