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Rhizoplegma densum Blueford, 1982

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Description: Two shells, 160-240 and 40-60 Ám in diameter. Outer surface dense, spongy layer of varying thickness (20-120 Ám), by-spiny. Five to eight spines radiating from inner shell, bladed with serrated edges with budlike branches; unbroken spines 400 Ám in length. Pores of outer shell extremely variable in size and shape, forming irregular meshwork. Inner shell delicate, with irregular pores.
Holotype: Plate 3, Figure 7, DSDP Site 66, core 1-4, section 3, 25-27 cm, England finder W 29/4 (USNM 315056).
Distinguishing features: Large, dense, spongy outer shell with two long-bladed spines having serrated edges. Differs from Rhizoplegma radiactum Haeckel, 1887 and R.lychnosphaera Haeckel, 1887 by its smaller size, delicate inner shell and spines with serrated edges.
Derivation of name: In reference to the dense spongy network, from the Latin dens, thick.
Occurence: The paucity of specimens at Site 77 and their absence at Site 289 suggest that this species is selectively dissolved or endemic to eastern Pacific equatorial waters. Examination of Site 66 confirms the conclusion that Rhizoplegma densum is endemic to the eastern part.
Blueford 1982


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