S33

Actinomma haysi Bjorklund

Echinomma leptodermum Jorgensen, Hays, 1965, p. 169, pl. 1, fig. 2

Hexacontium cf. heteracantha (Popofsky), Benson, 1966, p. 156, pl. 4, figs. 6-7.

Hexacontium cf. hericliti (Haeckel), Benson, 1966, p. 158, pl. 4, figs. 8-10.

Echinomma sp. Bjorklund,1973 (in table).

Actinomma sp. group aff. Hexacontium arachnoidale Hollande and Enjumet, Petrushevskaya and Kozlova, 1972, p. 515, pl.9, figs.4-7

Not Echinomma leptodermum Jorgensen, 1900, p. 57., Jorgensen, 1905, p. 116, pl. 8, fig. 33a-c.

DESCRIPTION:

"An actinommatin characterized by a heavy, spiny third cortical shell furnished with needle-shaped by-spines. 8-15 radial main spines, usually about 10....

"Skeleton consists of three, occasionally four concentric shells. Outermost (fourth) shell very rarely completely developed, in most cases only indicated as transverse processes on the spines. The cortical (third) shell is spherical, 130-240mu, thick-walled, rarely thin-walled, pores very unequal in size, 5-30mu, commonly circular to oval but also polygonal pores may occur. On the bars, where the pores join, small nodes extend, often armed with short thorn-like to needle-shaped by-spines, in some specimens half the length of the main spines. The middle (second) shell is thinwalled, 44-68mu, irregular in outline, pores circular to subcircular, almost equal in size, 5-7mu. Surface smooth with scattered needle-shaped by-spines. Main spines start out from the middle shell, about 8-15 in number, threebladed, about half the diameter of the third shell of equal breadth between the cortical and the middle shell. At the base where they pierce the cortical shell, they are two to three times broader than between the cortical and middle shells. Innermost (first) shell spherical, 20-27mu, thin-walled, with large polygonal pores. The innermost shell connected to the middle shell by thin radial beams, which are more numerous than the radial beams that connect the middle and the cortical shell; the latter beams continue outside the cortical shell as main spines". (from Bjorklund, 1977).

DIMENSIONS: "cortical shell 209mu, middle shell 57mu, and innermost shell 22mu". (from Bjorklund, 1977).

REMARKS:

1. For further taxonomic notes see Bjorklund, 1977.

cf. Bjorklund, 1977 for illustrations

S34

RECENT DISTRIBUTION

1. Hays, 1965, fig. 15 (Echinomma leptodermum): "It has not been observed in the tops of cores taken from south of the Polar Front. In surface sediments from north of the Polar Front Echinomma leptodermum together with Axoprunum stauraxonium frequently constitute the major part of the radiolarian fauna."

2. Bjorklund, 1977; see text-figure 2 and text for Atlantic Ocean occurrences and significance of size variation.

3. Morley, 1977; "This species loads highest in factor 4 (subtropical). At present it occurs most frequently in the central southern portion of the Subtropical Gyre and is absent in most samples south of 47degS. At 18,000 YBP this species is absent in all samples south of 39degS and appears to be slightly more abundant in tropical samples when compared to today's values."