S29

Actinomma arcadophorum Haeckel

Actinomma arcadophorum Haeckel, 1887, p. 225, pl. 29, figs. 7, 8; Nigrini, 1967, p. 29, pl. 2, fig. 3

DESCRIPTION

"Similar to Actinomma medianum, but cortical shell is generally larger and much more delicate with many more pores and thinner bars. Radial spines more numerous, occasionally supporting an extracortical shell.

"Medullary shell and meshwork as in A. medianum and A. antarcticum but more delicate." (from Nigrini, 1967).

DIMENSIONS "Diameter of cortical shell 191-236 microns of medullary meshwork 81-100 microns. Inner medullary capsule approximately one-third the diameter of the medullary meshwork." (from Nigrini, 1967).

Plate 3, figure 4

S30

RECENT DISTRIBUTION

1. Nigrini, 1967, fig. 12; "Indian Ocean occurences - A. arcadophorum is sparsely distributed in low latitudes and does not occur in middle latitude samples. Though rather rare in Recent sediments, it appears to be a useful member of the low latitude assemblage."

2. Nigrini, 1970, fig. 10; belongs to a tropical assemblage derived by recurrent group analysis of North Pacific samples, but the species does range as far north as 40 degrees N in the western Pacific.

3. Molina-Cruz, 1975; "It is assumed that this species is a morphological variant of A. medianum and is grouped with this species in the counts."