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?Prunopyle antarctica Dreyer

Prunopyle antarctica Dreyer, 1889, p. 24, pl. 5, fig. 75; Riedel, 1958, p. 225, pl. 1, figs. 7, 8.

Cromyechinus antarctica (Dreyer), Petrushevskaya, 1967, p. 25, pl. 3, figs. 5 I-VI, pl. 14, figs. I-VII.

DESCRIPTION

"Skeleton consisting of four concentric shells connected by numerous radial bars. Three inner shells are spherical, or approximately so, while the fourth is ovate. The two inner and the two outer shells lie rather close together, and a larger space separates the second shell from the third. Pores of the second shell (counting outward) subcircular, separated by relatively thin bars. Pores of the fourth (outermost) shell small, circular or subcircular, in many specimens arranged in groups over the pores of the third shell in such a manner that 2-8 pores of the fourth shell overlie one larger pore of the third shell. Fourth shell apparently rather thick, with smooth or ridged surface, in some individuals partially united with the third shell. Short, thorn-like spines are sparsely distributed over the shell surface; those surrounding the large pylome are longer and stronger, and some specimens have a group of large spines also on the aboral pole." (from Riedel, 1958).

The connecting bars are 3-bladed and pierce the outermost shell. In complete specimens there is one spine longer than the others on the long axis of the fourth shell. Fourth shell often incomplete, but is always indicated by transverse processes on the radial spines. (Gail Lombari, personal communication).

DIMENSIONS

"Diameter of the innermost shell approximately 15-17 microns, of second shell 12-35 microns (occasionally to 61 microns?), of third shell 75-98 microns, of fourth shell (major axis) 115-160 microns, (minor axis) 105-110 microns.

"Emended description differing principally in the ranges of variation of the shell diameters, based on 15 specimens from Sta. 91. Although Dreyer stated that the diameter of the second shell is approximately 61 microns, the present author has found no specimen in which it exceeds 42 microns." (from Riedel, 1958).

Based on 20 specimens from the North Pacific, near the Oregon coast. Diameter of inner medullary 12-14 microns; outer medullary 26-39 microns; third shell 66-84 microns; long axis of fourth shell 89-126 microns; short axis of fourth shell 84-120 microns. Length of principle spine 26-40 microns. (Gail Lombari, unpublished data).

Plate 16, figure 4

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The above dimensions are generally smaller than those found by Riedel (1958) in Antarctic sediments. This difference supports Bjorklund's (1974) conclusion that there are two forms of this general type i.e., one boreal-arctic and one antiboreal-antarctic. See Remarks 2 below.

REMARKS

1. Petrushevskaya (1975) and Bjorklund (1977) believe that forms of this general type with 3 concentric shells are growth stages of similar forms having a fourth spherical or ellipsoidal shell with an opening at one pole. Bjorklund (personal communication) is in favor of making such forms cogeneric (Actinomma) and dividing them at the species level. This is centainly a useful approach for the purpose of counting morphologically distinct entities and for that reason it is followed herein, for the most part. However, forms with a pylome presently belong to the Family Prunoidea rather than the Family Actinommidae and it would be inappropriate to make major, undocumented taxonomic changes herein. There is a further difficulty in moving this particular species to the genus Actinomma in that the specific name antarcticum is preoccupied.

2. Bjorklund (1974) concludes that there is a boreal-arctic form of this general type (Cromyechinus borealis) and an antiboreal-antarctic form (Cromyechinus antarctica in Bjorklund's paper).

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RECENT DISTRIBUTION

1. Riedel, 1958 "This species, first described from the southern Indian Ocean, occurs in both the American and Indian Ocean sectors of antarctic waters. A rather similar form, which may belong to the same species, occurs in the northern Pacific-the material at present available is however insufficient for accurate identification of the northern form. No form resembling P. antarctica has been found in the tropical parts of the Pacific or Indian Oceans. Thus this species may possibly be restricted to high northern and southern latitudes."

2. Benson, 1966 (Sphaeropyle langii Dreyer, p. 166); "..rare at all stations where it is present...". It is uncertain whether or not this species is conspecific with P. antarctica.

3. Sachs, 1973, Code 3I; "Infrequent and very patchy, loads on Polar factor."

4. Molina-Cruz, 1975, Code S8 (Cromyechinus antarctica); used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S8 at each station.

5. Robertson, 1975; "Only those specimens which were ellipsoidal and had an outermost shell with a pylome were counted. The descriptions of Riedel (1958) and Petrushevskaya (1967) were followed although additional work is needed to determine if the forms described by Petrushevskaya which have spines should be included in this species..."This species loads most heavily in factors 3 (transitional) and 1 (subpolar). Its greatest abundances at the present and 18,000 Y.B.P. are in the northern-most part of the northwest Pacific."