N57

Theocalyptra davisiana (Ehrenberg)

Cycladophora ? davisiana Ehrenberg, 1861, p. 297

Theocalyptra davisiana (Ehrenberg), Riedel, 1958, p. 239, pl. 4, figs. 2, 3 text-fig. 10

Cycladophora davisiana Ehrenberg, Petrushevskaya, 1967, p. 122, pl. 69, I-VII.

DESCRIPTION "Shell conical-campanulate, of moderately heavy structure, consisting of two, three or four segments. Cephalis subglobose, with small, sparse pores, and bearing two short, acicular spines - one vertical, approximately apical, and the other lateral, oblique. Collar stricture slight. Subsequent part of shell, comprising its main bulk, will be termed the thorax, though in some specimens it appears to be divided by an ill-defined internal transverse ridge into an upper and a lower portion. Thorax approximately conical, in many specimens flared at a wider angle distally than proximally. Thoracic pores subcircular proximally, becoming polygonal distally, arranged in usually 4-7 transverse rows which are indefinite in some specimens. In most specimens, three short, downwardly directed acicular spines penetrate the thoracic wall near its junction with the cephalis. In many specimens a further shell-segment is present marked off from the thorax by an internal septal ring. When present, this abdomen is short, truncate-conical, usually flared at a wider angle than the thorax, with usually 2-4 transverse rows of polygonal pores separated by more delicate bars than those of the thorax." (from Riedel, 1958).

DIMENSIONS

"Length of cephalis usually 17-25 microns, of thorax 40-80 microns, of abdomen 15-35 microns. Maximum breadth of shell 70-130 microns." (from Riedel, 1958)

"Length of shell: 91 +\- 16 microns; maximum width of "thorax" (before basal stricture, if any): 66 +\- 7 microns; cephalic width: 23 +\- 2 microns; (15 specimens)" (from Sachs, 1973).

REMARKS

1. For a more complete synonymy see Riedel (1958); for further description see Petrushevskaya (1967).

2. Petrushevskaya (1975) tentatively placed davisiana in the genus Diplocyclas Haeckel and placed bicornis in the genus Clathrocyclas Haeckel. Until the entire group can be studied, further generic manipulation seems only to add to an already confusing situation.

Plate 24, figures 2a,b

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3. Petrushevskaya (1967) distinguished 2 varieties of this species besides the typical one, i.e., Cycladophora divisiana. C. davisiana var. semeloides, C. davisiana var. cornutoides, Lozano (1974) notes:

"Petrushevskaya described this species in detail and distinguished two varieties besides the typical one. All three are found in our samples. The variety semeloides ... is rarely found but it may be present anywhere. Well developed specimens of the typical variety...seem to be more common in samples in which the Antarctic fauna predominates but is found at all latitudes (present in V27-199). The variety cornutoides ... seems to be present at all latitudes in our area.

"In the mixed zone and under subtropical waters, forms with only three segments... of the typical variant seem to be more common along with a variety in which the second segment may have five to six rows of well ordered pores increasing distally in size... This latter form seems to have a subtropical distribution."

Ling et.al. (1971) recognized the variety C. davisiana var. cornutoides and placed it in synonymy with Halicalyptra (?) cornuta Bailey... Ling et. al. note:

"The specimens found in the present Bering Sea study agree with the description given by PETRUSHEVSKAYA (1967), except that we frequently found specimens with longer lateral spines extended beyond the thoracic wall and even branched at the distal ends as illustrated in the figures. Because of the small size, BAILEY's species was not included within her new variety by PETRUSHEVSKAYA, we believe that it is best considered here as within the range of variation. KRUGLIKOVA ... illustrated a similar radiolarian species under the name of Cycladophora (?) cornuta, from core sediments of the North Pacific."

Sachs (1973), Moore (1974) and Molina-Cruz (1975) all placed Halicalyptra cornuta Bailey, 1856, in synonymy with Pterocorys bicornis (Popofsky), 1908 without changing the specific name to that of the senior synonymy, i.e., cornuta.

Petrushevskaya (1975) published the following synonymy with respect to her 1967 varieties, cornutoides and semeloides.

Diplocyclas sp. aff. D. bicorona Haeckel group

Diplocyclas bicorona Haeckel, 1887, p. 159, fig. 8; Petrushevskaya and Kozlova, 1972, p. 540, pl. 33, fig. 17, 18.

Cycladophora davisiana Ehrenberg cornutoides Petrushevskaya, 1967, pl. 70, fig. 1-3.

Cycladophora davisiana Ehrenberg semeloides Petrushevskaya, 1967, pl. 70, fig. 4-7.

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RECENT DISTRIBUTION

1. Benson, 1966; "cosmopolitan in the Gulf [of California] but has a much greater frequency in the southern half of the Gulf."

2. Ling et. al., 1971, Cycladophora davisiana var. cornutoides; "This variety is found commonly in most of the sediments studied. The senior author also noticed that this taxon was found in the central and eastern subarctic Pacific, and thus, it is widely distributed in the middle to higher latitudes of both hemispheres."

3. Sachs, 1973, Code 13N; "... only one form of this general morphology has been recognized. Ubiquitous, with distinct northern tendencies. Maximum frequency in surface sediments 15%."

4. Lozano, 1974, Fig. IV-22 (Cycladophora davisiana); "In chapter II it was shown that C. davisiana was more abundant at different times in the past that anywhere in recent sediments. Its presence in relative amounts over 5.5 percent was considered to be an indication of reworked or older than recent sediments. It is particularly abundant in cores along the western part of the Crozet and to the south in the Atlantic-Indian basins. Although this was tentatively explained by reworking, it seems that for some unknown reason the conditions in the Crozet basin and south of it are favorable for this species. During certain times in the past these conditions were even more favorable and widespread, especially during the last glaciation. Gordon and Goldbert (1970) show a temperature profile (their profile 3) at about 55 degrees E. It differs from the other profiles around Antarctica in the presence of a larger body of water with a temperature between 2 degrees and 30 degrees C which covers a zone about 5 degrees of latitude wide in the surface and more than 10 degrees of latitude wide at a depth of about 500 m. It is possible that this is a favorable type of environment for C. davisiana which is probably a deep living species as discussed in chapter II. The shallowest core we studied (V16-65) was taken at a depth of 1618 m and it has C. davisiana so, at least at the location of that core, it lives at depths shallower than 1618m.

"C. davisiana is found in almost all the samples studied. Its distribution does not show a preferentially latitudinal pattern but its lowest values of relative abundance (one percent or less) occur under subtropical waters."

5. Molina-Cruz, 1975, Code N35 (Cycladophora davisiana); "In this study, it was mostly abundant along the coast in areas of high nutrients content." Used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent N35 at each station.

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6. Robertson, 1975, (Cycladophora davisiana); "...in this study no distinction of these three varieties is made and all forms are counted together... This species loads in factor 4 (Davisiana). At the present this species is most abundant in the northwestern most part of the Pacific and Sea of Okhotsk. At 18,000 YBP its abundances extned well into the northwest Pacific."