N53
Theocalyptra bicornis (Popofsky)
Pterocorys bicornis Popofsky, 1908, p. 228, pl. 34, figs. 7, 8
Theocalyptra bicornis (Popofsky), Riedel, 2958, p. 240, pl. 4, fig. 70, I-VIII.
DESCRIPTION
"Shell conical campanulate, consisting usually of two or three segments. Cephalis subglobose, with numerous small pores, bearing two three-bladed spines of approximately the same length as the cephalis - one vertical, approximately apical, and the other lateral, oblique. Collar stricture slight. Major portion of the shell in most specimens now showing segmental division, and therefore termed the "thorax". Thorax conical proximally, campanulate distally, with subcircular to polygonal pores separated by rather narrow intervening bars. Thoracic pores increase in size distally, and are arranged in usually 9-11 transverse rows. Three short, downwardly directed acicular spines penetrate the wall of the thorax near the collar stricture. In some specimens, there is a marked change in thoracic contour at the position of the rather abrupt transition from subcircular proximal thoracic pores to more regular polygonal distal thoracic pores; it is apparently this change in contour, which in some specimens gives the impression of a segmental division, which Popofsky regarded as a lumbar stricture. In many specimens, one or two rows of pores are marked off from the distal end of the thorax by an internal septal ring; these may be considered to constitute an abdomen.
"... This species differs from T. davisiana principally in more delicate structure and larger thorax." (from Riedel, 1958).
"The specimens found under Antarctic and subantarctic waters are in agreement with the descriptions given by Riedel (1958) and Petrushevskaya (1967). Some specimens are closed below the fourth segment ... but generally the closing plate is missing...
"Other forms are found as constituents of the subtropical assemblage. Some of them are similar to those found by Petrushevskaya (1967) under subtropical and tropical waters of the Indian Ocean. They have essentially the same shape and differ from the southern forms in size... Generally they are closed at the bottom of the third segment but many specimens are found in which only three segments are preserved and the closing plate is missing... Where a fourth segment is present it is represented by one or two rows of pores... The abdominal pores increase distally in size but in some cases the last one or two rows of pores are smaller...
"A variety is found which is distinct enough and has not been previously described... It has a wider abdomen which is separated from the fourth segment by a brim that, where well developed, consists of three rows of small elongated pores. The fourth segment is closed at the bottom and consists of two to four rows of subelliptical to very irregular pores which
Plate 24, fig. 1
N54
are similar to the ones in the sieved flat plate which closes the segment at the bottom. As suggested by Petrushevskaya, the subtropical forms may belong to a different species." (from Lozano, 1974).
This latter form may be the same as Moore's (1974) N36 (see remarks herein).
DIMENSIONS Length of cephalis 15-27 microns, of thorax 80-97 microns; maximum breadth 95-120 microns." (from Riedel, 1958).
"width of cephalis: 22 +\- 3 microns; width of thorax: 84 +\- 13 microns; based on 17 specimens." (from Sachs, 1973).
REMARKS
1. For a more complete synonymy see Riedel (1958, synonymy and notes) and Petrushevskaya (1967). Petrushevskaya (1972, with Kozlova, and 1974) placed this species in the genus Clathrocyclas. The present author prefers to maintain the status quo until a thorough revision of this entire group can be made.*
2. Sachs (1973), Moore (1974) and Molina-Cruz (1975) all placed Halicalyptra? cornuta Bailey, 1856, in synonymy with P. bicornis Popofsky, 1908, without changing the specific name to that of the senior synonym, i.e., cornuta.
3. "Two forms of this highly variable species were distinguished. That form counted under the category N38... is most similar to previous descriptions and illustrations. The form listed under category N36 (Clathrocyclas bicornis in Moore, 1973) is distinguished by the presence of a marked abdominal brim... The N36 category may be more properly placed under Coracalyptra cervus (Ehrenberg) ...;however, Haeckel's (1887, p. 1292) description of this latter species indicated a conical straight-sided thorax and polygonal pores. Neither of these features is typical of N36; therefore this form is considered a variety of Theocalyptra bicornis." (from Moore, 1974).
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*Note that in placing Popofsky's bicornis species in the genus Clathrocyclas, Clathrocyclas bicornis Hays, 1965, becomes a junior homynym and the specific name must be replaced. Petrushevshkaya (1975 and previous Russian language papers) has suggested the name Clathrocyclas antebicornis.
N55
RECENT DISTRIBUTION
1. Sachs, 1973, Code 12N; "Ubiquitous at frequencies to 8% of surface samples. Tends to be concentrated southern and eastern samples."
2. Lozano, 1974, fig. IV-23; "It is present in almost every sample. In nine cores located between 40 degrees E and 61 degrees E and 38 degrees S and 42 degrees S it attains values between 3.9 and 12.9 percent (RC8-44). In none of the other samples, T. bicornis reaches values over three percent. The cause of the abnormal abundance in this restricted area is unknown but it is partially coincident with the area in which C. davisiana is also more abundant. However, T. bicornis does not show the marked changes in the past that are characteristic for C. davisiana. T. bicornis constitutes less than one percent of the total Radiolaria south of the APF but seems to increase in relative abundance in a belt approximately coincident with the APF.
"In the Atlantic Ocean sector there is a decrease in abundance between 40 degrees S and 45 degrees S but there is a general increase to values over two percent in samples north of about 37 degrees S and east of about 30 degrees W. These changes in abundance in the Atlantic Ocean are clearly related with a change in morphology of the specimens (see Taxonomic Notes section). The subtropical forms decrease in abundance to the south as the typical Antarctic forms increase in abundance. In the Indian Ocean the same transition occurs but it seems to take place in a more gradual way. The distinct change in the Atlantic Ocean may be due to the influence of the Aguhlas current. Its distribution for the whole area does not show good correlation with temperature."
3. Molina-Cruz, 1975, Code N38; used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent N38 at each station.
4. Robertson, 1975; The two forms recognized by Moore (1974) were counted together. "This species loads most heavily in factor 3 (transitional). In comparison to the present, at 18,000 YBP the greatest abundances of this species are farther to south and east."
5. Morley, 1977, Fig. I-23; "this species loads highest in factor 3 (gyre margin). At present it is most frequently found in samples from under the subantarctic waters. Although there is a substantial reduction in abundance at 18,000 YBP, the area of maximum concentration is very similar to the present-day pattern."