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Phormostichoartus corbula (Harting, 1863)

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Lithocampe corbula

Lengte 130 mmm. Drie geledingen, de achterste half holvormig, de beide andere bijna cylindrisch, met op dwarse rijen geplaalste kleine vierhockige openingen.
Harting 1863
Benson, 1966, p. 513-517; pl. 35, figs. 5-8; text-fig. 27:

Siphocampium cf. polyzona Haeckel

?Tricolocampe polyzona Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 1412, Pl. 66, fig. 19; Riedel, 1953, Journal of Paleontology, vol. 27, no. 6, p. 812, Pl. 85, fig. 1.
?Tricolocampe stenozona Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 1413, Pl. 66, fig. 20.
?Siphocampium sp. Riedel, 1958, B.A.N.Z.A.R.E. Repts., ser. B, vol. 6, pt. 10, pp. 243-244, Pl. 4, figs. 9, 10; text fig. 12.

Cylindrical to spindle-shaped test with four joints of unequal size. Main part of cephalis subspherical, its dorsal face covered by a pronounced dorsal lobe; a relatively long but inconspicuous ventral tubule extends from its ventral face and adheres to the upper ventral surface of the thorax (text-fig. 27A). The presence of the dorsal lobe and ventral tube makes it difficult to distinguish the cephalis from the thorax; in side view the cephalis appears cap-shaped and merges with the outline of the thorax on its dorsal and ventral sides; in dorsal or ventral view the cephalis appears subconical or cap-shaped with a slight stricture between it and the thorax. Pores of the cephalis small, subequal, circular, to subcircular. Apical spine generally absent but in a few tests it is a short, stout, triangular, inconspicuous, three-bladed spine which extends from the apical bar in the dorsal wall of the main subspherical part of the cephalis; the dorsal lobe barely distinguishable from the main part of the cephalis and covers the jugular pores. Vertical spine barely distinguishable; as seen in apical view (text-fig. 27C) it projects as a short spine into the proximal part of the interior of the ventral tube. Ventral tube hyaline, subcylindrical, but of greater diameter proximally with a change of contour to a cylindrical distal portion of smaller diameter. Six collar pores defined by the dorsal, secondary lateral, primary lateral and vertical bars which originate from a non-horizontal (ventrally descending) median bar (text-fig. 27B); dorsal and primary and secondary lateral bars either terminate at the collar ring or extend a short distance as inconspicuous ribs in the thoracic wall; in a few specimens the ribs prolonged as short spines. Thorax campanulate to truncate-conical, with 3-5 transverse rows of subequal, sibcircular to subrectangular pores. Thorax separated from the first abdominal joint, which is slightly longer, by a distinct stricture coincident with a continuous internal septal ring. First abdominal joint subcylindrical to truncate-conical, slightly broader at its base with 6-10 transverse rows of subpolygona1 (subrectangular) to subcircular pores which are smaller than those of the thorax; this joint separated from second abdominal joint by a disinct stricture coincident with an internal septal ring. Second abdominal joint 2-3 times longer than the first, generally the broadest joint, subcylindrical but broader proximally than distally, with a definite constricted mouth at its base, in most specimens, with a hyaline peristome having a few, short, terminal thorns or spines; with 8-17 transverse rows of pores similar to those of the first abdominal joint. No specimens were observed with more than four joints.

Measurements; based on 30 specimens from stations 27 and 34: maximum length of test 111-166 Ám; maximum breadth 55-71 Ám; length of cephalis 15-21 Ám, of thorax 18-31 Ám, of first abdominal joint 23-42 Ám, of second abdominal joint 49-100 Ám; breadth of cephalis (including dorsal lobe in some specimens) 18-31 Ám, of thorax (maximum) 39-57 Ám, of first abdominal joint (maximum) 52-66 Ám, of second abdominal joint (maximum) 55-71 Ám, of basal mouth 37- 43 Ám; length of ventral tube 9-19 Ám, of hyaline peristome (17 specimens) 2-14 Ám.

Remarks. This species is tentatively identified as Tricolocampe polyzona Haeckel, although Haeckel (1887, p. 1412) does not discuss or illustrate a subspherical cephalis with a dorsal lobe and ventral tube. If study of his type material reveals the presence of these structures his species is identical with the Gulf species and should be placed within Siphocampium Haeckel. T. stenozona differs from T. polyzona in the presence of a thinner wall, a wider basal mouth, and a slightly different proportion of the joints. All these features are of intraspecific variation in the Gulf species and are not of taxonomic significance; therefore, T. stenozona is conspecific with T. polyyzona. Riedel (1953, p. 812) identified some late Tertiary forms from the island of Rotti as T. polyzona but did not observe the cephalis. From Antarctic sediments Riedel (1958, pp. 243-244) described a species of Siphocampium Haeckel that agrees well with the Gulf species in details of the collar pores, cephalis, and ventral tube but differs in the apparent lack of internal septal rings separating the joints and in the presence of a fifth or even a sixth joint in some specimens. No Gulf specimens were observed with more than four joints although the fourth joint in some tests is incomplete; the fourth joint in complete specimens consistently has a constricted mouth and in most specimens a hyaline peristome.
A few of Popofsky's illustrations of Lithamphora furcaspiculata Popofsky (1909, pp. 295-296; 1913, pp. 408-412) are identical or nearly identical with this species but differ in the presence of long axial spines, a feature not observed in the Gulf species. In
his publication of 1909, figure 6 of plate 36 resembles the Gulf specimens. In his 1913 publication only two of his ten text figures resemble the Gulf species, namely 138 and 139.

Distribution. This species is rare but nearly cosmopolitan in the Gulf. It is present as far north as stations 191 and 192 but is absent at station 194 and all those to the north as well as at stations 90, 99, and 130. In the northern half of the Gulf, except for station 184, it is confined to stations located within the diatomite facies. Its presence in this region of the Gulf may be a function of upwelling, but its low frequency prohibits a definite statement regarding this. Its absence nearshore and in the northern shelf region of the Gulf indicates its preference for more nearly oceanic offshore waters.
This species may be cosmopolitan because forms resembling if not identical with it are present at all latitudes. Further taxonomic study is needed before analysis of its world-wide distribution can be made.
Benson 1966


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