Description - Add description
Shell thin-walled, papillate with obliterated collar stricture. Length of the two joints=2:7, breadth=3:5. Cephalic hemispherical, with small, circular pores. Thorax slenderly ovate, with larger, subregular, circular pores, separated by oblique series of conical papillae. Mouth with a broad, hyaline peristome (the “third articulus” of Ehrenberg), separated by a stricture from the little broader thorax.
Dimensions: Cephalis 0.02 long, 0.03 broad; thorax 0.07 long, 0.05 broad.
Cephalis approximately hemispherical, with small subcircular pores in a hyaline shell-wall, set off from thorax by a pronounced change in contour. Many specimens have a small, inconspicuous lateral tubule projecting slightly from the cephalis near its junction with the thorax, and a short, acute apical horn. Thorax ovate, usually with a rough surface, and with a conspicuous subcylindrical or flared peristome surrounding the mouth which is approximately one-half to two-thirds as broad as the thorax. Thoracic pores subcircular to circular, usually of different sizes and without regular arrangement, separated by rather wide and often thick intervening bars. In the upper part of the thoracic wall are three, usually conspicuous longitudinal ribs, which in many specimens terminate in three short, solid, triangular lateral wings at or about the level at which the thorax reaches its maximum breadth. Length of cephalis 18-25 ì, of thorax (including peristome) 60-90 ì. Maximum breadth of thorax 58-70 ì.
|Benson, 1966, p. 439-441; pl. 29, fig. 13:|
Dictyocephalus mediterraneus Haeckel
Dictyocephalus mediterraneus Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 1307, Pl. 62, fig. 2.
Dictyocephalus australis Haecke1, 1887, Challenger Rept., Zool., vol. 18, p. 1306, Pl. 62, fig. 2.
Cephalis cap-shaped, with a small, inconspicuous, dorsal lobe that covers the jugular pores of the collar ring; smooth with small circular pores; separated from a generally smooth, ovate or spindle-shaped thorax by a distinct change in contour. Six collar pores present in most specimens. Apical bar a rib in the dorsal cephalic face which is covered by a small, latticed, dorsal lobe; extends vertically as a short, conical apical spine in some tests; vertical bar extends as a short spine into a short, inconspicuous, hyaline, ventral tubule which is absent in a few specimens; dorsal and primary lateral bars continue for a short distance in the thoracic wall as ribs, raised in a few specimens, in several tests terminating in short spines. Pores of thorax circular, increasing in size distally, separated by heavy intervening bars, arranged hexagonally in longitudinal rows (7-8 on half the circumference), with hexagonal frames present in a few specimens. Mouth of thorax constricted, with a thick, long, lamellar, hyaline peristome generally without terminal teeth but in a few tests with as many as eight, large, triangular teeth which either extend vertically or are convergent inward.
Measurements; based on 13 specimens from station 27: length of test (including peristome) 95-123 µm, of cephalis 17-22 µm, of apical. spine (generally unobservable) 2-6 µm, of hyaline peristome 12-21 µm; breadth of cephalis 25-28 µm, of thorax (maximum) 62-77 µm.
Remarks. Dictyocephalus australis Haeckel differs from D. mediterraneus Haeckel only in the presence of double-contoured thoracic pores. This feature was observed in one specimen from the Gulf and, therefore, is subject to intraspecific variation.
D. mediterraneus differs from an Antarctic species identified by Riedel (1958, pp. 236-238) as D. papillosus (Ehrenberg) in the more regular hexagonal arrangement of pores in vertical rows, a less rough thoracic surface, and less conspicuous primary lateral and dorsal, raised, longitudinal thoracic ribs. Because Riedel's original material, was not examined, synonymy of D. mediterraneus with D. papillosus is not proposed, but they may be the same species.
Distribution. In the Gulf this species is very rare and occurs only as far north as station 136. It is absent at stations 64, 90, 95, 130, 133, 151, and all those to the north. It is, therefore, an oceanic species with little affinity for Gulf waters and does not respond to upwelling in the southern Gulf.
Riedel (1958, p. 238) states that D. papillosus is probably cosmopolitan, occurring in Antarctic waters, tropical parts of the Indian and Pacific Oceans and in the northern Pacific. D. mediterraneus was reported by Haeckel from the Mediterranean Sea and D. australis from the east coast of Australia, in both localities from near the surface. If the Gulf species is the same as Riedel's species it is an apparently cosmopolitan species; otherwise, it is widespread only in Recent tropical seas.