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|Shell biconvex-discoidal, consisting of a spiny disc of spongy structure which is in some (fully developed ?) individuals surrounded by a lenticular lattice-shell. Spongy disc thickened in its central portion (a quarter to a half of its total diameter), with numerous acicular or acutely conical spines of different lengths around its circumference and in most specimens also on the two surfaces, particularly on the thickened central portion. When present, the enclosing lenticular lattice-shell is apparently in contact with the spongy disc at or near its circumference, but it is separated by a distinct space from its two surfaces. In most specimens, the spines arising from the thickened central part of the spongy disc penetrate the lattice-shell. The lattice-shell has an uneven surface, with subcircular or circular pores of varying sizes, the diameters of which are a half to ten times as great as the breadth of the intervening bars.|
Dimensions: Diameter of shell 195-465 micrometer. Length of free parts of spines on circumference 5-170 micrometer (often about 70 micrometer).
|Benson, 1966, p. 218-219; pl. 11, fig. 4; text-fig. 16: |
Spongotrochus cf. glacialis Popofsky
?Spongotrochus glacialis Popofsky, 1908, Deutsche Südpolar-Exped., vol. 10, pp. 228-229, Pl. 26, fig. 8, Pl. 27, fig. 1, Pl. 28, fig. 2.
Test circular in outline, spongy-appearing, with a thick, biconvex, circular central region surrounded by a thinner flattened margin; with a variable number (5-30 or more) of cylindrical to conical radial spines arising from both surfaces as well as from the margin of the disc and continuous within the test as radial beams which do not reach the center. Internal structure of central biconvex region consisting of several closely and equally spaced, concentric, discoidal shells; flattened margin of test consisting of several concentric and closely spaced latticed rings between the two parallel latticed plates of the margin; the latticed plates cover the central area as well as the margin but are not distinct from the inner shells (these relationships illustrated in text-fig. 16). Radial spines of variable number and state of development, but their inward continuations as beams are generally visible.
Measurements; based on 30 specimens from stations 27, 46, and 81: diameter of disc 111-332 µm, of central dark area 43-123 µm; length of radial spines 6-86 µm.
Remarks. Because of Popofsky's poor illustrations of Spongotrochus glacialis the Gulf species is only tentatively identified with it. S. brevispinus Haeckel (1862, p. 462, P1. 27, figs. 4, 5) differs from the Gulf species in the presence of more and shorter, more nearly equal radial spines and in the lack of a distinctly biconvex central region. No specimens conforming to Riedel's (1958, pp. 227-228, P1. 2, figs. 1, 2, text fig. 1) concept of S. glacialis were observed from the Gulf. Riedel states that in fully developed forms an outer lenticular lattice-shell is present in contact with the spongy disc at or near its circumference but separated by a distinct space from its two surfaces. No rudimentary structures of this shell were observed on the radial spines of the Gulf specimens. No specimens were observed with short, stout spines as in the majority of specimens Riedel studied.
Distribution. This species is rare but cosmopolitan in the Gulf. It is absent at stations 90, 130, 136, 194, 203, 206, 208, and 214. Its highest frequency (1.4%) was recorded from station 64 located in a region of upwelling off the Mexican mainland. Throughout the remainder of the Gulf it is very rare and undergoes no significant changes in frequency. It is of more general occurrence in the southern half of the Gulf than in the northern half and, therefore, is more nearly oceanic.
Due to the uncertain taxonomic relationships of this species and others similar to it, little can be stated about its world-wide distribution. If later studies reveal its inclusion in Riedel's concept of S. glacialis, it then would have a cosmopolitan distribution, occurring in the Antarctic as well as in the tropical Pacific and Indian Oceans.
|Spongy skeleton in form of biconvex lens. Its structure examined in detail by Riedel: inner disk of dense spongy tissue encircled above and below by finer and looser spongy tissue. Surface of shell in adult specimens covered by porous simple mantle. Formation of a mantel in skeletons possessing spongy structure (in our material in Spongurus pylomaticus, Spongodiscus (?) osculosus, and Spongotrochus glacialis) is the result of the growth of spongy tissue, i.e. it signifies the growth of the skeleton. In these species the mantel is very thin, somewhat differentiated in its structure from the basic spongy tissue. Usually mantel developed only in central part, absent near margins, impression created that shell is covered by two caps or hoods. Mantle fused to main spongy tissue of disk. |
Numerous radial needle of various length and thickness. Needles faceted and expanded at base, extending fairly deeply into shell in form of radial pieces. These pieces laid down at the same time as the basic spongy tissue, constantly growing thicker with the growth of shell. Radial needles extending outside both around equator of shell and along entire surface. Strongest needles about 12 in number, distributed on margin of disk, not less than five stout needles are on each flattened side of shell. Space of spongy tissue observed on surface of disk as pores, of approximately same size as in Spongodiscus (?) setosus. Pores on mantle more regular and smaller. In adult large specimens marked pylome usually present, in form of funnel in spongy tissue, running through radius to center. Presence of pylome not remarked by Riedel; actually, it is noted in less than one-third of all specimens encountered.
Dimensions: diameter of disk (in adult specimens with mantle) 270-500 micrometer, diameter of spaces at margin of disk 8-12 micrometer, in center of disk about 5 micrometer, diameter of pores on porous plates of mantle 2-5 micrometer. Needles usually broken off more or less near to base, but even needles known to be incomplete are up to 200 micrometer long, thickness of needle at base up to 30 micrometer.
|...it is difficult to differentiate Spongopyle osculosa from Spongotrochus glacialis without its characteristic mantle and pylome...|