Description - Add description
The four primary spines with the ventral, sagittal one. All five protrude as single spikes, the dorsal one, A, down on the thorax, the ventral, sagittal one in the neck stricture, the one marked D, on the cephalis as an apical spine.
The lower part of this latter spine is inside the wall of the cephalis, while it a little higher up runs in the very wall. It is therefore no genuine columella.
There is also an axial spine, as in the other species here mentioned of the Cyrtoidea group. This axial spine starts as usual from the ventral end of the central rod, in the interior of the lattice shell, a little below the neck stricture, and is in elder individuals of Helotholus histricosa divided in two.
The thorax is broadly campanulate, nearly semispherical.
The ventral sagittal spine about equal in strength to the others and is directed a little upwards. The primary, lateral spines are nearly horizontal, bent slightly downwards; they protrude at the neck stricture, rather far up. The dorsal spine, A, is directed downwards and pierces the thorax rather far down.
Only the dorsal spine, A, runs for a short distance in the very wall of the thorax, the others pierce only the wall.
The cephalis is semispherical, or a little higher, in cross section circular. The thorax is broadly campanulate.
The pores are irregular in shape and size, most of them being roundish or oblong, smallest on the cephalis (1-16µ), largest on the thorax, especially down below on young individuals. Here the brim of the thorax is furnished with numerous, irregularly placed, short spines, which are not true byspines, but only the walls of meshes which are not yet developed.
On the cephalis and thorax, narrow needle shaped byspines are scattered, the longest being about equal in length to the diameter of the cephalis.
I have not seen any individuals which could be supposed to be fully developed. The species does not answer well to any of Haeckel’s genera. From the genus Lithomelissa, as I have understood it in the species L. setosa, there are such important differences that it does not seem reasonable to place these two forms in the same genus. It might rather be united with the following species. I have not, however, done so, more especially as the definition of Haeckel’s genus Dictyophimus requires that there should be three thoracic ribs which are lengthened out to “basal feet”, and this definition may at a pinch be made to apply to the two following species, but not at all to Helotholus histricosa.
Rather rare, sparse, in deep water samples.
Distribution: Seems also to be a boreal, oceanic species.
|Benson, 1966, p. 459-464; pl. 31, figs. 4-5, 7-8, (not fig. 6):|
Helotholus histricosa Jørgensen
Helotholus histricosa Jørgensen, 1905, Bergens Mus. Skrifter, p. 137, Pl. 16, figs. 86-88.
?Dictyophimus histricosus Jørgensen, 1905, op. cit., p. 138, Pl. 16, fig. 89.
Test broad, conical, with generally a broadly rounded, partially to completely hidden cephalis, in most tests separated from the thorax by an indistinct stricture but in many tests no stricture present. In tests with a definite stricture the pores of the cephalis are small, subcircular, unequal; in tests with a completely hidden cephalis which is more or less broadly rounded and cap-shaped, the pores are much larger and similar to the thoracic pores. Pores of the thorax relatively large, increase in size distally, with variable shape, size, and arrangement but generally irregular, in a few tests subhexagonally arranged. Basal margin of thorax incomplete, with numerous, thin, conical spines representing incipient intervening bars. Surface of cephalis and thorax varies from completely smooth, particularly in tests with a completely hidden cephalis, to spinose with thin, conical spines of variable length (5-75 µm) scattered over the surface. A large, complete or incomplete, collar ring consists of the two apical-lateral arches and in most tests of the ventral arch and is represented by a distinct, relatively heavy, continuous rib at the proximal limit of the thorax. The median bar is below the ring, well within the interior of the thorax. Apical bar cylindrical, its proximal portion a columella, its distal portion a dorsal rib of the cephalis; it extends nearly vertically as a relatively long, generally conical, heavy apical horn. Vertical bar long, cylindrical, heavy, extends as a horizontal or slightly downward curved, conical, vertical spine. Primary lateral bars long, heavy, cylindrical, in several specimens nearly perpendicular to the median bar, extend horizontally or slightly upward joining the thoracic wall at the collar ring and continuing as conical spines which are generally collinear with them. Dorsal bar long, heavy, cylindrical, descends dorsally, pierces the wall of the thorax and extends as a relatively heavy, conical spine, collinear with it. The four collar pores are relatively large; cardinal pores are of type B. Most tests characterized by a long axial spine with arborescent branches distally; in several tests the spine is absent, either broken or not developed.
Measurements; based on 30 specimens from stations 60, 115, 133, and 151: length of cephalis (its top to collar stricture if latter is evident) 16-30 µm; breadth of cephalis 25-39 µm; maximum length of test 80-189 µm; maximum breadth of test 95-248 µm; length of apical horn 6-70 µm, of vertical spine 12-74 µm, of dorsal and primary lateral spines 5-80 µm.
Remarks. Specimens from the Gulf that are identified as Helotholus histricosa Jørgenson are of two general types. The first includes tests with a partially hidden cephalis and a discernible but indistinct collar stricture (Pl. 31, figs. 4-5). These forms generally have numerous spines but a few are relatively smooth. In nearly all specimens the arborescent axial spine is present or traces of it are distinguishable. The second type includes tests with a completely hidden cephalis that consists of a broadly rounded, cap-like structure with relatively large pores (Pl. 31, figs. 6-8). The tests are generally smooth with large thoracic pores, but a few tests have scattered spines arising from the surface. The first type conforms to figure 86a of Jørgensen's (1905, Pl. 16) illustration of H. histricosa; the second type is more like his figure 87a (loc. cit.). Both types, however, are characterized by the large collar pores separated by the long, heavy, primary lateral, vertical, dorsal, and median bars. The first type, however, generally has the long axial spine, but the second type has a shorter one, although in a few tests this structure was observed with distal arborescent branches. Whether or not the two types mentioned above represent a single species or two separate species must await further study. Due to the unfavorable orientation of specimens in permanent slides, many of their structures could not be observed. At present it is best to consider this species as a species-group. The distribution of both types in the Gulf, however, is nearly identical, a fact which may indicate that the two should be considered as a single species.
A few specimens tentatively identified as Helotholus histricosa Jørgensen have dorsal and primary lateral ribs in the thoracic wall. These extend as terminal feet or foot-like spines (Pl. 31, fig. 6). They more or less conform to Jørgensen's illustration of Dictyophimus histricosus Jørgensen (1905, Pl. 16, fig. 89). However, they may be variant forms of D. gracilipes Bailey from the Gulf. Study of Jørgensen's type material should settle the question whether or not D. histricosus is synonymous with Helotholus histricosa.
Riedel (1958, pp. 234-235, Pl. 3, fig. 8; text-fig. 6) described and illustrated a species from the Antarctic that he identified as Helotholus histricosa Jørgensen. This species, however, has a much more distinct cephalis than either Jørgensen's species or the Gulf species. The thorax is more nearly cylindrical, not broadly conical and resembles species of the genus Lithomelissa. He apparently based his identification of the Antarctic forms on Popofsky's illustrations of forms he identified as Helotholus histricosa Jørgensen (Poposky, 1909, pp. 279-281, Pl. 32, figs. 1-5; Pl. 36, fig. 2). Riedel placed Popofsky's species as well as Helotholus histricosa micropora Popofsky (1909, p. 282, Pl. 33, figs. 2, 3) and H. longus Popofsky (1909, pp. 282-283, Pl. 34, fig. 2) in synonymy witti H. histricosa Jørgensen. Only two of Popofsky's illustrations of H. histricosa Jørgensen (Popofsky, 1909, Pl. 32, figs. 1, 3) approach any degree of similarity either to the Gulf species or Jørgensen's species. Riedel's and Popofsky's concepts of H. histricosa Jørgensen are similar but differ from Jørgensen's and mine. Their species should be given a new name, but further study is needed on this highly variable group of species.
Distribution. The distribution in the Gulf of the two forms of this species or species-group as discussed above is similar; therefore, the counts at each station for both forms are combined. This group is cosmopolitan in the Gulf but has a greater frequency in the northern half of the Gulf. It is absent at stations 27, 90, 130, 194, 203, and 214. It is common at stations 81, 91, 93, 106, 115, 133, 136, 151, 184, and 208 and rare at all others. Most of the stations where it is common are located within or near the diatomite facies; therefore, the increased frequency of this group in the northern half of the Gulf is the result of upwelling. This group may respond to upwelling near stations 81, 91, and 93 in the southern half of the Gulf. South of station 81 and at marginal stations throughout the Gulf this species-group is very rare or absent. It is apparently an oceanic group whose greater frequency in the northern Gulf is the result of upwelling but may be in part the result of its tolerance of waters with higher than average temperature and salinity.
Riedel (1958, p. 235) states that no closely similar form of his species has been found in the tropical Indian Ocean nor in the tropical or northern Pacific, and only Jørgensen's (1905) record of its occurrence in Norwegian waters indicates its bipolar distribution. Because the Gulf species is identified with Jøgensen's species, not Riedel's or Popofsky's, it is apparently a cosmopolitan species, present in the eastern tropical Pacific and the North Atlantic. Further taxonomic study is needed before a definite statement concerning its world-wide distribution can be made.