Back
Hystrichosphaeridium difficile
Hystrichosphaeridium difficile Manum and Cookson 1964
Now Heterosphaeridium. Originally Hystrichosphaeridium, subsequently (and now) Heterosphaeridium. See also Cordosphaeridium? (combination not validly published).
Holotype: Manum and Cookson, pl.3, figs.1-3,7
Locus typicus: Graham Island, Arctic Canada
Stratum typicum: Cenomanian
Original description: Manum and Cookson, 1964, p. 12-13
Shell roughly circular in outline, original shape presumebly spherical, with about 30 appendages evenly distributed on the shell and following no definite pattern. Length of appendages approximately 1/3 to 1/4 of the diameter of the shell. Shell-wall c. 1 Ám thick, finely reticulate in surface view with meshes c. 0.5 Ám across, in profile the muri appear as fine rods and granules resting on an exceedingly thin basal membrane.
The archeopyle is apical and the line of rupture shows V-shaped notches at intervals. The apical portion, which is usually missing, has a slight median
projection.
The appendages are rather constant in length in individual specimens but vary considerably in width from 1 Ám to about 20 Ám. Their general appearance is also variable and their structure difficult to determine. Basically they are tubular and widened at both ends. The distal end is expanded into a more or less everted rim the edge of which is irregularly serrated and sometimes has thread-like extensions which may unite w ith neighbouring appendages. The rims of the slender appendages also tend to unite with those of nearby appendages. The walls of the appendages are perforated to varying degrees. The perforations vary both in size and shape being circular to oval in the terminal expansions and longitudinally elongate and often slit-like in the stalks. More or less distinct lines which proximally may divide and merge with the reticulum of the shell-wall can be observed in the wall of the appendages.
Dimensions: Holotype: diameter of shell 91 Ám, length of appendages c. 25 Ám. Range in shell diameter 58-93 Ám in length of appendages 19-28 Ám.
Affinities:
Manum and Cookson, 1964, p. 13: One of the main diagnostic characters used in the distinction of Hystrichosphaeridium-like forms is the structure of the appendages, namely whether they are tubular or solid, fibrillate or membraneous, and whether thev are arranged on the shell according to any definite pattern.
As far as H. difficile is concerned none of these questions are easy to answer. The medium-sized appendages are definitely tubular, but no decision has been reached regarding the finest ones, and the same applies to some of the widest ones which are often so compressed that their original form is obscured. One feature common to all of the appendages is that their tips are expanded.
The stalks of the appendages of H. difficile appear to be fibrillate under a medium-powered objective (c. 40 x). However, at a high magnification (oil immersion) many of the apparent "fibrils" prove to be narrow individual portions of the wall which are separated from one another by elongate perforations, while some appear to be folds, others, in contrast, seem to be genuine longitudinal thickenings in the wall which, proximally, merge into the reticulum of the shell-wall. In addition, faint and exceedingly fine lines which seem to anastomose can be observed in favourably preserved specimens. The appendages seem to originate from the reticulate layer of the shell-wall.
The number of appendages is difficult to determine accurately, our estimate is approximately thirty. As far as we can tell they do not seem to be arranged according to any definite pattern. As for comparisons with other species H. difficile seems to approach H. inodes as illustrated by Klumpp (1953, pl. 18, fig. 2) in certain respects. The two species agree in number, size, and variability of the appendages, and in their origin from a reticulate outer layer of the shell-wall. However, in H. inodes the appendages seem to be more deeplv subdivided distally and to lack perforations. Recently Eisenack (1963) made H. inodes the type species of a new genus Cordosphaeridium on the strength of the fibrillate and "string-like" construction of the appendages. This character reduces the possibility of a relationship between H. inodes and H. difficile.
The connections between the rims of the appendages in H. difficile are reminiscent of certain species of Cannosphaeropsis (e. g. C. aemula Defl. and C. pulchra Alb., cp. Alberti 1961, pl. 10, figs. 5 and 8), but in H. difficile this feature is far less diagnostic than in Cannosphaeropsis.
Now Heterosphaeridium. Originally Hystrichosphaeridium, subsequently (and now) Heterosphaeridium. See also Cordosphaeridium? (combination not validly published).
Holotype: Manum and Cookson, pl.3, figs.1-3,7
Locus typicus: Graham Island, Arctic Canada
Stratum typicum: Cenomanian
Original description: Manum and Cookson, 1964, p. 12-13
Shell roughly circular in outline, original shape presumebly spherical, with about 30 appendages evenly distributed on the shell and following no definite pattern. Length of appendages approximately 1/3 to 1/4 of the diameter of the shell. Shell-wall c. 1 Ám thick, finely reticulate in surface view with meshes c. 0.5 Ám across, in profile the muri appear as fine rods and granules resting on an exceedingly thin basal membrane.
The archeopyle is apical and the line of rupture shows V-shaped notches at intervals. The apical portion, which is usually missing, has a slight median
projection.
The appendages are rather constant in length in individual specimens but vary considerably in width from 1 Ám to about 20 Ám. Their general appearance is also variable and their structure difficult to determine. Basically they are tubular and widened at both ends. The distal end is expanded into a more or less everted rim the edge of which is irregularly serrated and sometimes has thread-like extensions which may unite w ith neighbouring appendages. The rims of the slender appendages also tend to unite with those of nearby appendages. The walls of the appendages are perforated to varying degrees. The perforations vary both in size and shape being circular to oval in the terminal expansions and longitudinally elongate and often slit-like in the stalks. More or less distinct lines which proximally may divide and merge with the reticulum of the shell-wall can be observed in the wall of the appendages.
Dimensions: Holotype: diameter of shell 91 Ám, length of appendages c. 25 Ám. Range in shell diameter 58-93 Ám in length of appendages 19-28 Ám.
Affinities:
Manum and Cookson, 1964, p. 13: One of the main diagnostic characters used in the distinction of Hystrichosphaeridium-like forms is the structure of the appendages, namely whether they are tubular or solid, fibrillate or membraneous, and whether thev are arranged on the shell according to any definite pattern.
As far as H. difficile is concerned none of these questions are easy to answer. The medium-sized appendages are definitely tubular, but no decision has been reached regarding the finest ones, and the same applies to some of the widest ones which are often so compressed that their original form is obscured. One feature common to all of the appendages is that their tips are expanded.
The stalks of the appendages of H. difficile appear to be fibrillate under a medium-powered objective (c. 40 x). However, at a high magnification (oil immersion) many of the apparent "fibrils" prove to be narrow individual portions of the wall which are separated from one another by elongate perforations, while some appear to be folds, others, in contrast, seem to be genuine longitudinal thickenings in the wall which, proximally, merge into the reticulum of the shell-wall. In addition, faint and exceedingly fine lines which seem to anastomose can be observed in favourably preserved specimens. The appendages seem to originate from the reticulate layer of the shell-wall.
The number of appendages is difficult to determine accurately, our estimate is approximately thirty. As far as we can tell they do not seem to be arranged according to any definite pattern. As for comparisons with other species H. difficile seems to approach H. inodes as illustrated by Klumpp (1953, pl. 18, fig. 2) in certain respects. The two species agree in number, size, and variability of the appendages, and in their origin from a reticulate outer layer of the shell-wall. However, in H. inodes the appendages seem to be more deeplv subdivided distally and to lack perforations. Recently Eisenack (1963) made H. inodes the type species of a new genus Cordosphaeridium on the strength of the fibrillate and "string-like" construction of the appendages. This character reduces the possibility of a relationship between H. inodes and H. difficile.
The connections between the rims of the appendages in H. difficile are reminiscent of certain species of Cannosphaeropsis (e. g. C. aemula Defl. and C. pulchra Alb., cp. Alberti 1961, pl. 10, figs. 5 and 8), but in H. difficile this feature is far less diagnostic than in Cannosphaeropsis.