Back
Avellodinium culmula
Avellodinium culmulum, (Norris, 1965), Davey, 1982
Now Dichadogonyaulax. Originally Gonyaulax, subsequently (and now) Dichadogonyaulax, thirdly Ctenidodinium, fourthly Avellodinium. Lentin and Williams (1985, p.105) and Benson (1985, p.152) retained this species in Dichadogonyaulax.
Holotype: Norris, 1965, figs.8-9
Age: Portlandian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Norris, 1965]:
Diagnosis:
Midbody spheroidal to ovoid with fields disposed according to the following scheme: 3', 6", 6"', 1p, 1"". Both field and girdle borders ornamented with regularly spaced, long, stout processes with briefly bifurcate distal ends whose branches are oriented at right angles to the length of the border. Girdle distinctly spiralled, ends separated by an undivided, undepressed, ventral area. Shell of organic material, thick, complex, consisting of a thin inner layer and a fibrous, infrapunctate, thicker outer layer. Outer layer gives rise to the spines.
Epithecal archeopyle usually developed.
Description:
Midbody spheroidal, slightly longer than broad or broader than long; equatorial section circular to slightly oval. Both epitheca and hypotheca broadly rounded.
Precingular fields approximately equidimensional, except 3", which may be smaller.
Postcingular fields always relatively larger except 1"', which is always smaller. Posterior intercalary field situated close to the posterior end of the ventral area, bounded by 1"', 2"', 6"', and 1"".
Antapical field large, 20 µm to 30 µm in diameter.
Processes on field and girdle borders fairly regularly spaced, 7 µm to 10 µm long and 3 µm apart. Bases 1 µm to 2 µm wide, occasionally confluent either only at the base or almost along the entire length to the distal ends. The bifid tips, oriented transversely to the rows of processes, have a total span of 3 µm to 6 µm and are reflexed almost at right angles to the trunks of the processes (Fig. 2). The bases of the processes have a radially striated appearance owing to the encroachment of elongated punctations from the shell surface, but the remainder of the trunk is apparently unperforated, tapering to the simple, closed, pointed, bifid tips.
Girdle 5 µm wide, usually not distinctly separated into fields; anteriorposterior separation varying between 1 and 2 girdle widths; lateral separation 10 µm to 15 µm. Ventral area not depressed, but the ventral side is flattened in equatorial sections.
Total shell thickness varying from 0.75 µm to 1.75 µm; inner shell layer usually less than 0.5 µm, frequently indistinct; outer layer usually about 1 µm composed of a loose mass of fibres which give rise to the processes and in surface view have an irregularly infrapunctate to microreticulate appearance. It is difficult to determine whether the outer layer is a single layer of fibrils separated from the inner layer by a cavity or whether it consists of a thick, loosely bound, fibrilar matt.
Margin of epithecal archeopyle clean-cut, not coinciding with field boundaries, almost always developed at a constant distance of 1 µm to 2 µm forward of the anterior girdle border. Operculum integral, consisting of 9 fields (1'-3' and 1"-6"), attached, hinging on the ventral area. Opening of the archeopyle starts on the dorsal surface. The margin of the archeopyle is always shown by a slender line indicating incipient separation. The most posteriorly placed process in most of the rows delimiting the precingular fields is not connected by a basal ridge to the anterior girdle border. The archeopyle margin runs through the gap thus created. The wall may be thinner in this region of archeopyle development.
Dimensions:
Midbody apex to antapex - 36 µm to 47 µm (holotype 36 µm). Equatorial diameter - 37 µm to 50 µm (holotype 40 µm).
Remarks:
Gonyaulax culmula is distinctive on account of its complex shell, transversely oriented tips of the processes, and epithecal archeopyle. It is so far known only from one sample from the Okusensis zone (Portlandian) of the Isle of Portland.
Now Dichadogonyaulax. Originally Gonyaulax, subsequently (and now) Dichadogonyaulax, thirdly Ctenidodinium, fourthly Avellodinium. Lentin and Williams (1985, p.105) and Benson (1985, p.152) retained this species in Dichadogonyaulax.
Holotype: Norris, 1965, figs.8-9
Age: Portlandian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Norris, 1965]:
Diagnosis:
Midbody spheroidal to ovoid with fields disposed according to the following scheme: 3', 6", 6"', 1p, 1"". Both field and girdle borders ornamented with regularly spaced, long, stout processes with briefly bifurcate distal ends whose branches are oriented at right angles to the length of the border. Girdle distinctly spiralled, ends separated by an undivided, undepressed, ventral area. Shell of organic material, thick, complex, consisting of a thin inner layer and a fibrous, infrapunctate, thicker outer layer. Outer layer gives rise to the spines.
Epithecal archeopyle usually developed.
Description:
Midbody spheroidal, slightly longer than broad or broader than long; equatorial section circular to slightly oval. Both epitheca and hypotheca broadly rounded.
Precingular fields approximately equidimensional, except 3", which may be smaller.
Postcingular fields always relatively larger except 1"', which is always smaller. Posterior intercalary field situated close to the posterior end of the ventral area, bounded by 1"', 2"', 6"', and 1"".
Antapical field large, 20 µm to 30 µm in diameter.
Processes on field and girdle borders fairly regularly spaced, 7 µm to 10 µm long and 3 µm apart. Bases 1 µm to 2 µm wide, occasionally confluent either only at the base or almost along the entire length to the distal ends. The bifid tips, oriented transversely to the rows of processes, have a total span of 3 µm to 6 µm and are reflexed almost at right angles to the trunks of the processes (Fig. 2). The bases of the processes have a radially striated appearance owing to the encroachment of elongated punctations from the shell surface, but the remainder of the trunk is apparently unperforated, tapering to the simple, closed, pointed, bifid tips.
Girdle 5 µm wide, usually not distinctly separated into fields; anteriorposterior separation varying between 1 and 2 girdle widths; lateral separation 10 µm to 15 µm. Ventral area not depressed, but the ventral side is flattened in equatorial sections.
Total shell thickness varying from 0.75 µm to 1.75 µm; inner shell layer usually less than 0.5 µm, frequently indistinct; outer layer usually about 1 µm composed of a loose mass of fibres which give rise to the processes and in surface view have an irregularly infrapunctate to microreticulate appearance. It is difficult to determine whether the outer layer is a single layer of fibrils separated from the inner layer by a cavity or whether it consists of a thick, loosely bound, fibrilar matt.
Margin of epithecal archeopyle clean-cut, not coinciding with field boundaries, almost always developed at a constant distance of 1 µm to 2 µm forward of the anterior girdle border. Operculum integral, consisting of 9 fields (1'-3' and 1"-6"), attached, hinging on the ventral area. Opening of the archeopyle starts on the dorsal surface. The margin of the archeopyle is always shown by a slender line indicating incipient separation. The most posteriorly placed process in most of the rows delimiting the precingular fields is not connected by a basal ridge to the anterior girdle border. The archeopyle margin runs through the gap thus created. The wall may be thinner in this region of archeopyle development.
Dimensions:
Midbody apex to antapex - 36 µm to 47 µm (holotype 36 µm). Equatorial diameter - 37 µm to 50 µm (holotype 40 µm).
Remarks:
Gonyaulax culmula is distinctive on account of its complex shell, transversely oriented tips of the processes, and epithecal archeopyle. It is so far known only from one sample from the Okusensis zone (Portlandian) of the Isle of Portland.