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Lithodinia araneosa
Lithodinia araneosa Muir and Sarjeant, 1978, p.197-198, pl.1, fig.1; text-fig.1.
Holotype: Muir and Sarjeant, 1978, pl.1, fig.1; text-fig.1.
Originally (and now) Meiourogonyaulax, subsequently Lithodinia, thirdly Lithodinia?. This species is here retained in Meiourogonyaulax following the retention of the genus by Riding and Helby (2001d, p.81,83).
Age: Mid Callovian.
Original description (Muir and Sarjaent, 1978)
Derivation of name: Latin, araneosus, full of webs; with reference to the patterning on the plate-areas.
Diagnosis: Cyst very broadly spheroidal to almost subpolygonal. Form of the apex (lacking in all specimens seen) not known; antapex slightly to markedly flattened. Tabulation: ?5', ?0a, 6", 6c, 6'", lp, lpv, 1'"'. Cingulum moderately broad, slightly laevorotatory; sulcus very broad, occupying only the central part of the ventral surface, and divided into at least four plate-areas. Crests of moderate height, consisting of low ridges giving rise to irregular projections or spines of variable length and degree of proximal interlinkage; these spines may be blunt or acuminate, simple or bifid, with or without distal capitation, branching or anastomosis. The entire surface of the phragma exhibits an intricate reticulation, the mesh sizes and shapes being highly variable.
Holotype: Specimen HY756/5/12, slide GMUS Pd. 12, lodged in the collections of the Dept. of Geological Sciences, University of Saskatchewan, Saskatoon, Canada. Type locality and horizon: Langdale Beds (Middle Callovian; E. coronatum Zone), 2.7 m below the base of the Hackness Rock, Hackness Quarry,Yorkshire.
Description: In all specimens seen, the apex was lacking as a result of archaeopyle formation. The angularity of the margin of the archaeopyle suggests that five plates bounded the precingular series anteriorly, but it is of course possible that these may have been anterior circle (or intercalary) plates rather than apicals. The size of the portion of the cyst lost indeed supports this latter hypothesis; and it is noteworthy that the six precingular plate-areas, of which 3" is the largest, are all broad and rather short. The rather ragged edge of the archaeopyle suggests the partial retention of a crest bounding the lost plate areas,but it may well in fact merely be an extension of the surface reticulation. The cingulum forms a weak laevorotatory spiral whose two ends differ in
antero-posterior position by slightly less than the (moderate) cingulum breadth. The sulcus extends for similar distances onto epitract and hypotract and is quite broad. Cingulum, sulcus and plate-areas are all bounded by crests. Because of the elaborate patterning of raised ridges forming the surface reticulation, these crests are only readily perceived at the margins; however, on close study at high magnifications (and especially under phase- and
Nomarski interference-contrast), their pattern may with difficulty be determined.The crests each consist of a low, irregular flange from which arises a series of outgrowths varying from simple acuminate or bifurcating spines to
angular or quadrate projections. These outgrowths may be linked together proximally, distally or at intermediate levels by crest extensions or very short trabeculae. The height of the complete crest (including outgrowths) is only
moderate, much lower than in several other species of this genus. The hypotract exhibits the tabulation typical of gonyaulacoid cysts, with plate-area 1 '" the smallest of six precingulars, a large posterior intercalary plate-area, and an antapical plate-area of moderate size. Unusual are the large, almost bean-shaped posterior ventral plate-area and the transverse division of the sulcus into four (or more?) plate-areas. It must be stressed, however, that
the crests crossing the sulcus are low and can be perceived only under phase or Nomarski interference-contrast illumination; the identification of their pattern should not, therefore, be considered an essential criterion in the
recognition of this species.
Dimensions: Holotype: length (apex lacking) 56 µm, breadth 62 µm, height of crests variable up to 6 µm. Range: Length 42--70 µm (mean 57.5 µm), breadth 49--63 µm (mean 57.5 µm), maximum height of crests 4--8 µm
(mean 5.5 µm). Material: 20 specimens.
Remarks: Only one relatively coarsely reticulate species of Meiourogonyaulax has been reported to date -- M. deflandrei Sarjeant, 1968, from the Upper Callovian of France. However, ~n earlier species, M. callomonii Sarjeant, 1972 (as yet known only from the Up'per Bathonian of Jameson Land, Greenland) exhibits a fine surface reticulation, visible under phase contrast illumination. The species here described, Meiourogonyaulax araneosa, occurs at an intermediate horizon and may well be a descendent of the latter and an ancestor of the former. It resembles M. callomonii quite closely in overall tabulation, differing in the subdivision of the sulcus, the lesser height and greater complexity of the crests, and the much coarser reticulation. It resembles M. deflandrei in reticulation and basic tabulation but is proportionately broader, with the midventral area not much sunken and consistently ornamented; its sulcus is broader and less long, the posterior ventral plate-area larger, and six
postcingulars are present instead of five.
Holotype: Muir and Sarjeant, 1978, pl.1, fig.1; text-fig.1.
Originally (and now) Meiourogonyaulax, subsequently Lithodinia, thirdly Lithodinia?. This species is here retained in Meiourogonyaulax following the retention of the genus by Riding and Helby (2001d, p.81,83).
Age: Mid Callovian.
Original description (Muir and Sarjaent, 1978)
Derivation of name: Latin, araneosus, full of webs; with reference to the patterning on the plate-areas.
Diagnosis: Cyst very broadly spheroidal to almost subpolygonal. Form of the apex (lacking in all specimens seen) not known; antapex slightly to markedly flattened. Tabulation: ?5', ?0a, 6", 6c, 6'", lp, lpv, 1'"'. Cingulum moderately broad, slightly laevorotatory; sulcus very broad, occupying only the central part of the ventral surface, and divided into at least four plate-areas. Crests of moderate height, consisting of low ridges giving rise to irregular projections or spines of variable length and degree of proximal interlinkage; these spines may be blunt or acuminate, simple or bifid, with or without distal capitation, branching or anastomosis. The entire surface of the phragma exhibits an intricate reticulation, the mesh sizes and shapes being highly variable.
Holotype: Specimen HY756/5/12, slide GMUS Pd. 12, lodged in the collections of the Dept. of Geological Sciences, University of Saskatchewan, Saskatoon, Canada. Type locality and horizon: Langdale Beds (Middle Callovian; E. coronatum Zone), 2.7 m below the base of the Hackness Rock, Hackness Quarry,Yorkshire.
Description: In all specimens seen, the apex was lacking as a result of archaeopyle formation. The angularity of the margin of the archaeopyle suggests that five plates bounded the precingular series anteriorly, but it is of course possible that these may have been anterior circle (or intercalary) plates rather than apicals. The size of the portion of the cyst lost indeed supports this latter hypothesis; and it is noteworthy that the six precingular plate-areas, of which 3" is the largest, are all broad and rather short. The rather ragged edge of the archaeopyle suggests the partial retention of a crest bounding the lost plate areas,but it may well in fact merely be an extension of the surface reticulation. The cingulum forms a weak laevorotatory spiral whose two ends differ in
antero-posterior position by slightly less than the (moderate) cingulum breadth. The sulcus extends for similar distances onto epitract and hypotract and is quite broad. Cingulum, sulcus and plate-areas are all bounded by crests. Because of the elaborate patterning of raised ridges forming the surface reticulation, these crests are only readily perceived at the margins; however, on close study at high magnifications (and especially under phase- and
Nomarski interference-contrast), their pattern may with difficulty be determined.The crests each consist of a low, irregular flange from which arises a series of outgrowths varying from simple acuminate or bifurcating spines to
angular or quadrate projections. These outgrowths may be linked together proximally, distally or at intermediate levels by crest extensions or very short trabeculae. The height of the complete crest (including outgrowths) is only
moderate, much lower than in several other species of this genus. The hypotract exhibits the tabulation typical of gonyaulacoid cysts, with plate-area 1 '" the smallest of six precingulars, a large posterior intercalary plate-area, and an antapical plate-area of moderate size. Unusual are the large, almost bean-shaped posterior ventral plate-area and the transverse division of the sulcus into four (or more?) plate-areas. It must be stressed, however, that
the crests crossing the sulcus are low and can be perceived only under phase or Nomarski interference-contrast illumination; the identification of their pattern should not, therefore, be considered an essential criterion in the
recognition of this species.
Dimensions: Holotype: length (apex lacking) 56 µm, breadth 62 µm, height of crests variable up to 6 µm. Range: Length 42--70 µm (mean 57.5 µm), breadth 49--63 µm (mean 57.5 µm), maximum height of crests 4--8 µm
(mean 5.5 µm). Material: 20 specimens.
Remarks: Only one relatively coarsely reticulate species of Meiourogonyaulax has been reported to date -- M. deflandrei Sarjeant, 1968, from the Upper Callovian of France. However, ~n earlier species, M. callomonii Sarjeant, 1972 (as yet known only from the Up'per Bathonian of Jameson Land, Greenland) exhibits a fine surface reticulation, visible under phase contrast illumination. The species here described, Meiourogonyaulax araneosa, occurs at an intermediate horizon and may well be a descendent of the latter and an ancestor of the former. It resembles M. callomonii quite closely in overall tabulation, differing in the subdivision of the sulcus, the lesser height and greater complexity of the crests, and the much coarser reticulation. It resembles M. deflandrei in reticulation and basic tabulation but is proportionately broader, with the midventral area not much sunken and consistently ornamented; its sulcus is broader and less long, the posterior ventral plate-area larger, and six
postcingulars are present instead of five.