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Moorodinium spinatum
Moorodinium spinatum Backhouse, 1988
Holotype:Backhouse, 1988, pl.34, fig.8, text-fig.30E
Locus typicus: Perth Basin, Western Australia
Stratum typicum: Late Thithonian-?earliest Valanginian
Original description: Backhouse, 1988, p.100
Small proximate cysts, ovoid, with a slight preferred lateral orientation. Autophragm membranous, finely granular under SEM. Hypocyst bears narrow spinose parasutural septa. up to 3 Ám high, and intratabular spines, up to 2 Ám high. Observed with SEM, some septa are penitabular in position with a less prominent row of grana in the parallel adjacent penitabular position. Antapical plate bears central cluster of 2 or 3 connected spines; largest up to 5 Ám long. Spines reduced in size in some populations. Septum bordering right side of parasulcus high and prominent. Under SEM, epicystal paratabulation indicated by penitabular rows of discrete or fused grana which enclose pandasutural areas of smaller grana. Epicystal intratabular areas bear isolated grana and rugulae. Epicystal paratabulation arranged around two dorso-ventral ridges which, on some specimens, develop into low narrow septa. These dorso-ventral structures impart a preferred lateral orientation to the cyst. Paratabulation formula not determined, at least 5 and possibly 6 postcingular paraplates and one antapical paraplate indicated by parasutural features on suitably oriented detached hypocysts (Fig. 30F). Paracingulum indicated by prominent transverse septa, not subdivided, 3 to 4 Ám wide, offset 2 to 3 Ám. Parasulcus not usually observed owing to lateral compression; distinguishable on one specimen under SEM (Fig. 30D). Archeopyle combination epicystal, type [tA, tP], operculum often only partly separated; primarily archeopyle suture immediately above anterior transverse paracingular septum.
Dimensions: Length of holotype 54 Ám, width 49 Ám. Range of length of 20 specimens with prominent spines from Dandaragan Trough 36(43)54 Ám, width 32(37)49 Ám. Range of length of 13 specimens with reduced spines from Roe I 44(50)59 Ám, width 37(40)49 Ám.
Affinities:
Backhouse, 1988, p.100: Specimens of M. spinatum with reduced spines possess a longer, more inflated hypocyst than more spinose forms. The two forms are recorded from different sets of samples. The form with reduced spines is present in the Carnac Member in Roe 1, Peel 1. and Artesian Monitoring 7; the spinose form is present in the Carnac Member in Moora Line 3C and 2B, and in Watheroo Line 3. Correlation between all these sections is not possible, but the positions of the two forms within the Carnac Member suggests that the less spinose form occurs stratigraphically below the more spinose form. Moorodinium spinatum is larger than M. simplex and smaller than M. quindalupense. It is further distinguished from M. simplex by possessing paratabulation and from M. quindalupense by possessing spinose septa and a multibranched antapical spine rather than a single long antapical spine.
Holotype:Backhouse, 1988, pl.34, fig.8, text-fig.30E
Locus typicus: Perth Basin, Western Australia
Stratum typicum: Late Thithonian-?earliest Valanginian
Original description: Backhouse, 1988, p.100
Small proximate cysts, ovoid, with a slight preferred lateral orientation. Autophragm membranous, finely granular under SEM. Hypocyst bears narrow spinose parasutural septa. up to 3 Ám high, and intratabular spines, up to 2 Ám high. Observed with SEM, some septa are penitabular in position with a less prominent row of grana in the parallel adjacent penitabular position. Antapical plate bears central cluster of 2 or 3 connected spines; largest up to 5 Ám long. Spines reduced in size in some populations. Septum bordering right side of parasulcus high and prominent. Under SEM, epicystal paratabulation indicated by penitabular rows of discrete or fused grana which enclose pandasutural areas of smaller grana. Epicystal intratabular areas bear isolated grana and rugulae. Epicystal paratabulation arranged around two dorso-ventral ridges which, on some specimens, develop into low narrow septa. These dorso-ventral structures impart a preferred lateral orientation to the cyst. Paratabulation formula not determined, at least 5 and possibly 6 postcingular paraplates and one antapical paraplate indicated by parasutural features on suitably oriented detached hypocysts (Fig. 30F). Paracingulum indicated by prominent transverse septa, not subdivided, 3 to 4 Ám wide, offset 2 to 3 Ám. Parasulcus not usually observed owing to lateral compression; distinguishable on one specimen under SEM (Fig. 30D). Archeopyle combination epicystal, type [tA, tP], operculum often only partly separated; primarily archeopyle suture immediately above anterior transverse paracingular septum.
Dimensions: Length of holotype 54 Ám, width 49 Ám. Range of length of 20 specimens with prominent spines from Dandaragan Trough 36(43)54 Ám, width 32(37)49 Ám. Range of length of 13 specimens with reduced spines from Roe I 44(50)59 Ám, width 37(40)49 Ám.
Affinities:
Backhouse, 1988, p.100: Specimens of M. spinatum with reduced spines possess a longer, more inflated hypocyst than more spinose forms. The two forms are recorded from different sets of samples. The form with reduced spines is present in the Carnac Member in Roe 1, Peel 1. and Artesian Monitoring 7; the spinose form is present in the Carnac Member in Moora Line 3C and 2B, and in Watheroo Line 3. Correlation between all these sections is not possible, but the positions of the two forms within the Carnac Member suggests that the less spinose form occurs stratigraphically below the more spinose form. Moorodinium spinatum is larger than M. simplex and smaller than M. quindalupense. It is further distinguished from M. simplex by possessing paratabulation and from M. quindalupense by possessing spinose septa and a multibranched antapical spine rather than a single long antapical spine.