Back
Wanaea lacuna
From Fensome et al., 2019:
Wanaea lacuna Riding and Helby, 2001b, p.39,41, figs.3A–L.
Holotype: Riding and Helby, 2001b, fig.3J.
Age: late Bathonian.
---------------------------------------------------------------------------------------------------
Originall description (Riding & Helby, 2001b):
Wanaea lacuna sp.nov. (Figs 3A-L)
Previous Australian usage
M.P. 1016 – Helby.
Description: A smooth cavate species of Wanaea intermediate is size and lacking a posterior paracingular flange and with a subconical hypocyst which has an antapical horn or protuberance. The short , broad antapical horn is slightly inclined and is blunt and rounded distally. A hemispherical epicyst is present. The endophragm is approximately 0.5 µm thick; the periphragm is markedly thinner; both the cyst layers are irregularly smooth to microscabrate. This species is hypocave to circumcavate; the two wall layers are consistently separated in the antapical region. There is a distinct paraphragmal antapical horn developed but no corresponding protuberance on the endocyst. Most specimens are cornucavate. Occasionally, the endophragm and periphragm are slightly separated in the lateral and apical areas, therefore ranging to bicavate and circumcavate organization. No unequivocal parasutural features are present. On the ventral side, the parasulcus is marked by a narrow, shallow concavity or depression. The smooth principal endoarcheopyle and periarcheopyle sutures are interpreted as being immediately anterior of the anterior paracingular parasuture; the simple operculum is generally attached ventrally.
Dimensions (µm, n=45): Min.(Mean)Max.
Length of the entire cyst: 65 (80) 96
Length of the epicyst: 12 (21) 40
Length of the hypocyst (incl. paracingulum): 35 (61) 75
Equatorial width of the hypocyst (in lateral view): 56 (70) 99
Length of antapical horn: 5 (9) 15
Width of the antapical horn (at midpoint): 5 (9) 13
Length of pericoel excl. at antapex: 1 (4) 13
The measured specimens are from conventional core samples in Sunrise-2 well at 2122.33m, 2122.25m and 2122.05m.
Comments: This species of Wanaea s distinguished by being cavate. The principal area where the endophragm is separated from the periphragm is at, and adjacent to, the antapical horn. Most specimens are therefore hypocavate, however the cavation style is somewhat variable and bicavate, circumcavate and cornucavate forms have also been observed. Wall separation in the lateral regional and in the epicyst is minor. No definite indications of paratabulation were observed, however occasional discontinuous low ridges which may represent parasutures are present. The fact that there is no ridge, crest or flange at the paracingulum is unusual of Wanaea even the ‘energlynioid’ species such as Wanaea acollaris Dodekova 1975 have paracingular ridges or rims (Woollam, 1982, p. 47). The endophragm and periphragm are both susceptible to folding as a result of compression and this leads to the formation of arcuate folds. The epicyst is distinctly hemispherical and lacks horns or protrusions. Few specimens were observed where the epicyst is absent and many opercula were inly slightly displaced. The lack of paracingular features and the frequent retention of the operculum in this species may make the differentiation of the epicyst and hypocyst difficult in some specimens.
Comparison: The only other species of this genus which is cavate is Wanaea cornucavata. However, that species is ornamented, has a trabeculate paracingular flange, is partially paratabulate and has a flat, lid-like epicyst (Feist-Burkhardth & Pross, 1999). Wanaea enoda is closely similar, smooth-walled, acingulate, epicystaly domes Wanaea but lacks cavate wall organization. Wanaea indotata like W lacuna, lacks parasutural features, however the former is acavate and has a prominent paracingular rim.
Derivation of name: From the Latin lacuna, meaning cavity or hollow and referring to the cavate cyst organization of this species.
Holotype and type locality: Figure 3J, CPC 35859, from conventional core, Sunrise-2 well at 2122.25m
Statigraphical distribution: Wanaea lacuna is Bathonian, from the middle subzone (7ciaii) of the Wanaea verrucosa Zone (Figs 11, 12; Foster, this volume; Helby & Partridge, in prep.)
Wanaea lacuna Riding and Helby, 2001b, p.39,41, figs.3A–L.
Holotype: Riding and Helby, 2001b, fig.3J.
Age: late Bathonian.
---------------------------------------------------------------------------------------------------
Originall description (Riding & Helby, 2001b):
Wanaea lacuna sp.nov. (Figs 3A-L)
Previous Australian usage
M.P. 1016 – Helby.
Description: A smooth cavate species of Wanaea intermediate is size and lacking a posterior paracingular flange and with a subconical hypocyst which has an antapical horn or protuberance. The short , broad antapical horn is slightly inclined and is blunt and rounded distally. A hemispherical epicyst is present. The endophragm is approximately 0.5 µm thick; the periphragm is markedly thinner; both the cyst layers are irregularly smooth to microscabrate. This species is hypocave to circumcavate; the two wall layers are consistently separated in the antapical region. There is a distinct paraphragmal antapical horn developed but no corresponding protuberance on the endocyst. Most specimens are cornucavate. Occasionally, the endophragm and periphragm are slightly separated in the lateral and apical areas, therefore ranging to bicavate and circumcavate organization. No unequivocal parasutural features are present. On the ventral side, the parasulcus is marked by a narrow, shallow concavity or depression. The smooth principal endoarcheopyle and periarcheopyle sutures are interpreted as being immediately anterior of the anterior paracingular parasuture; the simple operculum is generally attached ventrally.
Dimensions (µm, n=45): Min.(Mean)Max.
Length of the entire cyst: 65 (80) 96
Length of the epicyst: 12 (21) 40
Length of the hypocyst (incl. paracingulum): 35 (61) 75
Equatorial width of the hypocyst (in lateral view): 56 (70) 99
Length of antapical horn: 5 (9) 15
Width of the antapical horn (at midpoint): 5 (9) 13
Length of pericoel excl. at antapex: 1 (4) 13
The measured specimens are from conventional core samples in Sunrise-2 well at 2122.33m, 2122.25m and 2122.05m.
Comments: This species of Wanaea s distinguished by being cavate. The principal area where the endophragm is separated from the periphragm is at, and adjacent to, the antapical horn. Most specimens are therefore hypocavate, however the cavation style is somewhat variable and bicavate, circumcavate and cornucavate forms have also been observed. Wall separation in the lateral regional and in the epicyst is minor. No definite indications of paratabulation were observed, however occasional discontinuous low ridges which may represent parasutures are present. The fact that there is no ridge, crest or flange at the paracingulum is unusual of Wanaea even the ‘energlynioid’ species such as Wanaea acollaris Dodekova 1975 have paracingular ridges or rims (Woollam, 1982, p. 47). The endophragm and periphragm are both susceptible to folding as a result of compression and this leads to the formation of arcuate folds. The epicyst is distinctly hemispherical and lacks horns or protrusions. Few specimens were observed where the epicyst is absent and many opercula were inly slightly displaced. The lack of paracingular features and the frequent retention of the operculum in this species may make the differentiation of the epicyst and hypocyst difficult in some specimens.
Comparison: The only other species of this genus which is cavate is Wanaea cornucavata. However, that species is ornamented, has a trabeculate paracingular flange, is partially paratabulate and has a flat, lid-like epicyst (Feist-Burkhardth & Pross, 1999). Wanaea enoda is closely similar, smooth-walled, acingulate, epicystaly domes Wanaea but lacks cavate wall organization. Wanaea indotata like W lacuna, lacks parasutural features, however the former is acavate and has a prominent paracingular rim.
Derivation of name: From the Latin lacuna, meaning cavity or hollow and referring to the cavate cyst organization of this species.
Holotype and type locality: Figure 3J, CPC 35859, from conventional core, Sunrise-2 well at 2122.25m
Statigraphical distribution: Wanaea lacuna is Bathonian, from the middle subzone (7ciaii) of the Wanaea verrucosa Zone (Figs 11, 12; Foster, this volume; Helby & Partridge, in prep.)