Sicula of a crustoid? graptolite
The single finding of a sicula assigned to the Order
Crustoidea (Class Graptolithoidea) was reported by
Kozłowski (1971) from an Ordovician erratic
boulder found in Poland. However, affiliation of this
form to crustoid graptolites seems highly probable.
This microfossil may correspond to the 'embryonal
vesicle' of a
Rhabdopleura-like form as well as to
tuboid or camaroid graptolites.
    
    The unusual sicula, consisting of prosicula and an
incipient metasicula, measures about 0.3 mm.
Sicula of ?Crustoidea: A upper face, B profile, C
inferior face. Abbreviations: as - attachment face of
prosicula, m - marginal membrane, ms - metasicula, x-
x - boundary between prosicula and metasicula.
From
Kozłowski
.
Source:
Kozłowski, R. 1971. Early development stages and the mode
of life of graptolites.
Acta Palaeontologica Polonica 16, 4, 313-
343.
A
B
C