Siculae of tuboid graptolites
The siculae of the Tuboidea are composed of bottle shaped or vesicular prosicula and tubular
metasicula. They attached themselves to the substratum by a wide basal surface or basal disc.The sicula
of
Epigraptus represent a primitive condition, strongly resembling the 'embryonal vesicle' of
Rhabdopleura. A more advance stage is represented by the sicula of Kozlowskitubus.
Epigraptus sp. (=Idiotubus sp.). Sicula, profile view. Glacial
boulder, Ordovician, Baltic Coast.

d - dorsal apertural process (fragmental), m - marginal
membrane, ms - metasicula, ps - prosicula, v - ventral process.
Kozlowskitubus erraticus (Kozlowski, 1963). A.
sicula (attachment surface damaged). B.
diagrammatic illustration of central part of
thecorhiza. Glacial boulder, Ordovician, Poland,
Vistula Valley.

d - diaphragms, h - trace of helicoidal line, ps -
prostolon, si - base of prosicula, st - thecal stolon, ss
-stolothecal stolon, t - thecae.
Source:

Kozlowski, R. 1971. Early development stages and the mode of
life of graptolites. -
Acta Palaeontologica Polonica 16, 4,
313-343.
A
B