Portal of Graptolites and Pterobranchs
Dietmar Andres's  (1976) dissertation on pterobranchs and primitive graptolites:

Graptolithen aus ordovizischen Geschieben und die fruhe Stammesgeschichte der Graptolithen

The results confirm KOZLOWSKI's statement of near phylogenetic
relationship of the recent pterobranch
Rhabdopleura and the

1.   Sutures of periderm of some primitive Ordovician graptolites and
of the recent pterobranch
Rhabdopleura are similar. The
similarities extend to structures lacking obvious adaptative features.

2.   Like
Rhabdopleura the graptolites possessed one pair of arms.

3.   The described primitve graptolites are probably little modified
descendants of Cambrian graptolites.

4.   The ancestors of the described primitive graptolites were sessile
and creeping.

5.   The described primitive graptolites display features implying a
nearer phylogenetic relationship with
Rhabdopleura than all more
modern graptolites.
Rhabdopleura is a "living fossil",; similar forms
must have existed already in the Cambrian and should have been
the ancestors of primitive graptolites.

6.   Suggestions regarding cortex-formation:
The observed
ribbon-like cortex elements conform to movements of
the cortex secreting cephalic shields of the graptolite individuals
creeping outside their tubes. The ribbon like cortex elements are
thinner and less regular arranged than the fuselli. The increase in
thickness of the cortex is due to a similar process as has been
observed in
Cephalodiscus. To build the cortex no soft tissue
existed on the outside of the fuselli. Hence cortex formation does
not imply a principal difference between graptolites and
This dissertation was published
independently as:

Andres, D. 1977. Graptolithen aus
ordovizischen Gechieben und die
fruhe Stammesgeschicht der
Graptolithen -
(51, 1/2, 52-93).

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Graptolites and pterobranchs
Sztandary Mierzejewski