Moulting of jaws of recent Eunicida (Annelida, Polychaeta) has not been definitely proved
so far. It is undoubted that pharate jaws (two or more jaws one inside the other
according to "cone in cone" principle, known since Ordovician to Devonian, show that
casting of jaws took place in Palaeozoic placognath eunicids (Kielan-Jaworowska Z.,
Palaeont. Pol. 16, 1966, Mierzejewski P., Acta Palaeont. Pol., 1978). This paper presents
initial investigations on pharate jaws using TEM method.

Material and methods. Double polipharate jaws of Mochtyella fragilis Szaniawski em.
Mierzejewski and Gen. et sp. indet. ("parataxonomic species"  Cheiridogenys sp.). The
material was etched from Ordovician erratic pebbles with hydrochloric acid, embedded in
Epon 812, cut on Tesla BS490A ultramicrotome and observed on a Tesla BS 500 electron
microscope. The studies were carried out in the Electron Microscopy Laboratories of the
M. Nencki Institute of Experimental Biology (Pol. Acad. Sci.) and the Institute of Botany
(Warsaw University).

Results and discussion. Single jaws making up the pharate jaw of Mochtyella fragilis show
on cross section identical ultrastructure as the jaws of
Mochtyella cristata (vide:
Mierzejewska G. and Mierzejewski P., Annals Med. Sect. Pol. Acad. Sci. 21, 99-100,
1975).  The jaws composing the pharate jaw are rather firmly packed. There is an
occacsional contact (continuity?) between some of them (Fig. 1, c, x 15,500). In the
present state of investigations it is difficult to say whether this contact is of primary
character, or the result of diagenetic processes. The growth of gaps between jaws is
observed on the level of main ridge. In peripheral parts of jaws  losses of tissue from
ventral side have been found (Fig. 1, arrows). Especially notable subsidences were
observed in Gen. et sp. indet. The jaw N of this double polipharate jaw is thin and
corresponds only to the outer part of the jaw N+1 (Fig. 2, x 9,000). Matrix from the pulp
cavity shows clearly desintegration, especially strongly marked in the oldest jaw (jaw N).
The youngest jaw (jaw N+2) is not shown on the presented electron micrograph. Tha black
streak (bs) is the remnant after the evaporation of the specimen with gold for the SEM
 The described subsidences of tissues suggest the possibility of enzyme activity
digesting the ventral parts of jaws during the moulting process. Possible proof of this
suggestion would make moulting of Palaeozoic eunicid jaws very close to the apolysis of the
arthropod cuticle. This problem requires, however, some further investigation.

Piotr Mierzejewski and Grazyna Mierzejewska

Acta Medica Polona  1977,18, 4, 347-348
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Edited by

Piotr Mierzejewski, the Count of Calmont and Countess Maja A. Korwin-Kossakowska