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