Mémoire

Oncomiracidiums et phylogenèse des Monogenea (Plathelminthes)

Deuxième partie : Structures argyrophiles des oncomiracidiums et phylogenèse des Monogenea

Oncomiracidia and phylogenesis of Monogenea (Plathelminths).

Part two: The argyrophilic structures of oncomiracidia and phylogenesis of Monogenea.

Laboratoire de Parasitologie comparée, Université des Sciences et Techniques du Languedoc, place E.-Bataillon, 34060 Montpellier Cedex, France.

Accepté : 2 Janvier 1980

Résumé

Cet article développe les deux derniers chapitres consacrés à l’étude des oncomiracidiums des Monogenea. Ce sont successivement :

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  Les structures argyrophiles des oncomiracidiums (cellules ciliées et chétotaxie). Leur étude met en évidence des plans d’organisation à faible variabilité qui sont importants sur les plans systématiques, phylétiques et biologiques.

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  L’évolution des Monogenea.

Dans ce paragraphe où sont confrontés les données traditionnelles et les résultats obtenus, nous proposons une nouvelle phylogénèse des Monogenea.

Abstract

The ciliated cells and the larval chaetotaxy of 35 species of 16 different families are described for the first time.

A. CILIATED CELLS.

Their study establishes the similarity of the Monopisthocotyleans studied. On the other hand, in Polyopisthocotyleans, we observe a greater diversity: we distinguish three great types corresponding to Polyopisthocotyleans of Teleostei, Hexabothriidae and Polystomatidae.

The comparison of 5 genera of Polystomatidae shows important correlations for the phylogenesis of this family.

The phylogenetic value of the “ciliated cells” as criterion is discussed.

B. CHAETOTAXY.

1. Monopisthocotylea with ciliated oncomiracidium.

In every case, numerous dorsal sensillae are formed in a longitudinal line. We, however, defined two chaetotaxical types:

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  “Dactylogyridea type” which includes Dactylogyridae, Calceostomatidae, Diplec- ianidae, Ancyrocephalidae, Tetraonchidae and Monocotylidae.

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  “The Capsalidea type” defined from Benedenia, Entobdella and Trochopus.

2. Polyopisthocotylea with ciliated oncomiracidium.

Their similarity is remarquable: all have three pairs of dorsal post ocular sensillae. Polystomatidae belong to this group because of their chaetotaxy.

Generally, interspecific and intergenic changes are negligible, even unexisting. As for inter-family variations, they are of little importance.

3. Post larval evolution of chaetotaxy.

In Monopisthocotylea and Polyopisthocotylea, the evolution of chaetotaxy is identical; there are two types of sensillae: those which disappear during the attachment of the oncomiracidium on the host and those which remain and multiply in post larva. Thus there are sensitive deciduous receptors associated to the free stage of the cycle.

4. Monopisthocotylea with non-ciliated oncomiracidium.

In Epicotyle torpedinis and Udonella cligorum, there are no dorsal sensillae which characterize swimming oncomiracidia.

5. Gyrodactylidae.

They have an original chaetotaxy which led us to suggest a new hypothesis on their origins: they would have appeared by a neoteny phenomenon on Monogenean larvae which also are at the origin of Polyopisthocotylea.

6. Discussion.

The data of chaetotaxy are discussed and interpreted in a phyletic perspective of the group.

The importance of data on argyrophil structures stands on two views points:

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  On the phyletic and systematic level because they show simple organisation patterns with low variability, scarcely linked to parasitism (opposed to haptor).

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  The demonstration of sensorial receptors associated to free life leads to biological problems of contamination and infestation of hosts.

EVOLUTION OF MONOGENEA.

We successively develop and discuss the case of Monopisthocotylea, Polystomatidae, Gyrodactylidae, Euzetrema knoepffleri, Monocotylidae and Udonella caligorum.

The patterns of larval organisation defined in the former chapter, from argyrophil structure, are used to set up a phylogenesis of Monogenea.

We distinguish two great phyla: Monopisthocotylea and Polyopisthocotylea. Gyrodactylidae are excluded from Monopisthocotylea (they would descend, according to us, by neoteny, from the ancestral stock at the origin of Polyopisthocotylea).

— Monopisthocotylea include two important groups:

Dactylogyridea (which include Monocotylidae) and Capsalidea. [Euzetrema (and perhaps Iagotrema) represent a different isolated relict family from these two lines].

— Polyopisthocotylea include Polystomatidae, Polyopisthocotylea of Teleostei and Hexabothriidae.

A further study of the argyrophil structures of oncomiracidia should specify the taxo-nomical position of Microbothriidae, Acanthocotylidae, Dionchidae, Chimaericolidae and Diclibothriidae.