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Les Didemnidae (Prochordata) d'Helgoland

The didemnidae (prochordata) of helgoland

Abstract

This paper is part of a systematic reconsideration of the family Didemnidae. Two SCUBA-diving series (October 1970, June 1971) have been carried out at the island of Helgoland (North Sea), in order to recaptureDidemnum helgolandicum Michaelsen, 1921. Two species of Didemnidae have been sampled. They represent a new combination of the four species quoted in the literature to occur near Helgoland. The first of these species,Didemnum maculosum (Milne Edwards 1841), is abundant and also present all along the french coasts.Didemnum helgolandicum Michaelsen, 1921 is synonymus with this species, whereasD. helgolandicum sensuCarlisle, 1954, represents a different species:Didemnum coriaceum (von Drasche 1883). Furthermore, it was erroneous to considerD. maculosum as synonymous withD. candidum Savigny, 1816 which is a distinct species with a different distribution. The description ofDiplosoma migrans (Menker &Ax 1970) shows that this species is mobil but normally adapted to the benthic mode of life. Up to now it had been confused withD. listerianum (Milne Edwards 1841). The mesopsammic speciesArenadiplosoma migrans differs from the benthic species only by the reduction in size of the zooids (expressing an adaptation to interstitial life). This difference does not seem sufficient to justify a separation at the specific or generic level. The mesopsammic species should be considered as a form derived from the benthic species, and adapted to interstitial life.

Resume

1. Deux séries de plongées à Helgoland, localité-type de la Mer du Nord, ont permis à l'auteur de récolter deux espèces de Didemnidae:Didemnum maculosum Milne Edwards, 1841 etDiplosoma migrans (Menker &Ax 1970), nouvelle combinaison des quatre espèces signalées dans la littérature concernant cette île.

2. La redescription de la première espèce conduit: (a) à séparer trois espèces confondues jusqu'ici:Didemnum maculosum Milne Edwards, 1841,Didemnum coriaceum (Von Drasche 1883) etDidemnum candidum Savigny, 1816; (b) à établir une synonymie nouvelle entreD. helgolandicum Michaelsen, 1921 etD. maculosum.

3. La description d'unDiplosoma benthique mobile, permet de penser: (a) que l'espèce mésopsammique:Arenadiplosoma migrans Menker &Ax, 1970 n'est qu'une forme dérivée de l'espèce précédente et adaptée à la vie interstitielle; (b) que ceDiplosoma benthique, mobile, avait été confondu jusqu'ici avecDiplosoma listerianum (Milne Edwards 1841).

Literature citee

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Lafargue, F. Les Didemnidae (Prochordata) d'Helgoland. Helgolander Wiss. Meeresunters 23, 100–116 (1972). https://doi.org/10.1007/BF01616312

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  • DOI: https://doi.org/10.1007/BF01616312