THE HOLOTHURIOIDEA COLLECTED BY THE VELERO 



HI DURING THE YEARS 1932 to 1938 



Part I, Dendrochirota 



(Plates 10-30) 

 Elisabeth Deichmann 



Introduction 



The Panamic region, that is, the stretch of coast which extends from 

 Cerros Island on the western coast of Lower California and southward 

 (including the entire Gulf of California) to Ecuador (with the Galapa- 

 gos Islands) and Peru, forms zoogeographically a natural unit. As far as 

 holothurians are concerned, it has been almost unknown, undoubtedly 

 because the coast in most localities is so exposed that many species live at a 

 greater depth than in other places, as, for example, in the more sheltered 

 bays and coves of the West Indies. 



The study of the fauna has tempted zoologists for many years, and as 

 early as 1866 Verrill began to compile lists of Echinoderms and Coelen- 

 terates from east and west of Central America. The purpose was chiefly 

 to accumulate data to show the relation of the two faunas to each other. 

 It was Alexander Agassiz's idea that, since so many foi-ms, especially 

 Echinoderms, in the two areas were closely related, one had here a chance 

 to study the effect of separation, or isolation, on the origin of new species, 

 since it was almost certain that the two faunas had once been identical — 

 before the isthmus had been formed. Verrill's lists included 7 species from 

 the Panamic region; of these, 3 are Dendrochirotes. Since then a few 

 more have been described by various workers. The general impression 

 gained was merely that the holothurian fauna was extremely poor and 

 showed some affinities to that of the West Indian seas. It is only recently 

 that the Allan Hancock Expeditions with the Velero III have been able 

 to explode this myth and show that the holothurian fauna actually is as 

 rich as that of the West Indies. During the past six years the Velero III 

 has made extensive collections in the Panamic region and particularly 

 dredgings in that zone hitherto so sadly neglected, between 10-100 

 fathoms. Almost all the species hitherto described from the region during 

 the last hundred years have been secured and in addition a large number 

 of new species. Thanks to the thorough and methodical way in which 



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