Report on the Hydroida collected during the Exploration of the Gulf Stream by L F de Poutalès

Abstract

THIS report forms No. 2, vol. ii. of the quarto memoirs of the Museum of Comparative Zoology at Harvard College, and has been published by permission of the Superintendent of the United States Coast Survey, and is illustrated by thirty-four plates. It forms one of the most important contributions to the natural history of the hydroids that have appeared of late years, and it describes a very large number of most interesting and new forms. One of the sub-orders of the hydroida is well characterised by having the hydroids quite unprotected—not covered by any external protective receptacle. In this sub-order (Gymnoblastea) but nine species were found in Pourtalès' collection. Although they are all referable to known genera, yet all of them are new. The great bulk of the collection belonged, however, to another sub-order, in which the hydroids are provided with external protective receptacles (hydrotheca), and which is more or less familiar to us as containing the Campanularian and Sertularian forms. Of this sub-order (Calyptoblastea) some fifty-six species are described, and among the Sertularinæ no less than seven new genera are described, with forty-two new species out of a total of forty-three. Among the Campanularinæ two new genera are described, with twelve new species out of a total of thirteen. In addition to these new species there were but seven others which, so far as their identification was possible, were already known as European forms. The collection had been preserved in spirits and was for the most part in excellent preservation. It would seem obvious that the region from which this collection had been obtained, and which includes an area between the Florida Reef on the north and west and Cuba the Salt Key and Bahama Banks on the south and east, is characterised by a very distinct hydroid fauna, and must form part of a special province in the geographical distribution of the Hydroida, though of course further researches may greatly extend the area of the new forms. The greatest depths at which any species had been dredged was 470 fathoms. The collection was rich in the plume-like hydroids (Plumulariadæ). In some genera of this beautiful family of hydroids the ultimate generative zooids which give origin to either the germ or the sperm cells (gonophores) are developed within a horny covering (gonangium), groups of which are often to be found inclosed in most curious basket-like receptacles (corbula). Such basket-like receptacles are well seen in Aglaophenia, and in a new species described as A. bispinosa, they attain a very large size and form most beautiful objects. In this genus the twigs of the cradle are much altered pinnæ which are pressed into a protective service. In one of Dr. Allman's new genera nearly allied to Aglaophenia (Cladocarpus) the groups of gonangia are not inclosed in corbulæ, but are borne on the sides or at the base of special protective branches which are not altered pinnæ but appendages to them. They certainly seem to act the part of corbuæ, and to form very effective organs of defence to the gonangia—though they do not present so effectual a covering as in Aglaophenia. In one magnificent species (Cladocarpus paradised) the stem of which attains a height of fourteen inches, these phylactogonia, as Dr. Allman calls them, are in the form of pinnately-branched offshoots. In another species (Cladocarpus dolichotheca) the stem for nearly the whole of its course carries a longitudinal series of tubular receptacles which contain sarcode in which thread-cells are found. These nematophores, which are situated at short and equal intervals from one another, give to this part of the hydroid colony a very close resemblance to certain forms of graptolites. Elsewhere Dr. Allman has called attention to the close affinity that appears to exist between the so-called denticles of the graptolites and the nematophores in these Plumularian hydroids; and, as we know, that these bodies in the hydroids are not only filled with protoplasm, and that this is capable of developing pseudopodia after the manner of some rhizopods, this might seem to point to a relationship between the graptolites and the rhizopods through some ancestral form in which the affinities looked on the ope side to the hydroids and on the other to the rhizopods, the graptolites having stopped short of the progress which the hydroids were enabled to make.

Report on the Hydroida collected during the Exploration of the Gulf Stream by L. F. de Poutalès.

By G. J. Allman, President of the Linnean Society. (Cambridge, U.S., 1877.)