Conus
academicus (Dall & Ochsner, 1928)
Description:
Shell of
moderate size with an acute apex and slightly concave sides to the spire, with
eight whorls excluding the (lost) nucleus; suture distinct, not channelled or
turreted; surface between the sutures axially sculptured with hardly curved,
close-set incremental lines and very slightly excavated; shoulder rounded,
surface in front of the shoulder two-thirds of the distance towards the
anterior end smooth, slightly convex; the anterior third sculptured with
distant grooves, then interspaces wider and smooth, the grooves becoming closer
and more channelled anteriorly, about four on the body and six or seven more
crowded on the region of the canal; aperture long and narrow, the inner lip
smooth, the canal short, straight, and as wide as the aperture behind and
hardly differentiated from it (1).
Height of shell,
31 mm.; of aperture, 25 mm.; maximum diameter at shoulder, 16 mm.
The fauna of the
Galapagos Islands has been the subject of much discussion. The
islands have been held by some to have been a part of the American continent,
separated by subsidence of a connecting area; others have considered them
to be a permanently isolated group formed by volcanic action
and built from the depths of the ocean by volcanic ejections.
Still another hypothesis is that they form the remnants of an outlying
archipelago of a former Pacific continent now submerged below the sea.
A discussion of the recent fauna by eminent specialists has led to the
conclusion that in large part it is of American derivation, modified by long
isolation. This is especially true of the land animals, while the
marine invertebrates, although predominantly of American affinities, also
include a small proportion of forms now more characteristic of the Pacific
islands to the westward and southward. However, the marine
invertebrate fauna of Clarion Island, one of the nearest to the Galapagos, so
far as yet explored, is of a strictly Indo-Pacific type and presents a
strong contrast to the fauna of the Galapagos(1).
One of the most interesting and important of the discoveries made by the
Academy's Expedition of 1905-1906 was the discovery of fossil Mollusca in
several places.
Formerly it was supposed
that the islands were wholly of volcanic origin, or at least destitute of fossil-bearing sedimentary rocks. The discovery of these not only affords a clue to the
minimum age of the Galapagos group, but also an indication of the sources from
which its fauna has been derived. It is known that about the end of the
Oligocene period, or in the early Miocene, a movement in elevation of the
earth's crust in the Panamic region resulted in the union of the continents of North and South America and the closing of the gap between them
through which the Eocene marine fauna of the north and west shores of
South America had previously extended.
It seems a reasonable
hypothesis that, during the widespread volcanic activity of the Miocene, the
Galapagos group, or its preexisting nucleus, underwent enlargement and
elevation, a process which the discoveries made by the
Academy's expedition show continued, perhaps intermittently, into
Pleistocene time(1).
The characteristics of the fossils collected are, with hardly an
exception, typically American. The faunas are tropical, as might be
expected, but there is nothing of a typical Indo-Pacific nature, although some
of the species belong to groups widely distributed in tropical seas, both
of America and elsewhere(1).
While most of the species belong to groups now represented in the Panamic fauna there are a few which recall forms now existing only on the Antillean side, and quite a number which belong rather to the subdivision of the Panamic fauna now existing in the Gulf of California, than to the warmer waters of the Gulf of Panama. The inference might be drawn from this that at the time the Galapagos fossil forms were living, the temperature of the local seas was somewhat cooler than at present(1).
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Conus
academicus
Pl. 2 fig. 5 mm. 31 x 16 Indefatigable Island, Galapagos Probably Pliocene |
Conus
academicus
Mus. Calif. Acad.
Sci. collected by W. H. Ochsner and Joseph R. Slevin, November 17, 1905, from upper horizon (zone D), on east hore of Indefatigable Island,
Galapagos Group. Probably Pliocene. |
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Conus
academicus
Mus. Calif. Acad.
Sci.
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Conus
academicus
Mus. Calif. Acad.
Sci.
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Bibliografia
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(1) - Dall, W. H., and Ochsner, W. H., 1928. Tertiary and Pliestocene Mollusca from the
Galapagos Islands. Proceedings of the California Academy of Sciences, ser.
4. vol. 17 (4 ): 89 -139