Pelagic organisms, floating on the surface of the open sea, propelling themselves feebly by the pumping movements of the umbrella produced by contraction of the sub-umbral musculature, and capturing their prey with their tentacles.
Certain that there is no int., pelagic larval form.
On the pelagic mollusc Phyllirrhoe, attached to it by the subumbral surface, and its tentacles have become rudimentary or absent.
The Heteropoda belong to the " pelagic fauna " occurring near the surface in the Mediterranean and great oceans in company with the Pteropoda, the Siphonophorous Hydrozoa, Salpae, Leptocephali, and other specially-modified transparent swimming representatives of various groups of the animal kingdom.
Dr Natterer, the chemist of the " Pola " expeditions, has expressed the opinion that the poverty of the pelagic fauna is solely due to the want of circulation in the depths.
- A great part of the bottom of the Mediterranean is covered with blue muds, frequently with a yellow upper layer containing a considerable proportion of carbonate of lime, chiefly shells of pelagic Foraminifera.
In the shallower tropical waters, especially on the central ridge, considerable areas are covered by Pteropod ooze, a deposit consisting largely of the shells of pelagic molluscs.
Order Procellariiformes.-Well flying, pelagic, nidicolous.
The violent personalities of a pamphlet entitled Marie Joseph Chenier et le prince des critiques (1844), in reply to Jules Janin, brought him a six months' sojourn in La Pelagic, in the cell just quitted by Lamennais.
Fusus, Pyrula, Purpura, Murex, Nassa, Trophon, Voluta, &c. The float of the pelagic Janthina, to which the egg-capsules are attached, probably is also formed by the secretion of the pedal gland.
The odontophore also is remarkably developed, its lateral teeth being mobile, and it serves as an efficient organ for attacking the other pelagic forms on which the Heteropoda prey.
They are true Pectinibranchia which have taken to a pelagic life, and the peculiarities of structure which they exhibit are strictly adaptations consequent upon their changed mode of life.
Shell thin; operculum absent; tentacles bifid; foot secretes a float; pelagic. Janthina.
Pelagic Taenioglossa with foot large and laterally compressed to form a fin.
It is now understood that they are Euthyneurous Gastropods adapted to natatory locomotion and pelagic life.
They are all pelagic, the foot being entirely transformed into a pair of anterior fins; eyes are absent, and the nerve centres are concentrated on the ven tral side of the oesophagus.
They are all pelagic. Fam.
No anterior tentacles, and no dorsal appendages; body laterally compressed, transparent; pelagic. Phyllirhoe.
Body furnished with three pairs of lateral lobes, bearing the tegumentary papillae; foot very narrow; pelagic. Glaucus.
Dorsal papillae with a membranous expansion; male and female apertures at some distance from each other; pelagic. Fiona.
All fishes of the mackerel family are strictly carnivorous; they unceasingly pursue their prey, which consists principally of other fish and pelagic crustaceans.
NEMERTINA, or Nemerteans (Nemertea), a subdivision of worms,' characterized by the ciliation of the skin, the presence of a retractile proboscis, the simple arrangement of the generative apparatus, and in certain cases by a peculiar pelagic larval stage to which the name " pilidium " has been given.
In accordance with these more sedentary habits during the first phases of life, the characteristic pilidium larva, which is so eminently adapted for a pelagic existence, appears to have been reduced to a close-fitting exterior layer of cells, which is stripped off after the definite body-wall of the Nemertine has similarly originated out of four ingrowths from the primary epiblast.
The investigation of the microscopic pelagic life of the sea has also developed to a great extent.
Plankton Expedition, ii., 1897) has described, a few larval brachiopods of undetermined genera, two of which at least were pelagic, or at any rate taken far from the coast.
The larvae usually live in Molluscs, the mature worm in vertebrates, and the immature but metamorphosed Trematode in either host and also in pelagic and littoral marine and fresh-water invertebrates.
The alimentary canal, which may be represented by a vestigial structure, is accordingly not functional, and the larva does not become pelagic. A pyriform organ is present in most Gymnolaemata as well as the sucker by which fixation is effected.
Hemipelagic deposits are a mixture of deposits of terrigenous and pelagic origin.
When the proportion of calcium carbonate in the blue mud is considerable there results a calcareous ooze, which when found on the continental slope and in enclosed seas is largely composed of remains of deep-sea corals and bottom-living foraminif era, pelagic organisms including pteropods being less frequently represented.
Pelagic Deposits (formed in deep water remote from land) B.
Murray and Renard define globigerina ooze as containing at least 30% of calcium carbonate, in which the remains of pelagic (not benthonic) foraminifera predominate and in which remains of pelagic mollusca such as pteropods and heteropods, ostracodes and also coccoliths (minute calcareous algae) may also occur.
This fact, together with the extraordinarily rare occurrence of such remains and meteoric particles in globigerina ooze, although there is no reason to suppose that at any one time they are unequally distributed over the ocean floor, can only be explained on the assumption that the rate of formation of the epilophic deposits through the accumulation of pelagic shells falling from the surface is rapid enough to bury the slowgathering material which remains uncovered on the spaces where the red clay is forming at an almost infinitely slower rate.
Radiolarian ooze was recognized as a distinct deposit and named by Sir ' John Murray on the " Challenger " expedition, but it may be viewed as red clay with an exceptionally large proportion of siliceous organic remains, especially those of the radiolarians which form part of the pelagic plankton.
Animals usually freeliving, pelagic (Giesbrecht and Schmeil).
Free-living (rarely pelagic) or parasitic (Giesbrecht and Schmeil).
He has applied the theory with especial ingenuity to the interpretation of the circular bony plates in the carapace of the aberrant leather-back sea-turtles (Sphargidae) by prefacing an initial land phase, in which the typical armature of land tortoises was acquired, a first marine or pelagic phase, in which this armature was lost, a third littoral or seashore phase, in which a new polygonal armature was acquired, and a fourth resumed or secondary marine phase, in which this polygonal armature began to degenerate.
A medusa with a remarkable habit of life is Mnestra parasites, which is parasitic on the pelagic mollusc Phyllirrhoe, attaching itself to the host by its subumbral surface; its tentacles, no longer required for obtaining food, have become rudimentary.
A, Notholca longispina, lorica only; b, Anuraea aculeata, like the former, a floating pelagic type (plankton proper); c, Synchaeta stylata; corona with accessory antennae and sensory styles; auricles for swimming - an actively swimming pelagic type (nekton); d, Pterodina patina, with bdelloid corona and retractile foot with terminal ciliated cup; e, Distyla gissensis partly extended; f, Rattulus tigris.
Its eggs are buoyant and pelagic and easily recognized.
The negotiations were wrecked upon the question of pelagic sealing.
The United States, nevertheless, insisted that such prohibition was indispensable on the grounds - (t) that pelagic sealing involved the destruction of breeding stock, because it was practically impossible to distinguish between the male and female seal when in the water; (2) that it was unnecessarily wasteful, inasmuch as a large proportion of the seals so killed were lost.
On the other hand, it was contended by Great Britain that in all known cases the extermination of seals had been the result of operations upon land, and had never been caused by sealing exclusively pelagic. The negotiations came to nothing, and the United States fell back upon their claim of right.
On the other hand, pelagic sealing, being a method of promiscuous slaughter, was illegitimate; it was contra bonos mores and analogous to piracy.
On the other hand, Boas and Pelseneer have shown that the Pteropoda have nothing to do with the Cephalopoda, but are Gastropoda modified for a pelagic life; they are therefore now united with the Gastropoda.
Some, like many Cephalopods and the Pteropods, are pelagic or free-swimming; others creep or lie on the sea bottom.
Leuckhart to a small group of transparent and for the most part pelagic organisms, whose position in the animal kingdom is a very isolated one.
The great bulk of the group is pelagic, as the transparent nature of all their tissues indicates.
During the middle ages the Scandinavians were the first to revive geographical science and to practise pelagic navigation.
The Knipovich expedition in 1004 found no traces of organic life below the depth of 220 fathoms except micro-organisms and a single Oligochaete; but above that level there exist abundant evidences of rich pelagic life, more particularly from the surface down to a depth of 80 fathoms.
The families Diatomaceae, Peridiniaceae and Protococcaceae are best represented in the pelagic plankton, while in addition the Volvocaceae are an important element in freshwater plankton.
- Anterior region of two pelagic larvae of A.
Hansen concludes that "they are all typically ground animals, and as yet no species has been taken under such conditions that it could be reckoned to the pelagic plankton."
The hatching of eggs, whether of fresh-water or salt-water fishes, presents no serious difficulties, if suitable apparatus is employed; but the rearing of fry to an advanced stage, without serious losses, is less easy, and in the case of sea-fishes with pelagic eggs, the larvae of which are exceedingly small and tender, is still an unsolved problem, although recent work, carried out at the Plymouth laboratory of the Marine Biological Association, is at least promising.
It is recognized that the great fertility of fishes is nature's provision to meet a high mortality - greater in sea-fishes with minute pelagic eggs than in fresh-water fishes with larger-yolked eggs, partly because of the greater risks of marine pelagic life, and partly because of the greater delicacy of marine larvae at the time of hatching.
They are chiefly pelagic organisms, floating at or near the surface of the water, but occur also at great depths, and are sometimes fixed and sessile in habit.
None has the power of flight, though certain pelagic Copepoda are said to leap from the surface of the sea like flying-fish.
Many of the larger species of Crustacea are used as food by man, the most valuable being the lobster, which is caught in large quantities on both sides of the North Altantic. Perhaps the most important of all Crustacea, however, with respect to the part which they play in the economy of nature, are the minute pelagic Copepoda, of which incalculable myriads form an important constituent of the " plankton " in all the seas of the globe.
As in many other " pelagic " organisms, spines and processes from the surface of the body are often developed, which are probably less important as defensive organs than as aids to flotation.
The walrus is now found mainly far N.; the sea otter, once fairly common throughout the Aleutian district, is now rarely found even on the remoter islands; the fur seal, whose habitat is the Pribilof Islands in Bering Sea, ha .s been considerably reduced in numbers by pelagic hunting.
The egg of the pilchard is very easily distinguished from other pelagic eggs by the unusually large space separating the vitelline membrane from the contained ovum.
- Phyllirhoe bucephala, twice the natural size, a transparent pisciform pelagic Opisthobranch.