Aboral Surface Research Articles

INHIBITION OF THE SWIMMING RESPONSE BY FOOD AND OF NEMATOCYST DISCHARGE DURING SWIMMING IN THE SEA ANEMONE STOMPHIA COCCINEA.

ABSTRACT The discharge of tentacular nematocysts in response to food was studied in Stomphia coccinea before and during swimming, and during the period of resettling. The tendency of Stomphia’?, nematocysts to discharge on contact with food virtually disappeared during the swimming response. The disappearance of the nematocyst response coincided with the release of the pedal disk; its reappearance coincided with the re-attachment of the pedal disk. Objects rubbed on the aboral surface of Dermasterias can cause swimming if brought into contact with a single tentacle of Stomphia. A general inhibition of the swimming response to objects rubbed on Dermasterias was set up by flooding the tentacular crown with a food extract. A local inhibition was set up when food was applied to a single tentacle just before the same tentacle was touched with material from Dermasterias. The results are discussed in relation to the view that nematocysts function as independent effectors.

THE FEEDING MECHANISM IN THE SAND DOLLAR MELLITA SEXIESPERFORATA (LESKE)

1. A brief description of Mellita sexiesperforata is given and the process of food collection and defecation are described.2. Sand pushed onto the aboral surface is sorted by club-shaped spines. Fine particles drop down between the spines and are carried round to the oral surface by ciliary currents, thence to the ambulacral grooves. Mucus is probably secreted by the miliary spines on the aboral surface; podia play an accessory role in food gathering.3. Defecation is an intermittent process and feeding stops while it is in progress. Spines and pedicellariae prevent feces from reaching the mouth.

NOTES ON THE BIOLOGY OF THE FIVE-LUNULED SAND DOLLAR

The five-lunuled sand dollar, Mellita quinquiesperforata (Leske, 1778), is abundant on the sand flats at Beaufort, North Carolina, where the following ob servations were made during a short stay in August, 1957, at the Duke Uni versity Marine Laboratory. Burrowing. The animal lives in shallow water in a horizontal position, usually completely covered by a thin layer of sand although sometimes the posterior lunule remains visible. Specimens observed were motionless although the animal can progress under the sand. On being removed and placed on top of the sand under water it promptly burrows under again. The statements about its method of burrowing in Pearse, Humm and Wharton (1942) are totally at variance with my observations and appear wholly erroneous. They say that in burrowing the animal moves directly downward, waving its spines and tube feet so as to move sand from beneath the test to the upper surface, and does not progress anteriorly as it descends. My observations on animals in their natural habitat agree with those of Kenk (1944) on the closely related Mellita lata at Puerto Rico. Unlike regular urchins, sand dollars and other irregular urchins are polarized with definite anterior and posterior ends and can move only in the anterior direction, that opposite the posterior lunule in the present species. When placed on the sand under water in its natural habitat Mellita promptly begins to bury itself. It does this by simply advancing into the sand in a horizontal or slightly oblique orientation, using its ordinary method of locomotion by waves of movement along the spines of the oral surface. Kenk gives a suc cession of photographs showing Mellita advancing into the sand, which rapidly covers it. I did not time the reaction but only a couple of minutes is required for the five-lunuled species to cover itself with a thin layer of sand whereupon it comes to a halt. It positively does not move downward, does not remove sand from beneath it, and does progress forward. It is improbable that the tube feet play any role in locomotion as they are small and feeble and of limited distribution. Lunules. Contrary to the statement of the Berrills (1957), in Mellita sand positively does not pass through the lunules from the oral to the aboral surface during the burrowing process. To the contrary as the animal advances into the sand, sand falls through the lunules to the oral surface, thus if anything retarding the burying process. It is known for a Japanese species (Ikeda, 1941) that the lunules are important in burrowing and righting but this is definitely not the case in Mellita. The further suggestion of the Berrills that the lunules strengthen the test by fusing the oral and aboral surface is extremely im probable because the two surfaces of the test are so much connected by interior

Interambulacral Plate Atrophy in Lovenia woodsi (Etheridge Fil.)

AbstractPlate atrophy (“plate crushing”) giving rise to interambulacral plates analogous to demi-plates immediately above the ambitus is described in the Miocene spatangoid Lovenia woodsi, from Beaumaris, Victoria. It appears to be caused by the development of large primary tubercles on the aboral surface, which causes the expansion of the lowest tubercle-bearing plates during ontogeny, so that the more ventral interambulacral plates are squeezed against the ambitus.

THE ZOOLOGICAL AFFINITIES OF THE CONODONTS

THE ZOOLOGICAL AFFINITIES OF THE CONODONTS

LOCOMOTOR ORGANS OF ECHINARACHNIUS PARMA

1. The integumentary cilia in Echinarachnius cover the tips of the short spines and the sides of the long ones. On the oral surface they beat radially; on the aboral they beat from anterior to posterior. They play no essential part in the locomotion of the animal, but are probably concerned with feeding, with cleaning the outer surface, and with the respiratory currents.2. The ambulacral feet form five complicated radial bands on the oral and the aboral sides of the test and a complete marginal fringe. Their tips are deep pink and provided with suckers. They are significant in locomotion to only a limited extent in that on the anterior edge of the test they pile up the sand on the aboral surface.3. Spines cover the oral and aboral surfaces. They are of two types, long and short. They are best developed over the anterior portion of the oral surface where their distribution exhibits bilateral symmetry in relation to the axis of locomotion. In this region waves of coördinated spine movement pass from the anterior edge of the test posteriorly. In these waves each spine makes a vigorous posterior thrust in a vertical plane and an unimpeded recovery in a plane more nearly lateral. Forward locomotion, burrowing, and righting are types of motion dependent primarily on these spine movements.

THE PIGMENT OF VELELLA SPIRANS AND FIONA MARINA

The siphonophore, Velella spirans Esch. occurs in enormous numbers during the months of March and April in the Mediterranean and adjacent seas. Especially after two or three days of the sirocco, the enervating tropical wind from the south and southeast, these beautiful animals often appear in thousands. There are records of their being cast up on the beaches of Sicily in such large numbers as to form a broad blue line hundreds of yards in length. The animal consists of a flat ovoid plate of chitin surmounted by a triangular set perpendicularly to the plate and obliquely to its longest axis. The plate is usually 6 to 10 cm. long and 3 to 6 cm. wide. The sail rises about two cm. above the surface of the plate. Like all other members of the order, Velella is free-swimming and is carried by wind and current. Velella is striking because of its color,-a very deep blue. The pigment is present in varying amounts in all cells of the ectoderm, endoderm and mesoglea on both oral and aboral surfaces of the disc. It is especially dense in the tissues immediately surrounding the pneumatophore on the aboral side, but in the blastostyles, dactylozooids and sail the pigment is more diffuse and imparts a pale blue color to those organs. Associated with Velella are relatively large numbers of two molluscs, -the nudibranch Fiona marina Forsk., and the prosobranch Janthina communis Lam. Each of these species may be found by itself, but the presence of Velella invariably means the presence, in greater or less degree, of these two molluscs also. Both Fiona and Janthina were found feeding on Velella, and the eggs of each were found on partly devoured animals or on their chitinous skeletons. Fiona creeps readily at the surface inverted, but in a Velella swarm it is most often found clinging to the oral or aboral surface of the siphonophore and occasionally to the sail. Here it feeds on the soft tissues, beginning at the periphery usually, and abandoning the skeleton when all else has been eaten. When removed from Velella, Fiona is deep blue and its color

On some New Features in Pelanechinus corallinus .

In vol. xxxiv. p. 924, of the ‘Quarterly Journal of the Geological Society,’ Mr. Walter Keeping, F.G.S., described two specimens of a form previously referred by Dr. Wright to the genus Hemipedina . He showed that this form was quite distinct from Hemipedina , and gave it the name of Pelanechinus . It showed, in his opinion, affinities with the Echinothuridæ on the one hand and the Diadematidæ on the other. These two specimens have hitherto been the only ones known, with the exception of a few fragments described by Dr. Wright. I was fortunate enough to find in 1881 in the Coral Rag at Calne, in a quarry at the north end of the town, a third specimen which shows some interesting features hitherto undescribed. The diameter of the test is about 85 millim.; it is considerably flattened from above downwards. The whole of the oral surface is beautifully preserved, with the exception of a sector including one ambulacral and the greater part of two interambulacral areas. The teeth are exposed in situ , together with most of the peristomial imbricating plates; the latter, however, are not exhibited so clearly as in the specimen in the Woodwardian Museum. A zone, about 15 millim. wide, belonging to the oral surface is also preserved. My specimen quite confirms Mr. Keeping's opinion that the test was flexible. The plates have frequently separated along the line of suture, especially on the aboral surface, while the median interambulaeral line and the lines of junction between the ambulacral and

An Abnormal Starfish

A FEW weeks ago I dredged, off the north end of Arran, an interesting specimen of Porania pulvillus, Gray (= Goniaster templetoni, Forb.). It is rather more than 5 cm. in diameter, and one of the five short rays (that opposite to the madreporite), when viewed from the aboral surface, is seen to be distinctly bifurcated about 1 cm. from its termination. On examining the oral surface, it is found that the ambulacral groove of the abnormal ray divides into two branches at a distance of 2 cm. from the edge of the mouth. One of these branches runs along one of the forks of the ray to its extremity without further complication, but the other branch, belonging to the second fork, divides again 2 mm. from the first bifurcation, so as to form two tracts, which unite with one another 3 mm. further on, thus inclosing a small piece of the ordinary integument in an ambulacral area. Finally, this ambulacral area divides once more close to the tip of the ray. Consequently, there are three bifurcations of the ambulacral area in a space of not more than 1 cm. in length. As there are no signs of injury or disease on the specimen, the abnormal condition seems to have been caused by a tendency to dichotomous division like that seen in the rays of Crinoids and of the Astrophytidae.