Mantle Edge Research Articles

Cleansing Mechanisms and the Function of the Fourth Pallial Aperture inSpisula Subtruncata(Da Costa) andLutraria Lutraria(L.)

Spisula subtruncatais a shallow-burrowing member of the Mactridae which inhabits silty sand. Adaptations to such conditions include long frontal cilia on the gills (Atkins), and the presence of a siphonal membrane with associated mantle folds over-arching a waste canal, as postulated by Kellogg for allied species.The mantle edges are free ventrally, but are normally closely applied except for a short distance at the base of the inhalant siphon, an effective fourth pallial aperture being so formed. Through this opening material from the waste canal is ejected.Lutraria lutrariais a deep-burrowing species belonging to the same family. The general resemblance toMya arenariais due to convergence. Cleansing currents resemble those ofSpisula subtruncataand there is a similar waste canal, but the siphonal membrane and the long frontal cilia associated with a silty environment are absent.

Formation of Siphons in Lamellibranchia

THE mantle edge in the Lamellibranchia consists, as is well known, of three lobes. Of these the one adjacent to the shell (Fig. I, I) is concerned with the secretion of this, while the bounding periostracum is secreted as a thread from the base of the groove (PG) between this and the next lobe. This middle lobe (2) has sensory functions, bearing tentacles and in certain cases, for example, Pecten and Spondylus, eyes. The innermost lobe (3) is characteristically muscular. It contains radial muscles attached to the shell along the pallial line and, between upper and lower strands of these, other muscle running longitudinally. Action of these muscles, in conjunction with distension caused by pressure of blood, is responsible for the movements of this lobe, usually known as the velum or, better, the pallial curtain. By this means the entrance of water into the mantle cavity is controlled, for example, in Ostrea1. In extreme cases, such as Pecten and Lima, it also controls the direction in which water is expelled during the swimming movements2.

On the Habits and Adaptations ofAloidis (Corbula) Gibba

1.Aloidis (Corbula) gibbais a eulamellibranch specialized for life in muddy gravel substrata to depths of up to about 80 fathoms.2. The shell is asymmetrical, the margin of the smaller, left valve being uncalcified and so fitting within the marginal region of the right valve. A possible manner in which this asymmetry is produced by the differential secretory activities of the two mantle edges is discussed.3. The marginal periostracum of the left valve has strengthening calcined regions posteriorly, probably to protect the siphons when extruded.4. The external ligament is reduced and the resilium condensed, possibly permitting some antero-posterior rocking of the shell valves when the adductors contract.5. The process of burrowing is described; on its completion the animal is anchored by a single byssus thread.6. The siphons are very short, the tentacles of the siphonal sheath lying on the surface of the substratum. The inhalant siphon is wide and relatively insensitive; it draws in much bottom material. The exhalant siphon is tubular and very sensitive. It is controlled by two paired bands of muscle.7. The great quantities of pseudo-faeces which accumulate are expelled by periodical contractions of the 'quick' portions of the adductor muscles, the asymmetry of the shell valves causing great reduction in the size of the inhalant chamber. The foot may also assist in clearing the chamber. 8. The large ctenidia create a very powerful current; they are adapted for dealing with large amounts of sediment by means of specialized terminal, guarding and cirrus-like cilia. Control of 'pumping' is primarily by means of the exhalant siphon.9. The stomach is large in correlation with the great amounts of inorganic material carried in with the food.

Source and Fate of the Zooxanthellæ of the Visceral Mass of Tridacna elongata

ZOOXANTHELLÆ have been recorded from the visceral mass of Tridacna by Yonge1, who assigned to them together with those of the mantle edge a very significant role in nutrition. According to this author the zooxanthellæ are transported, by means of the blood-cells via the blood stream, from the mantle edge where they are ‘farmed’ to the visceral mass where they undergo phagocytic digestion.

Communication between the Dorsal Edge of the Mantle and the Stomach of Tridacna

THE part of the mantle edge of Tridacna which is reflected upwards and forwards round the exhalant chamber is highly muscular, greatly thickened and harbours myriads of zooxanthellæ (7 µ each) in the connective tissue. During the study of the food and feeding habits of this form1, it was noticed that appreciable numbers of free zooxanthellæ invariably occur in the stomach, especially of big specimens. The presence of zooxanthellæ in the stomach of Tridacna was previously recorded by Boschma2 and Yonge3. The latter author concluded that such zooxanthellæ were introduced accidentally through handling after the animal was opened for examination.

牡蛎體各部の一般組成に就て

The present analysis was planned to see mainly the difference in the chemical composition among different organs and also between the sexes of the oyster during the time of reproduc-tion. Concerning the seasonal variation in the chemical composition of the whole body, the present results agreed in a general way with those of SEIINE et al. (1929), OKAZAKI & KOBAYASHI (1929) and MASUMOTO et al. (1934). The average amounts of glycogen were as follows ; in the mantle edges 33•58%, hepato-pancreas 19•12%, gills 14•73% and adductor muscle 7•89%. In May when the oyster was not yet ripen, the glycogen content in the gonads was very high, amounting to 34•00%. Thusglycogen was mainly stored during the fattening period in the mantle edges and the gonads. While in August, when the oyster was matured, the amounts of glycogen in the gonads de-creased down to 1•20-6•68%. From these facts there seems to be little doubt that much of the glycogen stored were utilized in the formation of reproductive elements. The percentages of protein varied inversely with those of glycogen, showing lowest in the mantle edges and highest in the adductor muscle. The percentage of fat was high in the hepatopancreas and matured eggs, and low in the adductor muscle. The fat content of the hepatopancreas decreased as the maturation of gonads proceeded. Speaking the percentage composition, the eggs contained more fat and glycogen and less inorganic matters and protein than the sperm. Sexual difference in the chemical composition was also found in the mantle edges, gills and adductor muscle.

The microscopic structure of the shell and ligament of cardium (cerastoderma) corbis martyn

AbstractThe shell of Cardium corbis is composed of three layers, an outer periostracum of conchyolin and two layers of aragonite. The outer aragonitic layer presents a laminated appearance, but in reality is made up of fibers which extend across several of the curved lamellar lines. Each fiber is enclosed in an organic sheath which can be dissolved in potassium hydroxide. The inner aragonitic layer is composed of vertical prisms which are made up of two sets of fibers inclined to each other at an angle of 55 to 60°. The outer layer of aragonite is secreted by glands on the mantle edge outside the pallial line; the inner layer is secreted by glands on the mantle area within the pallial line. The dentition is formed of the same material as the inner aragonitic layer.The ligament is composed of two layers, the outer being less impregnated with calcium carbonate than the inner. Both layers are continuous with the organic matrix of the shell.

III —The Cruciform Muscle of Lamellibranchs

In 1900 von Ihering directed attention to the presence in certain Lamellibranchs of a special muscle lying in the posterior portion of the ventral mantle edge, close to the inner end of the inhalent siphon. This muscle consisted of two strands, each running diagonally from an origin on one valve to be inserted on the other, and crossing one another in the mid-ventral line so as to form a muscular apparatus with the appearance of a St Andrew's cross. He regarded this cruciform muscle as a specially differentiated group of fibres belonging to the pallial edge, acting as an accessory adductor muscle, a point of view in which he has been followed by all subsequent observers. To this von Ihering added the speculation that it had been by some similar process of specialisation of marginal pallial muscle fibres that the two other true adductor muscles of Lamellibranchs had originated.