Are mollusks protostomes or deuterostomes? | Socratic
Molluscans are protostomes. Their mouth arise from the embryonic blastopore. Blastopore is the opening of primitive gut that appears during. The mollusks are among the most diverse, and well-known of the .. of segmentation and a sister group relationship with the sipunculans (they. Protostomia is a clade of animals. Together with the deuterostomes and xenacoelomorpha, its members make up the Bilateria.
There is also a shortage of specialists who can identify all the animals in any one area to species. For comparison, the great majority of mollusc species are marine, but only 41 of these appeared on the Red List. Mollusc shell Anatomical diagram of a hypothetical ancestral mollusc Because of the great range of anatomical diversity among molluscs, many textbooks start the subject of molluscan anatomy by describing what is called an archi-mollusc, hypothetical generalized mollusc, or hypothetical ancestral mollusc HAM to illustrate the most common features found within the phylum.Molluscs - Educational Video for Kids
The depiction is visually rather similar to modern monoplacophorans. The shell is secreted by a mantle covering the upper surface.
The underside consists of a single muscular "foot".
It contains the body organs. It is lined with epidermis, and is exposed, according to habitatto sea, fresh water or air. The cavity was at the rear in the earliest molluscs, but its position now varies from group to group. The anusa pair of osphradia chemical sensors in the incoming "lane", the hindmost pair of gills and the exit openings of the nephridia "kidneys" and gonads reproductive organs are in the mantle cavity. Mollusc shell The mantle edge secretes a shell secondarily absent in a number of taxonomic groups, such as the nudibranchs  that consists of mainly chitin and conchiolin a protein hardened with calcium carbonate  except the outermost layer, which in almost all cases is all conchiolin see periostracum.
In gastropods, it secretes mucus as a lubricant to aid movement. In forms having only a top shell, such as limpetsthe foot acts as a sucker attaching the animal to a hard surface, and the vertical muscles clamp the shell down over it; in other molluscs, the vertical muscles pull the foot and other exposed soft parts into the shell.
- Are mollusks protostomes or deuterostomes?
Although molluscs are coelomatestheir coeloms are reduced to fairly small spaces enclosing the heart and gonads. Cephalopods squidoctopusescuttlefish also possess a chitinous beak.
The gills of mollusk extract oxygen from the water and dispose waste. Development passes through one or two trochophore stages, one of which the veliger is unique to the group.
These suggest a close relationship between the mollusks and various other protostomes, notably the annelids. Classification Mollusks are generally organized into nine or ten classes, with one that is known only from fossilsbut the others with extant living representatives.
Class Aplacophora — solenogasters, deep-sea wormlike creatures; species. Class Caudofoveata — deep-sea wormlike creatures; 70 known species; now generally recognized as a subclass of Aplacophora.
Class Polyplacophora — chitons; species, primarily animals that live on rocks on marine shorelines; shells divided into eight separate plates.
Class Scaphopoda — tusk shells; species, all marine Class Gastropoda — nudibranchssnails and slugslimpets, conches, sea hares; sea angel, sea butterfly, sea lemon; largest and most diverse mollusk class with an estimated 75, tospecies; most have a single shell, but slugs and some others have no shell; gastropoda means "stomach-foot. History of mollusks Mollusk fossils are some of the best known and are found from the Cambrian onwards.
The oldest fossil seems to be Odontogriphus omalus, found in the Burgess Shale.
It lived about million years ago. Based on comparison of living specimens, it is generally held that mollusks and annelids segmented worms, Phylum Annelida are closely related and share a common ancestor Towle They have similar patterns of embryological development and share a characteristic larval form the first stage of larval development, the trochophoreamong other factors Towle These were probably the first groups to have a true coelom.
Mollusk - New World Encyclopedia
Within the mollusks, Brusca and Brusca suggest that the bivalves and scaphopods are sister groups, as are the gastropods and cephalopods, so indicated in the relationship diagram below. The development of a shell of calcium carbonate would have been of significant adaptive value, but would also reduce the surface area for gas exchange, necessitating a structure such as gills Towle All major molluscan groups possess a skeleton, though it has been lost evolutionarily in some members of the phylum.
It is probable that the pre- Cambrian ancestor of the mollusks had calcium carbonate spicules embedded in its mantle and outer tissues, as is the case in some modern members.