What type of tissue is found in mollusks?
Mollusks have a thin layer of tissue called the mantle. The mantle covers the body organs, which are located in the visceral mass. Between the soft body and the mantle is a space called the mantle cavity. Mollusks contain gills.
What is the structure of a mollusk?
Mollusks have a thin layer of tissue called the mantle. The mantle covers the body organs, which are located in the visceral mass. Between the soft body and the mantle is a space called the mantle cavity. Mollusks contain gills. Gills are organs in which carbon dioxide from the mollusk is exchanged for oxygen in the water.
What type of circulatory system do mollusks have?
The circulatory system of most mollusks is an open system. In an open circulatory system, the heart moves blood out into the open spaces around the body organs. The blood contains nutrients and oxygen. the blood completely surrounds and nourishes the body organs. Most Mollusks have a well-developed head with a mouth and some sensory organs.
Do all mollusks have a mantle?
There are also some that do not have a shell at all, like octopus and slugs, with only a mantle for protection of organs. Mollusks have bilaterally symmetry, meaning that they have a body arrangement that is symmetrical, along the center. Also, when the body is divided into two, they are alike.
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Do mollusks have tissues or organs?
Most mollusk have two organs that are unique to this phylum: a specialized feeding organ called a radula and a dorsal layer of tissue called a mantle. Mollusks are the first animals to have evolved organ systems for respiration and circulation.
Do mollusks have tissue layers?
Mollusks are triploblasts meaning that they develop from three basic embryonic germ layers: an endoderm, a mesoderm, and an ectoderm. Most mollusk species have a distinct head region, a muscular foot, and a hard shell on the top, or dorsal, side that contains the internal organs.
Are Mollusca tissues?
Molluscs are mostly aquatic, and are named from the Latin molluscus, meaning "soft". Their soft bodies are enclosed in a hard shell made of calcium carbonate (CaCO3), which functions as an exoskeleton. This shell is secreted by a thin sheet of tissue called the mantle, which encloses the internal organs like a glove.
Do mollusks lack tissue?
All mollusks have a thin layer of tissue called a mantle which covers their internal organs.
What does a mollusk have?
WHAT FEATURES DO MOLLUSKS HAVE IN COMMON? As well as a shell, most mollusks have a muscular foot for creeping or burrowing. Some also have a head with sense organs. The soft body includes lungs or gills for breathing, and digestive and reproductive parts, all enclosed by a skinlike organ called the mantle.
What structure is found only in mollusks?
There are also two unusual organs that are found exclusively in mollusks: the mantle and the radula. These organs do not persist in higher organisms, but they were important adaptations to the environments inhabited by mollusks.
Do arthropods have tissues?
The arthropod body plan. Arthropods have a number of distinctive features in their body plan: Three tissue layers formed in embryo, like most animals.
Do sponges have tissues?
While sponges do not exhibit true tissue-layer organization, they do have a number of functional “tissues” composed of different cell types specialized for distinct functions.
What are the main features of molluscs?
Mollusca CharacteristicsThey are mostly found in marine and freshwater. ... They exhibit organ system level of organization.Their body has a cavity.The body is divided into head, visceral mass, muscular foot and mantle.The head comprises of tentacles and compound eyes.The body is covered by a calcareous shell.More items...•
Do clams have tissues?
Clams, like sponges, are filter feeders. The soft body of the clam is protected from predators by a two-parted shell that is hinged. The shell is produced by a tissue called the mantle that is adjacent to the shell.
How do molluscs differ from other animals?
Molluscs have a mantle or mass of soft flesh that covers the soft body and encloses the internal organs. In many species, the mantle produces a hard shell. Not all molluscs produce a shell. Many molluscs have a radula, which, in most species, is a rasp-like scraping organ used in feeding (Fig.
What best describes a mollusk?
mollusk, also spelled mollusc, any soft-bodied invertebrate of the phylum Mollusca, usually wholly or partly enclosed in a calcium carbonate shell secreted by a soft mantle covering the body.
What is the shell of a mollusc made of?
This has a single, " limpet -like" shell on top, which is made of proteins and chitin reinforced with calcium carbonate, and is secreted by a mantle covering the whole upper surface. The underside of the animal consists of a single muscular "foot". Although molluscs are coelomates, the coelom tends to be small.
How many classes of mollusks are there in the phylum?
The phylum is typically divided into 7 or 8 taxonomic classes, of which two are entirely extinct. Cephalopod molluscs, such as squid, cuttlefish, and octopuses, are among the most neurologically advanced of all invertebrates —and either the giant squid or the colossal squid is the largest known invertebrate species.
What are the most important things that molluscs have done for centuries?
Molluscs have, for centuries, also been the source of important luxury goods, notably pearls, mother of pearl, Tyrian purple dye, and sea silk. Their shells have also been used as money in some preindustrial societies. Mollusc species can also represent hazards or pests for human activities.
How many species of molluscs are there?
Estimates of accepted described living species of molluscs vary from 50,000 to a maximum of 120,000 species. The total number of described species is difficult to estimate because of unresolved synonymy.
What is the largest phylum of marine organisms?
Many taxa remain poorly studied. Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats. They are highly diverse, not just in size and anatomical structure, but also in behaviour and habitat.
Why are molluscs called archi-molluscs?
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. The depiction is visually rather similar to modern monoplacophorans.
When did gastropods appear?
Good evidence exists for the appearance of gastropods (e.g., Aldanella ), cephalopods (e.g., Plectronoceras , ? Nectocaris) and bivalves ( Pojetaia, Fordilla) towards the middle of the Cambrian period, c. 500 million years ago, though arguably each of these may belong only to the stem lineage of their respective classes. However, the evolutionary history both of the emergence of molluscs from the ancestral group Lophotrochozoa, and of their diversification into the well-known living and fossil forms, is still vigorously debated.
What are mollusks and annelids?
Mollusks and Annelids. The mollusks are a diverse group (85,000 described species) of mostly marine species. They have a variety of forms, ranging from large predatory squid and octopus, some of which show a high degree of intelligence, to small grazing forms with elaborately sculpted and colored shells. The annelids traditionally include the ...
What is the mollusk's scraping structure called?
In addition, many mollusks have a scraping structure at the mouth, called a radula (Figure 1). The muscular foot varies in shape and function, depending on the type of mollusk (described below in the section on mollusk diversity). It is a retractable as well as extendable organ, used for locomotion and anchorage.
What are annelids made of?
They have a variety of forms, ranging from large predatory squid and octopus, some of which show a high degree of intelligence, to small grazing forms with elaborately sculpted and colored shells. The annelids traditionally include the oligochaetes, which include the earthworms and leeches, the polychaetes, which are a marine group, ...
What is the coelomic cavity?
It is a retractable as well as extendable organ, used for locomotion and anchorage. Mollusks are eucoelomates, but the coelomic cavity is restricted to a cavity around the heart in adult animals. The mantle cavity, formed inside the mantle, develops independently of the coelomic cavity.
What are the different classes of phylums?
This phylum is comprised of seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. Class Aplacophora (“bearing no plates”) includes worm-like animals living mostly on deep ocean bottoms. These animals lack a shell but have aragonite spicules on their skin.
What is the second most diverse phylum of animals?
It is the second most diverse phylum of animals with over 75,000 described species. The name “mollusca” signifies a soft body, as the earliest descriptions of mollusks came from observations of unshelled, soft-bodied cuttlefish (squid relatives). Although mollusk body forms vary, they share key characteristics, such as a ventral, ...
How do radulas feed?
They feed by filtering particles from water and a radula is absent. They exchange gases using a pair of ctenidia, and excretion and osmoregulation are carried out by a pair of nephridia. In some species, the posterior edges of the mantle may fuse to form two siphons that inhale and exhale water.
What are the organs of a mollusk?
Mollusks contain gills. Gills are organs in which carbon dioxide from the mollusk is exchanged for oxygen in the water. The mantle also protects the body if the mollusk does not have a shell. the shell is made up of several layers. The inside layer is the smoothest but it is usually the thickest layer because it's added to throughout the life ...
What is the body plan of a mollusk?
Body Plan. Mollusks have a thin layer of tissue called the mantle. The mantle covers the body organs, which are located in the visceral mass. Between the soft body and the mantle is a space called the mantle cavity. Mollusks contain gills. Gills are organs in which carbon dioxide from the mollusk is exchanged for oxygen in the water.
Which layer of the body protects the soft body?
The inside layer is the smoothest but it is usually the thickest layer because it's added to throughout the life of the mollusk. The inside layer protects the soft body. The circulatory system of most mollusks is an open system.
Do mollusks have tentacles?
Most Mollusks have a well-developed head with a mouth and some sensory organs. Some Mollusks, such as the squid, have tentacles. The muscular foot, which is used for movement, is in the underside of the mollusk.
Description
Habitat
- Most mollusks are marine animals that live in habitats from shallow coastal areas to deep waters. Most stay within the sediments at the bottom of water bodies, although a few—such as cephalopods—are free swimming.
Gastropods Or Bivalves
- Of the roughly 100,000 known mollusk species, about 70,000 are gastropods, and 20,000 are bivalves or 90 percent of the total. It is from these two families that most people derive their general perception of mollusks as small, slimy creatures equipped with calcareous shells. While the snails and slugs of the gastropod family are eaten the world over (including as escargot in a …
Octopuses, Squids, and Cuttlefish
- Gastropods and bivalves may be the most common mollusks, but cephalopods (the family that includes octopuses, squids, and cuttlefish) are by far the most advanced. These marine invertebrates have astonishingly complex nervous systems, which allows them to engage in elaborate camouflage and even display problem-solving behavior—for example, octopuses have …
Diet
- With the exception of cephalopods, mollusks are by and large gentle vegetarians. Terrestrial gastropods like snails and slugs eat plants, fungi, and algae, while the vast majority of marine mollusks (including bivalves and other ocean-dwelling species) subsist on plant matter dissolved in the water, which they ingest by filter feeding. The most advanced cephalopod mollusks—octo…
Behavior
- The nervous systems of invertebrates in general (and mollusks in particular) are very different from those of vertebrate animalslike fish, birds, and mammals. Some mollusks, like tusk shells and bivalves, possess clusters of neurons (called ganglions) rather than true brains, while the brains of more advanced mollusks like cephalopods and gastropods are wrapped around their e…
Reproduction and Offspring
- Mollusks generally reproduce sexually, although some (slugs and snails) are hermaphrodites, they still must mate to fertilize their eggs. Eggs are laid singly or in groups within jelly masses or leathery capsules. The eggs hatch into veliger larva—small, free-swimming larvae—and metamorphose into different stages, depending on the species.
Evolutionary History
- Because modern mollusks vary so widely in anatomy and behavior, sorting out their exact evolutionary relationships is a major challenge. In order to simplify matters, naturalists have proposed a "hypothetical ancestral mollusk" that displays most, if not all, of the characteristics of modern mollusks, including a shell, a muscular "foot," and tentacles, among other things. We do…
Extinct Fossil Families
- Examining the fossil evidence, paleontologists have established the existence of two now-extinct classes of mollusk. "Rostroconchians" lived in the world's oceans from about 530 to 250 million years ago, and seem to have been ancestral to modern bivalves; "helcionelloidans" lived from about 530 to 410 million years ago, and shared many characteristics with modern gastropods. S…
Overview
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks . Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.
Etymology
The words mollusc and mollusk are both derived from the French mollusque, which originated from the Latin molluscus, from mollis, soft. Molluscus was itself an adaptation of Aristotle's τὰ μαλάκια ta malákia (the soft ones; < μαλακός malakós "soft"), which he applied inter alia to cuttlefish. The scientific study of molluscs is accordingly called malacology.
The name Molluscoida was formerly used to denote a division of the animal kingdom containin…
Definition
The most universal features of the body structure of molluscs are a mantle with a significant cavity used for breathing and excretion, and the organization of the nervous system. Many have a calcareous shell.
Molluscs have developed such a varied range of body structures, finding synapomorphies (defining characteristics) to apply to all modern groups is difficult. The most general characteristic of mol…
Diversity
Estimates of accepted described living species of molluscs vary from 50,000 to a maximum of 120,000 species. The total number of described species is difficult to estimate because of unresolved synonymy. In 1969 David Nicol estimated the probable total number of living mollusc species at 107,000 of which were about 12,000 fresh-water gastropods and 35,000 terrestrial. The Biv…
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. The depiction is visually rather similar to modern monoplacophorans.
Ecology
Most molluscs are herbivorous, grazing on algae or filter feeders. For those grazing, two feeding strategies are predominant. Some feed on microscopic, filamentous algae, often using their radula as a 'rake' to comb up filaments from the sea floor. Others feed on macroscopic 'plants' such as kelp, rasping the plant surface with its radula. To employ this strategy, the plant has to be large enough for the mollusc to 'sit' on, so smaller macroscopic plants are not as often eaten as …
Classification
Opinions vary about the number of classes of molluscs; for example, the table below shows seven living classes, and two extinct ones. Although they are unlikely to form a clade, some older works combine the Caudofoveata and Solenogasters into one class, the Aplacophora. Two of the commonly recognized "classes" are known only from fossils.
Classification into higher taxa for these groups has been and remains problematic. A phylogenet…
Evolution
Good evidence exists for the appearance of gastropods (e.g., Aldanella), cephalopods (e.g., Plectronoceras, ?Nectocaris) and bivalves (Pojetaia, Fordilla) towards the middle of the Cambrian period, c. 500 million years ago, though arguably each of these may belong only to the stem lineage of their respective classes. However, the evolutionary history both of the emergence of molluscs …