phylum MOLLUSCA
Mollusca is one of the most diverse groups of animals on the planet. It includes snails, octopuses, squid, clams, scallops, oysters and chitons.
ECOLOGICAL ROLE
Molluscs are important to humans as a food source, jewelry, and tools.
Molluscs are important to humans as a food source, jewelry, and tools.
MOVEMENT STRUCTURES/ TYPE
Mollusks have a muscular foot capable of complex muscle contractions. The ventral foot helps move molluscs by using muscular waves and or cilia in combination with mucus. Protruding from the bottom of the mollusk, the foot used by some species to dig in the sand, move along rocks, and divided into tentacles for others. Some mollusks are highly adapted and use jet propulsion for movement.
Mollusks have a muscular foot capable of complex muscle contractions. The ventral foot helps move molluscs by using muscular waves and or cilia in combination with mucus. Protruding from the bottom of the mollusk, the foot used by some species to dig in the sand, move along rocks, and divided into tentacles for others. Some mollusks are highly adapted and use jet propulsion for movement.
BODY COVERING; CELL LAYERS; LEVEL OF ORGANIZATION; PROTECTION
Mollusks are triploblastic, bilaterally symmetrical, and cephalized. Molluscs all have soft bodies which typically have a “head”, a “foot” and visceral mass. Head-foot contains sensory organs and muscles. The digestive, reproductive, circulatory, and respiratory organs are located in the visceral mass. Molluscs have a true coelom; and internal body cavity enclosed by mesodermal membranes. However, molluscs have a reduced coelom and is represented by the kidneys, gonads, and the main body cavity which surrounds the heart. It is reduced to a small space around the heart called a hemocoel. Molluscs is secrete a thin sheet of tissue called the mantle, which encloses the internal organs like a glove. The mantle creates a small empty space called a mantle cavity which is modified for different functions in different molluscs groups.
Mollusks are triploblastic, bilaterally symmetrical, and cephalized. Molluscs all have soft bodies which typically have a “head”, a “foot” and visceral mass. Head-foot contains sensory organs and muscles. The digestive, reproductive, circulatory, and respiratory organs are located in the visceral mass. Molluscs have a true coelom; and internal body cavity enclosed by mesodermal membranes. However, molluscs have a reduced coelom and is represented by the kidneys, gonads, and the main body cavity which surrounds the heart. It is reduced to a small space around the heart called a hemocoel. Molluscs is secrete a thin sheet of tissue called the mantle, which encloses the internal organs like a glove. The mantle creates a small empty space called a mantle cavity which is modified for different functions in different molluscs groups.
SUPPORT
Their bodies are often covered by a hard exoskeleton, such as the shells of snails and clams or the plates of chitons. Other species have lost their protective outer layer over the course of evolution, and maintain shape and support through hydrostatic pressure.
Their bodies are often covered by a hard exoskeleton, such as the shells of snails and clams or the plates of chitons. Other species have lost their protective outer layer over the course of evolution, and maintain shape and support through hydrostatic pressure.
OBTAINING NUTRIENTS
Majority of molluscs are herbivorous, graze on algae, or are filter feeders. Most molluscs use their muscular mouths with a radulae (tongue), and many rows of chitinous teeth for eating food. Molluscs mouths also have glands that secrete slimy mucus to which the food sticks to and forms one long string of mucus (a food string). They beat their cilia to push the mucus towards the stomach which is later sent to the prostyle, which rotates the mucus string onto itself
Majority of molluscs are herbivorous, graze on algae, or are filter feeders. Most molluscs use their muscular mouths with a radulae (tongue), and many rows of chitinous teeth for eating food. Molluscs mouths also have glands that secrete slimy mucus to which the food sticks to and forms one long string of mucus (a food string). They beat their cilia to push the mucus towards the stomach which is later sent to the prostyle, which rotates the mucus string onto itself
RESPIRATION
Aquatic molluscs such as snails, clams, and octopi typically use gills inside their mantle cavity for exchanging oxygen and carbon dioxide in respiration. Cilia on the gills create a flow of oxygenated water through the mantle cavity, carrying off carbon dioxide and nitrogenous waste. Terrestrial molluscs respire using the mantle cavity as a lung. Diffusion can also occur through the skin of moist molluscs.
Aquatic molluscs such as snails, clams, and octopi typically use gills inside their mantle cavity for exchanging oxygen and carbon dioxide in respiration. Cilia on the gills create a flow of oxygenated water through the mantle cavity, carrying off carbon dioxide and nitrogenous waste. Terrestrial molluscs respire using the mantle cavity as a lung. Diffusion can also occur through the skin of moist molluscs.
CIRCULATION
Their main body cavity is a hemocoel, through which blood and coelomic fluid circulate and which encloses most of the other internal organs. Molluscs have a heart, blood, and blood vessels. Oxygen and nutrients are carried to all parts of the molluscs body by a circulatory system. Most molluscs have an open circulatory system where the blood is collected from the gills, pumped through the heart and released directly into the tissue spaces. This system works well for slow moving molluscs like snails and clams since oxygen is not of a high demand. Faster moving molluscs like octopi and squid have closed circulatory systems because this system can transport blood through the animal’s body quicker.
Their main body cavity is a hemocoel, through which blood and coelomic fluid circulate and which encloses most of the other internal organs. Molluscs have a heart, blood, and blood vessels. Oxygen and nutrients are carried to all parts of the molluscs body by a circulatory system. Most molluscs have an open circulatory system where the blood is collected from the gills, pumped through the heart and released directly into the tissue spaces. This system works well for slow moving molluscs like snails and clams since oxygen is not of a high demand. Faster moving molluscs like octopi and squid have closed circulatory systems because this system can transport blood through the animal’s body quicker.
EXCRETION
The circular muscles at the hindgut pinch off and the anus excretes a piece of the prostyle, stopping it from growing too large. Molluscs have a well-developed excretory system using tubular nephridia (kidneys) that collect liquid wastes (filter blood for metabolic waste) from the coelom and dump them in the mantle cavity, where they are pumped out of the shell through the anus.
The circular muscles at the hindgut pinch off and the anus excretes a piece of the prostyle, stopping it from growing too large. Molluscs have a well-developed excretory system using tubular nephridia (kidneys) that collect liquid wastes (filter blood for metabolic waste) from the coelom and dump them in the mantle cavity, where they are pumped out of the shell through the anus.
RESPONSE
The molluscan nervous system consists of a pair of ganglia and nerve cords, with statocysts (balance organs) and eyes as major sense organs. They have sense organs for taste and touch as well.
The molluscan nervous system consists of a pair of ganglia and nerve cords, with statocysts (balance organs) and eyes as major sense organs. They have sense organs for taste and touch as well.
REPRODUCTION
Molluscs only reproduce sexually, with some molluscs relying on external fertilisation. Most remain one sex their whole life and females produce eggs from which larvae or miniature adults emerge from. Other molluscs rely on internal fertilisation and are hermaphrodites with more complex reproductive systems.
Molluscs only reproduce sexually, with some molluscs relying on external fertilisation. Most remain one sex their whole life and females produce eggs from which larvae or miniature adults emerge from. Other molluscs rely on internal fertilisation and are hermaphrodites with more complex reproductive systems.
class mollusca
Polyplacorphora: dorso ventrally flattened body, head without eyes and tentacles, shell composed of 8 calcareous plates, 17 teeth in radula, seperate sexes, has a foot to help move and cling onto surfaces, ovally elongated,
Gastropoda (snails and slugs): meaning stomach foot, the internal organs of slugs and snails have been twisted back so that the stomach lies above the large fleshy foot of these animals, moves by gliding along surface with secreting mucus or slime with their muscular foot, well developed head with eyes, 1-2 pairs of tentacles, hermaphrodites, herbivores and scavengers.
Bivalva (clams, oysters, mussels, scallops): bivalve meaning two-part shell, filter feeders and food goes through the gills, simple sensory systems, moving ones have foot to hop from place to place, seperate sexes.
Cephalopoda (squid, cuttlefish, ocotopus): highly adpated for swimming, ring of arms or tentacles usually 8 that are attached directly to head, tentacles will either have suckers or hooks on their undersides, some have internal, external or no shells, carvivorous, powerful beaks, radula, highly developed nervous system, seperate sexes.
Gastropoda (snails and slugs): meaning stomach foot, the internal organs of slugs and snails have been twisted back so that the stomach lies above the large fleshy foot of these animals, moves by gliding along surface with secreting mucus or slime with their muscular foot, well developed head with eyes, 1-2 pairs of tentacles, hermaphrodites, herbivores and scavengers.
Bivalva (clams, oysters, mussels, scallops): bivalve meaning two-part shell, filter feeders and food goes through the gills, simple sensory systems, moving ones have foot to hop from place to place, seperate sexes.
Cephalopoda (squid, cuttlefish, ocotopus): highly adpated for swimming, ring of arms or tentacles usually 8 that are attached directly to head, tentacles will either have suckers or hooks on their undersides, some have internal, external or no shells, carvivorous, powerful beaks, radula, highly developed nervous system, seperate sexes.