Protostomes vs Deuterostomes Animals that have a true coelom and complete digestive system can be divided into two main groups. This division is based on the way their embryos develop and the way in which the mouth and anus form in the ball-shaped embryo: 1. Protostomes ( first mouth ): form the mouth from the first opening (or blastopore) and include molluscs, annelids and arthropods 2. Deuterostomes ( second mouth ): form the anus from the first opening (or blastopore) and the mouth at the other end and include echinoderms and chordates Phylum Mollusca 1. General Characteristics Mollusca means soft body Second largest invertebrate phylum All members go through a free-swimming larval stage of development called the trochophore larva Most molluscs have separate sexes. Many sails, however, are hermaphrodites General body plan features include: o Muscular foot locomotion o Mantle tissue fold that hangs down around some or all of the body and may secrete a shell o Shell consists of calcium carbonate, may be internal or external o Gills respiratory structures of the mantle wall o Visceral mass internal organs (gut, kidneys, heart and reproductive organs) o Radula rasping, tongue-like organ with hard teeth used to scrape up food
2. Major Classes A) Chitons -marine -eat algae -muscular foot located on bottom surface -upper surface has 8 overlapping shell valves for protection B) Gastropoda -largest group of mollusks - most marine, but some freshwater and terrestrial -most are protected by spiral shell -distinct heads, eyes at tips of tentacles -eg. Garden snails, slugs, nudibranchs (sea slugs), snails C) Bivalvia - have shells divided into two halves connected by a ligament along one edge - two strong muscles pull the halves together - complex filter feeding mechanisms that involves the use of gills (covered in cilia); trap fine food particles in mucus that coats the gills and use cilia to move the particles to the mouth. -digestion occurs in the stomach and undigested material exits via the anus, which is near the excurrent siphon. -most are sedentary (inactive) because of heavy shells -eg s. Clam, oysters, scallops, mussels
D) Cephalopoda ( head-footed ) -most complex mollusks - built for speed, adaptation that fits their carnivorous diet -efficient respiratory system and closed circulatory system -highly developed nervous system with a large brain (octopus have been trained to solve simple problems, and have the ability to remember); imageforming eyes and depend on their vision to find prey -beak-like jaws to bite prey -inject poison to immobilize the victim -mouth is at the center of several long tentacles -muscular mantles designed for water flow; contractions of mantle for fast swimming -shell either reduced and internal (squids) or missing all together (octopuses) -Nautilus is the only shelled cephalopod living today -octopus have 8 appendages, all with suckers -squid have ten appendages -dioecious = male and female gonads are carried by separate individuals (separate sexes) 3. Ecological Roles of Mollusks Sources of food for humans and other animals Live as predators, herbivores, detritus (silt) feeders, parasites and other symbiotic relationships Recycle sediment back into the environment Empty shells provide shelter and homes for other invertebrates Snails and slugs cause damage to agricultural crops Snails can be intermediate hosts for parasitic flukes
Protostomes vs Deuterostomes Animals that have a true coelom and complete digestive system can be divided into two main groups. This division is based on the way their embryos develop and the way in which the mouth and anus form in the ball-shaped embryo: 1. Protostomes ( first mouth ): form the mouth from the first opening (or blastopore) and include molluscs, annelids and arthropods 2. Deuterostomes ( second mouth ): form the anus from the first opening (or blastopore) and the mouth at the other end and include echinoderms and chordates Phylum Mollusca 1. General Characteristics Mollusca means soft body Second largest invertebrate phylum All members go through a free-swimming larval stage of development called the trochophore larva Most molluscs have separate sexes. Many sails, however, are hermaphrodites General body plan features include: o Muscular foot locomotion o Mantle tissue fold that hangs down around some or all of the body and may secrete a shell o Shell consists of calcium carbonate, may be internal or external o Gills respiratory structures of the mantle wall o Visceral mass internal organs (gut, kidneys, heart and reproductive organs) o Radula rasping, tongue-like organ with hard teeth used to scrape up food
2. Major Classes A) Chitons -marine -eat algae -muscular foot located on bottom surface -upper surface has 8 overlapping shell valves for protection B) Gastropoda -largest group of mollusks - most marine, but some freshwater and terrestrial -most are protected by spiral shell -distinct heads, eyes at tips of tentacles -eg. Garden snails, slugs, nudibranchs (sea slugs), snails C) Bivalvia - have shells divided into two halves connected by a ligament along one edge - two strong muscles pull the halves together - complex filter feeding mechanisms that involves the use of gills (covered in cilia); trap fine food particles in mucus that coats the gills and use cilia to move the particles to the mouth. -digestion occurs in the stomach and undigested material exits via the anus, which is near the excurrent siphon. -most are sedentary (inactive) because of heavy shells -eg s. Clam, oysters, scallops, mussels
D) Cephalopoda ( head-footed ) -most complex mollusks - built for speed, adaptation that fits their carnivorous diet -efficient respiratory system and closed circulatory system -highly developed nervous system with a large brain (octopus have been trained to solve simple problems, and have the ability to remember); imageforming eyes and depend on their vision to find prey -beak-like jaws to bite prey -inject poison to immobilize the victim -mouth is at the center of several long tentacles -muscular mantles designed for water flow; contractions of mantle for fast swimming -shell either reduced and internal (squids) or missing all together (octopuses) -Nautilus is the only shelled cephalopod living today -octopus have 8 appendages, all with suckers -squid have ten appendages -dioecious = male and female gonads are carried by separate individuals (separate sexes) 3. Ecological Roles of Mollusks Sources of food for humans and other animals Live as predators, herbivores, detritus (silt) feeders, parasites and other symbiotic relationships Recycle sediment back into the environment Empty shells provide shelter and homes for other invertebrates Snails and slugs cause damage to agricultural crops Snails can be intermediate hosts for parasitic flukes