Phylum Mollusca: Anatomy and Characteristics PDF

Phylum Mollusca  Phylum Mollusca Includes Classes: ✔Gastropoda (snails, slugs) ✔Bivalvia (oysters, clams) ✔Cephalopoda (octopuses, squids) Mostly marine, some freshwater, some terrestrial Soft-bodied animals, but most protected by hard calcium carbonate shell. Slugs, squids,...

Phylum Mollusca  Phylum Mollusca Includes Classes: ✔Gastropoda (snails, slugs) ✔Bivalvia (oysters, clams) ✔Cephalopoda (octopuses, squids) Mostly marine, some freshwater, some terrestrial Soft-bodied animals, but most protected by hard calcium carbonate shell. Slugs, squids, and octopuses have reduced or lost their shells completely during their evolution.  Molluscs have: muscular foot a visceral mass mantle  Molluscs Despite their apparent differences, all molluscs have a similar body plan with: ◻ a muscular foot (typically used for locomotion), ◻ a visceral mass with most of the internal organs, and ◻ a mantle - secretes the shell, drapes over the visceral mass and creates a water-filled chamber, the mantle cavity, with gills, anus, and excretory pores. ◻ a shell- used for protection- it is mostly found on the outside of the organism and it is mineralized Many molluscs feed by using a straplike rasping organ, a radula, to scrape up food.  Molluscs Most molluscs have separate sexes, with gonads located in the visceral mass. However, many snails are hermaphrodites. The basic molluscan body plan has evolved in various ways in the eight classes of the phylum. The four most prominent are the ◻ Polyplacophora (chitons), ◻ Gastropoda (snails and slugs), ◻ Bivalvia (clams, oysters, mussels, scallops…) and * ◻ Cephalopoda (squids, octopuses, cuttlefish, and chambered * nautiluses).  Class Bivalvia Include many species of clams, oysters, mussels, and scallops Bodies - laterally compressed Shell divided into two halves- left and right valves. Two parts - hinged at mid-dorsal line, and powerful adductor muscles close shell tightly to protect animal. Bivalves have no distinct head, and radula has been lost Some bivalves have eyes and sensory tentacles along outer edge of mantle  Bivalves Mantle cavity contains gills used for feeding and gas exchange. Most bivalves are suspension feeders, trapping fine particles in mucus that coats gills. Cilia convey particles to mouth. Water flows into mantle cavity via incurrent siphon, passes over gills, and exits via excurrent siphon Most bivalves live rather sedentary lives, a characteristic suited to suspension feeding Clams can burrow into the sand or mud, using muscular foot  Class Bivalvia - Shell Adductor muscle scars Umbo Hinge ligament Dr. Iwantsch, Fordham University Gills https://www.youtube.com/watch? Minute 9:53 v=ADGkuX8IL9c Minute 14:05  Class Cephalopoda Includes squids, octopuses and cuttlefish Active predators, carnivores with beak-like jaws surrounded by tentacles of their modified foot. They use these jaws to bite their prey and then inject poison- neurotoxin (secreted by salivary glands) to immobilize victim. Mantle covers visceral mass, but shell is reduced and internal in squids, missing in many octopuses, and exists externally only in chambered nautiluses. Fast movements by a squid occur when it contracts its mantle cavity and fires a stream of water through excurrent siphon- funnel. By pointing the siphon in different directions, the squid can rapidly move in different directions- water jet propulsion  Class Cephalopoda Foot of a cephalopod has been modified into muscular siphon and parts of tentacles and head. Tentacles contain suckers for capturing prey. Have digestive system (separate mouth and anus) specialized for its carnivorous lifestyle Only molluscs with a closed circulatory system Breathing structures - pair of gills, ventillated by muscle movements of mantle Well-developed sense organs such as single lens eyes and a complex brain SQUID ANATOMY