Phylum Molluska Ms. Martel

General Characteristics of Mollusks 2nd largest animal phylum ~100,000species Extremely diverse, so why are they all classified under the same phylum?

1) They all start off as a TROCHOPHORE This is their larval stage where they swim in open water and feed on tiny floating plants. Hard to believe this diverse group of organisms start off as the same type of larvae

2) They share the same BODY PLAN • A mantle - a soft, outer layer of their bodies which generally produces a protective shell • A muscular foot - used for locomotion or attachment, usually contains mouth • Visceral mass - contains most of the internal organs • Gills or lungs - enclosed within the mantle cavity o Mollusks definition: soft-bodied animals that have an internal or external shell.

7 Essential Life Functions FEEDING Obtain food in different ways: Filter-feeders Predators Herbivores Complete digestive tract (mouth → esophagus → stomach → intestine → anus) Many different feeding mechanisms: Radula: scraping/dilling organ, or a beak, found inside mouth of some species.

o Octopi use sharp jaws to eat prey, some produce poison that can hurt or kill humans. o Clams and oysters are filter feeders, trap food particles in mucous layer of their gills.

RESPIRATION Gills help to filter feed but they are also important for respiration!! Aquatic: breathe using gills. Clams: inhalant siphon takes in H2O and passes over gills(gas exchange occurs!!). Exhalant siphon gets rid of water and CO2. Terrestrial: highly folded mantle for O2/CO2 gas exchange (must stay moist!!!)

INTERNAL TRANSPORTATION o Open circulatory system (OCS)- the heart pumps blood through open spaces called sinuses, instead of through blood vessels. • OCS works for slower moving or sessile animals. • Faster moving octopi and squid need closed circulatory system. • Blood always moves inside blood vessels.

EXCRETION o Undigested food becomes solid waste that leaves through anus. o Cellular metabolic wastes(ie. Ammonia) are removed through nephridia.

MOVEMENT Very different throughout phylum. Muscular foot for movement. Some are sessile or slow-moving like clams and snails. Fast swimmers like squid and octopi use tentacles to swim.

RESPONSE All have statocysts (balance), and ocelli (light detection) Clams and other two-shelled mollusks- have reduced nervous system; no head. Snails and slugs- basic touch receptors etc. Octopi and squid- very well developed. Developed brain and have good memory. Can be trained to perform tasks to get reward or avoid punishment. Able to distinguish shapes by sight, and texture by touch.

REPRODUCTION o Most have both male and female sex organs and fertilization is external. • Females lay eggs. Males release sperm in open water. o Tentacled mollusks, fertilization takes place inside body of the female. o Some like snails and oysters are hermaphrodites.

4 Classes Mollusks 1) Class Polyplacophora 2) Class Gastropoda Chitons 2) Class Gastropoda Snails, slugs 3) Class Bivalvia Mussels, clams 4) Class Cephalopoda Squid, octopus

1. Class Polyplacophora o Most primitive of mollusks (eg. chitons) o 2-5 cm in length o Overlapping plates as their shell o Shallow water along seashores o Attach to rocks with a broad, flat, suctioning foot o Eat algae using a tongue-like organ called a radula o Tiny teeth scrape algae from surfaces o 2 pairs of longitudinal nerve cords (connect near the mouth) o Senses allow detection of light & chemicals

2. Class Gastropoda o Snails, slugs, nudibranchs o Largest class of mollusks o Includes mollusks with: • One piece shells (snails and conchs) • No shell (slugs and nudibranches)

o Respiration through their gills (aquatic) and simple lungs (land) o Air enters and exits via respiratory pores in the shell o Radula scrape up algae & tear up leaves o Pairs of ganglia connected by nerves o Sense organs concentrated in the head region Pair of tentacles and stalked eyes o Open circulatory system Two or three chambered heart Allows blood to leave the vessels at different points in the body

Fun Fact o Many snails can lift 10 times their own weight up a vertical surface!! So if you’re approximately 120 lbs, do you think you’d be able to carry 1200 lbs up a tree???

3. Class Bivalvia o Name means “two-shells”, they are hinged together at the back and are held together by 2 or more powerful muscles. o Eg. Mussels, clams, oysters o Sense receptors line edge near opening between the shells o Bivalve motility: Slow moving (eg. clams) Some are swimmers, they can swim fast when they flap their shells to escape danger. (eg. scallops) Sessile (oysters)

Pearls Giant Clam o Filter feeders (lack radula) • Cilia on the gills bring water in via incurrent siphon • Bathe the gills • Food particles stick to mucus on gills • Respiration takes place concurrently • Wastes and water leave through the excurrent siphon Giant Clam Pearls

4. Class Cephalopoda o Name means “head foot”, because their head is attached to their foot and divided into tentacles or arms. o Eg) Squid, octopus, nautilus

o Most intelligent invertebrates Large brain Extensive network of nerves Allows for quick responses and excellent body control Advanced vision Statocysts to sense gravity

o Most have 8 tentacles with suckers used to grab and hold onto prey. Squids and cuttlefish have 2 longer arms, with suckers on the end. o Foot is considered to be the tentacles Fused to the head

o Shell can be internal (eg. Squid) or external (eg. Nautilus) Nautilus have external shells Cuttlefish have small shells inside of body. Squids internal shell has evolved into flexible rod known as the pen. Octopi have lost shell completely.

o Closed circulatory system o Highly motile Use siphon to shoot out water at high pressures (ie. Jet propulsion) o Ink sac Used to confuse predators by creating an ink screen

Cuttlefish Giant Squid