Know the basics of mollusc anatomy. What is the composition of a mollusk
shell? What is the nacreous layer? What is the mantle, foot, and radula?
mollusc have a shell that is made of calcium carbonate arranged in layers which is why its hard.
the nacreous layer is a shiny, iridescent layer found in some mollusk shells, like oysters and abalones
The mantle is like a cloak that covers the mollusk’s body and secretes the shell. It’s responsible for making the shell and can also repair damage to the shell if needed.
The foot is a muscular structure that helps mollusks move around. It’s like a big, fleshy foot that can be used for crawling, digging, or even swimming, depending on the type of mollusk.
The radula is a specialized feeding structure found in most mollusks, except bivalves like clams. It’s like a rough, tongue-like ribbon covered in tiny teeth.
Know what monoplacophorans are, and where they are found today.
Monoplacophorans are a type of ancient, snail-like mollusk that lived hundreds of millions of years ago. They have a single, cap-like shell covering their soft body.
Today, monoplacophorans are found in deep ocean environments, where they live on the ocean floor. They were thought to be extinct until they were rediscovered in the 1950s, and since then, scientists have found them living in deep-sea habitats around the world.
Know what a polyplacophoran is, what the common name is, why they are
rarely preserved, and where we find them today
A polyplacophoran is a type of mollusk commonly known as a chiton. They have a long, oval-shaped body covered by eight separate, overlapping shells, kind of like wearing a suit of armor.
Chitons are rarely preserved as fossils because their shells are made of a softer material called aragonite, which tends to dissolve easily over time.
Today, we find chitons living in rocky intertidal areas and along coastal shores worldwide. They cling to rocks using their strong foot and graze on algae and other small organisms.
- Gastropods:
a. Soft anatomy: What is torsion? What is the foot used for? What is a
siphon, and what is it used for? What is the radula used for?
b. Know the difference between prosobranch and pulmonate gastropods.
Where do you find them? What are the three major prosobranch groups,
and how is the siphon/siphonal notch different in all three?
c. What do nearly all neogastropods do for a living?
A. Torsion: Torsion is when the body of a gastropod twists during development, bringing the head and foot to the front of the body. This helps them move better.
Foot: The foot is like a muscular “foot” that helps gastropods crawl or move around.
Siphon: Some gastropods have a siphon, which is like a tube they can extend to siphon in water for breathing or to detect smells.
Radula: The radula is like a rough tongue with tiny teeth that gastropods use to scrape food into their mouths.
b. Difference between Prosobranch and Pulmonate Gastropods:
Prosobranchs: These gastropods typically have a coiled shell and a siphon for breathing. They’re found in oceans, freshwater, and on land.
Pulmonates: Pulmonate gastropods don’t have a siphon and breathe air through a specialized area called a “lung.” They’re mostly found in freshwater and on land.
c. Nearly all Neogastropods:
Most neogastropods are predators and hunt for other animals, like snails, clams, or fish, for food. They’re often found in marine habitats around the world.
- Bivalves:
a. Soft anatomy: What is the foot used for? What is the siphon used for?
Know that the siphon has incurrent and excurrent tubes. How are
bivalves different from brachiopods in how they open and close the
shells? What are the marks that the mantle, siphon, and adductor muscles
leave on the shell?
b. Bivalve shells: Know the difference between taxodont, dysodont, isodont,
and heterodont hinges.
c. What is unusual about pectins (scallops)? You should be able to name at
least three. Which part do you eat?
d. Which group do most marine clams belong to? Most terrestrial clams?
e. What are rudistids? Why are they important in the history of marine life,
and when did they live?
a. Soft Anatomy:
Foot: The foot is a muscular part that helps bivalves dig into sand or mud, move around, and anchor themselves.
Siphon: Bivalves have a siphon that acts like a tube to bring in water for breathing and filter feeding. It has two tubes: one for taking in water (incurrent) and one for expelling water (excurrent).
Difference from Brachiopods: Bivalves open and close their shells using powerful muscles called adductor muscles, while brachiopods have a different way of opening and closing their shells.
b. Bivalve Shells:
Taxodont: Shells with many small, parallel teeth on their hinge.
Dysodont: Shells with irregular or few teeth on their hinge.
Isodont: Shells with equally sized teeth on their hinge.
Heterodont: Shells with different-sized teeth on their hinge.
c. Scallops (Pectins):
Scallops are unusual because they can swim by clapping their shells together. Some well-known scallops are the bay scallop, the sea scallop, and the calico scallop. We usually eat the muscle part of the scallop.
d. Marine and Terrestrial Clams:
Most marine clams belong to the group called Bivalvia. Terrestrial clams are not as common, but some belong to the same group.
e. Rudistids:
Rudistids were a group of extinct marine clams that formed large reef structures during the Cretaceous period. They were important reef builders during this time, but they went extinct along with the dinosaurs about 65 million years ago.
- Cephalopods:
a. Soft anatomy: What is the foot modified into? What sense is especially
well developed in cephalopods? What is the hyponome and what is it
used for? What do most cephalopods do for a living?
b. Know when different cephalopods were abundant:
i. Nautiloids, specifically orthocones. Why were orthocones
ecologically important?
ii. Goniatitic ammonoids
iii. Ceratititc ammonoids
iv. Ammonitic ammonoids
c. How are coeloids different from nautiloids and ammonoids? Know that
the most common modern cephalopods are coeloids. Which group went
extinct at the end of the Cretaceous?
a. Soft Anatomy:
Modified Foot: The foot of cephalopods is modified into tentacles, which they use for catching prey and moving around.
Well-developed Sense: Cephalopods have an excellent sense of vision. Their eyes are very sophisticated and can detect even subtle changes in light and movement.
Hyponome: The hyponome is a muscular structure found in some cephalopods, like squid and cuttlefish. It’s located on the underside of the body and is used to expel water forcefully, helping them move quickly and escape from predators.
Living: Most cephalopods are predators, hunting for fish, crustaceans, and other small marine creatures.
b. Abundance of Different Cephalopods:
Nautiloids (Orthocones): Orthocones were abundant during the Paleozoic Era, particularly in the Ordovician and Silurian periods. They were ecologically important as they were top predators in ancient seas.
Goniatitic Ammonoids: Goniatitic ammonoids were common during the Devonian and Carboniferous periods.
Ceratitic Ammonoids: Ceratitic ammonoids were abundant during the Triassic period.
Ammonitic Ammonoids: Ammonitic ammonoids were prevalent during the Jurassic and Cretaceous periods.
c. Coeloids vs. Nautiloids and Ammonoids:
Coeloids: Coeloids are the most common modern cephalopods, including squid, octopuses, and cuttlefish. They have internal shells or no shell at all.
Extinction: Nautiloids went extinct at the end of the Cretaceous period, along with the ammonoids, while coeloids survived and are still present today.
