1. Tom McTernan Brian Munger
Mollusca and Annelida
Tom McTernan
Brian Munger

2. Mollusca General Info 150,000 known species
Most mollusks are marine, but some live in fresh water environments
Mollusks are soft-bodied animals that are sometimes protected by a hard shell, depending on the class

3. Symmetry in Mollusca
In the beginning of the life cycle of a mollusk, bilateral symmetry is present, but this may be lost by adulthood

4. Body Development in Mollusks
3 main parts: muscular foot, a visceral mass, and a mantle
The muscular foot is used for movement
The visceral mass contains most of the internal organs
The mantle is a fold of tissue that secretes the shell if present, covers the visceral mass
The shell secreted by the mantle is made of CaCO3

5. Movement
In Polyplacophora, Gastropoda, and Bivalvia, a muscular foot is used for locomotion
In Cephalopods, siphon made from the mantle allows jet propulsion

6. Germ Layers and Coelom
Mollusks are triploblastic, the condition of the blastoderm is divided into 3 layers: ectoderm, ectoderm, and mesoderm
Open circulatory system, where the body cavity is a blood-filled hemocoel filled with hemophyll (blood and lymph between organs)

7. Life Cycle/Reproduction
Starts with a ciliated larva, otherwise known as a trochophore
No true segmentation unlike Annelids
Normal sexual reproduction is present, although some are hermaphrodites
Most have external fertilization

8. Specialized Tissue
The radula is a tissue unique to the phylum Mollusca, and is a tongue-like structure that scrapes up food
The mantle cavity is a water-filled chamber that houses the gills, anus, and excretory pores
Torsion is a process in Gastropoda where one set of muscles grows faster than the other, which creates the shell to grow in a spiral pattern

9. Chiton (Polyplacophora) Octopus (Cephalopoda)
Snail (Gastropoda)
Squid (Cephalopoda)
Scallops (Bivalvia)

10. Annelids General Info
There are about 15,000 species of Annelids that range from less than 1mm to 3m
They live in the sea, many freshwater habitats and soil
Annelida means “little rings” for the segmentations present in all species

11. Symmetry in Annelids Annelids posses bilateral symmetry
They never lose this symmetry, or gain another type throughout their lifetime

12. Body Development in Annelids
The Coelom in an Annelid is sectioned off by septa, but the digestive tract, nerve cords, and blood vessels run the length of the whole organism

13. Digestive System
There are a few specialized regions in the digestive system of an Annelid; the pharynx, the esophagus, the crop, the gizzard, and the intestine. The metanephridia excrete waste from the blood and coelom fluid our of the worm

14. Germ Layers/Coelom
Annelids are triploblastic, the condition of the blastoderm is divided into 3 layers: ectoderm, ectoderm, and mesoderm
They have closed circulatory systems, and have true segmentation
Oligochaeta and Polychaeta have more spacious coeloms while the coeloms in leeches (Hirudinea) are filled with tissue

15. Movement
While there are three classes of Annelids, only two have setae, which are bristle-like structures that assist in burrowing
The parapodia are the actual extensions on either side of the organism from which the setae attach to
Earthworms (Oligochaeta) eat their way through soil

16. Circulatory system
Consists of networks of vessels that carry hemoglobin
Dorsal and ventral vessels are connected by other segmental pairs of vessels
Five pairs of vessels and the dorsal vessel pump blood throughout the circulatory system

17. Life Cycle/Reproduction
Some Annelids use fission, or breaking off of the main body to create another organism
Earthworms cannot reproduce like, this but do have the ability to regenerate if a segment is amputated
Some Annelids are hermaphroditic while others are different sexes within a species
Polychaeta have ciliated larva, just like Mollusks
Oligochaeta and Hirudinea are hermaphroditc and mate throughout the year
The clitella is the thickened band on a part of a segmented worm that secretes a viscid sac where eggs are deposited

18. Bristle worm (Polychaeta)
Christmas Tree Worm (Polychaeta)
Leech (Hirudinea)
Earthworm (Oligochaeta)
Marine Leech (Hirudinea)