life in the sea

Bilateral Symmetry: The ability to divide organisms into right and left sides.
- Example: Humans have a symmetrical right and left side; internal anatomy may vary (e.g., heart is on the left).
- Snails have a twisted shell that allows for bilateral symmetry: drawing a line from the tip of the shell through the head reveals more or less symmetrical sides.
- Clams can also be divided into right and left sides.
Gills: Most mollusks are aquatic and possess gills for respiration.
Shell Growth:
- Mollusks can grow their shells without shedding them, unlike arthropods with chitinous exoskeletons that must be molted.
- Mollusks have mantle tissue that forms the shell.
- Growth rings on shells indicate the number of seasons lived.

Clams and Oysters:
- Feeding Type: Filter feeders; pull water in and filter out organic material.
- Importance: Filtering improves water quality.
Snails:
- Utilize a structure called a radula to scrape food (like algae) off surfaces; acts like a tongue (metaphor to cat tongue).
Cone Snails:
- Possess a modified radula for capturing prey; includes venom for harpooning fish.
- Notable for being potential threats while collecting shells in regions like Central America.

Definition: Includes about 35,000 species, known as "stomach-foot" organisms (gastro = stomach, pod = foot).
Metamorphosis: Unique process called torsion, which results in the twisting of the body and internal organs as the organism grows its shell.
Torsion:
- Larval snails start as straight lines; as they grow, their bodies must twist to accommodate the growing shell.
- Anus shifts from posterior to anterior during development.
- Torsion is unique to gastropods; arthropods do not exhibit this.
Subclasses:
- Prosobranchia: Includes common marine snails.
- Opisthobranchia: Includes sea slugs (nudibranchs) which lack a shell and torsion.
- Growth occurs in a straight line; possess gills on their backs.
- Pulmonata: Land snails with lung-like adaptations for breathing air.

Definition: Organisms with eight plates on their shells.
- Live on rocky surfaces; feed on algae using a muscular foot for adhering to rocks.
- Cannot undergo torsion.

Definition: Organisms with a single shell.
- Once thought extinct; rediscovered at depths of 11,000 feet in the 1950s.

Definition: Worm-like, deep-sea organisms without a conventional shell, possess spicules instead.

Definition: Organisms with two shells held together by adductor muscles and ligaments.
Common examples include clams and scallops.
- Adductor muscles help retain the shell's position; important in food preparation practices.

Definition: Organisms that resemble tusks, primarily living buried in sand.
- Use tentacles for filtering the sand for nutrition.

Definition: Considered the most intelligent invertebrates; includes species like the nautilus, cuttlefish, squid, and octopus.
- Name derivation: cephalopod (cephla = head, pod = foot) signifies the fusion of the head and foot region.
Characteristics:
- Highly developed nervous systems, better sensory organs (especially eyes) than other mollusks.
- Advanced locomotion and ability to produce ink as a defense mechanism.
- Eyes: Cephalopod eyes are structurally sophisticated, lacking a blind spot, in contrast to human eyes.
Nervous System: Grouping of nerve cells leads to primitive brain function.

Chromatophores: Color-changing capabilities of cephalopods, controlled by the nervous system, allowing rapid color changes.
Inking: Production of ink serves as a defense mechanism against predators, creating a smokescreen.

Summary of important points regarding mollusks, emphasizing taxonomy, anatomy, ecology, and feeding mechanisms.
Prepare for upcoming exam by understanding the differences between classes of mollusks and their unique features.