Notes

Molluscs (Mollusca):
Invertabrates
Includes; Squid, Octopuses, Cuttlefish, Nudibranchs, Snails, Slugs, Limpets, Sea Hares, Mussels, Clams, Oysters, Scallops, and many less well-known animals
Estimate of more than 100,000 species alive today
The second largest phylum of animals to arthropods

Molluscs vary in form so much that is difficult to use a single representative species to make many generalizations about the group's common anatomical structures

Instead, textbooks often describe a hypothetical "mollusc" that exhibits the features common to many species.

This hypothetical mollusc has a mantle, shell, muscular foot, and visceral mass.
- Mantle: A Layer of Tissue covering Visceral Mass & many Molluscs contain glands that secrete the mantle
- Muscular Foot: A muscular structure located on the underside of the body
[The Mollusc secretes mucus from the bottom of its foot which lubricates the underlying surface. This helps the mollusc move, a task accomplished by repeated contraction and stretching of the foot muscle.]
- Visceral Mass: [Located above the foot and below the mantle] containing; the digestive system, the heart, and other internal organs.

Open Circulatory System

[Most] Single Pair of Gills to Breathe
[Some] One gill while Pulmonates (terrestrial slugs and snails) have Rudimentary Lungs

Molluscs use Haemocyanin, which is a copper-based molecule.
Vertebrates use hemoglobin, which is an iron-based molecule.

Haemocyanin is less efficient at transporting oxygen than Haemoglobin, therefore Molluscs tires more easily than vertebrates do. That's why molluscs are more apt to move in quick bursts but cannot sustain their action for long periods of time. This may have prevented them from dominating marine environments the way modern vertebrates do.

Majority of Marine Molluscs begins as ciliated & free-swimming larvae and develop into an adult form.
Freshwater & Terrestrial Snails develop within an egg and emerge as tiny fully-formed versions of the adult form.
Molluscs are most diverse in marine habitats but also inhabit freshwater and terrestrial habitats.

Molluscs Groups:

•Caudofoveates and Solanogastrates (Aplacophorans):
- About 70 species of Caudofoveates alive today
- 250 species of Solanogastrates alive today
- Worm-like molluscs
- Lack a shell
- Covered with tiny calcareous spicules.

Chitins (Polyplacophorans) - There are about 600 species of Polyplacophorans alive today. Members of this group resemble flat slugs that have a series of calcareous plates covering the upper surface of their body. Most polyplacophorns inhabit intertidal zones where they adhere to rocky surfaces to graze.
Monoplacophorans - The members of this group were thought to have been extinct until 1952 when zoologists discovered 11 living species. Monoplacophorans live in the deep-sea and are somewhat limpet-like in appearance, though they have a number of unique physical attributes that set them apart from all other molluscs, such as six (or seven) pairs of kidneys.
Tusk shells (Scaphopods) - There are about 350 species of scaphopods. Members of this group have a long cylindrical shell that narrows towards the tip and is open at both ends. Their head is located towards the broader end of the shell and they have numerous tentacles which protrude from the shell opening.
Bivalves (Bivalvia) - Bivalves are among the more diverse groups of molluscs with 9200 species alive today. Bivalves are notable for their two, mirror-image shell halves (also called valves). Bivalves include clams, oysters, mussels and scallops. They inhabit marine and freshwater habitats.
Gastropods (Gastropoda) - There are between 60,000 and 80,000 species of gastropods alive today. Gastropods are the most diverse of the mollusc groups. Members of this group include limpets, top shells, periwinkles, sundial shells, sea hares, nudibranchs, snails and slugs.
Cephalopods (Cephalopoda) - There are about 800 species of cephalopods alive today. Members of this group include squids, octopuses and natiluses.

Cephalopods Characteristics:
•Large & Prominent Head
•Tentacles
•Large Complex Eyes
•Exhibit Complex Behavior
•Majority: -Breathe with Gills
-Have a Radula
-Have a Mantle
Largest Difference in Cephalopods:
Presence or Absence of an external shell
{Squids, cuttlefish and octopuses do not have an external shell}
They either have a gladius or lack a shell entirely
The nautilus has an external shell (it is the only living cephalopod to have an external shell)

Unique Traits:

•Many rely on ACUTE VISION to detect predators & locate prey

•Their vision is advanced enough to detect differences in the; size, shape, brightness, and orientation of objects.

•Move with JET PROPULSION

• Part of the mantle forms a siphon through which water is forced. As the water pressure moves through the siphon, it forces them forward and in this way produces jet propulsion. Cephalopods also use tentacles to move and help maintain their velocity.

• Have a BEAK-LIKE STRUCTURE that they use to feed. They capture their prey using their tentacles and bring it to their mouth where they use their beak to bite chunks off before ingesting their prey.

• Most have a RADULA which consists of several rows of teeth.

• Have pigment-filled cells in the skin called CHROMOTAPHORES that they can expand and contract to expose or hide spots of color. This enables cephalopods to quickly change color to blend in with their surroundings or aid in courtship and other communication. In some cephalopods, chromatophores are bioluminescent and can shine light in such a way as to conceal their shadow from any predators and thereby escape detection.

• Unique to Molluscs: -Have a closed circulatory system

• Coleoids (Squids, Cuttlefish and Octopuses) have a two gill hearts (that pump blood through the gills) and a third systemic heart (that pumps blood throughout the body).

• Have a large & centralized brain

• Have well-developed senses

• Obtain the Ability to Teach Themselves through Observation Complex Behavior

• Brain resides within a protective cranium made up of cartilage

• Nautilus & Some Octopuses lack an ink sac [A Muscular Bag containing a dark ink called Melanin]

• Ink is expelled into the water in the presence of a predator to produce a state of confusion.

• Inking Habits have earned them the commonly given name, InkFish.

• Ring of arms surrounding; - Head
- Beak [made of Chitin]
- Shell [Only Nautilus has an Exterior Shell]
- Merged Head & Foot
- Eyes that form images

• Size ranges from: less than 1/2' to about 30 ft.

• Carnivorous Diet includes; Mollusks, Fish, Crustaceans, & Worms

Reproduction:
- [Usually] Have Courting Ritual
- May change into brilliant colors
Male transfers sperm packet (spermatophore) to Female.
The female lays eggs that hatch as Juveniles.

• Human Importance: - Eaten
- The Cuttle Bone of the Cuttlefish is Sold in Pet Stores as Calcium for Birds


Two Basic Divisions of Cephalopods:

1) Nautiluses [Nautiloidea]:
- 2,500 known species ever discovered
- Only 6 species Present to this Day
- Coiled Spiral Shell with Dark Orange Stripes
- The Shell is Composed of Numerous Chambers
- Nautilus Resides in the Largest Chamber [The Open End of The Shell]

2) Squids, Cuttlefish, & Octopuses [Coleoidea]:
- About 794 species alive today
- Soft-bodied with either; • Outer Shell
• Internal Shell
• No Shell
Octopi:
• Groups of Octopus:
1) Cirrina: [AKA Finned Deep-Sea Octopuses]

Characterized by:
- 2 Fins on Head
- Small Internal Shell
- Cirri: small cilia-like filaments on arms ( Pairs of cirri adjacent to each sucker on arm ) [Structures may have role in Feeding]

2) Incirrina: [AKA Benthic [Bottom-Dwelling] Octopi (Plural for multiple Octopus) & Pelagic [Open Sea] Argonauts]
- Argonauts: Small Floating Octopus (Live Close to Sea Surface) [Females have webbed arms like sails & secretes a thin, coiled, papery shell in which the eggs are laid]

Octopus FACTS:
•FACT: Octopi have arms, not tentacles
It is a common mistake to refer to an octopus' arms as tentacles. Tentacles are longer than arms. Tentacles usually have suckers only at their tips.
•FACT: There are three plural forms of the word octopus:
• Octopi
• Optopuses
• Octopodes
•FACT: Octopi have short lifespans: 6 months to 5 years


• 300 Species alive today
• Each arm has two rows of suction cups
• Preys: Oysters, Clams, Lobsters, & Crabs
- Uses suction cups to pull shells apart & retrieve food inside
- Uses sharp beak to break through prey's shell & produces poison in it's mouth killing the prey

Reproduction:
- Mother lays thousands of eggs & guards eggs for weeks
- Mother Octopus dies soon after her eggs hatch
- Many babies will not survive being eaten by; fish, birds, or other creatures

Early Cephalopods:

The earliest cephalopods:
Nautiloids- appeared in Late Cambrian
• Thought to be predators at the top of their food chain
- Most Ancient Cephalopods had External Shells
- Most Living Species (except for the nautilus) either lack a shell or Internal shell.
• [Thought to have] Originated About 500 Million years ago


Links for more information: [that I didn't read into deeply due to the time at the moment (2 AM)]

http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/cephalopoda.php
http://www.linsdomain.com/totems/pages/octopus.htm
http://www.reefed.edu.au/home/explorer/animals/marine_invertebrates/molluscs/squid,_octopus,_cuttlefish
http://www.aqua.org/explore/animals/chambered-nautilus
http://www.bumblebee.org/invertebrates/Cephaopoda.htm