Molluscs, Annelids, and Ciculatory Systems

What are the general structures of a mollusc?

Mantle, shell, foot, visceral, mass, ctenidia (gills), and radula.

What is the function of the mantle?

Thick epidermal sheet that secretes shell

What is the function of the shell?

Protection

What is the function of the foot?

Locomotion, forms arms and tentacles in cephalopods

What is the function of the visceral mass?

Where most organs lay

What is the function of the ctenidia (gills)?

Respiration (gas exchange), also filter food in most bivalves

What is the function of the radula?

Rasping, tongue-like structure used in feeding (scrape algae or drill through shells of other molluscs)

What class lacks radula?

Bivalves

How many layers is a shell made of, typically?

2 layers of calcium carbontte

Where are pearls formed?

Inner layer of a shell (nacre) - between shell and mantle

Why do cephalopods have a closed circulatory system while other molluscs have an open circulatory system?

It is more efficient and includes faster transport of oxygen to tissues

What is the first larval stage of many molluscs called?

Trochophore

What is the second larval stage is most molluscs called?

Veliger

What organisms are included in class Polyplacophora?

Chitons (grazing herbivores)

Describe the main characteristics of class Polyplacophora.

8 overlapping dorsal calcareous plates make up their shell, broad foot

What organisms are included in class Gastropoda?

Snails, slugs, limpets

Describe the main characteristics of class Gastropoda.

One shell, 1 pair of tentacles on their head

What is unique about class Gastropoda?

Includes the only terrestrial molluscs

How do nudibranchs (sea slugs) defend themselves?

Secrete distasteful or toxic chemicals, some steal nematocysts from cnidarian prey and transfer them to body surface for defense

What organisms are included in class Bivalvia?

Clams, scallops, oysters

Describe the main characteristic of class Bivalvia.

Two shells (valves) with a hinge

What characteristics does class Bivalvia not have?

No radula, no distinct head

What organisms are included in class Cephalopoda?

Octopus, squid, cuttlefish, nautilus

Describe the main structural characteristics of class Cephalopoda.

Beak-like jaw (venom), foot modified into arms or tentacles

What two systems do class Cephalopoda exhibit?

Highly developed nervous system (large brains), closed circulatory system,

What do most cephalopods lack?

External shell, except chambered nautilus

How do cephalopods defend themselves and/or hide from predators?

Squid and cuttlefish have internal shells and use ink to distract predators

How do cephalopods move?

Jet propulsion via siphon

What cells do cephalopods use to change skin texture and color?

Chromatophores (communication, camouflage)

What key feature do Annelids exhibit?

Segmentation: made of repeated units

What are the general structures of an annelid?

Septa, chaetae, segments, hydrostatic skeleton, parapodia (in some), and clitellum (in some)

What is the function of the septa?

It divides the body cavity into segments

What is the function of the chaetae?

Bristle-like structures on the end of parapodia to help with movement or grabbing things

What is the function of the segments in annelids?

Each segment has repeating structures (ganglion, excretory organs, reproductive organs)

What is the function of the hydrostatic skeleton?

Allows for alternating muscle contractions

What happens when circular muscles contract?

Becomes skinnier and longer

What happens when longitudinal muscles contract?

Becomes squished and wider

What is the function of the parapodia?

Locomotion and gas exchange (clade errantia)

What is the function of the clitellum?

Secretes mucus to stick two earthworms together during reproduction (clade Clitellata)

What are the two major clades of annelids?

Errantia and Sedentaria

What organisms are included in clade Errantia?

Clamworms, scaleworms, lugworms

Describe the main characteristics of clade Errantia.

Highly mobile, parapodia, predators

Where do most of clade Errantia live?

Marine environment

What type of fertilization does clade Errantia exhibit?

External fertilization

What organisms are included in clade Sedentaria?

Tubeworms, earthworms, leeches

Describe the main characteristics of clade Sedentaria.

Burrow or live in tubes (less mobile)

How do organisms in clade Sedentaria feed?

Various feeding mechanisms (sediment, feathery tentacles, symbiotic bacteria)

What do annelids in genus Riftia lack?

Digestive system

What is unusual about the way in which annelids in genus Riftia acquire nutrients?

Live in hydrothermal vents with chemoautotrophic bacteria (bacteria oxidize sulfur into organic compounds)

What organisms are included in clade Clitellata?

Earthworms

Describe the main characteristics of earthworms.

Have a clitellum, head not well differentiated, segments look similar

What type of sexuality are earthworms?

Hermaphroditic

What structures do earthworms not have?

No parapodia, no eyes (but can sense light, touch, chemicals)

Describe the main characteristics leeches don't have.

No internal fertilization, parapodia, or chaetae

What clade are leeches a part of?

Clade Clitellata

What sexuality are leeches?

Hermaphroditic

Where do most leeches live?

Freshwater

What can leeches feed on?

Detritus, small animals, or blood

Do all animals have a circulatory system?

No - sponges, most cnidarians, and pseudocoelomates do not

What characterizes an open circulatory system?

No distinction between blood and extracellular fluid (hemolymph)

What organisms have an open circulatory system?

Molluscs (most), arthopods

What characterizes a closed circulatory system?

Distinct blood in blood vessels

What organisms have a closed circulatory system?

Cephalopods, annelids, all vertebrates