Week 5: The Molluscs and Annelids

Question 1

What are the major clades of clade Mollusca?

Answer 1

• Gastropoda (stomach foot)
• Bivalvia (two valves)
• Cephalopoda
• Polyplacophora
• Scaphopoda

Question 2

What are the general characteristics of clade Mollusca?

Answer 2

• Triploblastic protostomes
• True coelom - 1st TRUE COELOMATES
• Exoskeleton
• Bilateral symmetry
• Unsegmented
• Complex nervous and digestive systems
• Open circulatory system (except cephalopods)
• Hemolymph instead of blood

Question 3

What is the common body plan of clade Mollusca?

Answer 3

• Shell (reduced in some species)
• Foot - locomotion of attachment to substrate
• Mantle - secretes the shell
• Visceral mass - contains various organs

Question 4

What distinguishes an open circulatory system?

Answer 4

• The heart pumps hemolymph instead of blood
• Hemolymph is pumped into open cavities that house organs
• Organs contain sinuses (instead of capillaries) that fill with hemolymph allowing gases/nutrients to reach cells of the organs

Question 5

What is adaptive radiation?

Answer 5

Evolution of many different morphological types or species from a single common ancestor following migration into new environment

• New niches to explore
• Little competition for resources

Question 6

What are the major species of Gastropoda?

Answer 6

-Snails, Slugs, Perriwinkles, and Conch

Question 7

What is the phenomenon that causes gastropods to appear asymmetrical?

Answer 7

-Torsion, the uneven growth of left and right muscles that attach the shell to the head foot.

Question 8

What are some example species of clade Bivalvia?

Answer 8

-Clams, Mussels, Oysters, and Scallops.

Question 9

What is a rasping radula, and what clade(s) does it appear in?

Answer 9

It is a tongue-like organ used for feeding. The radula appears in all Gastropoda, Cephalopoda, Polyplacophora, and Scaphopoda.

Question 10

How do bivalves feed?

Answer 10

They are suspension feeders; they trap food particles from the water in ciliated gills. Particles are then transported to the mouth by the labial palps. NO RADULA.

Question 11

What is the umbo?

Answer 11

The oldest part of the shell, most resistant to predators.

Question 12

What are the distinguishing characteristics of clade Cephalopoda?

Answer 12

• “head foot”
• Shell reduced or absent
• Locomotion: the mantle draws in water and contracts to force it through the siphon. creating propulsion.
• Well developed head with radula and eyes
• Closed circulatory system

Question 13

What some examples of species in clade Cephalopoda?

Answer 13

-Squid, Octopus, Cuttlefish, and Nautilus

Question 14

What is interesting about the eyes of cephalopods as compared to the eyes of vertebrates?

Answer 14

Eyes of cephalopods and vertebrates are analogous traits, traits which perform a similar function, but are have evolved from a different ancestor (convergent evolution). The cephalopods’ eyes are from skin tissue, and vertebrates’ are from nervous tissue.

Question 15

What are the characteristics of clade Polyplacophora?

Answer 15

• “many shells”
• Elongated, flat body
• Shells of 8 dorsal plates
• reduced head
• bilateral symmetry
• Foot is broad and flat
• Use radula to feed

Question 16

What clade do chitons belong to?

Answer 16

Clade polyplacophora.

Question 17

What are the characteristics of clade Scaphopoda?

Answer 17

• Tusk shells
• Body enclosed in a one-piece shell
• mouth has tentacles
• Absent head
• Marine

Question 18

What are the characteristics of clade Annelida?

Answer 18

• Triploblastic protostomes
• True coelom
• Closed circulatory system
• More developed organ systems
• Hydrostatic skeletons
• Monoecious (hermamphroditic)
• Metamerism (segmentation) - provides foundation for the specialization of body regions, makes movements more effective.
• Setae - chitinous bristles on ventral side used for locomotion

Question 19

What are the major clades of Annelida, and what is the defining characteristic of each?

Answer 19

• Polychaeta - many setae
• Oligochaeta - few setae
• Hirudinea - No setae

Question 20

What are the main characteristics of clade Polychaeta?

Answer 20

• Many bristled setae
• Found on sea floor / reefs
• Beautifully colored
• Parapodia

Question 21

What are parapodia?

Answer 21

External gills that provide skin surface area for gas exchange and function in locomotion.

Question 22

What are the major characteristics of clade Oligochaeta?

Answer 22

-Few setae
-Longitudinal and circular muscles
Longitudinal (shorten/thicken)
Circular (lengthen/thin)
-Gas exchange through skin
-Very complex organ systems
-Clitellum present

Question 23

Describe Oligochaeta mating?

Answer 23

• Two hermaphroditic worms line seminal vesicles with seminal receptacles
• Held together by mucous secreted by the clitellum
• Sperm goes out seminal vesicles and is stored in the seminal receptacle of the other worm.
• Eggs are carried out genital pore
• A chitin-like band forms a cocoon around the clitellum
• This cocoon slides forward, collects eggs and sperm, and fertilization takes place
• The cocoon slides off and is left behind

Question 24

What are the major characteristics of clade Hirudinea?

Answer 24

• No setae
• Includes leeches
• High level of parental investment
• Secretes an anesthetic and anticoagulant before attachment
• Medicinal leech - relieves edema during surgery