Phylum Mollusca

Question 1

Molluscan systems

Answer 1

Complete digestive tract: with salivary gland, digestive gland and rasping tongue(radula).
Reproductive system; monoecious and dioecious .
Nervous system: brain, sensory organs.
Respiratory: ctenidis (gills), lungs in some.
Excretory: kidney-like nephridia
Circulatory : heart (generally 2 chambers) -open system except for Cephalopoda

Question 2

Description of open circulatory system

Answer 2

Blood does not circulate entirely within vessels, blood collected from gills, heart, spaces in tissues, gills

Question 3

Which molluscan has a closed circulatory system ?

Answer 3

Cephalopods

Question 4

Body plan in Molluscans

Answer 4

The foot: highly modified among the groups, locomotion and attachment.
The visceral mass: contains internal organs.
The mantle: houses the gills and visceral mass, secretes shell, space between mantle & visceral mass is called mantle cavity.

Question 5

Radula in molluscs

Answer 5

Toothed tongue, in most molluscs modified in cephalopods , ribbon-like membrane with rows of tiny teeth, odontophore (muscular base supports the radula), scrape off food.

Question 6

Life cycle in molluscs

Answer 6

Female releases eggs- male releases sperm-zygote- trocophore larva- veliger (motile and pelagic)-spat and adult.

Question 7

Characteristics of polyplacophora

Answer 7

Common on rocky surfaces of interidal, simple head ( no eyes) , herbivorous (eat algae in rocks) , separate sexes and nocturnal.

Question 8

Body plan in polyplacophora

Answer 8

Shell: 8 overlapping plates
mantle: found between foot & girdle
Radula: magnetic -scrape algae off rocks.
Foot: broad&flat(locomotion &adhesion)
Head: simple few sensory structure
Ink: absent

Question 9

Characteristics of bivalvia

Answer 9

Freshwater/ marine, suspension feeders, burrowing-cemented-free living- swimming, some sessile, swim using valves, locomotion via foot.

Question 10

What are siphons?

Answer 10

Water is drawn in through one siphon, then across the gills and out another siphon.

Question 11

Shells in bivalvia

Answer 11

Laterally compressed and covered by two valves, together by hinge, umbo (oldest part of shell).

Question 12

Morphology of bivalves

Answer 12

Radula: absent
Foot: reduced ( locomotion in some)
Head: absent 
Ink: absent
Open circulatory system
Gills used for feeding as well as gas exchange

Question 13

Layers of shells

Answer 13

1. Periostraum : outside layer of shell.
2. Ostracum: densely packed prisms of calcium carbonate laid down in protein matrix.
3. Nacreous layer : adjacent to animal- composes of calcium carbonate sheets laid down over a thin layer of protein.

Question 14

Characteristics of gastropoda

Answer 14

Habitat: terrestrial, marine or freshwater.
Shell: coiled/ not coiled/ reduced /absent.
Operculum: absent/present.
Head: present (eyes, tentacles)
Radula : present-used for rasping foot.
Foot: well develops used for locomotion.
Mantle : secretes shell
Ink: absent
Torsion: in some

Question 15

Characteristics of opistobranchia ( sea slugs, sea hares, sea butterflies)

Answer 15

Detorsion: by some
Head region: tentacles, eyes, radula
Rhinophores on Head-chemosensory-sent/taste
Shells-absent/reduced internal- no operculum.
Defences: ink, warning coloration , chemicals defences.
Cerata: outgrowns-gas exchange/ defend with nematocysts

Question 16

Characteristics of pulmonates

Answer 16

Terrestrial/ marine or freshwater 
Shell : complete / absent , no operculum. 
Highly vascular mantle server as "lung" 
Lung opens to outside by pneumostome
Mucus important for land snails

Question 17

Characteristics of Cephalopoda

Answer 17

Mantle: locomotion via jet propulsion
Radula: present within break
Foot: modified siphon and tentacles 
Head: well developed , sensory structure present, eyes. 
Ink: present ( for protection) 
Beak : eating prey

Question 18

Cephalopod feeding

Answer 18

They Are carnivores , prey with armas & tentacles , beak kills & tear prey apart.

Question 19

Locomotion in cephalopods

Answer 19

They swim by means of jet propulsion using highly modified muscular mantle and siphon

Question 20

Characteristics of Mollusca

Answer 20

Triploblastic, coelomate, protostome, bilateral symmetry, non-segmented body, radula , ink.