Lecture 11 - Mollusca

Question 1

Explain Phylum: Mollusca

Answer 1

• The phylum Mollusca possess the following diagnostic characteristics:
• Visceral mass
• Mantle
• Foot
• Complex nervous system,
• Open vascular system in most
• A reduced coelom.
• Pronounced cephalization and radula( a rasping tongue) in most molluscs

Question 2

Explain the visceral mass in mollusca

Answer 2

Is the digestive system, kidneys, reproductive system

Question 3

Explain the mantle in mollusca

Answer 3

It secretes shell; gill/lungs derived from mantle

Question 4

Explain the foot in mollusca

Answer 4

Is muscular (food capture, locomotion & attachment)

Question 5

Explain the open vascular system fully in mollusca

Answer 5

• The fluid in the open vascular system is called haemolymph contains the pigment haemocyanin.
• Heamolymph is a mixture of nutrients and body fluids
• It is found in the heamocoel

Question 6

What are the classes og mollusca

Answer 6

• Class: Polyplacophora
• Class: Bivalvia
• Class: Gastropoda
• Class: Cephalopoda

Question 7

Explain Class: Polyplacophora

Answer 7

• They are also called Chitons
• Flat muscular foot
• Shell consists of 8 overlapping shell plates
• Algal feeders

eg) 1. Dinoplax gigas
2. Acanthochiton garnoti

Question 8

Explain Class: Bivalvia

Answer 8

• This class includes Clams, mussels, oysters, scallops
• Two-hinged shell with strong adductor muscles, responsible for closure of the shell.
• Head and radula is absent
• The foot is modified
• They are filter-feeders with ciliated ctenidia(respiratory organ)
• Feeding through incurrent siphon(water pumped into filtering system so that filter feeding can take place.
• Sexes separate

Question 9

What are examples of Class: Bivalvia

Answer 9

1. Mytilus galloprovincialis
2. Choromytilus meridionalis
3. Donax serra
4. Striostrea (= Crassostrea)
5. Margariticea (Cape rock oyster)

Question 10

Explain how the foot is modified in Class: Bivalvia

Answer 10

• Burrowing (clams)
• Burrowing/swimming (scallop)
• Mussel foot producing byssus threads for attachment

Question 11

Explain Class: Gastropoda

Answer 11

• They include snails, whelks, conchs, periwinkles and sea slugs)
• Usually found in marine environments, some are terrestrial (slugs and snails)
• Most are herbivorous ( radula adapted for scraping ) - some are predators with radula modified to bore through shell of prey items.
• Foot is elongated and flat.
• Prominent head with eyes and tentacles.
• Most gastropods (except slugs) have shells that protect visceral mass.
• Undergo process of torsion resulting in anus and mantle cavity facing forward and above the head.
• Possess gills (aquatic) or lungs (terrestrial forms). One group (Siphonaria spp.) possesses both.
• Gastropods are hermaphroditic.

Question 12

Explain Class: Cephalopoda

Answer 12

• Predators with beaks
• Defined cephalisation; well-developed brain
• Mantle cavity is able to squeeze water to create jet propulsion ability. This moves the animal forward
• Tentacles & arms assist in feeding. They are arranged around the head to assist with predation
• Shell external (nautilus),
• Internal shell (squid)
• Absent (octopus)NO Shell

eg) 1. Octopus vulgaris
2. Loligo vulgaris reynaudii (chokka)
3. Argonauta argo (paper nautilus)

Question 13

Explain Phylum: Nematoda

Answer 13

• Known as round worms.
• Unsegmented
• Lack specialized circulatory and respiratory organs
• Tube-within-a-tube body plan
• Nematodes are pseudocoelomates.
• The coelom is lined on only one side by mesoderm
• Pseudocoelom distributes nutrients and acts as a hydrostatic skeleton
• Recent molecular studies place them in the same clade as arthropods based on their ability to shed their cuticles (= ecdysis)

Question 14

Explain Phylum: Nematoda

Answer 14

• Unsegmented and generally small
• Present in all environments except the air.
• Can survive extreme conditions.
• Some are predators, scavengers or parasites
• Free living nematodes play an important role in nutrient cycling

eg) 1. Ascaris lumbricoides (human intestinal)

2. Trichinella (muscle tissue cysts)
3. Dirofilaria (heartworm in dogs)
4. Wuchereria (elephantiasis)
5. Sabatieria, Perepsilonema

Question 15

Signs of heartworm disease

Answer 15

• Mild persistent cough
• Reluctanceto exercise
• Fatigue after moderate activity
• Decreasedappetite
• Weight loss.
• Pets may developheart failure, appearance of a swollenbelly due toexcessfluid in the abdomen.