Plathelminthes, Nematoda, Annelida and Mollusca

Question 1

Phylum Platyhelminthes general chracteristics

Answer 1

1) Acoelomata
2) Dorsoventrally flat
3) Triploblastic – bilateral symmetrical
4) Free living, parasitic (ecto and endo)
5) Flame bulb cells for excretion of Nitrogenous waste products
6) Hermaphroditic
7) Thin cuticle
8) Limited cephilisation
9) Some with digestive systems some without.
10) One body cavity
11) Circular and longitudinal muscles
12) Protonephridea
13) No BVS

Question 2

Class Turbellaria

Plathelminthes

Answer 2

Free living – 3000 species - benthic
Eye spots
Complete digestive system with mouth and pharynx
Hermaphroditic
Unsegmented
Live in wet places (streams and under logs)
No organs of attachment
Epidermis contains rhabdoids.

Question 3

Class Monogenia

Plathelminthes

Answer 3

Ectoparasitic
Mainly on fish
Posterior organs of attachment
Body undivided

Question 4

Class Trematoda

Plathelminthes

Answer 4

No eye spots or sensory structures
Body undivided
Digestive system present
Organs of attachment present – oral suckers
Endoparasitic – reproduces inside host

Question 5

Class Cestoda

Plathelminthes

Answer 5

Body divided into proglottids
Complex life history
Organs of attachments (suckers and hooks)
No digestive tract in adult
Hermaphroditic
Lack sensory organs
Poorly developed muscles

Question 6

Phylum Nematoda general chracteristics

Answer 6

1) Round
2) Male and female Sexually dimorphic
3) Limited cephilisation
- Paired lateral sensory organs on head
4) Free living and endoparasitic
5) Some with some without digestive tract
6) Mouth and Anus
- Specialsisation and comparmentilisation
7) Thick multilayered cuticle of collagen
- Cuticle comprised of highly complex network of fibers
- Cuticle is permeable to water and gas exchange
- Limited protection from dehydration
- Cuticle is shed four times during development
8) Only longitudinal muscles
9) Reinette cells for N2 excretion
10) No BVS

20 000 described but highly diverse

Question 7

Phylum Annelida general characteristics

Answer 7

1) Round
2) Hermaphroditic
3) One or more pairs of chitinous setae
4) Limited cephilisation
5) Free living or ectoparasites
6) Some with some without digestive systems
7) Mouth and anus
8) Thin cuticle
9) Longitudinal and circular muscles
10) Udulate Nephridia
11) Closed blood vascular system

1 pair of chitinous bristles calles setae, vermiforms, soft bodied, circular in c/s – coelomate

Epidermis secretes protective cuticle – permeable to water and gasses
segmented

Question 8

Class Polycheata

Annelida

Answer 8

1) Paired lateral out folding of the body
2) 70% of all Annelids in this class, - largely marine
3) 1 pair of eyes

Question 9

Class Clitellata

Annelida

Answer 9

1) Permanent gonads
2) Two subclasses Oligocheates and Hirudinae
3) Hermaphoditic
4) Possesses a clitellum – are where cocoon is secreted

Question 10

Class Echina

Annelida

Answer 10

1) Serpent like
2) Muscular organs discharge coelomic fluid through the anus
3) Non segmented as adults
4) only 160 described species
5) Contains a cephalic projection
6) Musculature well developed

Question 11

Compare and contrast the parasitic and free living flat worms.

Question 12

Discuss the morphological attributes of the three vermiforms phyla.

Question 12

Phylum Mollusca general characterisitcs

Answer 12

1. Muscular foot
2. Shell
3. Radula

1) Dorsal epithelium forms mantle – which secretes spicules or a shell
2) Shell comprised of three layers -
a) periostracum – outer organic layer b) nacreous layer – the innermost layer
c) prismatic layer
3) Radula – a feeding structure in herbivores
4) A clinging foot – can be highly modified
5) 120 000 sp in 7 classes
6) Ancient fossil record – 450 million years
7) Mantle cavity houses ctenidia (gills) – mantle responsible for excretion, digestion and reproduction
8) very small coelome
9) Generally open BVS except for Cephalopoda

Question 13

Class polyplacophora

Answer 13

1) Shell form a series of 7 to 8 separate plates
2) Known as chitons about 800sp
3) 2-10cm long – only marine
4) series of articulating plates dorsally
5) fossil record extends back some 500 million years
6) relationship with other Mollusca unclear

Question 14

Class Aplacophora

Answer 14

1) Small group or marine Mollusca
2) about 320 species

Question 15

Class Monoplachophora

Answer 15

1) one shell
2) 3 to 6 pairs of ctenidia plus 6-7 nephridia
3) multiple pairs of foot retractor muscles
4) rediscovered in 1952
5) 20 living species all marine in >200m depth

Question 16

Class Gastropoda

Answer 16

1) Stomach foot
2) Visceral mass and nervous system become twisted 90-180 degrees during embryonic development – tortion
3) proteinaceous shield on the foot (operculum)
4) largest group of Mollusca
5) one shell
6) range from 1 mm to 60 cm

Question 17

Class Bivalvia

Answer 17

1) two shell plates
2) body laterally flattened – foot may be reduced in some species
3) 1500 species
4) largely marine and some freshwater
5) a hinged shell with two sides and 1 or 2 adductor muscles
6) a spring ligament
7) lack of cephalication
8) spacious mantle cavity
9) NO radula – large ctenidia – animal is a filter feeder

Question 18

Class Cephalopoda

Answer 18

1) head foot
2) Shell (when present) divided by septa – generally reduced or absent
3) Closed circulation system (why?)
4) foot modified to form flexible arms and siphon
5) Ganglia fused to form a large brain and encased in cartilaginous cranium
6) largest invertebrates – up to 18 m in length
7) Jet propulsion
8) Skin covered in chromatophores for camoflague, and defense