Worms (and Symbiosis in Cnidarians)

Question 1

What is the symbiosis in Cnidarians?

Answer 1

• Mutual symbiosis between clownfish and sea anemones
• Obligate mutualism (anemonefish can’t survive without protection of an anemone)
• Facultative mutualism (sea anemones can survive without an anemonefish)

Question 2

What are the benefits to anemone fish?

Answer 2

• Protection
• Most anemonefish are poor swimmers
• Hide from predators in the anemones tentacles

Question 3

What are the benefits to anemone?

Answer 3

• Anemonefish may aggressively chase other fish (protect anemone from getting eaten)
• Anemonefish provide nitrogen to their hosts (as excreted ammonia)
• Anemonefish increase water circulation

Question 4

How are Nemo and his dad protected from the anemones sting?

Answer 4

• Scientists think that the mucus coat of anemonefish protect them from nematocysts
• The anemone recognizes this mucus coat as self (i.e. same mechanism that prevents one tentacle from stinging another)
• Some anemonefish may have also evolved resistance to the toxin

Question 5

What is obligate mutualism?

Answer 5

• For the crab (nutritional and protective benefits)
• Crabs with missing anemones will steal from another crab and then tear the anemone in half
• Rare case of one organism inducing asexual reproduction in another

Question 6

What is the symbiosis with Zooxanthellae algae?

Answer 6

• Coral reefs get their colours from mutualistic zooxanthellae algae (coral gets energy from the zooxanthellae photosynthetic leftovers)
• This symbiotic relationship is threatened by ocean warming (zooxanthellae die and the coral tissues turns white a brittle = coral bleaching)
• Other Cnidarians can have symbiotic relationships with zooxanthellae algae

Question 7

What are worms?

Answer 7

• Elongated, bilateral, invertebrate animals without appendages
• Three Phyla
  Phylum Platyhelminthes
  Phylum Nematoda
  Phylum Annelida

Question 8

What are their body plans?

Answer 8

• Most Metazoans are triploblastic
• Acoelomate
• Pseudocoelomate
• Coelomate

Question 9

Explain Acoelomate

Answer 9

no coelom but have digestive cavity

Question 10

Explain Pseudocoelomate

Answer 10

internal body cavity surrounding the gut but not completely lines with mesoderm

Question 11

Explain Coelomate

Answer 11

body cavity that develops entirely from the mesoderm

Question 12

Intro to Phylum Platyhelminthes

Answer 12

• Commonly called flatworms
• Ancestral species were free-living in ancient oceans
• As more complex animals began yo evolve, the ancestral flatworms became easy prey
• Most species of flatworms are now parasitic but some are free living
• Triploblastic
• Acoelomate
• Bilateral symmetry
• Cephalization
• Hydrostatic skeleton
• Incomplete gut
• Asexual and sexual reproduction
• Tissue organ level of biological complexity

Question 13

What are the classes to the Phylum Platyhelminthes?

Answer 13

Class Turbellaria
Class Cestoda
Class Trematoda

Question 14

Explain Class Turbellaria

Answer 14

• Mostly free living
• 5mm to 50 cm
• Most are free living
  Only class of flatworms that has free living members
• Some symbiotic (commensals or parasites)
• Blind gut (waste ejected though mouth)
• Sexual (mostly monoecious) and asexual (transverse fission) reproduction

Question 15

Explain Class Cestoda

Answer 15

• Parasitic
• Tapeworms
• Long fall body compose of
  Scolex for attachment to the host
  Strobila, main body composed of chain of proglottids
  Proglottids, reproductive units
• Nearly all monoecious
  Proglottids fertilized by another proglottid on the same or a
  different strobila
• Shelled embryos form in the uterus of the proglottid
• Strobilation
  New proglottids form behind scolex
• Terminal gravid proglottids break off and are excreted in hosts
  feces

Question 16

What types of fission do Class Cestoda have?

Answer 16

- Binary fission 
    Irregular 
    Longitudinal 
    Transverse
- Multiple fission 
    Schizogony 
-  Strobilation 
     Repeated transverse segmentation

Question 17

Explain Class Trematoda

Answer 17

• Parasitic
• Flukes
• Almost all endoparasites of vertebrates
  Endoparasite = parasite that resides inside of its host
  Ectoparasite = parasite that resides outside of its host
• Generally leaflike body form
• Important parasites of humans

Question 18

What is the Phylum Nematoda?

Answer 18

• Roundworms
• Triploblastic
• Pseudocoelomate
• Bilateral symmetry
• Cephalization
• Hydrostatic skeleton formed by fluid filled pseudocoelom
• Ecdysozoans (have molted cuticle)
• Complete gut
• Reproduction: sexual, most dioecious
• Organ system level of biological complexity (have a full digestive system but lack a circulatory system)

Question 19

What is the Phylum Annelida?

Answer 19

• Marine and freshwater worms, earthworms, leeches
• Triploblastic
• Coelomate
• Bilateral symmetry, Cephalization, Hydrostatic skeleton
• Lophotrocozoan (has trochophore larvae)
• Complete gut
• Reproduction: asexual and sexual
• Organ system level of biological complexity
• Exhibit Metamerism
• Many have setae
• Clitellata (monophyletic) = Hirudinida + Obligochaeta
• Characterized by a reproductive structure called the clitellum
  Visible in earthworms
  Visible in leeches only during reproductive season

Question 20

What are the subgroups to the Phylum Annelida?

Answer 20

Polychaeta (marine worms)
Oligochaeta (freshwater worms, earthworms)
Hirudinida (leeches)

Question 21

What is the hydrostatic skeleton?

Answer 21

• Platyhelminths and Nematodes
  Precise control of body movements is not possible (force of
  muscle contraction in one area is carried throughout the body
  by fluid in an undivided coelom)
• Annelids also have hydrostatic skeleton
  But ancestor evolved distinct coelomic compartments
  This segmentation (division of the body into discrete segments)
  is known as metamerism

Question 22

What is metamerism?

Answer 22

• Being composed of serially repeating parts; serial segmentation
• Segments are called metameres or somites
• Allows for greater complexity in structure and function possible
• All members of Annelida, Arthropoda and Chordata exhibit metamerism
• Evolved separately in each of these groups
• Segments can be repetitive, but not identical
• Easy to see in Annelids and Arthropods
• In Chordates segments are more differentiated but they are still segments

Question 23

Metamerism in Earthworms

Answer 23

Nerves, blood vessels, excretory organs are found in each metamere

Question 24

What is pseudometamerism?

Answer 24

• Tapeworms exhibit this
• Repeated segments are independent of each other
• Each contains a complete set of organs (e.g. proglottids of the tapeworm break off and shed in the hosts feces)

Question 25

What are Oligochaeta?

Answer 25

• Earthworms and freshwater worms
• Bear setae (called chaetae in Annelids), but less numerous than in polychaetes
  Seta: Needlelike chitnous structures of the integument of
  annelids, arthropods and others

Question 26

What are animal ambassador?

Answer 26

• Common earthworm or nightcrawler
• Burrow in moist, rich soil
• Emerge at night to feed on surface detritus and vegetation
• In damp weather they stay near the surface, sometimes with mouth or anus protruding

Question 27

What is the reproduction of the Phylum Annelida?

Answer 27

• Monoecious (do not self-fertilize)

- Mate on the surface (at night)

Question 28

What are Polychaeta?

Answer 28

• Marine worms
• Differ from other annelids in the following ways:
  Well-differentiated head
  Specialized sense organs
  Paired paddlelike appendages
  Many chaetae on each parapodium
  No clitellum

Question 29

What is the Class Hirudinida?

Answer 29

• Leeches
• Fixed number of segments (usually 34)
• No parapodia or setae
• Variable dietary strategies
  Carnivores on small invertebrates
  Temporary parasites: sucking blood from vertebrates
  Permanent parasites: don’t leave host
• Monoecious, cross-fertilization
• Clitellum is evident only during the breeding season