Lecture 4

Question 1

What are the evolutionary features of the nemertea?

Answer 1

There are about 1400 species

Suggested that nemertea ancestors of vertebrates but more likely related to molluscs and annelids

Question 2

What are the ecological features of the nemertea?

Answer 2

Live in a mostly marine habitat though a few live in freshwater or damp soil
Most are predators
Have mobility through active swimmers though some are burrowers or live in secreted gelatinous tubes

Question 3

What are the features that nemertians share with Platyhelminthes?

Answer 3

They are both dorsoventrally flattened, acoelomate, have a body covering of ciliated epidermis, have a similar excretory system containing flame cells, have similar sensory and nervous systems

Question 4

What are the four important differences between Platyhelminthes and nemerteans?

Answer 4

Nermetians have a closed blood system made up of a dorsal vessel, two lateral vessels and several connecting vessels while Platyhelminthes have no blood system with gases simply diffuse in and out
Nemertians have a complete digestive tract with a mouth and an anus unlike Platyhelminthes which have a blind ending gastrovascular cavity
Nemertians have a proboscis which is an extensible structure kept in a rhynchocoel and can be everted via a proboscis opening for prey capture
Nemertians have a pilidium larva (though some have a planuliform larva)

Question 5

What are the evolutionary features of the rotifera?

Answer 5

There are about 1800 species
One class (the bdelloid rotifers) are famous in evolutionary biology as there are no males despite 40 million years of evolution

Question 6

What are the ecological features of the rotifera?

Answer 6

Mostly freshwater though a few are marine, littoral and terrestrial
Many are benthic (live on the bottom)
Some are epizoic (live on the surface of other animals) as either commensals or parasites
Many species are very tolerant to desiccation

Question 7

What is the basic body from of the rotifera?

Answer 7

They are very small from .05 mm to 2mm
Have a head which has a ciliated corona used to in feeding and swimming
Have a trunk containing organ systems
Foot and toes for attachment (through pedal glands which secrete “glue”), crawling the foot is reduced in swimming forms

Question 8

What features do rotifers have in common with nemerteans and Platyhelminthes?

Answer 8

Protonephridia with flame bulbs
Anterior brain with eyespots
Complete digestive system with a separate mouth and anus (not seen in Platyhelminthes)

Question 9

What are the important differences between rotifers when compared to platyhelminthes and nemertea?

Answer 9

Rotifers are pseudocoelomate, meaning they have a body cavity (psuedocoelom) between the meso and endoderm
Which allows for a more complex gut containing a mouth, mastax (muscular pharynx), salivary glands, gastric glands, stomach, intestines and a cloacal balder (disposes of both urine and faeces) and an anus

Question 10

What are the important consequences of having a pseudocoelom?

Answer 10

The fluid filled cavity allow organs to develop and function independently
The fluid cushions organs to prevent injury
Provides a hydrostatic skeleton giving a solid axis against which muscles can work
Bathes the organs in fluid allowing free diffusion of nutrients, waste hormones over a much larger distances than a solid mass of tissue
Allows an overall increase in size and complexity