lecture 4 - 08/10/24

Question 1

Describe a bilaterian body plan

Answer 1

within bilateria there is incredible diversity of body plans and origins of other complex features

most possess a:
- complete gut
- specialized excretory systems (nephridia, kidneys)

Question 2

What 2 groups made up bilateria?

Answer 2

protostomia
deuterostomia

divided into groups based on embryology

(overturned by deeper sampling and molecular phylogenetics)

Question 3

What 3 groups are bilaterians now split into?

Answer 3

deuterostomia
ecdysozoa
lophotrochozoa

most but not all lophotrochozoans and ecdysozoans undergo protostomal development

deuterostomia undergo deuterostomal development

Question 4

What group contains over half of all recognized animal phyla?

Answer 4

lophotrochozoa

Question 5

Describe a typical lophotrochozoa

Answer 5

• group is supported by molecular data
• generally have a complete gut, at least a partial coelum, ventral nerve cord
• a protostome blastopore fate is seen in most phyla but not all

Question 6

What is the origin of the name lophotrochozoa?

Answer 6

lophophore - a feeding organ used by some of its phyla

trochophore - a larval form seen in some of its other phyla

(some phyla have neither feature)

Question 7

What animals are in phylum mollusca?

Answer 7

octopus, squid, clams, snails, slugs

Question 8

Which phyla in lophotrochozoa is most evolutionary and ecologically successful?

Answer 8

mollusca

Question 9

How many species of mollusca are there?

Answer 9

~100000 described species

marine, freshwater and terrestrial environments

Question 10

Describe the mollusca body plan

Answer 10

very evolutionarily flexible
adaptive to different lifestyles

3 main sections:
- head - contains circular nerve ring, mouth, radula
- foot - main locomotory organ
- visceral mass - contains most organs all suspended
in a mixed coelum/hemocoel

mantle covers visceral mass and secretes the biomineralized shell

an open pocket (mantle cavity) houses the gills

Question 11

What is the hemocoel?

Answer 11

a pseudocoelomic cavity

acts as an open circulatory system - organs bathed in nutrient and oxygen rich hemocoel fluid

Question 12

Describe a gastropod body plan

Answer 12

adapted for crawling, grazing lifestyle

head has prominent sensory tentacles

toothy radula for scraping food

muscular, crawling foot secretes mucus for protection and locomotion

shell protects visceral mass
(some specie, slugs, have internalized shells)

in terrestrial species the gills in the mantle cavity are expanded and act as lungs

Question 13

What animals are gastropods?

Answer 13

snails, slugs

Question 14

describe the bivalve body plan

Answer 14

adapted for sedentary, filter-feeding lifestyle

body protected by a hinged 2 part shell that can be closed and held shut

muscular foot used for burrowing

mouth reduced - no radula (not needed)

gills are expanded and used to filter particles from water sucked into mantle cavity

Question 15

What animals are bivalves?

Answer 15

clams, mussels, oysters

Question 16

Describe the cephalopod body plan

Answer 16

adapted to fast swimming, predatory lifestyle

shell is reduced and internalized or lost

mantle is flexible and muscular for fast swimming via jet propulsion and fin flapping

foot is modified to form muscular arms and tentacles covered in suckers and sensory receptors

head has a mouth with a prominent beak, slicing radula, highly developed eyes, large brain

Question 17

Which animals are cephalopods?

Answer 17

octopus, squid

Question 18

Which cephalopod facilitated early insights into neurobiology?

Answer 18

squid
specifically their nerves as they are large and easy to dissect

Question 19

describe cephalopod neurobiology

Answer 19

eyes similar to human eyes - convergent evolution

some capable of problem solving and tool use - most intelligent invertebrates

research requires stricter regulations due to potential sentience (perception and feeling)

Question 20

How do molluscs reproduce?

Answer 20

sexual reproduction typical
- hermaphroditism common in some groups, especially terrestrial gastropods

asexual parthenogenesis (larval development from an unfertilized egg) occurs in a few groups

broadcast spawning is typical

though copulation (direct sperm transfer) has evolved repeatedly
- penises
- copulatory tentacles (give female parcel of sperm)
- love darts - for pheromone transfer

some reproduce once then die

Question 21

What is semelparity?

Answer 21

a single reproductive period before death

Question 22

what is iteroparity?

Answer 22

multiple reproductive periods before death

Question 23

describe molluscan development

Answer 23

embryos undergo protostome development

most species undergo indirect development - ciliated, swimming trochophore larva

development is direct in cephalopods and in terrestrial snails (juveniles hatch from eggs)

in some freshwater mussels the larvae develop as parasites on fish gills

Question 24

describe molluscan ecology

Answer 24

global - marine, freshwater, terrestrial habitats
(many terrestrial and freshwater species are endangered)

feeding ecology ranges from algal herbivory to vertebrate predation
- some obtain nutrients from microbiol symbionts

some bivalves can form reefs (e.g. oyster reefs)
- habitat formation and shore protection

variety of anti-predation strategies have evolved, especially in species that lack a protective shell
- dynamic camouflage
- aposematism

Question 25

What is the difference between dynamic camouflage and aposematism?

Answer 25

dynamic camouflage - adaptive colour pattern changes

aposematism - toxins and warning colouration

Question 26

What is the human relevance of lophotrochozoans?

Answer 26

many species valued as food sources or aesthetic/cultural reasons
- mussel aqauculture, snail heiculture, squid fisheries
- clam sheels and oyster pearls

potential source of bioactive compounds
- snail slime ingredient in some skincare products

snails/slugs are destructive plants pests with major costs to agriculture and horticulture

some bivalves cause considerable damage to aquatic infrastructure
- encrusting zebra mussels

Question 27

What are phylum annelida?

Answer 27

segmented worms

includes familiar earthworms, freshwater leaches, many filter feeding and predatory marine worms

Question 28

What does the typical annelid look like?

Answer 28

long and slender worm
body made up of a large number of bristly segments

Question 29

how many species of annelida are there?

Answer 29

~20000 described species

many more predicted

Question 30

Describe annelid external morphology

Answer 30

body plan consists of 3 parts
- head - highly cephalized, mouth and feeding
structures surrounded by various sensory organs

• trunk - divided into many sections (serial
  repetition) - structurally v. similar sections, each
  segment bears lateral appendages (parapodia) and
  bristles
• pygidium - the tail - consists of anus and
  sometimes additional sensory structures

Question 31

describe annelid internal morphology

Answer 31

digestive tube (intestine) runs from head to pygidium, and is regionally specialized

coelomic body cavity is divided into segments by septa (sheets of connective tissue)
- annelids segmented internally and externally

blood vessels and a ventral nerve cord supply each segment with nutrients and neural control

respiration occurs across cuticle
- if present, parapods can act as respiratory organs
(provide greater SA for gas exchange)

excretory organs (nephridia) are found in each segment

Question 32

What are the benefits of repetition in annelids?

Answer 32

provides mechanical, developmental and evolutionary flexibility

mechanical - each segment has its own hydrostatic skeleton, facilitating localized muscle action

developmental - new segments can be added as the animal grows

evolutionary - segments can be modified to meet specific physiological needs - can be adapted for specific roles

Question 33

describe annelid ecology

Answer 33

globally distributed and highly abundant in aquatic and terrestrial habitats

earthworms are soil detritivores
- provide key ecosystem services (boost soil health,
and linking below-ground and above-ground
ecosystems)

marine species may be motile predators and scavengers, or tube-dwelling filter feeders
- some rely entirely on symbiotic bacteria for
nutrients
- some tube-dwellers can form reefs

many leaches are parasites

Question 34

describe annelid reproduction

Answer 34

sexual reproduction is typical
- earthworms and leeches are hermaphroditic and
copulatory
- most marine annelids have separate sexes and
adopt some form of broadcast spawning

some marine species produce epitokes (swimming mini-adults filled with gametes)
- these are short-lived and non-feeding reproductive stages that swim, mate, die

asexual reproduction via parthenogenesis or fragmentation occurs in some groups

Question 35

describe annelid development

Answer 35

embryos undergo protostome development

annelid larva is trochophore
- embryological evidence for a close relationship
between molluscs and annelids

typical life cycle involves indirect development
- larval stage eventually metamorphoses and strats
adding segments to its tail region

direct development (no larval stage) is seen in some species, such as earthworms and leeches

Question 36

What is the human relevance of annelids?

Answer 36

common fish food used by anglers and aquaculture industry

vermicompsting - use of worms to produce nutritious compost from food waste, garden cuttings, sewage etc

‘medicinal’ leeches are sometimes used to aid in wound healing (produce anticoagulants that prevent clotting)