lecture 4 - 08/10/24 Flashcards
Describe a bilaterian body plan
most possess a:
- complete gut
- specialized excretory systems (nephridia, kidneys)
What 2 groups made up bilateria?
protostomia
deuterostomia
divided into groups based on embryology
(overturned by deeper sampling and molecular phylogenetics)
What 3 groups are bilaterians now split into?
deuterostomia
ecdysozoa
lophotrochozoa
most but not all lophotrochozoans and ecdysozoans undergo protostomal development
deuterostomia undergo deuterostomal development
What group contains over half of all recognized animal phyla?
lophotrochozoa
Describe a typical lophotrochozoa
- 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
What is the origin of the name lophotrochozoa?
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)
What animals are in phylum mollusca?
octopus, squid, clams, snails, slugs
Which phyla in lophotrochozoa is most evolutionary and ecologically successful?
mollusca
How many species of mollusca are there?
~100000 described species
marine, freshwater and terrestrial environments
Describe the mollusca body plan
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
What is the hemocoel?
a pseudocoelomic cavity
acts as an open circulatory system - organs bathed in nutrient and oxygen rich hemocoel fluid
Describe a gastropod body plan
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
What animals are gastropods?
snails, slugs
describe the bivalve body plan
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
What animals are bivalves?
clams, mussels, oysters
Describe the cephalopod body plan
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
Which animals are cephalopods?
octopus, squid
Which cephalopod facilitated early insights into neurobiology?
squid
specifically their nerves as they are large and easy to dissect
describe cephalopod neurobiology
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)
How do molluscs reproduce?
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
What is semelparity?
a single reproductive period before death
what is iteroparity?
multiple reproductive periods before death
describe molluscan development
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
describe molluscan ecology
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
What is the difference between dynamic camouflage and aposematism?
dynamic camouflage - adaptive colour pattern changes
aposematism - toxins and warning colouration
What is the human relevance of lophotrochozoans?
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
What are phylum annelida?
segmented worms
includes familiar earthworms, freshwater leaches, many filter feeding and predatory marine worms
What does the typical annelid look like?
long and slender worm
body made up of a large number of bristly segments
how many species of annelida are there?
~20000 described species
many more predicted
Describe annelid external morphology
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
describe annelid internal morphology
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
What are the benefits of repetition in annelids?
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
describe annelid ecology
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
describe annelid reproduction
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
describe annelid development
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
What is the human relevance of annelids?
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)
