lecture 5 - 09/10/24 Flashcards
What is phylum ectoprocta?
moss animals
typically small, aquatic, filter feeders that form sedentary colonies
filter feeding accomplished using a lophophore
sometimes referred to as phylum bryozoa
~6000 described species
What is a lophophore?
a ciliated, tentacular organ that surrounds the mouth
describe ectoproct morphology
zooids - are superficially similar to coral polyps - different internally
- physically connected via body wall pores and/or tubes made of connective tissue
lophophore - filter feeding and respiration
body wall secretes an exoskeleton (in some species is biomineralized)
soft body can be retracted inside for protection
reduced cephalization
no obvious excretory or circulatory systems
How are zooids specialized?
- zooids for gamete production, colony anchoring,
colony defence - zooids have biomineralized, hinged exoskeletons,
muscular bodies, no lophophores - anti-predator defence
describe ectoproct ecology
most are marine, some groups are successful in freshwater habitats
a few species are reef-builders (bioconstructors)
- e.g. australia’s western port bryozoan reef
lots of variation in colony morphology
- colony form is associated with environmental factors like depth, substrate stability and sedimentation rate
Describe ectoproct reproduction and development
colonies are hermaphoditic
- individual zooids may be hermaphroditic or
male/female
sex typically involves broadcast spawning of sperm, followed by internal fertilization and brooding of embryos
larvae metamorphose (indirect development) and establish new colonies via asexual budding
many freshwater species undergo seasonal asexual reproduction
- produce statoblasts - embryonic stem cells
(survival pods), can survive unfavourable conditions
then develop into zooids when conditions improve
How are ectoprocts relevant to humans?
biofueling - colonies grow on ships, pipes causing damage and blockages
potential source of bioactive compounds
(the bryostatins - drug discovery)
- actively being studied as a potential treatment for
Alzheimer’s disease
- produced not by the ectoprocts themselves, but by
the bacterial symbionts
How are ectoprocts ‘simple’ lophotrochozoans?
ecologically reminiscent of filter-feeding poriferans
morphologically reminiscent of sessile cnidarians (superficially at least)
bilaterally symmetrical, but have limited cephalization
lack key organ systems (circulatory, excretory) that were seen in molluscs and annelids
the evolution of the bilateria is associated with increased complexity, but not a universal trait across all groups
- complexity can be lost
What is phylum platyhelminthes?
free-living flatworms
dorsoventrally flat, bilaterally symmetrical, non-segmented worm
triploblastic but lack a coelom (acoelomate)
they are lophotrochozoans according to molecular data, yet have neither a lophophore nor a trochophore
~30000 described species, with ~20000 of them being parasites
describe turbellarian morphology
dorsoventrally flattened
cephalized body plans
the gut is ‘blind’ (no anus) and the mouth is ventral
they lack circulatory and respiratory systems
have organ systems dedicated to excretion and gamete production (including copulating structures)
acoelomate - body lacks coelum
coordinated waves of muscle action cause the worm to ripple, facilitating crawling or swimming
the ventral surface covered in cilia and mucus-secreting glands, can also be used for locomotion (gliding)
describe turbellarian reproduction
asexual reproduction via budding and dividing
sexual reproduction is widespread
- most are simultaneous hermaphrodites that
fertilize via reciprocal copulation, and lay eggs
describe turbellarian development
protostome-like development seems to be the ancestral state, but some undergo ‘dispersive cleavage’
- early cell division result in unconnected (dispersed)
cells, not a cohesive connected mass of cells
- the cells float freely in the egg yolk, then eventually
reunite and differentiate
both direct and indirect development is seen
larval stages are lobed with multiple eyespots
- dont resemble trochophore larvae
describe turbellarian ecology
mostly marine, but also live in freshwater and moist terrestrial habitats
most are predators, use toxins to subdue their prey
- terrestrial hammerhead flatworms eat earthworms
and may harm soil ecosystems (especially invasive)
- some marine species eat coral and are pests of
aquarium facilities
parasitism has evolved multiple times within this group
What are parasitic platyhelminths?
main group of parasitic flatworms is called the neodermata
3 subgroups - all are vertebrate parasites, but thay vary in life cycle and anatomy:
MONOGENEANS - external parasite, direct lifecycle, non-segmented
TREMATODES (flukes) - internal parasite, indirect lifestyle, non-segmented
CESTODES (tapeworms) - internal parasite, indirect life cycle, pseudo-segmented
Describe monogeneans
external parasites, usually of fish
have a direct lifecycle - infect a single host species
- infectious larvae attach to host, mature and
reproduce (via hermaphroditic crossing, selfing, or
parthenogenesis)
- eggs or larvae released, go on to infect same host
species
non-segmented body plan, but with complex attachment structures (haptors)
describe Trematodes (flukes)
internal parasites of vertebrates
- infect the lungs, liver, or blood vessels, depending
on species
indirect lifecycle
- infect both the definitive host and one or more
intermediate hosts (often molluscs)
indirect lifecycle helps ensure transmission back to the definitive host
- intermediate hosts are often linked to the
definitive hosts via the food chain -v via same
trophic web
- asexual reproduction within the intermediate host
amplifies population size, increasing transmission
odds
- some species manipulate host behaviour
describe cestodes (tapeworms)
internal parasites of vertebrates
- typically in gut, absorb nutrients via skin (no
mouth)
indirect lifecycles (usually involving crustaceans)
attach head to intestinal wall using a scolex (hooks and suckers)
have a pseudosegmented body plan, long tail consisting of hermaphroditic reproductive units called proglottids
- unlike annelids, internal body isnt partitioned by
septa
- segments form via constriction of non-segmented
body plan
can be more than 10m long, with 1000s of proglottids, each capable of producing 1000s of eggs per day
What is the impact of parasitic flatworms?
more than 100 million people are infected - normally due to contaminated meat or water
- symptoms include nutritional deficiencies
(intestinal infection), cancer (tissue encystation)
- usually reside within digestive tract or associated
organs, but not always (e.g. brain)
global problem, with largest effects on the poor (cant afford fuel and energy for safe cooking and storage of meats)
- platyhelminths have impacts on health of livestock,
pets and aquaculture facilities, large economic
consequences
Are flat worms ‘simple’ lophotrochozoans?
yes
they are acoelmate
lack a complete gut and other organs seen in annelids and molluscs
evolution of bilateria is associated with increased complexity, but it is not a universal trait across all groups
- complexity can be lost
