lecture 3 - 02/10/24 Flashcards
What is phylogeny?
A branching diagram that shows how biological groups are related
(also an evolutionary tree)
Why are phylogenies important?
to classify organisms into groups
to understand evolutionary change and relationship patterns
Are phylogenies set in stone?
No
they are estimates
can change with new data or new analysis methods
How many phyla are there?
over 30 recognised phyla
What are our most distant animal relatives?
Poriferans
Ctenophores
Cnidarians
What are Phylum Porifera?
The sponges
What does sessile mean?
unmoving
What is a porifera?
- sessile
- irregularly-shaped
- filter-feeder
- wide variety of shapes and colours
How many species of porifera are there?
> 5000 descibed species
(1000s more species suspected but undescribed)
Describe a sponges morphology?
simple bag-like body plan - inner/outer cell layers and a mostly non-cellular internal matrix
What is the non-cellular internal matrix of a sponge called?
mesohyl
How do sponges generate a water current?
The choanocytes (inner layer of cells) pump their whip-like flagella
Are sponges symmetrical or asymmetrial?
asymmetrical
How do sponges consume food?
water is drawn through pores within the body wall and inflowing organic material filtered and consumed
What does the mesophyl contain?
structural elements
ameboid cells - irregular shaped microbes
Do sponge have organs?
no organs, no nervous system, no muscle tissues
very simple anatomy
How do sponges boost filter feeding efficiency?
develop channels and pockets - increase SA and boosts inflow
more choanocytes so more filter feeding
Why are sponges important?
important in ecosystems, increases water quality
Why are choanocytes called ‘collar cells’
due to the ring of microvilli that surrounds the flagellum, and that are used for filter-feeding
What are choanoflagellates?
the mostly closely related microbial relatives of animals
have a similar appearance to choanocytes
What is homology?
shared ancestry
What nis biomineralization?
the biological production of hard, inorganic mineral structures
What do many sponges secrete?
hard spicules
what is a spicule?
inorganic mineral structure
function of sponge spicules
strengthen the body wall - help deter predators
history of sponge spicules
provide some of the earliest fossil evidence of animals
What do many invertebrates have poor fossil records?
due to lack of mineralized body parts
Describe a sponges distribution
distributed globally, from nearshore to ocean floor, as well as (rarely) freshwater
What do filter feeders consume?
microscopic/dissolved organic matter
Why are a few species of sponge carnivores?
adapted to live in nutrient poor deep waters where filter-feeding is ineffective
How do carnivorous sponges catch food?
secrete sticky substance which sticks to very small organisms
What is the sponge loop?
carbon cycling in coral reefs
how do sponges carbon cycle?
convert dissolved carbon to cellular material that other species can eat
What is a reef?
underwater mound, biological or geographical
What is sequential hermaphroditism?
an individual can switch sex as it ages
What is broadcast spawning?
gametes are released into external environment of the ocean
How do sponges reproduce sexually?
males release gametes in their outflow (broadcast spawning) but females usually do not
internal fertilization and brooding of embryos
how do sponges reproduce asexually?
freshwater species produce asexual spores (gemmules) to ensure survival under poor conditions - seasonally challenging
tiny fragments of sponges can survive and form new individuals (regeneration)
Do sponge embryos undergo gastrulation?
no
early sponge embryos are usually hollow or filled, not layered, and cell-fate is more flexible
what is indirect development?
where larvae and adults have distinct body plans, and maturation requires metamorphosis
How are soft poriferans relevant to humans?
farmed for use as bath sponges
and used as a source of bioactive compounds (pharmaceuticals)
can be grown in active aquaculture facilities to improve water quality by filter feeding (bioremediation)
What are soft poriferans?
those that lack spicules
What is bioremediation?
fixing a polluted environment
What is phylum ctenophora?
comb jellies
describe a typical comb jelly
gelatinous, radially symmetrical, actively-swimming predator
How do comb jellies swim?
using eight rows of fused cilia (combs or ctenes) and are the largest animals who use cilia for locomotion
How many species of phylum ctenophora are there?
~200
(many more but too delicate to easily collect and study)
What adaptation do ctenophores have that increases stomach SA?
stomach is branched
What is between the skin and digestive lining in ctenophores?
between the epidermis and the gastrodermis is the mostly acellular and gelatinous mesoglea
What are locomotory combs?
fused cilia rows
how many locomotory combs do ctenophores have?
8 run top-to-bottom along the outside
How are the locomotory combs controlled?
neurally controlled
linked to an optical sensory organ that is used for orientation
Do ctenophores have integrated tissues?
yes
and simple organs
describe ctenophore muscles
muscular, retractable tentacles covered in sticky, toxic cells found in most species
most have a round body
describe ctenophore gut morphology
mouth at bottom, anal openings at top
(a through/complete gut)
describe ctenophore symmetry
symmetrical - more organised body plan
radially symmetrical
what is radial symmetry?
revealed by rotation around an axis and not a reflection across a plane
describe ctenophore ecology
exclusively marine, globally distributed
prey upon microbes, marine invertebrates, fish larvae
can have large effects on food webs including fisheries (especially invasive species)
some species eat jellyfish and reuse the sting cells as weapons when hunting
some species are flattened and adapted for benthic lifestyles
What is benthic lifestyle?
crawling on the sea floor
what is a pelagic lifestyle?
swimming/floating
describe ctenophore reproduction
most species are simultaneous hermaphrodites
sexual reproduction typically involves broadcast spawning and external fertilization (potential for self fertilization)
benthic species are atypical, internal fertilization and asexual reproduction via fragmentation and regeneration
What happens to the embryo after cleavage in ctenophore development?
the embryo undergoes gastrulation
results in 2 germ layers
- outer ectoderm
- inner endoderm
What does formation of germ layers facilitate?
tissue/organ development
Do most species of ctenophores undergo direct development?
yes
no metamorphosis - young are ‘juveniles’ not ‘larvae’
sponges vs comb jellies
biologists are conflicted on which are our most distant animal relatives
data is messy and incomplete
analysis methods are complex and debated
answer has implications for understanding the evolution of complex nervous systems
What does sessile mean?
attached to the ground
describe a typical cnidarian
marine
radially symmetrical
gelatinous predator that alternates between sessile and swimming phases
over 10000 species
What are the exceptions for cnidaria?
many lack one of the 2 phases
many acquire nutrients from symbiotic photosynthetic microbes (zooxanthellae)
many secrete hard mineralized skeletons
many are colonial
a few freshwater and parasitic species exist
describe a polyps
sessile, with mouth facing up
describe medusae
mobile, with mouth facing down
Describe cnidarian symmetry
radially symmetrical with notable tentacles
describe cnidarian gut morphology
gut is blind (no anus) - gametes and waste expelled through mouth
Describe cnidarian nervous system morphology?
a diffuse nerve network controls the body and tentacle musculature
Describe cnidarian body morphology?
filled with gelatinous mesoglea - acts as a hydrostatic skeleton
Describe cnidarian sensory system morphology?
tend to be more complex in medusae (some jellyfish have eyes)
use muscles to locomote
What are cnidocytes?
special type of cell produced only by cnidarians
What are nematocysts?
in cnidocytes
tiny but most species are covered in them (particularly tentacles)
subcellular organelles that consist of a hollow-tube coiled up in a capsule
capsule can explode outward, tangling or piercing enemies or prey and delivering potent toxins
some creatures can steal and use them (like ctenophores)
Describe the biphasic life cycle of a cnidarian
(especially jellyfish) alternate between medusa and polyp phases
medusae reproduce sexually, producing larvae that swim to ocean floor and grow into polyps
polyps reproduce asexually, completing the cycle by producing numerous immature medusae
What are the exceptions for cnidarian biphasic life cycle?
anemones and corals are sexually reproductive polyps
some hydrozoan jellyfishes skip the polyp stage, with larvae that mature into medusae
a few species are potentially immortal, with medusae that can revert to the immature polyp stage
describe cnidarian coloniality
many species are colonial - consist of zooids
in some species the zooids are morphologically and functionally similar to one another
in some species (e.g. siphonophores) the zooids can be morphologically and functionally distinct (highly specialized zooids effectively act as the organs of a superorganism)
What does colonial mean?
survive as part of a larger unit
what is a zooid?
asexually produced clusters of connected, interdependent individuals
Describe cnidarian reproduction
both sexual and asexual reproduction are widespread
polyps can reproduce asexually by splitting or fragmenting, then regenerating
jellyfish usually have separate sexes while corals and sea anemones tend to be hermaphroditic
synchronized broadcast spawning is common
(depends on environment cues)
the males of some box jellyfish have mating behaviours and transfer sperm directly to females
Describe cnidarian development
Diploblastic
their embryos undergo gastrulation and have 2 germ layers, ectoderm and endoderm
embryo develops into a planula larvae - uses cilia to swim and find a suitable spot to settle and metamorphose
Describe cnidarian ecology
Biomineralizing - sensitive to pH
reefs formed by colonial, stony corals are a critically important habitat for many species
- sensitive to ocean acidification
many species host symbiotic zooxanthellae - provide nutrients via photosynthesis
- sensitive to ocean warming
- mutually advantageous relationship
many animals prey on cnidarians
- e.g. sea turtles
Describe cnidarian human relevance
tropical reefs - major ecotourism industries
jellyfish are farmed and eaten
many produce pharmaceutical bioactive compounds
cnidarian fluorescent proteins (GFPs) are a valuable tool in molecular/cell biology research
name the key similarities among sponges, ctenophores and cnidarians
mostly marine, very few freshwater, no terrestrial
sexual reproduction typically involves broadcast spawning
hermaphroditism and/or sexual reproduction are widespread
all lack tissues/structures dedicated solely to respiration and excretion, relying instead on cellular-level processes
name the important differences between ctenophores and cnidarians vs sponges
they have embryos with 2 germ layers due to gastrulation - sponges do not
they have complex organs formed of nervous and muscle tissues - sponges do not
they have well defined symmetrical body plans - sponges generally do not
they display greater embryological, anatomical and behavioural complexity than sponges
