Module 5 Flashcards
Cnidaria
placed after sponges in the animal kingdom - this suggests they are similar in terms of anatomy
- restricted to aquatic environments
- mostly marine
- many organisms depend on them for food and shelter
Characteristics of Cnidaria
radial or bilateral symmetry
- mostly radial
polyps and medusa body plans
Polyps body plan
benthic and sessile
- largely exist attached to the seafloor
- sit with their tentacles and mouths up
Medusae body plan
pelagic and free-swimming
- floating in and around water using water currents and waves
Diploblastic
cnidarians are diploblastic - have two cell layers
- endoderm
- ectoderm
- these are seperated by the mesoglea
Mesoglea
non-cellular jelly-like matrix in cnidarians that separates the endoderm and ectoderm
- serves as an internal skeleton
- aids with structural support and provides elastic properties
Hydrostatic skeleton
contain no rigid bones
- maintained by the internal pressure of fluids within organisms
- provides structural rigidity
- muscle contractions create changes in hydrostatic pressure – allows animals to hold their shape without bones or solid skeletal structures
Why is a hydrostatic skeleton beneficial in cnidarians?
the lack of rigidity in hydrostatic skeletons is beneficial for the functioning of their tentacles
Cnidae
stinging cells
- nematocysts rest coiled inside cnidocyte cells in the mouth and tentacles of cnidarians
-when triggered, these are fired out in a cnidoblast
- water rapidly fills the cells to increase hydrostatic pressure and fire the cnidoblast
- chidas are shed after firing but rapidly regenerate
- can be used for attachment and locomotion on some species
Simple nervous, digestive, and muscular system in cnidarians
cnidarians have true tissues, nervous and muscular systems
- nerve net: range of sensory neurons distributed around their bodies
- nervous system network in replacement of a cephalisation
- have a neuromuscular system with bi-directional signal transfer between sensory and muscular systems
rhophalia: sensory cells which host statocysts for balance and orientation and ocelli for photosensor reception
epitheliomuscular cells: run longitudinally and circularly around the body with contractions that result n movement and locomotion in any direction
Cephalisation
concentration of cells forming the head or brain
- cnidarians do not have these but make up for it with a nervous system network/nerve nets
Nerve net
range of sensory neurons distributed around the body
Rhopalia
sensory cells
- statocysts: balance and orientation
- ocelli: photosensory
Epitheliomuscular cells
run longitudinally and circularly around the body with contractions that result in movement and locomotion in any direction
Cnidarians lack excretory, circulatory or respiratory systems
blind gut: oral and asborel end with one opening
gastrovascular cavity – differs for species
Gastrovascular cavity
siphonoglyph: ciliated groove at the mouth and pharynx that helps to create in-current water flow
- assists in assessing prey
mesenteries and septa: body-wall extensions that create folds and surface area inside the gastrovascular cavity
- paired or unpaired
mesentrial filaments: long and thin digestive structures that can be expelled to help capture and reel in food
- used as an offensive weapon
Four main classes of cnidaria
Anthozoa
Hydrozoa
Scyphozoa
Cubozoa
Anthozoa
mostly benthic
- Hexacorallia
- Scleractinia
- Ceriantharia
- Octocorallia
Hexacorallia
anthozoa
- anemones and corals
- both solitary and colonial forms
- have tentacles and mesenteries in multiples of six
- 0 to 2 siphonoglyphs
- tentacles are unbranched with polyps that are diverse in structure
- hard or soft skeletons
Scleractinia
order with Hexacorallia - Anthozoa
- true hard corals
- secrete a calcium carbonate skeleton in colonies formed of tiny polyps that are identical clones
- have a symbiotic relationship with zooxanthellae
- tentacles in multiples of 6
Ceriantharia
Anthozoa
- tube-dwelling anemones
- unpaired mesenteries and unpaired tentacles
- long outer tentacles are used for food capture and defence
- small inner tentacles are used for food manipulated and ingestion
- solitary animals that bury in soft sediment with their tentacles sticking out, waiting to capture foo
Octocorallia
Anthozoa
- soft corals, including sea pens and sea fans
- more uniform in structure with 8 pinnate tentacles and mesenteries
- pinnate: tiny branches on each tentacle
- have a single siphonoglyph
- almost all are colonial
Coral polyps
autotrophic or heterotrophic
Hydrozoa
marine and freshwater ecosystems
solitary and colonial forms
polyp and medusae forms