phylum echinodermata. characteristics n echinodermata are all marine, triploblastic unsegmented...
DESCRIPTION
Characteristics n There is no cephalization F Which explains why Patrick isn’t the smartest creature in bikini bottom! n There is a meaningful gradient in all echinoderm bodies: u one surface has the mouth and tube feet (oral or ambulacra), u while one does not (aboral) n The anus is often, but not always, aboral.TRANSCRIPT
Phylum Echinodermata
Characteristics Echinodermata are all marine,
triploblastic unsegmented coelomates
Phylum has 3 unique features: pentagonal symmetry (bilateral in
larvae) calcite spicules embedded in the
skin, often partly fused Tube feet (podia)
Characteristics There is no cephalization
Which explains why Patrick isn’t the smartest creature in bikini bottom!
There is a meaningful gradient in all echinoderm bodies: one surface has the mouth and tube
feet (oral or ambulacra), while one does not (aboral)
The anus is often, but not always, aboral.
An unhurried phylum.. No echinoderm moves fast, apart
from a very few deep sea holothurids which swim actively
Crinoids are sessile, the others crawl at a rate of mm / minute
During one Antarctic marine survey a starfish was tagged. A year later the same animal was in the same exact spot, having apparently done nothing at all!
Originally… The ancestral echinoderm was a
sessile filter-feeder, extending its oral surface upwards to capture food
This sedentary design has evolved into motile forms where the feeding surface faces downwards
Characteristics The only connected phylum is our
own, the chordates - based on embryological evidence.
Look at Evolutionary Tree in textbook
Deuterosome Radial cleavage Anus forms first
First species to evolve with this type of development
Characteristics The aboral surface is rough and
spiny Around the base of the spines are
pedicillaria: tiny jaws used to keep the body surface free of debris, protection and aide in food capture
Water Vascular System Primary function is locomotion and food
gathering, in addition to respiration and excretion
From the aboral surface is a madreporite (allows pressure equalization and top up water supply) which is the only asymmetrical tube in the system
It connects to an inner Ring Canal in which branches into 5’s lateral canals (one down each of the star fishes arms)
Water Vascular System From the Lateral canals is many
ampulla (muscular sacs) which connected to the suckers on the outer surface of the starfish
Some lack suckers By filling the ampulla and coelom
with liquids and applying pressure, allows arms to stiffen creating a hydraulic system.
Tube feet Podia (tube feet) are not scattered over
the body surface They lie in 10 rows (5 pairs), the
ambulacral grooves Each tube foot + its ampulla is isolated
from the water vascular system by a valve
Tube feet vary - starfish have muscular suction cups, other forms have sticky tips.
Crinoids are different - primitive
Reproduction Gonads lie as 10 (2N) paired
structures at the base of ambulacral grooves.
External reproduction Sexes are separate, and discharge
gametes into the sea water
Development Larval Stage- free-swimming, bilateral
(some with direct development) Metamorphosis
Metamorphosis involves a dramatic reorganization of a bilateral larva into a radial juvenile
Larval mouth and anus disappear and a new mouth and anus will form.
What was the left side becomes the oral surface
What was the right side becomes the aboral surface
Phylum Echinodermata
EVOLUTION
Sadly... Of the 13 classes of echinoderms
known, 8 are extinct. Echinoderms were dominant forms
in Carboniferous seas, but have suffered a long-term decline in phyletic richness
Phylum Echinoderm ataL iv in g fo rm s o n ly
OphiuroideaB rit t le s ta rs
CrinoideaC rin o id s - fe a th e r s ta rs
EchinoideaS e a u rch ins
Astero ideas ta rf ish
Holo thurideas e a cu cu m b e rs
Concentricyclo idead isco v e re d 1 9 8 6
Classes Class Crinoidea Class Asteroidea Class Ophiuroidea Class Echinoidea Class Holothuroidea
Class Crinoidea Feather stars & Sea lilies Abyssal filter feeders 5000 fossil spp, 620 living Body made of ossicles 10 arms have podia (no
ampullae) feeding particles to the mouth.
Arms can move Mouth and anus are both on
oral side
Class Asteroidea “Starfish” Active predators
feed on bivalves use suction cups to pull open the
shells with forces of up to 5kg The stomach is eversible, and
can be partially inserted inside prey’s shell (enzymes but no toxins)
Class Ophiuroidea Brittle Stars Have arms sharply
demarcated from the body disc.
The internal structure of the arms involves interlocking internal ossicles (also called vertebrae)
Are primarily filter feeders, raising their arms in a current to capture particulates
Class Echinoidea Recipe: take a starfish and roll
its 5 arms together into a ball, then fuse and calcify with an external armor
The armor is called the test Very small aboral surface
Class Echinoidea Sea Urchins Herbivores, preferring macro-algae They can be highly effective
grazers, creating “urchin barrens” devoid of algae
The mouthparts are unique, known as Aristotle’s Lantern. 5 continually growing chisel teeth Each tooth with 8 supporting
skeletal pieces
Class Holothuridae Sea Cucumber They have no calcitic skeleton,
except for spicules embedded in a leathery skin
Most are immobile, and lie on the sea bed rolling back and forth with the swell. Some have limited mobility using their tube feet.
Despite retaining 5-radiate anatomy, they have re-evolved bilateral symmetry along their long axis (the oral-aboral)
Class Holothuridae They mainly feed on detritus Oxygen exchange is
performed using gills inside their anus
They have 2 odd defensive strategies: Squirting a sticky goo Voiding their entire
intestines