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