THE PHYLUM ECHINODERMATA

Echinoderms (Phylum
Echinodermata) are a phylum of marine animals.
Echinoderms are found at every ocean depth,
from the intertidal zone to the abyssal zone.
Aside from the problematic Arkarua, the first
definitive members of the phylum appeared near
the start of the Cambrian period.
The phylum contains about 7,000
living species, making it the second-largest grouping of deuterostomes, after the
chordates. Echinoderms are also the largest phylum that has no freshwater or
terrestrial representatives.

A. Asteroidea
The Asteroidea (star fish) is one of the largest and most familiar
classes within the Phylum Echinodermata. These animals, commonly known as
sea stars or starfishes, form a diverse and speciose group. There are
approximately 1600 extant species (Hyman 1955; Clark 1977; Clark and
Downey 1992) which are found throughout the world's oceans. Following the
classification of Blake (1987), these species are grouped into seven orders:
Brisingida, Forcipulatida, Notomyotida, Paxillosida, Spinulosida, Valvatida
and Velatida.

1. Body Structure of Star Fish

Starfish express pentamerism or pentaradial symmetry as adults.
However, the evolutionary ancestors of echinoderms are believed to have
had bilateral symmetry. Starfish, as well as other echinoderms, do exhibit
bilateral symmetry, but only as larval forms.
 The bodies of starfish are composed of calcium carbonate
components, known as ossicles. These form the endoskeleton, which takes
on a variety of forms that are externally expressed as a variety of structures,
such as spines and granules. The architecture and individual shape/form of
these plates which often occur in specific patterns or series, as well as their
location are the source of morphological data used to classify the different
groups within the Asteroidea. Terminology referring to body location in sea
stars is usually based in reference to the mouth to avoid incorrect
assumptions of homology with the dorsal and ventral surfaces in other
bilateral animals. The bottom surface is often referred to as the oral or
actinal surface whereas the top surface is referred to as the aboral or
abactinal side.

2. Ambulakral System
Ambulakral system is a system of waterways. This drainage system
consists of:
a. Madrepori t, is the hole where the ingress of water from outside the body.
b. Tract stones
c. Channels ring
d. radial lines, spreading throughout the body.
e. Lateral channels
f. Ampulla
g. Tube foot
This system serves to move, breathe or open their prey. In this
animal sea water entering through the dorsal plate of small holes
(madreporit) towards the stone vessels. Then proceed to the ring that has a
branch line to five radial arms or next to a canal called the lateral line. At
each branch there are rows of tube feet and paired with a sort of bubble
Muscular or also called the ampulla. From the lateral canal, water enters
into the ampulla. These channels ends in the ampulla. If the ampulla
contracts, then the water pressure and into the tube feet. As a result
 changing the tube feet long panhandle. When these animals will move to the
next right, then right foot tube will hold the objects in beneath and legs
others will be free. Next ampulla expands again and the water will move
opposite direction of entry. Right foot tube that holds the object was
This animal would drag the body towards him. That's how these animals
move. In besides these animals also move in water using arm movements
arm.

3. Digestion System
The mouth of a starfish is located on the underside of the body, and
opens through a short esophagus into firstly a cardiac stomach, and then, a
second, pyloric stomach. Each arm also contains two pyloric caeca, long
hollow tubes branching outwards from the pyloric stomach. Each pyloric
caecum is lined by a series of digestive glands, which secrete digestive
enzymes and absorb nutrients from the food. A short intestine runs from the
upper surface of the pyloric stomach to open at an anus in the center of the
upper body.
Many sea stars, such as Astropecten and Luidia swallow their prey
whole, and start to digest it in the stomachs before passing it into the pyloric
caeca. However, in a great many species, the cardiac stomach can be everted
out of the organism's body to engulf and digest food. In these species, the
cardiac stomach fetches the prey then passes it to the pyloric stomach,
which always remains internal.
Some species are able to use their water vascular systems to force
open the shells of bivalve molluscs such as clams and mussels by injecting
their stomachs into the shells. With the stomach inserted inside the shell, the
sea star is able to digest the mollusc in place. The cardiac stomach is then
brought back inside the body, and the partially digested food is moved to the
pyloric stomach. Further digestion occurs in the intestine. Waste is excreted
through the anus on the aboral side of the body.
 Because of this ability to digest food outside of its body, the sea
star is able to hunt prey that are much larger than its mouth would otherwise
allow, such as clams and oysters, arthropods, small fish, and molluscs.
However, some species are not pure carnivores, and may supplement their
diet with algae or organic detritus. Some of these species are grazers, but
others trap food particles from the water in sticky mucus strands that can be
swept towards the mouth along ciliated grooves.

4. Reproduction
Fertilization takes place externally, both male and female releasing
their gametes into the environment. The resulting fertilized embryos form
part of the zooplankton in most species. However, some species brood their
eggs, either by simply sitting over them, or using specialised brooding
baskets on their aboral surface. In at least one species (Leptasterias tenera),
the eggs are actually brooded inside the pyloric stomach. In these brooding
species, the eggs are relatively large, and supplied with yolk, and they
generally develop directly into miniature starfish, without a larval stage.
Brooding is especially common in polar and deep-sea species, environments
less favourable for larvae.
Sea stars commonly reproduce by free-spawning: releasing their
gametes into the water where they are fertilized by gametes from the
opposite sex. To increase their chances of fertilization, sea stars probably
gather in groups when they are ready to spawn, use environmental signals to
coordinate timing (day length to indicate the correct time of the year, dawn
or dusk to indicate the correct time of day), and may use chemical signals to
indicate their readiness to each other.
Some species of sea star also reproduce asexually by
fragmentation, often with part of an arm becoming detached and eventually
developing into an independent individual sea star. Sea stars can be pests to
fishermen who make their living on the capture of clams and other mollusks
at sea as sea stars prey on these. The fishermen would think they had killed
 the sea stars by chopping them up and disposing of them at sea, but each
fragment would regenerate into a complete adult, ultimately leading to their
increased numbers until the issue was better understood. A sea-star arm can
only regenerate into a whole new organism if some of the central disk of the
sea star is part of the chopped off arm. A starfish which is regenerating from
a severed arm, with one full-sized arm and the other arms small, is
sometimes called a comet starfish.

5. Nervous System
Echinoderms have rather complex nervous systems, but lack a true
centralized brain. All echinoderms have a network of interlacing nerves
called a nerve plexus which lies within, as well as below, the skin. The
esophagus is also surrounded by a central nerve ring which sends radial
nerves into each of the arms, often parallel with the branches of the water
vascular system. The ring nerves and radial nerves coordinate the sea star's
balance and directional systems.
Although the echinoderms do not have many well-defined sensory
inputs, they are sensitive to touch, light, temperature, orientation, and the
status of water around them. The tube feet, spines, and pedicellariae found
on sea stars are sensitive to touch, while eyespots on the ends of the rays are
light-sensitive. The tube feet, especially those at the tips of the rays, are also
sensitive to chemicals and this sensitivity is used in locating odor sources,
such as food.
The eyespots each consist of a mass of ocelli, consisting of
pigmented epithelial cells that respond to light and narrow sensory cells
lying between them. Each ocellus is covered by a thick, transparent, cuticle
that both protects them and acts as a lens. Many starfish also possess
individual photoreceptor cells across their body and are able to respond to
light even when their eyespots are covered.

B. Ophiuroidea
 The example of Ophiuroidea is brittle star. Brittle stars, or
ophiuroids, are echinoderms, closely related to starfish. They crawl across the
seafloor using their flexible arms for locomotion. The ophiuroids generally
have five long slender, whip-like arms which may reach up to 60 centimetres
(24 in) in length on the largest specimens. They are also known as serpent
stars.
Ophiuroidea contains two large clades, Ophiurida (brittle stars) and
Euryalida (basket stars). Many of the ophiuroids are rarely encountered in the
relatively shallow depths normally visited by humans, but they are a diverse
group.
There are some 1,500 species of brittle stars living today, and they
are largely found in deep waters more than 500 metres (1,650 feet) down.

1. Body Structure
Of all echinoderms, the Ophiuroidea may have the strongest
tendency toward 5-segment radial (pentaradial) symmetry. The body outline
is similar to that of starfish, in that ophiuroids have five arms joined to
central body disk. However, in ophiuroids the central body disk is sharply
marked off from the arms.
The disk contains all of the viscera. That is, the internal organs of
digestion and reproduction never enter the arms, as they do in the
Asteroidea. The underside of the disc contains the mouth, which has five
toothed jaws formed from skeletal plates. The madreporite is usually located
within one of the jaw plates, and not on the upper side of the animal as it is
in starfish.

C. Echinoidea
Spherical Echinoidea or pipih, without arm. Echinoidea that
spherical e.g. sea urchin (diadema saxatile) and oceanic porcupine (Arabcia
punctulata). Animal body surface this prickly elongated. Echinoidea memilki is
typical digestion tool, which is the so called complex crop lentera aristoteles.
 Function of that crop is subject to be mill its food that as algae or being
oddment. Echinoidea who gets pipih's body e.g. sand dollar (Echinarachnius
parma). oral's nurginal surface its body pipih, meanwhile aboralnya's flank
rather curve. Its body most covers by ground barb and meeting. Its barb is
functioning for moves, dig up, and protects its body surface of dirt.
ambulakral's foot just exists oral alongside that functioning utuk transports
food.

D. Holothuroidea
The example of Holothuroidea is Sea Cucumber. Sea cucumbers
are echinoderms from the class Holothuroidea. They are marine animals with a
leathery skin and an elongated body containing a single, branched gonad. Sea
cucumbers are found on the sea floor worldwide. There are a number of
holothurian species and genera, many of which are targeted for human
consumption. The harvested product is variously referred to as trepang, bêche-
de-mer or balate.
Like all echinoderms, sea cucumbers have an endoskeleton just
below the skin, calcified structures that are usually reduced to isolated
microscopic ossicles (or sclerietes) joined by connective tissue. In some
species these can sometimes be enlarged to flattened plates, forming an
armour. In pelagic species such as Pelagothuria natatrix (Order Elasipodida,
family Pelagothuriidae), the skeleton and a calcareous ring are absent.

Body Structure
Sea cucumbers are typically 10 to 30 centimetres (3.9 to 12 in) in
length, although the smallest known species is just 3 millimetres (0.12 in) long,
and the largest can reach 1 metre (3.3 ft). The body ranges from almost
spherical to worm-like, and lacks the arms found in many other echinoderms,
such as starfishes. The anterior end of the animal, containing the mouth,
corresponds to the oral pole of other echinoderms (which, in most cases, is the
underside), while the posterior end, containing the anus, corresponds to the
 aboral pole. Thus, compared with other echinoderms, sea cucumbers can be
said to be lying on their side.

E. Crinoidea
Resembling a plant more than an animal, sea lilies are some of the
most attractive but least-known animals of the deep oceans. Sea lilies are
members of the class Crinoidea (phylum Echinodermata), a class that also
includes the feather stars. Sea lilies are also related to more familiar
echinoderms such as sea urchins, starfish, and sea cucumbers. Unlike these
small, squat forms, however, the main body of a sea lily is composed of an
extended, slender stalk that is usually anchored by a simple rootlike
arrangement of arms. The main body, which has a jointed appearance, may
reach up to 27.5 in (70 cm) in length, but most living species are much smaller.
(Some fossil species have been discovered with a stalk exceeding 82 ft, or 25
m, in length.) Some sea lilies have a branched structure, while others are
simple and straight in design. Sea lilies vary considerably in color, but most are
delicate shades of yellow, pink, or red.
The main part of the body, the calyx, is carried at the top of the
stalk, rather like a crown. This contains the main body organs and is further
developed with a series of 5-10 featherlike arms. The number of arms appears
to vary with water temperature: some of the larger, tropical species may have
up to 200 arms. Each arm is further adorned with a large number of delicate
pinnules which, when extended, increase the area available for trapping food.
When the animal is not feeding, or if the arms are in danger of being eaten by a
predatory fish or crustacean, the arms may be folded and the entire crown
withdrawn. The mouth is located in the central disk at the base of these arms.
The arms and pinnules together trap fine particles of food from the swirling
water currents. Tiny grooves on the surface of each pinnule lead into larger
grooves on the main arm, like streams joining a river, and continue across the
surface of the calyx to the mouth.
 Rather than being composed of living tissue, much of the body is
made up of calcium carbonate, which provides a rigid framework that supports
the head of the animal. Within this protective armour, the actual movements of
the sea lily are restricted to simple bending, unlike the movements of feather
stars, which are mobile and may move from safe resting places to an exposed
site for feeding purposes.
Until recently, most sea lilies were only known from fossil remains.
These species appear to have been quite abundant at certain times in the
geological history of Earth. Today, some 80 species are known to exist.
Despite this, little is known about these animals, largely because the vast
majority tend to live in deep ocean trenches, often at depths of 3,935-4,265 ft
(1,200-1,300 m) and occasionally as deep as 29,530 ft (9,000 m). Virtually no
light penetrates the water at these depths, and living organisms are few and
widely scattered. Most species living at such depths need to conserve their
energy, and sea lilies, by virtue of their few living organs and tissues, probably
have a very low rate of metabolism. Most of the food they receive comes in the
form of "fecal rain" from the upper water levels: as animals and plants die,
parts of their bodies fall through the water column where it is scavenged by
other organisms. Although scavenging animals are widespread and numerous
in the oceans, some of these materials do eventually reach the deepest regions
and, in so doing, ensure a steady if limited supply of foodstuffs to specialized
species such as sea lilies.
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