Starfish Usually Reside in Coral Reefs, Sandy Regions, Rocks, and They Are Always Marine

Echinodermata

Asteroidea

Habitat:

Starfish usually reside in coral reefs, sandy regions, rocks, and they are always marine areas. (Saltwater)

Feeding:

Mainly scavengers and carnivores. They eat mollusks, using an eversible stomach to infiltrate and digest its prey from the inside with primary enzymes. Some species are also detritivores which means they absorb decomposed plant and animal matter floating around in the ocean.

Mouth is located on the underside, food goes through a short esophagus, a cardiac stomach a pyloric stomach, a short intestine, and then out the anus at the center of the top portion of the star. Digestive glands are in the arms.

They themselves are very vulnerable to predation, but losing some appendages is no big deal since they can utilize regeneration.

Reproduction:

Most starfish reproduce by dispersing buoyant eggs and sperm into the water for fertilization. These then attach to various surfaces like the underside of rocks. Some starfish brood their eggs as well either by sitting on them or carrying them in special structures. Sometimes they use pseudo copulation, which is when a male ejects sperm around the female and uses environmental signals to time the spawning.

Asexual reproduction is also possible through fragmentation. Even a single tip can regenerate into a full individual as long as the central disk is not included. Sometimes a regenerating starfish with one full arm and smaller regenerating arms is called a “comet” starfish.

Unique Characteristics

Pentaradial symmetry, though some star fish can exceed 5 rays (up to 50!).

Asteroids move using the water vascular system, using muscle contractions to squeeze fluid to the tube feet which elongate.

Madreporite plate is used to channel water for the water vascular system.

Some stars can live up to 35 years but life spans can vary.

Ophiuroidea

Habitat:

They are found in all seas, at all latitudes, and from the intertidal to the abyssal

zone (to a depth of 6,000 meters).

Feeding:

Carnivores, filter feeders, and scavengers. Can use the mucus on their feet to trap phytoplankton, bacteria, and sometimes medusae.

Some can capture small crustaceans or worms by looping them with rays.

Mouth contains five jaws and is used for ingestion as well as egestion.

10 sacs used for digestion but never extend into the arms.

Reproduction

Many species brood developing larvae in the bursa, like giving birth to live young.

Can regenerate limbs unless all arms are lost.

Ophiuroidea are very closely related to asteroidea but here are unique characteristics:

Five slender, flexible, whip-like arms for snake like movement (also known as serpent stars) instead of suckers. Much faster.

Some species lack a madreporite. Lack suckers and ampullae.

Gas exchange occurs in the bursae, located at the start of each leg. Water flows by means of cilia or muscular contraction

Echinoidea

Classified as regular (sea urchins) or irregular (sand dollars)

Habitat:

Inhabit all seas, sand dollars usually found in sandy soft ground, sea urchins on rocky substances and underwater.

Feeding:

Move slowly and graze on mostly anything they come across, whether it be algae, or a dead animal,

Mouth of sea urchin contains 5 calcium carbonate jaws, collectively known as Aristotle’s Lantern.

Reproduction:

Some sea urchins brood their young externally within their spines.

Regular have 5 gonads and irregular have 4.

Males reside in higher locations for broadcasting and Females in lower crevices for protection of larvae.

Unique Characteristics:

Spines and tube feet surround the center. Used for locomotion, burrowing, food gathering, respiration, sensation, and protection. Sometimes contain venom.

Sand dollars have shorter spines, creating a fuzzy look.

Holothuroidea

Habitat:

Common in shallow water areas to deep ocean floors.

Feeding:

Generally scavengers, feeding on plankton and decaying organic matter.

Use buccal tentacles to trap food from currents and to sift through sediment.

Have a pharynx with 10 calcareous plates, this is followed by an esophagus and a stomach, then the intestine out to the anus.

Reproduction:

Unique Characteristics:

Respiration occurs within the anus by withdrawing and expelling water.

Difference between bilateral surfaces.

Most have papillae which are conical projections with sensory tube feet at the ends.

Slow moving and tend to be burrowed or lodged in crevices under rocks.

Crinoidea

Habitat:

Mostly live in deep sea areas but also in coral reefs.

Feeding:

Crinoids are filter feeders that use their feather like arms that have mucus on them to trap small particles.

Reproduction:

No true gonads exist. Instead they produce gametes from genital canals in pinnules. Eventually, the pinnules rupture to release sperm and eggs into the water for fertilization.

Characteristics:

There are 3 basic sections to a crinoid: the stem or stalk, the calyx, and the arms or rays.

The stem anchors it to hard surfaces. The calyx contains most of the organs, and the rays are for trapping food. Pinnules are on the rays to increase surface area.

Sources:

http://en.wikipedia.org/wiki/Echinoderm

http://animaldiversity.ummz.umich.edu/site/accounts/classification/Echinodermata.html

http://biodidac.bio.uottawa.ca