Table of Contents Coral Reef Cart Collection

Reproduction and Development

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  After mating, females carry their eggs attached to tiny limbs on their abdomen.
  
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  The young hatch as larvae and are immediately swept into the plankton. When they have reached the right stage of development, they drop to the seafloor, metamorphose into their final form, and find an empty shell.
  

Conservation

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  Hermit crabs are abundant, but the number of available shells is important to their survival so empty shells should not be collected.
  

Remarks

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  Some hermit crabs have sea anemones growing on their shells.
  
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  This symbiotic pairing, called mutualism, provides protection and camouflage for the hermit crab and gives the hitchhiking anemones food scraps from the crab.
  
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  When disturbed, the anemones aboard for the free ride expel acontia (lengthy sting cells). Hermit crabs have been observed transferring their hitchhikers to a new shell.
  

To Notice

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  Use the hermit crab model to discuss body parts and the concept of shell change.
  

Echinoderms: Sea Stars

Sea Stars

Specimens

Chocolate Chip sea star

general information

Classification

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  Phylum Echinodermata, Class Asteroidea
  

Distribution

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  2000 species worldwide
  

Habitat

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  Sea stars live in all the world’s oceans; a few species inhabit brackish waters.
  

Appearance and Behavior

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  The name echinoderm means “spiny-skinned” and refers to the sea star’s possession of calcium-carbonate spines and plates that form an internal skeleton just under the skin. This offers protection. Many also have coloration that provides camouflage.
  
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  As adults, echinoderms are radially symmetrical with a five-sided body plan surrounding a central disk where the mouth lies. Most have five arms, but species with 10, 20, and even 40 arms exist.
  
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  Sea stars are famous for their ability to regenerate limbs, and in some cases, entire bodies. Some require the central body to be intact to regenerate, but a few species (like the blue linkia) can grow an entirely new sea star from a portion of a severed limb.
  
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  The phylum is also characterized by a water vascular system with canals that end in tube feet. Water enters the system through a madreporite, which maintains water pressure that, along with muscular contractions, works to move the tube feet, which may be adapted for respiration, feeding, movement, or sensory perception. The tube feet also enable the sea stars to hold on tightly to the substrate.
  

Diet

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  Sea stars can be carnivores, omnivores, scavengers, and herbivores.
  
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  Feeding strategies are varied. Some extrude their stomachs between the shells of bivalve mollusks and secrete enzymes that digest the prey’s soft tissues.
  

Reproduction and Development

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  Reproduction is predominately sexual.
  
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  Larvae are free-swimming and bilaterally symmetrical, a part of the plankton until, after a series of stages, they metamorphose into adult forms.
  

Mortality

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  The average life span of sea stars in the wild is up to 35 years.
  

Remarks

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  The early embryonic development of echinoderms, chordates, and two smaller phyla is so distinct from that of all other animal phyla that these four phyla are presumed to have evolved separately from a common ancestor. Echinoderms, then, are thought to be among our closest invertebrate relatives.
  
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  Often has a symbiotic relationship with other animals:
  
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  A commensal relationship with a shrimp, Periclimenes soror, which are often the same color as the sea star.
  
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  A parasitic relationship with a sea snail, Thyca crystalline, which may be found on the oral side of the animal partially imbedded in the ambulacral grooves.
  

To Notice

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  Point out the radial symmetry. Also, show the location of tube feet and mouth.
  
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  Does it look like the sea star ever regenerated a limb?
  
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  Compare to the test of a sea urchin.
  
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  Compare the sea star to a photo of the crown of thorns.
  
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  Show photo of Triton’s trumpet consuming a crown of thorns.
  
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  Show an actual Triton’s trumpet.
  

Specimen Detail

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  Distribution: Indo-Pacific
  
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  Habitat: Coral rubble or among seagrasses in shallow lagoons and to 60 m depth.
  
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  Appearance: Overall arm radius to 40 cm. Color bright blue overall, but olive-brown, pink and yellow variants exist. Has long, cylindrical, smooth arms.
  
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  Diet: Scavenger. Also consumes algae and microbes.
  
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  Predators: Pufferfishes and tritons are known to feed on blue linkias and harlequin shrimp nibble on the ends of their rays.
  
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  Reproduction and Development: Unlike most sea stars that can regenerate missing parts only if at least part of the central disk remains, linkias are able to regenerate into a complete sea star from a single ray. Initially four minute arms bud from the end of the lone ray; this form is called a comet, as it resembles a shooting star.
  

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  Distribution: Red Sea, Indian and western Pacific oceans
  
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  Habitat: Shallow sand and seagrass beds, typically in sheltered locations from 1 to 30 m.
  
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  Appearance: Diameter to 30 cm. Body color is variable—may be beige, brown, orange, red, green, or blue. Horn-shaped nodules are blue, dark green, brown, or black, sometimes surrounded by milk chocolate-colored margins.
  
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  Diet: Sponges, clams, snails, other invertebrates; also opportunistic carrion feeders.
  
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  Reproduction and Development: Eggs and sperm are stored in the rays and released simultaneously. Fertilization is external. Larvae are bilaterally symmetrical and planktonic. Larvae settle and transform to sea stars.
  
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  Conservation Status: Common but threatened in some areas, such as Singapore. They are overharvested for the shell trade because of their appearance; however, coloration fades upon death.