Starfish (Sea Star) Biology
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Taxonomy and Classification
Complete Taxonomic Hierarchy
Domain: Eukaryota
• Organisms with membrane-bound organelles and nucleus
Kingdom: Animalia
• Multicellular heterotrophs that develop from blastula
Phylum: Echinodermata
• Marine animals with pentaradial symmetry and water vascular system
• Name means "spiny skin" (echinos = spiny, derma = skin)
• Unique deuterostome development pattern
• Other classes include sea urchins, sea cucumbers, brittle stars, and crinoids
Subphylum: Asterozoa
• Echinoderms with star-shaped bodies and open ambulacral grooves
• Includes sea stars and brittle stars
Class: Asteroidea
• True sea stars with connected arms and central disk
• Arms not sharply set off from central disk as in brittle stars
• Tube feet with suction cups
• Approximately 2,000 species described
Orders: The Asteroidea class contains seven main orders:
1. Paxillosida
o Characterized by paxillae (umbrella-like structures) on upper surface
o Typically burrowing species with pointed arms
o Example genera: Astropecten, Luidia
2. Valvatida
o Often pentagonal with short arms
, o Well-developed marginal plates
o Example genera: Culcita (cushion stars), Linckia (blue sea stars)
3. Velatida
o Cushion stars and sun stars with numerous arms
o Reduced skeletal structure
o Example genera: Solaster (sun stars), Crossaster (sun stars)
4. Spinulosida
o Spiny upper surface without pedicellariae
o Example genus: Echinaster (spiny sea stars)
5. Forcipulatida
o Straight pedicellariae (tiny pincer-like structures)
o Often with more than five arms
o Example genera: Asterias (common sea stars), Pisaster (ochre sea star)
6. Brisingida
o Deep-sea species with small central disk and many long, slender arms
o Example genus: Brisinga
7. Notomyotida
o Deep-water sea stars with specialized muscle bands
o Example genus: Benthopecten
Further Classification Levels
Family, Genus, Species: Each order contains multiple families, which are further divided
into genera and species. For example:
Order Forcipulatida:
• Family Asteriidae
o Genus Asterias
▪ Species Asterias rubens (common starfish)
▪ Species Asterias forbesi (Forbes sea star)
o Genus Pisaster
▪ Species Pisaster ochraceus (ochre sea star)
▪ Species Pisaster brevispinus (giant pink sea star)
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Taxonomy and Classification
Complete Taxonomic Hierarchy
Domain: Eukaryota
• Organisms with membrane-bound organelles and nucleus
Kingdom: Animalia
• Multicellular heterotrophs that develop from blastula
Phylum: Echinodermata
• Marine animals with pentaradial symmetry and water vascular system
• Name means "spiny skin" (echinos = spiny, derma = skin)
• Unique deuterostome development pattern
• Other classes include sea urchins, sea cucumbers, brittle stars, and crinoids
Subphylum: Asterozoa
• Echinoderms with star-shaped bodies and open ambulacral grooves
• Includes sea stars and brittle stars
Class: Asteroidea
• True sea stars with connected arms and central disk
• Arms not sharply set off from central disk as in brittle stars
• Tube feet with suction cups
• Approximately 2,000 species described
Orders: The Asteroidea class contains seven main orders:
1. Paxillosida
o Characterized by paxillae (umbrella-like structures) on upper surface
o Typically burrowing species with pointed arms
o Example genera: Astropecten, Luidia
2. Valvatida
o Often pentagonal with short arms
, o Well-developed marginal plates
o Example genera: Culcita (cushion stars), Linckia (blue sea stars)
3. Velatida
o Cushion stars and sun stars with numerous arms
o Reduced skeletal structure
o Example genera: Solaster (sun stars), Crossaster (sun stars)
4. Spinulosida
o Spiny upper surface without pedicellariae
o Example genus: Echinaster (spiny sea stars)
5. Forcipulatida
o Straight pedicellariae (tiny pincer-like structures)
o Often with more than five arms
o Example genera: Asterias (common sea stars), Pisaster (ochre sea star)
6. Brisingida
o Deep-sea species with small central disk and many long, slender arms
o Example genus: Brisinga
7. Notomyotida
o Deep-water sea stars with specialized muscle bands
o Example genus: Benthopecten
Further Classification Levels
Family, Genus, Species: Each order contains multiple families, which are further divided
into genera and species. For example:
Order Forcipulatida:
• Family Asteriidae
o Genus Asterias
▪ Species Asterias rubens (common starfish)
▪ Species Asterias forbesi (Forbes sea star)
o Genus Pisaster
▪ Species Pisaster ochraceus (ochre sea star)
▪ Species Pisaster brevispinus (giant pink sea star)
