Sponges, Cnidarians, & Ctenophores

Phylum Porifera
Characteristics

• Includes marine & freshwater sponges

• Found in the kingdom Animalia & subkingdom Parazoa

• Sessile as adults

• Simplest of all animals

• Contain specialized cells, but no tissue

• Asymmetrical

• Bodies filled with holes or pores for water circulation

• Marine sponges are larger & more colorful than freshwater sponges

• Range in size from 2 centimeters to 2 meters

• Osculum is single, large body opening at the top for water & wastes to leave

• Spongocoel is the body cavity of sponges

• Have only 2 cell layers (ectoderm & endoderm) separated by jellylike material

• Flagellated cells called choanocytes or collar cells line their internal body cavity

• Flagella of choanocytes beat & pull in water containing food which the collar traps

• Spongin is a network of flexible, protein fibers making up the sponge's skeleton

• Spicules are tiny, hard particles shaped like spikes or stars in the  skeleton of some sponges

• Spicules are made of calcium carbonate or silica

Feeding

• Sponges are filter feeders that remove plankton (food) from the water that is brought in through pores lined with collar cells
•  Flagella pull in bacteria, protozoans, & algae that sticks to collar of choanocytes where it is digested
• Amebocytes are specialized cells in sponges that can roam to pick up food from choanocytes & distribute it to all other parts of the sponge
• Amebocytes also transport carbon dioxide & wastes away from sponge cells
• Excess water & food leaves through the excurrent osculum

Reproduction

• Sponges can reproduce asexually by external buds that break off & form new sponges or stay attached to form sponge colonies
• Gemmules are specialized, internal buds formed by sponges during cold or dry weather that can survive harsh conditions
• Gemmules consist of a food-filled ball of amebocytes surrounded by a protective coat with spicules & released when adult sponge dies
• Gemmules break open when conditions improve & the cells form new sponges

• Sponge can also asexually regenerate missing parts or a new sponge from a small piece of sponge
• Sponges are hermaphrodites (produce both eggs & sperm), but they exchange sperm & cross-fertilize eggs during sexual reproduction
• Planula is the flagellated, free-swimming larva that forms from the zygote
• Planula larva eventually settles to the bottom & attaches to develop into an adult, sessile sponge

Classes of Sponges

• Calcarea are chalky sponges with calcium carbonate spicules
• Hexactinella includes glass sponges & the Venus flower basket with silica spicules
• Demospongiae include horny & bath sponges with only spongin or spongin & silica spicules
• Sclerospongiae are coral sponges & have spongin & silica and calcium carbonate spicules

Phylum Cnidaria
Characteristics

• Includes marine organisms such as jelllyfish, Portuguese man-of-war, coral, sea anemone, & sea fans
• Hydra is a freshwater cnidarian

• All carnivorous
• Have 2 cell layers (epidermis -outer & gastrodermis-inner) with a hollow body called gastrovascular cavity
• Contain a jelly-like layer between epidermis 7 gastrodermis  called mesoglea
• Single opening (mouth/anus) to gastrovascular cavity where food & water enter & wastes leave; called two-way digestive system
• Have tentacles around mouth to pull in water & capture food

• Have a simple nerve net with to help with movement & senses
• Sessile members include corals, sea anemones, & sea fans
• Have radial symmetry as adults

• Contain stinging cells called cnidocytes in their tentacles that contain coiled stingers called nematocysts that can shoot out & paralyze prey 

• Polyp forms are usually sessile with upright tentacles arranged around the mouth at the top and with a thin layer of mesoglea

• Polyps are the asexual stage

• Corals, hydra, & sea anemones exist in the polyp form as adults 

CORAL POLYPS

• Medusa forms are usually free-swimming, bell-shaped animals with tentacles that hang down around the mouth and with a thick layer of mesoglea for support

• Medusa are the sexual stage

• Jellyfish & Portuguese man-of-war are medusa form as adults

• Some cnidarians are dimorphic or go through both polyp & medusa stages in their life cycle

JELLYFISH LIFE CYCLE

• Some are solitary (Hydra) others are colonial (corals)

• Three classes include Hydrozoa (hydra), Scyphozoa (jellyfish), & Anthozoa (sea anemones & corals)

Hydrozoa

• Includes freshwater, sessile hydra (exists only as polyps) 

• Portuguese man-of-war (exists as colony of polyps & medusa)

• Group of cells called basal disk produces sticky secretion for attachment & can secrete gas bubbles to unattach & let hydra float

• Hydra also move by somersaulting (tentacles bend over to bottom as basal disk pulls free)

• Tentacles pull food into gastrovascular cavity where enzymes digest it

• Reproduce asexually by budding during warm weather & sexually in the fall

• Hermaphrodites that release sperm into water to fertilize eggs of another hydra

HYDRA

Scyphozoa

• Includes bell-shaped jellyfish

• Medusa stage is dominant in the life cycle

• Tentacles may be meters in length & carry poisons that cause severe pain or death

• Have both asexual polyps & sexual medusa stages in their life cycles

• Adult medusa stage releases eggs & sperm into water

• Fertilization produces ciliated planula larva that settles to the bottom, attaches, & forms tentacles 

• New medusa bud off of reproductive polyps & form adult jellyfish

JELLYFISH

Anthozoa

• Include corals in a limestone case & sea anemones

• Called "flower animals"

• All marine

• Sea anemone is a sessile, polyp-form that uses its tentacles to paralyze fish

• Some anemones in the Pacific Ocean live symbiotically with the clownfish sharing food & protecting each other

• Corals are small, colonial polyps living in limestone cases

• Coral reefs form as polyps die & provide a home and protection for other marine animals

• Reefs form in warm, shallow water & only the top layer has living polyps

• Algae may live symbiotically with coral supplying them with oxygen

Phylum Ctenophora

Characteristics

• All marine

• Includes comb jellies

• Have eight rows of fused cilia called "comb rows"

• Largest animal to move by cilia

• Move by beating cilia

• Lack cnidocytes but have cells sticky cells called colloblasts that bind to prey

• Colloblasts located on two ribbon-like tentacles

• Have sensory structure called apical organ to detect direction in the water

• Most are hermaphrodites (make eggs & sperm)

• Produce light by bioluminescence