Invertebrates and Phylum Porifera

Invertebrates

• 97% of all species within Kingdom Animalia are invertebrates
• Lack a spine and cranium
• Include unicellular and multicellular organisms
• Inhabit land, freshwater and oceans
• Divided into eight phyla: Porifera, Cnidaria, Platyhelminthes, Mollusca, Annelida, Nematoda, Arthropoda, Echinodermata

Phylum Porifera – the sponges

• Lack “true” tissues, not truly diploblastic or triploblastic
• Don't create a true gastrula, no true endoderm or ectoderm
• Have specialized cells that perform "tissue-like" functions
• Larvae are flagellated and swim, settle on a substrate and grow into an adult
• Adults are not motile
• Obtain nutrients and oxygen from the water through filter-feeding
• Body is organized for efficient water movement

Poriferan morphology

• Body Plan: Asymmetrical, not protostome or deuterostome because they lack gastrulation
• General shape of a cylinder
• Large, internal cavity is called the spongocoel
• Water flows into the spongocoel through openings called ostia
• Water is expelled through a large opening at the top of the sponge: the osculum

Poriferan physiology

• Lack digestive, nervous, respiratory, and circulatory systems
• Food is digested intracellularly
• Gas exchange, circulation, and waste excretion occur through diffusion
• Reproduction through sexual and asexual means

Phylum Cnidaria – jellyfish, anemones

• Body Plan: Radial or biradial symmetry
• Tissues: Diploblastic, not protostome or deuterostome
• Incomplete Digestive System, food enters and waste leaves the same opening
• Nearly all are marine organisms
• Defining characteristic: a cnidocyte, or stinging cell, located on tentacles and around the mouth
• Cnidocytes contain stinging organelles called nematocysts

Cnidarian Morphology

• Two body types: Polyp and Medusa
• Polyp species are sessile
• Medusa species are motile
• Epidermis derived from ectoderm
• Gastrodermis derived from endoderm tissue
• Mesoglea: non-living tissue between them
• Have specialized, differentiated tissue cells but no true organ systems

Cnidarian Physiology

• No true nervous system, network of nerve cells throughout body
• Gastrovascular cavity has one opening, serves as both mouth and anus
• Digestion: Incomplete, begins extracellularly using enzymes, nutrients are distributed through mesoglea to epidermal cells
• Cells in gastrovascular cavity and epidermis absorb O2 and release CO2
• Nitrogenous waste diffuses out of cells into the gastrovascular or the surrounding water

4 Cnidarian Classes

• Class Anthozoa: Only sessile polyp species, includes coral, sea fans, sea anemones
• Class Scyphozoa: Medusa species, includes jellyfish
• Class Cubozoa: Medusa species, includes box jellies
• Class Hydrozoa: Sessile and medusa species, includes hydra and Portuguese man o’ war