Porifera (Sponges)

Porifera (Sponges)

• Lack true tissues; organized at the cellular level with choanocytes.
• Absence of true germ layers, thus, neither diploblastic nor triploblastic.
• Basal animals, outside the protostome-deuterostome division.
• Asymmetrical, though some can exhibit radial symmetry.
• Acoelomate, lacking a coelom due to the absence of tissues or organs that would require one.
• Defined by choanocytes (collar cells), porous bodies with water canal systems, and spicules for structural support.
• Mainly marine, but some freshwater species exist.
• Filter feeders; water enters through ostia, flows through choanocytes which trap food, and exits via the osculum.
• Classes: Calcarea (calcium carbonate spicules), Hexactinellida (silica spicules), and Demospongiae (silica and/or spongin).
• Possess porous bodies, a central spongocoel, choanocytes, amoebocytes, and skeletons made of spicules or spongin.
• Reproduce asexually via budding or fragmentation.
• Most are hermaphroditic (monoecious), producing both eggs and sperm at different times.
• Fertilization is usually internal, with sperm carried by water currents.
• Larvae are motile before settling as sessile adults.
• Lack a circulatory system; nutrients and gases distributed via diffusion and water movement.
• Gas exchange occurs by diffusion across body surfaces and through water currents.
• Lack specialized excretory organs; nitrogenous wastes (ammonia) diffuse into the water.
• Invertebrates with skeletons made of spicules (silica or calcium carbonate) or spongin, lacking exoskeletons and hydrostatic skeletons.

Cnidaria (Jellyfish, Corals, Anemones)

• Presence of true tissues.
• Diploblastic with ectoderm and endoderm, plus a mesoglea layer.
• Basal eumetazoans, outside the protostome/deuterostome lineage.
• Radial symmetry.
• Acoelomate because of no mesoderm development.
• Distinguished by cnidocytes that contain nematocysts, a gastrovascular cavity (single opening for mouth/anus), and a nerve net with muscle-like cells.
• Mostly marine; some freshwater species exist.
• Carnivorous, using cnidocytes to capture prey and digest it in the gastrovascular cavity.
• Classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa.
• Exhibit two main body forms: polyp (sessile) and medusa (free-swimming).
• Bodies are composed of a gastrodermis, epidermis, and mesoglea.
• Asexual reproduction occurs via budding (mostly in polyp stage).
• Many species alternate between sexual and asexual reproduction.
• Fertilization is often external, but can be internal.
• Lacking a circulatory system, nutrients are transported via diffusion within the gastrovascular cavity.
• Gas exchange happens by diffusion across the body surface.
• No specialized excretory organs exists; nitrogenous waste (ammonia) is eliminated by diffusion.
• Invertebrates supported by a hydrostatic skeleton (fluid in the gastrovascular cavity), with calcium carbonate exoskeletons in corals.

Platyhelminthes (Flatworms)

• Presence of true tissues.
• Triploblastic, possessing ectoderm, mesoderm, and endoderm.
• Protostomes belonging to Lophotrochozoa.
• Bilateral symmetry.
• Acoelomate; they have no true body cavity despite being triploblastic.
• Show cephalization (a head with sensory organs), flattened bodies for diffusion, organ-system level organization, and an incomplete digestive system.
• Occupy aquatic, moist terrestrial, and parasitic environments.
• Free-living species are predators/scavengers, while parasitic species absorb nutrients from hosts.
• Classes: Turbellaria, Trematoda, and Cestoda.
• Have flattened bodies and some possess eyespots.
• Parasites feature specialized hooks and suckers.
• Asexual reproduction via regeneration and fission.
• Mostly hermaphroditic, capable of cross- or self-fertilization.
• Fertilization is usually internal.
• Lack a circulatory system; diffusion moves nutrients and gases.
• Gas exchange occurs by diffusion across the body surface.
• Use flame cells (protonephridia) for osmoregulation and nitrogenous waste removal (ammonia).
• Invertebrates without a skeleton, supported by a hydrostatic skeleton.

Annelida (Segmented Worms)

• Presence of true tissues.
• Triploblastic; possess ectoderm, mesoderm, and endoderm.
• Protostomes within Lophotrochozoa.
• Bilateral symmetry.
• Coelomate; true body cavity lined with mesoderm.
• Exhibit segmentation, a closed circulatory system, setae (bristles), and a complete digestive tract.
• Reside in marine, freshwater, and terrestrial habitats.
• Exhibit diverse diets as predators, scavengers, deposit feeders, and filter feeders.
• Classes: Polychaeta, Oligochaeta, and Hirudinea.
• Feature segmented bodies with duplicated organs, parapodia (in polychaetes), and a clitellum (in earthworms/leeches).
• Some reproduce asexually via regeneration or fragmentation.
• Earthworms and leeches are monoecious, while most polychaetes are dioecious.
• Fertilization is internal in leeches and oligochaetes, external in many polychaetes.
• Many exhibit a trochophore larval stage.
• Closed circulatory system with hemoglobin or chlorocruorin.
• Gas exchange through skin, or parapodia in polychaetes.
• Utilize metanephridia to remove nitrogenous waste (urea or ammonia).
• Invertebrates with a hydrostatic skeleton provided by the fluid-filled coelom.

Nematoda (Roundworms)

• Presence of true tissues.
• Triploblastic; possess ectoderm, mesoderm, and endoderm.
• Protostomes belonging to Ecdysozoa.
• Bilateral symmetry.
• Pseudocoelomate; body cavity not fully lined with mesoderm.
• Defined by an outer cuticle that is molted (ecdysis), a pseudocoelom, and an unsegmented, tubular body.
• Inhabit soil, freshwater, marine environments, and other organisms.
• Free-living species consume bacteria, fungi, and decaying matter, while parasitic species infect various hosts.
• Examples: Ascaris, Trichinella, Caenorhabditis elegans, Enterobius, and Wuchereria.
• Have cylindrical, unsegmented bodies tapered at both ends and covered in a collagen-rich cuticle.
• Longitudinal muscles facilitate whip-like movement.
• Sexual reproduction only; most are dioecious.
• Internal fertilization.
• Lack a circulatory system; nutrients and gases distributed by diffusion in the pseudocoelom.
• Gas exchange occurs by diffusion across the body surface.
• Utilize renette cells or canals to excrete nitrogenous waste (ammonia).
• Supported by a hydrostatic skeleton and the cuticle.

Mollusca (Clams, Snails, Squid)

• Presence of true tissues.
• Triploblastic; possess ectoderm, mesoderm, and endoderm.
• Protostomes belonging to Lophotrochozoa.
• Bilateral symmetry (some are secondarily asymmetrical).
• Coelomate; true body cavity fully lined with mesoderm.
• Defined by a muscular foot, mantle, visceral mass, and typically a radula.
• Inhabit marine, freshwater, and terrestrial environments.
• Display diverse feeding strategies: herbivory, filter feeding, carnivory, detritivory, and grazing.
• Classes: Gastropoda, Bivalvia, Cephalopoda, Polyplacophora, Scaphopoda, and Monoplacophora.
• Soft-bodied, may have a hard external shell, and cephalopods have advanced nervous systems.
• Reproduction is mainly sexual; most are dioecious.
• Fertilization can be internal or external.
• Many have a trochophore larva, sometimes followed by a veliger larva.
• Open circulatory system (except cephalopods which have a closed one).
• Hemocyanin-based blood.
• Gas exchange via gills, mantle cavity, skin, or lungs.
• Utilize metanephridia to excrete nitrogenous waste (ammonia, uric acid, or urea).
• Most possess external calcium carbonate shells.

Arthropoda (Insects, Crustaceans, Arachnids)

• Presence of true tissues.
• Triploblastic; possess all three germ layers.
• Protostomes in Ecdysozoa (molt exoskeleton).
• Bilateral symmetry.
• Coelomate (reduced coelom, mostly a hemocoel).
• Feature jointed appendages, segmented bodies, chitinous exoskeletons, advanced sensory organs, and tagmatization.
• Found in diverse habitats.
• Highly diverse feeding strategies.
• Subphyla: Chelicerata, Myriapoda, Crustacea, and Hexapoda (Insecta).
• Segmented bodies, jointed limbs, and exoskeletons that must be molted.
• Primarily sexual reproduction; mostly dioecious.
• Fertilization can be internal or external.
• Metamorphosis is common.
• Open circulatory system with hemolymph.
• Hemocyanin is common.
• Gas exchange occurs via gills, tracheal systems, or book lungs.
• Utilize green glands or Malpighian tubules for excretion (uric acid or ammonia).
• Have a chitinous exoskeleton.

Echinodermata (Sea Stars, Sea Urchins)

• Presence of true tissues.
• Triploblastic.
• Deuterostomes.
• Bilateral symmetry in larvae, pentaradial in adults.
• Coelomate; well-developed true coelom.
• Unique water vascular system, tube feet, pentaradial symmetry, calcium carbonate endoskeleton, and regeneration capabilities.
• Exclusively marine.
• Diverse feeding habits.
• Classes: Asteroidea, Ophiuroidea, Echinoidea, Holothuroidea, and Crinoidea.
• Lack a true head or brain, have a decentralized nerve net, and use tube feet for locomotion.
• Mostly sexual reproduction, dioecious.
• External fertilization.
• Some reproduce asexually via regeneration or fragmentation.
• Lack a traditional circulatory system, relying on the water vascular system and coelomic fluid.
• Gas exchange via tube feet and dermal branchiae.
• Lack specialized excretory organs; nitrogenous waste diffuses through the body surface.
• Possess an internal endoskeleton made of calcium carbonate ossicles.

Chordata (Vertebrates)

• Presence of true tissues.
• Triploblastic.
• Deuterostomes.
• Bilateral symmetry.
• Coelomate.
• Characterized by a notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail at some point in development and an endoskeleton.
• Found in all environments.
• Diverse feeding strategies.
• Subphyla: Cephalochordata, Urochordata (Tunicata), and Vertebrata.
• Classes within Vertebrata: Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia.
• Vertebrates have a backbone and skull.
• Reproduction is mostly sexual; mainly dioecious.
• Internal or external fertilization.
• Closed circulatory system, with a 2-chambered heart in fish, 3-chambered in amphibians, 3-chambered with partial separation in reptiles, and 4-chambered in birds and mammals.
• Use gills, lungs, or skin for gas exchange.
• Excrete ammonia, urea, or uric acid as nitrogenous waste.
• Internal endoskeleton of bone or cartilage.