Non-Chordates Cheatsheet

Cheatsheet Content

### Introduction to Non-Chordates Non-chordates are animals that lack a notochord, dorsal hollow nerve cord, and pharyngeal gill slits at any stage of their life cycle. They represent a vast and diverse group, encompassing most of the animal phyla. This cheatsheet covers the major non-chordate phyla, highlighting their distinguishing features and important concepts. #### General Classifications - **Levels of Organization:** Cellular, Tissue, Organ, Organ-system - **Symmetry:** Asymmetrical, Radial, Bilateral - **Germ Layers:** Diploblastic (ectoderm, endoderm), Triploblastic (ectoderm, mesoderm, endoderm) - **Coelom:** Acoelomate (no body cavity), Pseudocoelomate (false coelom), Eucoelomate (true coelom) - **Segmentation:** Metameric segmentation (body divided externally/internally into segments) - **Notochord:** Absent ### Phylum Porifera (Sponges) - **Level of Organization:** Cellular level. Cells are loosely aggregated. - **Symmetry:** Mostly asymmetrical. - **Germ Layers:** Diploblastic (primitive). - **Coelom:** Absent (acoelomate). - **Habitat:** Mostly marine, some freshwater (e.g., *Spongilla*). - **Key Features:** - **Water Canal System:** Unique system for food gathering, respiration, and waste removal. Water enters through **ostia** (minute pores), flows into a central cavity (**spongocoel**), and exits through **osculum**. - **Choanocytes (Collar Cells):** Line the spongocoel and canals, trap food particles. - **Skeletal Support:** Spicules (calcareous or siliceous) and/or spongin fibres. - **Digestion:** Intracellular. - **Reproduction:** - **Asexual:** Fragmentation, budding, gemmule formation. - **Sexual:** Hermaphrodite (eggs and sperm produced by same individual). Internal fertilization. - **Development:** Indirect, with a free-swimming larval stage (e.g., amphiblastula, parenchymula). - **Examples:** *Sycon* (Scypha), *Spongilla* (freshwater sponge), *Euspongia* (bath sponge). ### Phylum Cnidaria (Coelenterata) - **Level of Organization:** Tissue level. - **Symmetry:** Radial symmetry. - **Germ Layers:** Diploblastic. - **Coelom:** Absent (acoelomate), possess a central gastro-vascular cavity (coelenteron). - **Habitat:** Aquatic, mostly marine. Sessile or free-swimming. - **Key Features:** - **Cnidoblasts/Cnidocytes:** Specialized stinging cells on tentacles and body, containing **nematocysts** (stinging capsules) for anchorage, defense, and prey capture. - **Gastro-vascular Cavity:** Single opening (mouth on hypostome) serving both for ingestion and egestion. - **Digestion:** Extracellular and intracellular. - **Body Forms:** - **Polyp:** Sessile, cylindrical form (e.g., *Hydra*, *Adamsia*). - **Medusa:** Free-swimming, umbrella-shaped form (e.g., *Aurelia* - jellyfish). - **Metagenesis (Alternation of Generation):** Some cnidarians exhibit this (e.g., *Obelia*). Polyps reproduce asexually to produce medusae, and medusae reproduce sexually to form polyps. - **Examples:** *Hydra*, *Obelia* (sea fur), *Physalia* (Portuguese man-of-war), *Aurelia* (jellyfish), *Adamsia* (sea anemone), *Meandrina* (brain coral), *Gorgonia* (sea fan). ### Phylum Ctenophora (Comb Jellies/Sea Walnuts) - **Level of Organization:** Tissue level. - **Symmetry:** Radial (biradial) symmetry. - **Germ Layers:** Diploblastic. - **Coelom:** Absent. - **Habitat:** Exclusively marine. - **Key Features:** - **Comb Plates:** Eight external rows of ciliated comb plates for locomotion. - **Bioluminescence:** Property of living organisms to emit light, well-marked in ctenophores. - **Colloblasts (Lasso cells):** Specialized adhesive cells for capturing prey (not cnidoblasts). - **Reproduction:** - Hermaphrodite. - Sexual reproduction only. - **Development:** Indirect. - **Examples:** *Pleurobrachia* (sea gooseberry), *Ctenoplana*. ### Phylum Platyhelminthes (Flatworms) - **Level of Organization:** Organ level. - **Symmetry:** Bilateral symmetry. - **Germ Layers:** Triploblastic. - **Coelom:** Acoelomate (no true body cavity). - **Body Form:** Dorso-ventrally flattened body. - **Habitat:** Mostly endoparasites (e.g., tapeworms, flukes), some free-living (e.g., *Planaria*). - **Key Features:** - **Hooks and Suckers:** Present in parasitic forms for attachment to the host. - **Flame Cells (Protonephridia):** Specialized excretory cells for osmoregulation and excretion. - **Digestion:** Incomplete digestive system (single opening) in some, absent in others (e.g., tapeworms absorb nutrients directly). - **High Regeneration Capacity:** Especially in *Planaria*. - **Reproduction:** - Hermaphrodite. - Internal fertilization. - **Development:** Indirect, with many larval stages. - **Examples:** *Taenia solium* (tapeworm), *Fasciola hepatica* (liver fluke), *Planaria* (Dugesia). ### Phylum Aschelminthes (Nematoda/Roundworms) - **Level of Organization:** Organ-system level. - **Symmetry:** Bilateral symmetry. - **Germ Layers:** Triploblastic. - **Coelom:** Pseudocoelomate (body cavity not lined by mesoderm). - **Body Form:** Circular in cross-section (hence, roundworms). - **Habitat:** Free-living (aquatic or terrestrial) or parasitic (plants and animals). - **Key Features:** - **Complete Digestive Tract:** Well-developed muscular pharynx. - **Excretory Tube:** Removes body wastes from the body pore. - **Cuticle:** Tough, resistant outer covering. - **Reproduction:** - **Dioecious:** Sexes separate. - **Sexual Dimorphism:** Females are generally longer than males. - Internal fertilization. - **Development:** Direct (young ones resemble adults) or indirect. - **Examples:** *Ascaris* (roundworm), *Wuchereria* (filarial worm, causes elephantiasis), *Ancylostoma* (hookworm). ### Phylum Annelida (Segmented Worms) - **Level of Organization:** Organ-system level. - **Symmetry:** Bilateral symmetry. - **Germ Layers:** Triploblastic. - **Coelom:** Eucoelomate (true coelom, schizocoelom). - **Body Form:** Metamerically segmented (body divided into ring-like segments). - **Habitat:** Aquatic (marine and freshwater) or terrestrial. Free-living, and sometimes parasitic. - **Key Features:** - **Locomotion:** Longitudinal and circular muscles present. Aquatic annelids (e.g., *Nereis*) have lateral appendages called **parapodia** for swimming. - **Circulatory System:** Closed type. - **Excretion & Osmoregulation:** **Nephridia**. - **Neural System:** Paired ganglia connected by lateral nerves to a double ventral nerve cord. - **Reproduction:** - Some are hermaphrodite (*Pheretima*, *Hirudinaria*), some are dioecious (*Nereis*). - **Development:** Direct. - **Examples:** *Nereis* (sandworm), *Pheretima* (earthworm), *Hirudinaria* (blood-sucking leech). ### Phylum Arthropoda - **Level of Organization:** Organ-system level. - **Symmetry:** Bilateral symmetry. - **Germ Layers:** Triploblastic. - **Coelom:** Eucoelomate (reduced true coelom, body cavity is hemocoel). - **Distinguishing Feature:** Largest phylum of Animalia, including insects. - **Key Features:** - **Chitinous Exoskeleton:** Tough, protective outer covering. - **Jointed Appendages:** For locomotion, feeding, sensory. - **Body Division:** Head, Thorax, Abdomen (or Cephalothorax and Abdomen). - **Respiration:** Gills, book gills, book lungs, or tracheal system. - **Circulatory System:** Open type (blood flows through sinuses). - **Excretion:** **Malpighian tubules**. - **Sensory Organs:** Antennae, eyes (compound and simple), statocysts (balance organs). - **Reproduction:** - **Dioecious:** Sexes separate. - Internal fertilization. - Mostly oviparous. - **Development:** Direct or indirect. - **Examples:** - **Economically Important:** *Apis* (honey bee), *Bombyx* (silkworm), *Laccifer* (lac insect). - **Vectors:** *Anopheles*, *Culex*, *Aedes* (mosquitoes). - **Gregarious Pest:** *Locusta* (locust). - **Living Fossil:** *Limulus* (king crab). - **Other:** Prawn, crab, spider, scorpion, cockroach. ### Phylum Mollusca - **Level of Organization:** Organ-system level. - **Symmetry:** Bilateral symmetry (some asymmetrical due to torsion). - **Germ Layers:** Triploblastic. - **Coelom:** Eucoelomate (reduced). - **Distinguishing Feature:** Second largest animal phylum. - **Key Features:** - **Body Division:** Head (sensory tentacles), Muscular Foot (locomotion), Visceral Hump (internal organs). - **Mantle:** Soft and spongy layer of skin over the visceral hump, secretes a calcareous shell (external, internal, or absent). - **Mantle Cavity:** Space between the hump and mantle, where feather-like **gills (ctenidia)** are present for respiration and excretion. - **Radula:** File-like rasping organ in the mouth for feeding (absent in bivalves). - **Circulatory System:** Open type (except cephalopods which have closed). - **Reproduction:** - **Dioecious:** Sexes separate. - Oviparous. - **Development:** Indirect, with larval stages (e.g., trochophore, veliger, glochidium). - **Examples:** *Pila* (apple snail), *Octopus* (devil fish), *Sepia* (cuttlefish), *Loligo* (squid), *Aplysia* (sea hare), *Dentalium* (tusk shell), *Chaetopleura* (chiton), *Unio* (freshwater mussel). ### Phylum Echinodermata - **Level of Organization:** Organ-system level. - **Symmetry:** - **Adults:** Radial symmetry (pentamerous). - **Larvae:** Bilateral symmetry. - **Germ Layers:** Triploblastic. - **Coelom:** Eucoelomate (enterocoelom). - **Habitat:** Exclusively marine. - **Key Features:** - **Endoskeleton:** Made of calcareous ossicles (spiny-skinned organisms). - **Water Vascular System (Ambulacral System):** Unique to echinoderms. Functions in locomotion, capture and transport of food, and respiration. Operates via **tube feet (podia)**. - **Digestive System:** Complete, mouth on the ventral side, anus on the dorsal side. - **Excretory System:** Absent. - **Regeneration:** High capacity for regenerating lost parts. - **Reproduction:** - **Dioecious:** Sexes separate. - External fertilization. - **Development:** Indirect, with a free-swimming larval stage. - **Examples:** *Asterias* (starfish), *Echinus* (sea urchin), *Antedon* (sea lily), *Cucumaria* (sea cucumber), *Ophiura* (brittle star). ### Phylum Hemichordata - **Level of Organization:** Organ-system level. - **Symmetry:** Bilateral symmetry. - **Germ Layers:** Triploblastic. - **Coelom:** Eucoelomate (enterocoelom). - **Habitat:** Exclusively marine. - **Body Form:** Worm-like, cylindrical body divided into **proboscis, collar, and trunk**. - **Key Features:** - **Stomochord:** A rudimentary structure in the collar region, similar to notochord, but derived from buccal diverticulum. - **Pharyngeal Gill Slits:** Present, indicating a link to chordates. - **Circulatory System:** Open type. - **Excretion:** By a proboscis gland. - **Reproduction:** - **Dioecious:** Sexes separate. - External fertilization. - **Development:** Indirect, with a tornaria larva. - **Examples:** *Balanoglossus* (acorn worm), *Saccoglossus*.