Echinoderms and Chordates Lecture Notes

Echinoderms are characterized by their radial symmetry, a water vascular system, and the presence of tube feet, while chordates are defined by the presence of a notochord, dorsal nerve cord, and pharyngeal slits at some stage of their development.

Echinoderms

• Echinoderms are invertebrates.

• They exhibit deuterostome development, unlike previous invertebrates with protostome development.

• Echinoderms are coelomates.

• Adult echinoderms have radial symmetry, while their larvae have bilateral symmetry, suggesting evolution from a bilateral ancestor.

• Echinoderms possess an internal skeleton covered by a thin skin.

• Most echinoderms move slowly or are sessile.

• Their internal body is supported by a water vascular system.

Water Vascular System

• The water vascular system is key to how echinoderms support their body structure with water.

Regeneration

• Starfish have excellent regeneration capabilities; they can regenerate from an arm or half a body.

• Fishermen cutting starfish and throwing them back unwittingly create more starfish.

Echinoderm Classes

• Six classes exist, but only four are essential for the lecture: Asteroidea, Ophiuroidea, Echinoidea, and Holothuroidea. Sea lilies and sea daisies are excluded.

Asteroidea (Sea Stars)

• Most sea stars have five arms but some may have more.

• Arms radiate from a central disc.

• The central disc is not very distinct, unlike brittle stars.

• Tube feet on the oral side (underside) of each arm are used for movement and grasping prey or substrates.

• Most organs, including digestive and reproductive organs, are located in the arms; this aids regeneration.

• Eyespots at the tip of each arm detect light vs. dark; used to move towards prey.

• Pincers called pedicellariae remove parasites and growth.

• Sea stars possess two stomachs: cardiac and pyloric.

• To feed, a sea star inverts its cardiac stomach, pushing it into a clam or mussel shell.

• The stomach wraps around the soft organs and secretes digestive enzymes.

• A madreporite on the backside allows water to enter.

• Water exits through the anus, located near the madreporite.

Ophiuroidea (Brittle Stars)

• Brittle stars have a distinct central disc.

• Arms are very flexible and used for movement.

• Tube feet are reduced and used for sensory purposes.

• Organs are primarily located in the central disc.

• They do not regenerate as well as sea stars.

• Brittle stars are suspension feeders or detritivores, feeding on dead and rotten material.

• Rarely, they may hunt smaller crustaceans or worms.

Echinoidea (Sea Urchins and Sand Dollars)

• Sea urchins have no arms but a pentaradial feature can be seen upon close inspection.

• They have radial body symmetry.

• Sea urchins have long, movable spines; sand dollars have shorter spines.

• Sea urchins use spines for movement; tube feet are present, but spines are used more.

• Sea urchins generally eat algae, but are omnivores and eat other animals.

• Sand dollars primarily feed on suspended matter in water.

• Uni is the reproductive organs (gonads) of sea urchins, commonly eaten in Japanese cuisine.

Holothuroidea (Sea Cucumbers)

• Sea cucumbers exhibit bilateral symmetry, unlike other echinoderms.

• Internal skeleton is reduced.

• They are scavengers, feeding on mud and extracting nutrients.

• They expel waste products that resemble poop.

• Sea cucumbers can liquefy their connective tissue (collagen) to squeeze into tight spaces.

• They protect themselves by expelling thread-like stuff or organs out of their anus to distract predators.

• Sea cucumbers are eaten in Asian countries, believed to have medical purposes, but no FDA-approved drug exists. Tastes gelatinous and slimy, with no flavor.

• Pearlfish sometimes live in the anal cavity of sea cucumbers for shelter.

Chordates

• Traceable back to the Cambrian explosion about 500 million years ago.

• Chordates gave rise to vertebrates.

• Vertebrates have a backbone.

Chordate Characteristics

• Bilateral symmetry

• True coelom

• Deuterostome development

• Neural cord: primitive structure that develops into the skeleton.

• Nerve cord: evolves into the brain and spinal cord/nervous system.

• Pharyngeal slits/clefts: slits near the head used for various functions.

• Post-anal tail

Pharyngeal Slits Functions

• Primitive chordates (like tunicates): suspension feeding

• Fish: breathing/respiration (gills)

• Mammals: evolve into parts of the head, ear, and neck

Tail Functions

• Terrestrial animals: balancing (monkeys)

• Aquatic animals: propulsion (whales, sharks)

• Adults of many vertebrates don't have tails, although embryos do.

• Humans have a tailbone (coccyx).

Chordate Subphyla

• Urochordata

• Cephalochordata

• Vertebrata

Urochordata (Tunicates/Sea Squirts)

• Chordate characteristics present only in the larval stage.

• Adult shape resembles a tunic.

• Larvae are mobile and attach to rocks before metamorphosis into adults.

• Tunicates are consumed in some countries, tasting like iodine.

Cephalochordata (Lancelets/Amphioxus)

• Chordate characteristics present in both larvae and adults.

• Relatively primitive animals without eyes and with a primitive brain.

• They filter feed by sticking their head into the sand and filtering water through their pharyngeal clefts.

• They extract oxygen directly through their skin.

• Eaten as food in some parts of the world.

Craniates

• Animals with a head-like region, but not an official taxonomic group.

• Many have a skull-like structure and a brain.

• Possession of neural crest cells that contribute to the formation of the face and skull in humans, and/or other body parts in other craniates.

Origin of Craniates

• Hycorrella and Hygreethys are believed to be early chordates/craniates.

Living Animals: Hagfish

• Believed to be craniates

• Skull made of cartilage, not bones.

• Surviving early craniates.

• Not eels.

• No jaws and no vertebrae.

• When threatened, they release slime that expands in water, clogging the mouths and gills of predators, making the water unusable for the predator.

• Generally scavengers.

• Hackfish will often enter the holes/orifices of living animals, also sometimes feeding on them.

• Reproduction of hackfish is something currently unknown.

• Hagfish are very slimy and not commonly eaten, but are eaten in Korea (meal congeo).

• Very flexible bodies.

Evolution of Vertebrates

• Change from neural cord to vertebrae.

• Neural cord turning into a brain and nervous tissue.

• Evolution of jaws.

• Paired fins evolving.

• Gills evolving into lungs in terrestrial vertebrates.

Origin of Jaws

• Evolved from structures supporting gill slits.

• These structures evolved into bone-crushing jaws through time.

Characteristics of Vertebrata

(As they evolve)

• Spinal cord inside vertebrae.

• Skull made of cartilage/no cartilage evolves into hard skull.

Summary of Chordata Classification So Far

• Phylum Chordata

  • Subphylum Urochordata (Tunicates/Sea Squirts)

    • Chordate characteristics only in larval stage

  • Subphylum Cephalochordata (Lancelets)

    • Chordate characteristics in young and adults

• Craniates (unranked: Animals with a "head-like region")

  • Agnathans (Craniates without jaws

    • Hagfish (no jaws, no vertebrae; basal group of chordates)

  • Lampreys (no jaws, possess vertebrae), are the basal group to the subphylum of Vertebrates.

Lamprey

• Do not possess jaws.

• Possess primitive vertebrae, which is composed of cartilage.

• Interesting life cycle, similar to salmon, as they live and breed in both freshwater & marine systems.

• Spend about 10 years in freshwater, move to the ocean for a year/two, return to freshwater to mate and die.

Lamprey as Ectoparasites

• Attach to animals, especially fish.

• Use teeth-like structures to scrape the skin until the fish bleeds.

• Feed on fish fluid.

• They impact the commercial fishing industry.

• Governments spent millions of dollars to eradicate the Lamprey populations.

Jawed Vertebrates

• Also known as Gnathostomes.

• They possess enhanced sensory systems

• Possess a mineralized endoskeleton.

Jawed Vertebrates Classification: Chondrichthyes

• Sharks, rays, and skates.

• Possess skeleton made of cartilage.

General Characteristics of Chondrichthyes

• They have no rib cage, so gravity can cause organs to collapse out of water.

• Red blood cells are made in the spleen, unlike other vertebrates where this is in the bone.

• Have no swim bladder; have to constantly move to stay afloat.

• Very large liver helps with buoyancy.

• Do have scales on their skin; have denticles instead.

• Breath by swimming constantly, letting water flow through their mouths & spiracles over their gills.

• Blood is isotonic to ocean water, preventing water loss.

Skin & Spiracles

• Skin: covered in Denicles.

• Breathing: Possess Spiricles, which is how water passes to into their mouth & onto their gills.

Rays vs. Skates

• Both are members of Chondrichthyes.

• Rays: viviparous (give birth to live young).

• Shape: kite-like bodies (Larger size).

• Possess long tails with flexible spinal structures that causes venom.

• How they swim: Flap their side like a bird. Swim like they are flying in the water.

• Skates: Lay eggs.

• Tails that are shorter and fatter.

• Fin on the tail (anal fins).

• Non-venomous & don't possess Spines. Have anal fins on their tales.

• How they swim: Move in a wave-like motion.

Shark Anatomy

• Pectoral Fins: Used for lighting.

• Pelvic, Dorsal and Anal Fins: Used to keep sharks stabilized.

• Caudal Fin: Used for propulsion.

Common Uses of Shark Products

• Shark Sin Soup: Shark cartilage. Has no flavor; only seen as and impressive luxury meal.

• Cartilage Supplements: No scientific proven function. Waste of money.

• Liver products: Sharks contain a lot of vitamin A.

• Sins used for shark fin soup.

FYI: Things to know about Sharks.

• Shark Attacks: Punch the shark in the nose to deter it from attacking.

• Tonic Immobility: Turning them upside down puts them in a Coma. Must be held in this position.

• Detect Magnetism: Repelled by magnets. Have a strong magnet, carry it when swimming.