Ecdysozoa, Arthropods, and Chordates: Key Concepts and Characteristics

What does 'ecdysis' mean?

Ecdysis refers to the process of shedding the outer layer or exoskeleton in certain animals, particularly arthropods and nematodes.

What does 'arthropoda' mean?

Arthropoda is a phylum name meaning 'jointed legs,' referring to the segmented body and jointed appendages of its members.

What are the general characteristics of ecdysozoa?

Ecdysozoa are characterized by a tough outer cuticle that is molted during growth, segmented bodies, and diverse body plans including both aquatic and terrestrial forms.

Compare and contrast Nematoda to Arthropoda.

Nematoda (roundworms) are unsegmented, have a simple body plan, and a pseudocoelom, while Arthropoda (insects, arachnids, crustaceans) are segmented, have jointed appendages, and a true coelom.

Describe the biodiversity of ecdysozoa.

Ecdysozoa includes a vast array of species, with high biodiversity in both terrestrial and aquatic environments, including insects, crustaceans, and nematodes.

How do you distinguish Chelicerata, Myriopoda, Crustacea, and Hexapoda?

Chelicerata have chelicerae (fang-like mouthparts), Myriopoda have many body segments with one or two pairs of legs per segment, Crustacea have two pairs of antennae and branched appendages, and Hexapoda (insects) have three body segments and six legs.

Where are nematodes found?

Nematodes are found in diverse environments, including soil, freshwater, and marine ecosystems, often in large numbers.

What is the size range of nematodes?

Nematodes range in size from about 0.3 mm to several meters in length.

What is the function of the nematode cuticle?

The cuticle provides protection, prevents desiccation, and aids in locomotion.

How can nematodes influence humans?

Some nematodes are agricultural pests or parasites that can affect human health, while others are used in research and biological control.

Which nematode has been used extensively in research?

Caenorhabditis elegans is a nematode widely used in genetic and developmental biology research.

Why have arthropods been so successful on land?

Arthropods have a protective exoskeleton, efficient respiratory systems, and versatile appendages that allow them to adapt to various terrestrial environments.

What are the general characteristics of arthropods?

Arthropods have segmented bodies, jointed appendages, an exoskeleton made of chitin, and a well-developed nervous system.

What is the function of the exoskeleton in arthropods?

The exoskeleton provides structural support, protection from predators, and prevents water loss.

Why can't arthropods become giants on land?

Arthropods cannot grow too large due to limitations of their exoskeleton and respiratory systems, which are less efficient at larger sizes.

What are chelicerae?

Chelicerae are specialized mouthparts found in chelicerates, often adapted for grasping or piercing.

Describe the sensory organs of arthropods.

Arthropods have compound eyes for detecting motion and light, antennae for sensing chemicals and touch, and various other sensory structures.

Describe the characteristics of Trilobites.

Trilobites are extinct marine arthropods characterized by their three-lobed body plan and numerous segments.

Describe the characteristics of Chelicerae.

Chelicerae are characterized by having two main body segments and lack antennae, with the first pair of appendages modified into fangs or pincers.

Describe the characteristics of Crustacea.

Crustacea have a hard exoskeleton, two pairs of antennae, and are primarily aquatic, including crabs, lobsters, and shrimp.

Describe the characteristics of Hexapoda.

Hexapoda are characterized by having three body segments, six legs, and often wings, making them the most diverse group of animals.

What are the unique characteristics of spiders?

Spiders have eight legs, chelicerae with fangs, and produce silk for webs or hunting.

How do horseshoe crabs respire?

Horseshoe crabs respire using book gills located on the underside of their bodies.

Describe millipedes.

Millipedes are myriopods with elongated bodies, two pairs of legs per body segment, and primarily detritivorous feeding habits.

Describe centipedes.

Centipedes are myriopods with one pair of legs per body segment, are carnivorous, and have venomous fangs.

Describe the major groups of Crustaceans.

Major groups of Crustaceans include decapods (crabs, lobsters), copepods, and barnacles, differing in size, habitat, and morphology.

What are the derived characteristics of hexapoda?

Hexapoda have three body segments, six legs, and often wings, allowing for diverse adaptations and ecological roles.

What are the advantages of having wings?

Wings provide the ability to escape predators, access new habitats, and exploit food resources more efficiently.

What are Malpighian tubules?

Malpighian tubules are excretory structures in insects that help conserve water and eliminate waste.

What are spiracles?

Spiracles are external openings in insects that allow air to enter the tracheal system for respiration.

What is the tracheal system?

The tracheal system is a network of tubes in insects that delivers oxygen directly to tissues.

Describe sexual reproduction in insects.

Insects typically reproduce sexually, with males and females mating, followed by fertilization of eggs, which may be laid in various environments.

What is metamorphosis?

Metamorphosis is the developmental process in which insects undergo significant changes in form and function from larva to adult.

What is complete metamorphosis?

Complete metamorphosis involves four stages: egg, larva, pupa, and adult, seen in insects like butterflies.

What is incomplete metamorphosis?

Incomplete metamorphosis involves three stages: egg, nymph, and adult, seen in insects like grasshoppers.

Describe the modification of mouth parts of insects.

Insect mouthparts are adapted for different feeding strategies, including chewing, sucking, and lapping, depending on their diet.

What are the classes of Echinoderms?

The classes of Echinoderms include Asteroidea (sea stars), Echinoidea (urchins), Holothuroidea (sea cucumbers), and Crinoidea (crinoids).

Why are echinoderms considered more closely related to chordates?

Echinoderms share a common ancestor with chordates and exhibit similar embryonic development and genetic traits.

What are the major distinguishing characteristics of echinoderms?

Echinoderms have a water vascular system, radial symmetry (pentaradial), and a calcareous endoskeleton.

What does it mean that echinoderms are pentaradial?

Pentaradial symmetry means that echinoderms have body parts arranged in fives or multiples of five around a central axis.

Describe the water vascular system.

The water vascular system is a network of fluid-filled canals used for locomotion, feeding, and respiration in echinoderms.

What are ossicles?

Ossicles are small calcareous plates that make up the endoskeleton of echinoderms.

What are tube feet?

Tube feet are extensions of the water vascular system used for movement, feeding, and attachment in echinoderms.

Compare and contrast sea stars and brittlestars.

Sea stars have a central disc and arms that are not distinct, while brittlestars have a distinct central disc and long, flexible arms.

What do sea stars eat?

Sea stars are carnivorous and often feed on bivalves by extruding their stomachs to digest prey externally.

Describe the respiratory tree of sea cucumbers.

The respiratory tree is a unique structure in sea cucumbers that aids in respiration and expels waste.

How do sea cucumbers defend themselves?

Sea cucumbers can expel their internal organs or release toxic substances as a defense mechanism.

What is a notochord?

A notochord is a flexible rod-like structure that provides support in the embryonic stage of chordates.

What is the function of the dorsal nerve cord?

The dorsal nerve cord is part of the central nervous system and is responsible for transmitting signals between the brain and the body.

Describe Cephalochordata.

Cephalochordata, or lancelets, are small, fish-like chordates that retain their notochord throughout life and are found in marine environments.

Describe Urochordata.

Urochordata, or tunicates, are marine organisms that exhibit chordate characteristics in their larval stage but lose them as adults.

Why is Urochordata considered a chordate?

Urochordata are considered chordates because they possess a notochord and dorsal nerve cord during their larval stage.

Describe the characteristics of Agnatha.

Agnatha includes jawless fish like lampreys and hagfish, characterized by their elongated bodies and lack of paired fins.

Describe the characteristics of Chondrichthyes.

Chondrichthyes includes cartilaginous fish like sharks and rays, characterized by a skeleton made of cartilage and the presence of gills.

Describe the characteristics of Osteichthyes.

Osteichthyes, or bony fish, have a bony skeleton, swim bladder, and operculum covering their gills.

What is the significance of a lateral line?

The lateral line is a sensory organ in fish that detects water movements and vibrations, aiding in navigation and prey detection.

What is a swim bladder?

A swim bladder is a gas-filled organ in bony fish that helps maintain buoyancy in water.

Describe the reproductive strategies of fish.

Fish reproduce in various ways: oviparous (laying eggs), ovoviviparous (eggs hatch inside the mother), and viviparous (live birth).

What is Tiktaalik?

Tiktaalik is a transitional fossil between fish and tetrapods, showcasing features for both aquatic and terrestrial life.

Describe the three classes of Amphibia.

The three classes of Amphibia are Anura (frogs and toads), Caudata (salamanders), and Apoda (caecilians), each with unique characteristics.

Describe the two-part life cycle of amphibians.

Amphibians typically have a two-part life cycle that includes an aquatic larval stage and a terrestrial adult stage.

Why are amphibians tied to water?

Amphibians are tied to water for reproduction and to maintain moisture for their permeable skin.

Describe the reproductive cycle of frogs.

Frogs reproduce by laying eggs in water, which hatch into tadpoles that undergo metamorphosis into adult frogs.

Where would you find the three classes of amphibians?

Anura are found in diverse habitats, Caudata prefer moist environments, and Apoda are often burrowing in tropical regions.

What is the amniotic egg?

The amniotic egg is a type of egg that contains specialized membranes to protect the embryo, allowing for reproduction in dry environments.

Why is the amniotic egg a major derived trait?

The amniotic egg allows vertebrates to reproduce away from water, facilitating the colonization of terrestrial habitats.

What are the functions of the shell, amnion, allantois, chorion, and yolk?

The shell protects the egg, the amnion cushions the embryo, the allantois stores waste, the chorion facilitates gas exchange, and the yolk provides nutrients.

What are the major groups of modern-day amniotes?

The major groups of modern-day amniotes include reptiles, birds, and mammals.

Why are mammals considered amniotes?

Mammals are considered amniotes because they have evolved from ancestors that laid amniotic eggs, despite most not laying eggs.

Describe the major groups of reptiles.

Major groups of reptiles include turtles, lizards, snakes, tuataras, and crocodiles, differing in habitat, diet, and physical characteristics.

Why are birds considered a sister taxon to crocodiles?

Birds and crocodiles share a common ancestor and exhibit similar features such as nesting behaviors and certain skeletal structures.

Describe reptiles' skeletons.

Reptiles have a bony skeleton, with variations in skull structure (anapsid, diapsid) that affect their evolutionary adaptations.

Describe the skin of mammals.

Mammalian skin contains glands, hair, and may have horns; it serves protective, sensory, and thermoregulatory functions.

How do horns differ from antlers?

Horns are permanent structures made of keratin, while antlers are temporary, branched structures made of bone that are shed annually.

Describe the circulatory system of mammals.

Mammals have a four-chambered heart, allowing for efficient separation of oxygenated and deoxygenated blood.

Describe the teeth of mammals.

Mammals have differentiated teeth (incisors, canines, molars) that reflect their feeding strategies, such as herbivory, carnivory, or omnivory.

How do digestive systems differ in mammals?

Mammals have varied digestive systems adapted to their diets, with ruminants having specialized stomachs for breaking down cellulose.

Describe the reproductive strategies of mammals.

Mammals exhibit diverse reproductive strategies, including gestation periods, mating seasons, and varying numbers of offspring.