Invertebrates: Arthropods and Echinoderms Overview

Ecdysozoa includes animals that

shed a tough external coat (cuticle) as they grow.

Arthropod body plan (3)

Consists of three general parts:

-segmented bodies (cephalothorax, abdomen)

-specialized appendages specialized in function

-exoskeleton that completely covers the body.

Exoskeleton advantages

-provides protection & serves as a sensory interface

-point of attachment for muscles

-prevents desiccation & provides structural support

Exoskeleton disadvantages

-Heavy in water & limits size

-requires vulnerability during molt and post-molt

-energy cost & wasteful when making a new exoskeleton after a molt

Size restriction of arthropods on land (2)

-exoskeleton

-open circulatory system.

Are aquatic arthropods limited/impacted by the same characteristics as terrestrial?

yes & no:

-both have open circulatory system:

-insects --> small and active

-crustaceans --> large and inactive

Gas exchange in terrestrial arthropods

Carried out using a tracheal system or book lungs.

Gas exchange in aquatic arthropods

smaller species = cuticle

larger species = gills

gas exchange in insects

gills with modified appendages that flick water onto gills

Chelicerates

A group of arthropods (e.g., arachnids- scorpions, spiders, and mites) characterized by claw-like feeding appendages called chelicerae and pedipalps for sensing and reproducing

Myriapods

Includes millipedes and centipedes, with 3 pairs of appendages modified as mouth parts like jaw-like mandibles.

milli = 2 pairs of leg per segment, herbivores and dertrivores

centi = 1 pairs of legs per segment, carnivores

Crustaceans

Aquatic arthropods (e.g., crabs, lobsters, shrimps) with highly specialized appendages and gas exchange across thin cuticle or gills.

Groups:

1) Isopods- pill bugs

2) Decapods- crabs, lobster, shrimp

3) Copepods- planktonic krill

4) Barnacles- sessile with cuticle hardened into a shell

Insects

one or two pairs of wings emerged from dorsal side of thorax- can fly without sacrificing walking legs. Undergo metamorphosis and sexual reproduction.

ex: grasshopper

What is the most specious group of animals?

Insects

3 characteristics that contributed to insects' great success

-high reproductive capacity

-social behaviors & systems

-highly motile (run, hop, & fly)

which form of motility has highly increased the success and why does it require a highly developed nervous system?

flight

all things during flight(take off, landing, flying), complex use of senses, and complexity of sensory function

Complete metamorphosis

Involves larval stages specialized for eating and growing, adult stages specialized for dispersal and reproduction. pupal stage during metamorphesis

Incomplete metamorphosis

nymphs resemble adults but are smaller and lack wings, undergoing a series of molts until they reach full size and acquire wings.

Echinodermata and Chordata are both called _____ due to similar embryonic development.

Deuterostomia

Echinoderm characteristics

-anus forms from the blastopore; mouth forms at opposite end

-larvae exhibit cephalization then is lost in adults

-sessile, predatory, filter feeders & consumers

-external sexual reproduction.