7 Animal Diversity: Protostome Phyla, Body Plans & Arthropods

What do protostome and deuterostome originally refer to?

The fate of embryonic blastopore: forms mouth in protostomes and anus in deuterostomes.

During which period do many bilaterian phyla become conspicuous in the fossil record?

The Cambrian period, during the Cambrian explosion.

What are the three major bilaterian clades in the course tree?

Lophotrochozoa, Ecdysozoa, and Deuterostomia.

What problems must animals solve to live on land?

Avoid drying out, exchange gases in air, support bodies, and reproduce without desiccation.

How do terrestrial adaptations in animals resemble those in plants?

Exoskeletons and plant cuticles prevent water loss; specialized surfaces enable gas exchange.

What is a modular body plan?

A body assembled from repeated units that can become specialized.

How can a conserved genetic toolkit generate diverse animal forms?

Changes in timing or expression location of genes like Hox alter structures.

What are the two main protostome clades and the key phyla in each?

Lophotrochozoa (Platyhelminthes, Annelida, Mollusca) and Ecdysozoa (Nematoda, Arthropoda).

Which protostome phyla discussed in class show obvious segmentation?

Annelida and Arthropoda.

What is a lophophore?

A ciliated tentacle-bearing feeding structure around the mouth in some lophotrochozoans.

What is a trochophore?

A ciliated larval form found in some mollusks and annelids.

What are the main body-plan features of flatworms?

Unsegmented, bilaterally symmetrical, triploblastic acoelomates with flattened bodies.

Why does a flat body help a flatworm?

It keeps cells near an exchange surface, shortening diffusion distances.

Which flatworms are free-living, and which are common parasites?

Planarians are free-living; flukes and tapeworms are parasites.

Why can a tapeworm survive without its own digestive tract?

It absorbs pre-digested nutrients from the host's intestine across its body surface.

What are the major annelid examples and lifestyles?

Earthworms (terrestrial detritivores), bristle worms (marine), and leeches (predators/parasites).

What body-plan features characterize annelids?

Segmented coelomates with a complete gut, chaetae, and fluid-filled hydrostatic compartments.

What is a typical annelid circulatory arrangement?

A closed circulatory system containing blood within vessels.

What are the three main molluscan body regions?

Muscular foot, visceral mass, and mantle.

Which molluscan structure secretes the shell?

The mantle.

What is a radula, and which major mollusk group lacks it?

A rasping feeding structure; Bivalvia lacks a radula.

Which organisms belong to Gastropoda?

Snails and slugs.

Which organisms belong to Bivalvia?

Clams, mussels, oysters, and scallops.

Which organisms belong to Cephalopoda?

Squid, octopuses, cuttlefish, and nautiluses.

What synapomorphy unites Ecdysozoa?

Ecdysis: periodic molting of an outer cuticle to permit growth.

What is a nematode?

An unsegmented roundworm with a complete gut, pseudocoelom, and molted cuticle.

How can free-living soil nematodes affect ecosystems?

They feed within soil food webs, influencing microbe populations and nutrient cycling.

How can nematodes affect human health?

Some species are human parasites, including intestinal roundworms and hookworms.

Why does a nematode move in a whipping or S-shaped pattern?

It has longitudinal muscles but lacks circular muscles, bending pressurized fluid side-to-side.

What are two benefits and one cost of an arthropod exoskeleton?

Benefits: protection and water-loss reduction. Cost: limits growth, requiring dangerous molting.

What three features strongly identify an arthropod?

Segmented body, jointed appendages, and chitinous exoskeleton.

What is a hemocoel, and why is it not the same as a true coelom?

A hemocoel is a hemolymph-filled open space; arthropod true coeloms are reduced.

Which three arthropod subphyla are used in this course?

Myriapoda, Chelicerata, and Pancrustacea.

Which classes include centipedes and millipedes?

Chilopoda (centipedes) and Diplopoda (millipedes).

How can leg arrangement distinguish a centipede from a millipede?

Centipedes have one leg pair per segment; millipedes have two pairs per segment.

How do centipede and millipede feeding habits usually differ?

Centipedes are venomous predators; millipedes are mostly detritivores.

Which class contains spiders, scorpions, ticks, and mites?

Arachnida.

What are chelicerae and pedipalps?

Chelicerae are feeding/defensive fangs; pedipalps assist in sensing, feeding, or mating.

What characters commonly distinguish crustaceans from other arthropods?

Two pairs of antennae, biramous appendages, and often calcified exoskeletons.

What habitats do crustaceans occupy?

Mostly marine and freshwater environments, with some terrestrial species like pillbugs.

What are four examples of crustaceans?

Crabs, shrimp, barnacles, and copepods.

What are an insect's main body regions, and where do legs and wings attach?

Head, thorax, and abdomen; legs and wings attach to the thorax.

How many legs and antenna pairs does an adult insect have?

Six legs (three pairs) and one pair of antennae.

What is incomplete metamorphosis?

Development via egg, nymph, and adult stages without a pupal stage.

What is complete metamorphosis?

Development via egg, larva, pupa, and adult stages.

How is a pupa different from a cocoon?

The pupa is the developmental stage; a cocoon is its protective outer covering.

Which protostome examples are acoelomates, pseudocoelomates, and coelomates?

Flatworms are acoelomates; nematodes are pseudocoelomates; annelids, mollusks, and arthropods are coelomates.

What are three visible differences between a typical spider and an insect?

Spiders have 8 legs, 2 body regions, no antennae; insects have 6 legs, 3 regions, 1 antenna pair.

Which animal phylum is most diverse in species in the course comparison?

Arthropoda.

How do diversity and abundance differ?

Diversity measures total species count; abundance measures total individual count.

What insect, order, and order-level fact can you use as a ready example?

Monarch butterfly (Danaus plexippus), order Lepidoptera (scaled wings, complete metamorphosis).

Which insect order has hardened forewings called elytra?

Coleoptera (beetles).

Which insect order has one flight-wing pair and balancing halteres?

Diptera (true flies).

Which order includes bees, wasps, and ants?

Hymenoptera.

Which order includes grasshoppers and crickets?

Orthoptera.

How does metamorphosis differ from evolution?

Metamorphosis alters one individual during development; evolution changes inherited traits across generations.