Protostomes - Bio 94

Lophotrochozoans

group of protostome animals that grow continuously without molting and include organisms like mollusks and annelids

spiral cleavage

pattern of embryonic cell division in some protostomes where cells divide at an angle, forming a spiral arrangement

lophophore

specialized ciliated feeding structure found in some lophotrochozoans used for filter feeding

trochophore

free-swimming larval stage with bands of cilia found in some lophotrochozoans like mollusks and annelids

ecdysozoans

A group of protostome animals, including arthropods and nematodes, that grow by molting their external cuticle.

exoskeleton

A rigid external covering that provides structural support and protection for ecdysozoans like arthropods.

cuticle

A tough, flexible outer layer that protects ecdysozoans and must be shed for growth.

molting

The process of shedding the cuticle or exoskeleton to allow growth in ecdysozoans.

mollusks

A diverse phylum of invertebrates including snails, clams, and squids, characterized by soft bodies and often a hard shell.

Visceral Mass

The part of a mollusk’s body containing most of the internal organs, including the digestive and reproductive systems.

Hemocoel

A primary body cavity in mollusks and arthropods where blood is circulated in an open circulatory system.

Radula

A toothed, chitinous ribbon-like structure used by many mollusks to scrape or cut food before ingestion.

shell

A hard, external protective structure secreted by the mantle in many mollusks.

Mantle/Mantle Cavity

A tissue layer in mollusks that secretes the shell and forms a cavity for respiration and excretion.

Hemimetabolous

A type of incomplete metamorphosis in insects where juveniles resemble adults but lack wings or reproductive structures.

Holometabolous

A type of complete metamorphosis in insects involving distinct egg, larval, pupal, and adult stages.

Cephalopods

A class of mollusks, including squid and octopuses, known for their intelligence, tentacles, and ability to change color.

Terrestrial Snails

Land-dwelling mollusks that use a muscular foot for movement and a shell for protection.

Bivalves

A group of mollusks, including clams and oysters, that have two hinged shells and filter-feed through gills.

Annelids

Segmented worms, including earthworms and leeches, that have a coelom and move with the help of setae or parapodia.

Flatworms

Soft-bodied, unsegmented invertebrates, including planarians and tapeworms, often with simple organ systems.

roundworms

Also known as nematodes, these are unsegmented worms with a complete digestive tract and a tough cuticle.

insects

The largest group of arthropods, characterized by a three-part body (head, thorax, abdomen), six legs, and often wings.

Crustacea

A diverse arthropod group, including crabs, lobsters, and shrimp, usually with a hard exoskeleton and aquatic habitats.

Chelicerates

A subgroup of arthropods, including spiders and scorpions, that have specialized mouthparts called chelicerae.

Myriapods

Arthropods with elongated bodies and many legs, including centipedes and millipedes.

what are protostomes

most diverse major group, major source of food for humans provide economic services, produce materials such as pearls can be parasites

explain protostome development

development of mouth before anus during gastrulation, isolated embryonic cells are unable to develop into complete embryo, formation of coelom by splitting of blocks of mesodermal cells

protostomes transitions from ——- to —-

aquatic, terrestial. needed adaptations to ensure they dont dry up and can hold their own weight.j

innovation of roundworms and earthworms

developed high surface area to volume ratio to increase efficiency of gas exchange

innovation of arthropods and mollusks

developed gills or other respiratory structures located inside of body to minimize water loss, and compartmentalized body plans

innovation of insects

waxy layer to minimize water loss, dry environment openings to respiratory passages can be closed, desiccation resistant eggs (eggs have thick membrane that maintains moisture)

If an animal has these three characteristics, it must be a lophotrochozoan

lophophore (feeding structure - suspension feeding), trochophore (larvae), and spiral pattern of cleavage. examples are rodifera, mollusca, and annelida

examples of mollusca

gastropods (snails), bivalve (clams), cephalopods (octopus)

3 types pf lophotrocozoans

molllusca, annelids, and flatworms

structure of mollusca

visceral mass, radula, hemocoel, shell, mantle

visceral mass

contains all main

internal organs and external gills

→ helps them breath

radula

tongue for mollusks

hemocoel

body cavity, not lined

in mesoderm (not a coelom), body

fluids bathe organs directly

shell

used for defense,

protection, armor

mantle

secrets a shell made of calcium

carbonate - many adaptations of mantle

→ diverse functions!!

explain mantle of terrestrial snails, bivalves, and cephalopods,

Terrestrial snails: mantle forms internal

lung

○ Bivalves: mantle is lined with muscle and

forms tubes called siphones

○ Cephalopods: mantle forms siphon that

functions in jet propulsions

what are annelids

Wormlike

○ Has coelom

○ Fully developed digestive tract with

mouth, anus, and segmented body

what are flatworms

Broad, flat shaped bodies

○ Large surface area for gas

exchange

○ Nutrients and gases to diffuses

efficiently to cells

● Reside in moist/aquatic environments

● Lack coelom and structures specialized

for gas exchange

what are ecdysozoans?

Cuticle and exoskeleton → structure

for muscle attachment + protection

from predators

● Molts frequently, uses hormone called

endysone to regulate molting cycle

● Once organism molts, fluid causes

body to expand and newer, larger

cuticle/exoskeleton forms

two types of ecdysozoans

arthropods and roundworms

arthropods and their four main lineages

Most important phylum in Ecdysozoa

○ Most abundant and diverse

duration in the fossil record!

● In aquatic and terrestrial

environments

● Four main lineages:

○ Myriapods (eg. centipedes)

○ Insects (eg. ladybugs)

○ Crustacean (eg. shrimp)

○ Chelicerates (eg. spiders)

insects are arthropods, explain them

The first animal to achieve

powered flight!

○ Allowed them to escape predators

and find food sources

incomplete metamorphosis (hemimetabalous)

Form of direct development

○ Nymphs (juveniles) look like smaller

version of adult

complete metamorphosis (holometabolous)

DISTINCT larval stage!

○ Larva becomes pupa

○ Pupas body completely remodeled

into new adult form

MORE COMMON THAN INCOMPLETE

roundworms are arthropods, explain them

Unsegmented worm with no

appendages

○ Tube within-a-tube body plan

○ Pseudocoelom