Protostomes

Importance of protostomes

• major source of food for humans

• Provide ecosystem services

• Some damage crops

• Some produce materials like silk + pearls

• Cause/transmit human diseases + are parasites

• Include 2 of the most important model organisms

  • fruit fly

  • Roundworm

What’s a protostome

• embryonic development of mouth before anus during gastrulation

• Inability of isolated early embryonic cells to develop into a complete embryo

• The formation of a coelom by splitting of blocks of mesodermal cells

Subgroups

• lophotrocozoa- mollusks and annelid worms

• Ecdysozoa- nematodes and arthropods

Water to land transition adaptations allow them to

• exchange gases

• Avoid drying out

• Hold up their bodies under their own weight

Gas exchange

• roundworms and earthworms have high SA to volume ratio

  • increases efficiency of gas exchange across their body surface in their moist envts

• Some terrestrial arthropods and mollusks have gills or other respiratory strucs inside their body

  • minimizes water loss when moving into land

Preventing water loss

• insects evolved ways to minimize water loss from body surface

  • if env’t dries, opening to respiratory passages can be closed

• Dessication resistant eggs evolved repeatedly in pops that made the transition to land

  • insect eggs have thick membrane that keeps in moisture

  • Snail + slug eggs have thick shell that retains water

Modular body plans

• morphological and physiological diversification has a genetic basis

  • multicellular animals have a common tool kit of genes that establish the animal body plan during development

  • Hox genes part of kit

What’s a lophotrichozoan

• include rotifers, flatworms, annelids, and mollusks

• 2 physical traits occur in some but not all

  • feeding structure: lophophore, found in 3 phyla.

  • Type of larvae- trochophore, common to many phyla

What’s loohophore and trochopore

Lophopore= specialized structure that rings the mouth of these animals and functions in suspension feeding

Trochopore= trochopore larvae have a ring of cilia around their middle that functions in sweeping and sometimes feeding

Platyhelminthes

• flat worms

• Lack coelom and structures specialized for gas exchange and circulation of oxygen and nutrients

• Phylum consisting of 4 major lineages

• Turbellia

• Cestoda

• Tematoda

• Monogenea

Turbellaria

• paraphyletic group of free living flatworms

• Most freshwater/marine

• Prey on protists, small animals, or scavenge dead animals

Cestodoa

• strictly endoparasitic tapeworms that parasitize vertebrates, absorbing nutrients by diffusion across their body wall

• Humans get tapeworms by eating undercooked pork, beef, fish

Trematoda

• endoparasitic/ectoparasitic flukes that parasitize vertebrates, arthropods, annelids, mollusks

• A flukes responsible for infecting more than 200 mill ppl worldwide

• Schistomiasjs idk

Monogenea

• tiny ectoparasities that parasitic rushes of particular species usually skin/gills of fishes

• Don’t need mates (hermaphroditic)

Annelids

• segmented worms

• Common ancestor of annelids had a key synaponirphy in addition to segmentation

  • numerous bristle like extensions called chaetae that extend from lobe like appendages called parapodia

• 3 groups

  • polychaeta

  • Oligochaeta

  • Hirudinea

Polychaeta

• diverse worms that live in variety of marine habitats

• Highly mobile often have large parapodia and chaetae

• More sedentary ones have reduced parapodia and smaller but still numerous chaetae

Oligochaeta

• earthworms and others

• Deposit feeding in soils

• Ecosystem services include:

  • tunnels that are inportant in aerating soil

  • Feces contribute large amounts of organic matter

hirudinea

• leeches

• Ectoparasites that attach themselves to fish, humans, or other hosts and suck blood/bodily fluids

• Nonparasitic leech species are predators or scavengers

Mollusks

• diverse monopohyletic group

• Characteristic body plan

  • foot- used in movement, large muscle at base

  • Mantle- outgrowth of the body wall that covers the visceral mass, forming an enclosure called the mantle cavity

4 main lineages of mollusks

• bivalves (have 2 shells)

• Gastropods

• Chitons

• Cephalopods

Gastropodia

• terrestrial and marine snails, slugs, nudibranchs

• Have a large muscular foot on their ventral side

• Terrestrial slugs and nudibranchs lack shells, snails shelled

• Use radula to scrape food

Chitons (polyplacophora)

8 caco3 plates along their dorsal side that forms protective shell

Cephalopoda

• cuttlefish, squid, octopuses

• Have well developed head and foot that’s modified to form long muscular tentacles

• Large brains with eyes and sophisticated lenses

What’s an ecdysozoan ( not segmented)

• grow indeterminately by molting unlike loohotrocians that grow continuously and incrementally

• They undergo succession of molts as they grow

• Once animal molts fluids case the body to expand then a larger cuticle or exoskeleton forms

Cuticle and exoskeleton of ecdysozoans

• protects them from predators

• provides effective struc for muscle attachement

• During molting the animals soft body exposed, and vulnaerable

• Lack specialized systems for exhanging gases and nturients

• gas exchange occurs across body wall and nutrients move by diffusion from the gut to other parts of the body

Nematode characteristics

• musculature- consists of longitudial muscles that shorten/lengthen body upon contracting or relaxing

• move using hydrostatic skeleton

• tardigrada similar to arthropods in having a segmented body and limbs

• UNLIKE arthropods their cuticle not hardened as an exoskeleton + limb’s aren’t jointed

  ex: Onychoporans- small caterpilla organisms that live in moist leaf leafer and prey on small invertebrates

Arthropod body plan 3 key features

• Segmented body

  • organized into prominent regions or tagmata

  • body of grasshopper + other insects divided into head, throrax, and abdomen

• Exoskeleton

  • made of chitin and strengthed by caco3

• Jointed appendages

  • Enable rigid body to move

Why are arthropod body plans so successful?

• Like mollusks arthropod bodies are modular in evolutionary terms

• Studied of hox genes + other tool kit genes show small changes in timing and location of gene expression can result in novel shapes and sizes.

• variation in gene expression combined with eoclogical opportunity through natrual selection can result in diversification of arthropod body segments + appendages

Origin of wing

• Insects 1st animals that had wings and could fly on earth

• gill co-option hypothesis most likely

  • wings arose form gill like projections on branched legs of a wingless ancestor

Lineages of arthropods

• Myriapods

• Hexapoda (insects)

• Crustaceans

• Chelicerates

Myriapods

• long segmented trunks

• simple bodies

• head region

Insects- Hexapoda

• 3 tagmata- head, thorax, abdomen

• 3 pairs of waling legs extend from sides of thorax

• most species have ½ pairs of wings on back of thorax

• head has 4 pairs of structure

  • 1 pair slender antennae used to touch and smell

  • pair of compound eyes

Crustaceans

• live in aquatic envts

• play important ecological roles

  • planktonic corepods- consume phytoplanktons + in turn are important food source for fish and marine mammals

• have segmented body divided into head, thorax, and abdomen

• some has cephalorothorx and the abdomen

Chelicerates

• Most prominent lineages of this are terrestrial (spiders, mites, daddy long legs)

• Body consists of 2 tagmata- the cephalothorax, and abdomen

• tagmata not homologous to those in other arthropods even though they’re functionally similar

• cephalothorax lack antennae but have eyes

2 types of metamorphosis

• incomplete

  • form of direct development

  • juvelines called nymphs look like smaller versions of adult (instars)

  • gradual changes occur in insect during development

• Complete metamorphosis

  • type insect development that includes egg, larva, pula, and adult stages which differ greatly in morphology

  • ex: butterflies, beetles, moths