Annelids and Mollusks Flashcards

Pogonophorans

• Marine annelids living around deep sea hydrothermal vents.

• Underwater volcanoes with boiling hot temperatures where only microbes can survive.

• Around the vents, a meter or two away, animal life explodes.

• No sunlight reaches these depths, so no photosynthesis occurs.

• Food web is based on chemolithotrophy - eating using high energy minerals.

• Chemoautotrophy produces sugars from carbon dioxide, powering anaerobic respiration.

• Anaerobic respiration uses a terminal electron acceptor that is not oxygen.

• Worms are big, over six feet tall, segmented, but without limbs.

• They create mineral tubes for protection, moving in and out.

• No digestive tract; rely on symbionts for survival.

• Highly vascularized surface full of chemolithotropic bacteria.

• Worms provide housing, bacteria produce sugar from minerals and CO_2.

• Some can reach two meters long, discovered in the 1970s or 1980s.

• Many groups exist, but major groups are focused on.

Phylogeny Question

Earthworm Characteristics

• Segmented bodies
• Terrestrial lifestyle
• Complete gut
• Blastopore develops into a mouth
• Tight junctions between cells
• Bilateral symmetry

Evolutionary Order (Reverse)

• Terrestrial came most recently, as not all animals are terrestrial but some are.
• Segmented, then blastopore develops into a mouth (protostome characteristic).
• Complete gut and bilateral symmetry are concurrent for the class level.
• Tight junctions are the anapomorphy of animals and the earliest trait.

Forward Order

• Tight junctions
• Complete gut and bilateral symmetry (tie)
• Blastopore develops into a mouth
• Segmented bodies
• Terrestrial

Mollusks

• Include some terrestrial groups (gastropods).
• Not segmented, but have a three-part body plan.

Three Part Body

• Present in ancestral mollusks.
• Modified in different groups.

Foot

• Muscular organ for locomotion; modified for feeding.
• Allows them to crawl

Mantle

• Covers the top of the animal.
• Secretes the shell.
• All mollusk ancestors had a shell.

Visceral Mass

• Between the foot and the mantle.
• Contains internal organs (digestive tract, glands, heart, gills).

Open Circulatory System

• Present in mollusk common ancestor; fluid not contained only in tubes, but rather squirts into the body cavity. Organs bathed in circulatory fluid.
• Blood vessels are like a closed system, where metabolic rate is higher. Organs bathed in the fluid are like an open system.
• Fluid drains back into the heart, slower.

Chitons

• Live in the intertidal zone (between high and low tide).
• Can withstand salinity changes and dry/wet environments.
• Clamp to rocks to protect from drying out when the tide is out.
• Evade predators like sea stars that cannot survive out of water when they retract at low tide.

Gastropods

• 85,000 species.
• Include snails and slugs (terrestrial members).
• Skin adapted to prevent drying, but require moist environments.
• Slugs lost shell ability.
• Snails retreat into shell and seal it with their foot.
• Aquatic gastropods include nudibranchs (marine slugs).
• Nudibranch gills (brachial plume) can be retracted into the body.
• Limpets and abalone are also gastropods often consumed by humans.

Bivalves

• 30,000 species
• Hinged two-part shell without a lophophore (unlike brachiopods).
• Use foot to burrow in the sand.
• Siphon draws in water, filters it through gills, and expels it.
• Primarily filter feeding animals.
• Found in intertidal zones.

Cephalopods

• Smallest group with 800 species.
• Includes squids, octopuses, nautiluses, and cuttlefish.
• Move via jet propulsion using a modified siphon.
• Squids draw water into their mantle cavity and expel it through the siphon.
• Giant squid exist in deep sea environments, rarely observed alive.
• Evidence from sperm whales that battle giant squid in the deep sea.
• Sucker scars on sperm whales provide clues about squid size.
• Sophisticated eyes converge with vertebrate eyes, but use a different focusing mechanism by the lens moving up and down like a microscope instead of vertebrate eyes that work by deforming the eye itself.

Ecdysozoans

• Includes insects (
  > 1 million species).
• More terrestrial animals (than lophotrochozoans), even in dry environments.
• Exoskeleton supports mass and prevents drying.
• Exoskeleton is a bug shell.
• Arthropods are numerous in terrestrial environments; insects are vital for angiosperm reproduction.
• Ecdysis means molting; synapomorphy is a cuticle.
• Cuticle doesn't stretch, so animals must shed it periodically to grow.
• Arthropods have a cuticle strengthened with chitin, forming an exoskeleton.
• Molting evolved ~500 million years ago; Cambrian explosion.
• Appendages appear. Limbs used for movement, grasping, and mating.
• Very diverse; estimated 30-50 million arthropods exist.
• Fogging trees and counting insects reveals high species diversity.

Small Worm Group

Preapulids, Kynorhynx, Lorisophyllis

• Have a very thin and unsupportive cuticle, but it is not synapomorphine as it is ancestral trait, not a developed one. So structural support is low.
• Live buried in soft sediment.
• Use a proboscis to grab prey.
• All marine bottom dwellers.
• Benefit: gas exchange across the thin cuticle.
• Kynorhynx and lorociferans are microscopic with a nose-like proboscis.

Nematodes and Horsehair Worms

• Relatively thin cuticle allows gas exchange if moist environment.
• This is most numerous animals on earth in terms of individuals, with roughly about 25,000 species.
• Small, often associated with other organisms.
• Many symbionts and parasites.
• C. elegans used in cell biology studies. Fully sequenced genome. Every signal protein that it can make, has a version of it that will glow in the presence of blue light.
• Agricultural pests, like nematodes that feed on carrots.

Parasitic Forms

• Nematodes parasitize ants, taking over behavior.
• Trichinosis from undercooked pork; larvae insist in striated muscle.
• Human symptoms include body aches and muscle pain; larvae can get into eyes.
• Elephantiasis (lymphatic filariasis) caused by nematodes transmitted by mosquitoes.
• These gets into the lymphatic system, and scarring blocks lymphatic tubes, which causes lymph fluid to pool, causing tissue swelling and thickening skin, which takes a while after infection.
• Can affect reproductive organs, leading to social ostracization.

Horsehair Worms

• Sister to nematodes with similar bodies.
• Thin, narrow, and long.
• Live in freshwater environments.
• Larvae are endoparasites of arthropods (crickets, grasshoppers, crawdads).
• Adult form is short-lived and may not feed.
• Larvae must be consumed by a host.
• The worm does its final molting and becomes adults in larvae and has to go back to the pond. The worm releases chemicals and hormones that causes the parasite to do something suicidal, which is to jump into the water.
• They release chemicals and hormones to control host behavior (e.g., causing crickets to jump into water).
• Adults mate and die in freshwater ponds or streams.
• Accidental parasitism in humans can cause vomiting; a meter-long worm is difficult to quantify.
• They get their name like horsehair worm because people know the trough of water for horse or in cattle, and they would see it look like a horsehair wound up in the bottom of the trough, and then the horsehair starts wiggling around and swimming because its the horsehair worm.

Appendages Evolve: Tardigrades, Velvet Worms, Arthropods

• Appendages, and is like a really important and different trait. The closest thing that we saw was in mollusks with cephalopods with the arms and tendons.
• Tardigrades - limbs don't have any joints. Also called moss piglets or water bears. Has little quad tips to each of their legs.
• Velvet worms have lots of legs with claws on the end.
• Velvet worms have chitin in their cuticle, linking them to arthropods.
• So velvet worms, can shoot slime to mobilize prey, and are an really unique methods used of predation.
• Arthropods have a highly chitinized exoskeleton, no longer squishy but rigid.
• Exoskeleton: key synapomorphy. The cuticle becomes exoskeleton.
• A jointed exoskeleton, is rigid and inflexible. The exoskeleton properties change and there for gas exchange is no longer possible. They the use appengages usually to handle doing gas exchange, they evolve different methods to do that.
• Arthropods have segmentation and an exoskeleton with specialized functions. This set up for an explosion of different function from different sections.

Arthropods

• Huge fossil record. Arthropods are rigid. One- two-hundred and hundred and two thousand species known of and describe.
• Segmentation and exoskeleton come together, although the arthropods become locked in it. Appendages are there for locomotion, predation, sensory, mating, and gas exchange.
• Fossils show the evolution of jointed appendages, sensory organs, and compound eyes.

Main Arthropod Groups

• Divided by mouth parts using fangs and has a grinding jaw.

Chelicerates

• Have fangs (chelicerae).
• Spiders

Mandibulates

• hinged grinding jaw (mandible).
  Centipedes and millipedes. It isn't as important but it is just a analogous, not the same.