Lophotrochozoan Phyla:

General Characteristics of Lophotrochozoans:

• Bilaterally symmetrical

• Triploblastic

• Protostome: blastopore develops into the anus

Function of Lophophore Structure:

• A horseshoe shaped feeding structure that is a common evolutionary link between members of the phyla. Each member will have this structure at one point in their lives

• Shows evolutionary relationship

Phylum Platyhelminthes:

How many species?

• 34,000 species

Characteristics:

• Flattened

• Triploblastic: has three tissue layers

• Acoelomate (has no coelom/no body cavity/no organs or organ systems)

• Bilaterally symmetrical

• Unsegmented worms

Classes of Platyhelminthes (4):

• Class Turbellaria (Planarians!!!!!!):

  • Free-living and aquatic

  • Can be both freshwater and marine

  • Predators and scavengers (first true hunters!)

  • 1 cm-60 cm

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Locomotion:

• They are bottom dwellers

• They move using cillia and muscular contractions

• They can free swim sometimes

Digestions:

• They have an incomplete digestive tract: they only have a mouth but they don’t have an anus

  • Branched digestive systems allows for diffusion of nutrients

  • No circulatory system

  • They have a Pharynx: muscular ingestion organ that is located on their underbelly and attaches to their mouth

  • Chemo receptors on their head that help them find prey

    • Chemo receptors: structures/cells that can sense chemicals/heat in the water to find prey

Exchanges in the Environment:

• No respiratory organs

• Gases are exchanged, nitrogenous waste (chemical waste/cellular waste) is eliminated through diffusion through body wall and flame cells

  • Flame Cells: a specialized excretory cell (they operate like kidneys)

Nervous and Sensory Function:

• Central ganglia: cluster of neurons located in the head region

• Platyhelminthes can detect touch, water current, and chemicals

• Auricles: projections on the side of the head; help locate food by using chemoreceptors

• Ocelli: “eye spots” that orient the animal towards light

  • Most platyhelminthes (turbeliina) are negatively photoreceptive (meaning they move away from the light)

Reproduction and Development:

• Asexually by transverse fission

  • Transverse Fission: They can pinch their bodies together horizontally and make two halfs called zooids. These half each grow the part that they need to become a new turbellina that being either a tail or a head.

• Sexually: monoecious (both male and female reproductive organs in one body)

  • Reciprocal sperm exchange between individuals

  • Fertilized eggs are laid in capsule called coccoon

    • Summer capsules: hatch in a fast time, 2 to 3 weeks and immature animals emerge

    • Autumn capsules: thick walls that resist freezing and drying out; hatch after winter when conditions are favorable

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Class Trematoda:

• These are called flukes

• Wide, flat shape

• 10,000 species; that are all parasitic

• They feed on host cells and cell fragments

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Class Monogenea:

• External parasites of fishes

• Attach to gill filaments

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Class Cestiodea:

• This class includes tapeworms

• They lack a mouth and simple digestive systems

  • Instead these cestiodea absorb nutrition from host through cell wall

• Proglottids: long, repeating sections that each contains a set of reproductive structures

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Phylum Nematoda:

Main Characteristics:

• Triploblastic

• Bilateral

• Unsegmented

• Pseudocoelomate (fake body cavity)

• Cuticle: outer body covering of nematodes that is made of the collagen protein

  • Covers body

• Digestive System:

  • Complete digestive tract: mouth and anus

  • Mouth surrounded by lip bearing sense organs

    • Located on the head

Nematode Parasites of Humans:

• Ascaris lumbricodes: Affects dogs and cats normally

  • Intestinal roundworm

  • 800 million people infected

  • Live in small intestines

  • Eggs exist in the feces that the dog and cats excrete

  • Eggs ingested and move to intestinal tract

• Enterobius vermicularis

  • Human pinworms

  • Most common roundworms in US

  • Live in lower region of large intestine

  • Females carry eggs out of rectum, deposit them, then die

  • Eggs are swallowed and move to intestines

• Necator americanus

  • The New World Hookworm

  • Found in Southern US

  • Live in small intestine

  • Eggs pass out in feces and hatch

  • Larva penetrate the skin, makes way to the intestines

• Trichenella spiralis (pork worm)

  • The pork worm

  • Live in small intestines of all carnivores and omnivores

  • Females give birth to live larvae that migrate to muscle tissue

  • Remain infective for years (trichinosis)

  • Transmission: Another animal eats muscle, migrates to that animal’s small intestines

• Wucheria species

  • The filarial worms

  • Live in lymphatic system of humans

  • Causes fluids to accumulate in appendages (elephantiasis)

  • Produce larvae: microfilariae

  • Circulates in bloodstream, carried by mosquitoes to next person (intermediate host)