Unit 5 Part 2: Intro to Lophotrochozoans, Phylum Platyhelminthes, Phylum Nematoda

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
  • 

==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

  • 

    

==Class Trematoda:==

• These are called ==flukes==
• Wide, flat shape
• 10,000 species; that are all parasitic
• They feed on host cells and cell fragments
  • 

==Class Monogenea:==

• External parasites of ==fishes==
• Attach to gill filaments
  • 

==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
  • 

^^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)