Invertebrate Zoology Lecture 10 Phylum Platyhelminthes Part 2
Invertebrate Zoology Lecture 10: Phylum Platyhelminthes Part 2
Lecture outline § Phylum Platyhelminthes « « « Asexual reproduction/regeneration (Class Turbellaria) Sexual reproduction (Class Turbellaria Life cycles: Class Monogenea Life cycles: Class Trematoda Life cycles: Class Cestoda Life cycles: Wrap-up discussion!
Asexual reproduction/ regeneration: Class Turbellaria § Transverse fission «Note eye development in each section «Develop separate
Asexual reproduction/ regeneration: Class Turbellaria § Capacity for regeneration «Transverse cuts new individuals § Capacity to regenerate is greatest at head (Planaria) § Polarity maintained § Undifferentiated mesenchyme cells particular cell types «Capacity depends on body position
Asexual reproduction/ regeneration: Class Turbellaria § Capacity for regeneration «Longitudinal cuts § Multiple heads § Multiple tails
Sexual reproduction Class Turbellaria (Planaria focus) § Reproductive systems «Hermaphroditic «Multiple testes and ovaries «Many variations «Male/female openings § Common vs. one for each § Planaria: common opening «Sperm have two tails!
Sexual reproduction Class Turbellaria (Planaria focus) § Mating « Penis everts during mating § § Stored retracted in “male atrium” Opening sometimes in mouth: Orogenital pore « Internal fertilization Sperm travel via oviducts to ovary
Sexual reproduction Class Turbellaria (Planaria focus) § Mating (cont. ) « If no female opening hypodermic impregnation (a. k. a. penis fencing) § Eggs travel through body to ovary.
Sexual reproduction Class Turbellaria (Planaria focus) § Fertilization «In ovary «Return trip via oviducts § Yolk deposited «Eggs encapsulated & released or brooded in “uterus” § Summer vs. resting eggs «Difference? § Direct development or larvae
Life cycles: Class Monogenea § § Single host Sample life cycle 1: Dactylogyrus vastator, a gill parasite of carp « Adult: on gills « Fertilized eggs encased zygotes § Drop to substrate, hatch into… « Oncomiracidium § Swimming form « Host attachment Maturation
Dactylogyrus vastator, a gill parasite of carp
Life cycles: Class Monogenea § Sample life cycle 2: Polystoma integerrimum, a parasite of frogs « Basic stages similar to Dactylogyrus « Key: Two variations tied to host life cycle « Young tadpoles as host § § Larvae attach to external gill Rapid life cycle « Older tadpole as host § § § Larvae attach to external gill of tadpole Migrate to bladder after frog metamorphosis Mature after ~2 -3 years in response to frog sex hormones
Polystoma integerrimum
Life cycles: Class Trematoda § Example: Chinese liver fluke, Clonorchis sinensis « Overview § § Definitive hosts: Humans and other carnivorous mammals Causes liver disease & associated symptoms Two intermediate hosts « Intermediate host 1 = snail « Intermediate host 2 = fish or crustacean How does the infection occur?
Life cycles: Class Trematoda § Clonorchis sinensis: life stages « « « « Egg Miracidium Sporocyst Redia Cercaria Metacercaria Adult From Pearse & Buchsbaum, Living Invertebrates
Life cycles: Class Trematoda § Clonorchis sinensis: life cycle (in hosts) From Pearse & Buchsbaum, Living Invertebrates
Life cycles: Class Cestoda § Anatomy of a proglottid « Hermaphrodites § Most mature/functional systems in posterior proglottids « Fertilized eggs stored in posterior proglottids § Eggs released or proglottids break off feces.
Life cycles: Class Cestoda § Example: Beef tapeworm, Taenia saginata « « « Proglottid with zygotes Onchospheres Cysticercus Maturation Reproduction
Parasite life cycle wrap-up § Advantages of multiple hosts? «Think carefully about life cycles presented! § Disadvantages of multiple hosts? «Think carefully about life cycles presented! «How are life cycles “broken”? § Mechanisms to insure transfer «Example 1: Killfish infected by trematodes «Example 2: Particular snails infected by trematodes
- Slides: 19