Chapter 8: Worms Part 1

Cephalization

Evolution of heads, found in worms and more complex animals

Direct Development

Development without a feeding larval stage found in worms

Hydrostatic Skeleton

Flexible skeleton that is supported by internal fluid pressure found in worms

Phylum Platyhelminthes

- "flatworms"
- Vary from millimeter to many meters in length
- Some free-living others are parasitic
4 classes of Platyhelminthes (getting redefined)
1. Turbellaria (free living (commensal not hurting or harming environment), or parasitic, oldest group)
2. Trematoda (endoparasitic flukes)
3. Monogenea (ectoparasitic flukes)
4. Cestoda (endoparasitic tapeworms)

Class Turbellaria

- Mostly free-living
- Move via wave
- Some may have multiple mouths
- Most have simple or no gut
- Simple pharynx
- Yolks can help define the egg types
- "Penis Fencing"

Class Trematoda

*parasitic flukes*
Adaptations
- Can produce cysts (allows them to be dormant
- Penetration glands
- Hooks and suckers for adhesion
- Increased reproductive capacity
- Lack of sense organs (poorly developed)
- Do not have cillia

Class Monogena

- Monogenetic flukes
- More related to cestoda (were part of trematoda)
- Mostly external fluke
- Likes to be on fins and gills of fish (very common)

Opisthaptor

a hook or sucker used by monogenea to attach (hook on) to organs

Class Cestoda

- Have a scolex and proglottid
- Receive their nutrition from diffusion of host nutrients
- Can get them from contaminated drinking water and food
- Requires at least 2 hosts
- Usually does not effect hosts unless they are already sick

Flukes

common name for trematodas and monogenea, type of parasite

Tapeworms

Part of the Class Cestoda, require two hosts and are internal parasites that can live off of the bacteria and nutrients in humans and animals stomachs (GI tracts)

Tegument

outer covering of a tape worm that absorbs nutrients since they lack a digestive system

Protonephridia

"before-kidney", an excretory tubule that lacks an internal opening, found in Platyhelminthes, rotifers, and some chordates, either not found or reduced in marine flatworms

Solenocytes

Flagella at the end of the tubules in the protonephridia that moves water and waste to be shot out of the pore of the body (used a lot with freshwater invertebrates)

Flame Cells

Cilia at the end of the tubules in the protonephridia that moves water and waste to be shot out of the pore of the body (used a lot with freshwater invertebrates)

Subepidermal Nerve Plexus

Nervous system found in worms that resembles nerve net of cnidarians

Ocelli

light sensitive eyespots, present in turbellarians, monogeneans, and larval trematodes

Auricles

ear-shaped (look like flaps), filled with nerve endings that pick up vibrations and sense pain, connected to nerve net, composed of tactile and chemoreceptive cells

Rheoreceptors

sense direction of water currents in some, composed of tactile and chemoreceptive cells

Asexual Fission

reproduction found in most worms where they constrict behind the pharynx and separate into two animals

Monoecious

One sex (synonym for hermaphrodites) Almost all worms are this. Opposite of dioecious

Hermaphordites

One sex (synonym for monoecious) Almost all worms are this. Opposite of gonochoric

Penis Fencing

Occurs in Turbellaria class where the sperm is not free swimming and has pierce the skin in order to fertilize. This can lead to a violent/aggressive battle of insemination

Clonorchis sinensis

"Human liver fluke" that can infect humans, cats, dogs, and pigs, very common in southeast Asia, flukes live in the bile passage of the host, causes sorosis of the liver

Schistosomes

"Blood Flukes" that infect the blood, common infection, found in Africa, south America, West Indies, and the Middle and Far East

Schistosome dermatitis

"swimmers itch", occurs when cercaria (snails) penetrate an unsuitable host such as a human (needs a bird instead), treated with praziquantel

Scolex

anterior (head) end in Cestoda (tapeworms) that has little suckers and hooks to burrow into the intestinal tract

Proglottids

repeated sections that allow them to grow, segmentation, when chained together become strobila, each section contains uterus, ovary, testes, genital pore, and vagina

Taenia saginata

Beef tapeworm that is found in undercooked beef (in the inner muscular tissue of cattle), mature adult worms can reach over 7 meters

Taenia solium

Pork tapeworm where pigs are intermediate hosts and humans are definitive, found in undercooked pork, infects the eyes and brain of the human and can lead to seizures and death from cysts.

Phylum Gastrotricha

- Have scales
- Covered in cillia (ciliated)
- Small
- Hermaphrodites

Phylum Gnathostomulida

- Very small, larger than gastrotricha
- About 80 species (probably more)
- They can endure low oxygen envionrments
- Scrappers (scrape of substrate of bacteria)
- Acoelmates

Phylum Rotifer

- *Has a rotating mouth piece that has ciliated crown (corona)*
- Very complex at a small size (max length 3mm)
- Have different lifestyles

Phylum Acanthocephala

- Spiny-headed worms
- Endoparasites in the intestines of vertebrates
- Found in fish, birds, and mammals

Defining Characteristics of Worms

- BILATERAL SYMMETRY
- Cephalization- evolution of heads
- Triploblastic (3 germ layers)
- Begin to have "hunters", actually seeking out food
- Has a nervous system, more complex than cnidarians

Body cavity

defining characteristic of worms, a fluid filled space or compartment in the body that houses organs and structures
3 types
1. Coelomates (have fluid filled cavities)
2. Acoelomates (organisms that lack a body cavity)
3. Psuedocoelomates (a partial coelom (body cavity))

Psuedocoelomates

a partial coelom (body cavity), Pseudo means false, organisms that have an internal cavity that is not completely lined with mesoderm tissue
2 phyla of pseudocoelomates
1. Rotifera
2. Acanthocephala

Syncytial Tegument

external body covering found in all parasitic Platyhelminthes

Strobila

a stacked section of proglottids in Cestoda

Proglottids hosts

requires two hosts, the first is invertebrate and second is vertebrates usually