Phylum Platyhelminthes

In which major evolutionary clade are most animals classified?

The Bilateria clade

What two key structural traits evolved within the Bilateria clade?

Bilateral symmetry and three tissue layers

What major multi-tissue eumetazoan group does the Bilateria clade branch from?

Eumetazoa

Approximately how many million years ago did the Ancestral Protist animal line begin?

770 million years ago

Approximately how many million years ago did the Eumetazoa lineage diverge?

680 million years ago

Approximately how many million years ago did the Bilateria clade split into sub-lineages?

670 million years ago

What non-bilaterian phylum branches earliest from the Eumetazoa lineage on the diagram?

Cnidaria

What are the three major evolutionary sub-clades contained within the Bilateria?

Lophotrochozoa, Ecdysozoa, and Deuterostomia

How many total animal phyla are contained within the Lophotrochozoa sub-clade?

18 phyla

What worm-like group positions as the earliest basal branch of the Bilateria line?

Acoela

What are four major evolutionary milestones explicitly highlighted in flatworms?

Bilateral symmetry, three tissue layers, cephalization/sensory structures, and locomotion

What major lifestyle development or "alert" is introduced with Phylum Platyhelminthes?

Parasites Section 2: Germ Layers & Body Plan TopographyWhat is the formal biological definition of a tissue?

What is the baseline tissue status of Phylum Porifera (sponges)?

Sponges have no true tissues

How many embryonic tissue layers do cnidarians possess?

Two tissue layers

What are the specific names of the two tissue layers found in cnidarians?

Epidermis and gastrodermis

How many embryonic tissue layers do bilaterian animals possess?

Three tissue layers

What are the specific names of the three tissue layers found in bilaterians?

Ectoderm, mesoderm, and endoderm

What term describes an animal body plan featuring only two embryonic cell layers?

Diploblastic

What term describes an animal body plan featuring three embryonic cell layers?

Triploblastic

What is an acoelomate body plan?

A body plan with no fluid-filled cavity (coelom) between the gut and ectoderm

Which embryonic tissue layer forms the internal gut lining of an acoelomate?

The endoderm

Which embryonic tissue layer forms the outer body wall covering of an acoelomate?

The ectoderm

Which animal group serves as the slide's example of a diploblastic acoelomate?

Cnidarians

Which animal group serves as the slide's example of a triploblastic acoelomate?

Platyhelminthes (flatworms)

What is a coelomate body plan?

A triploblastic plan with a fluid-filled cavity (coelom) completely enclosed by mesoderm

What tissue layer splits to entirely line the internal cavity of a coelomate?

The mesoderm

What are three examples of triploblastic coelomate animal groups listed on the chart?

Echinoderms, molluscs, and chordates

What macro-evolutionary directional trend occurs from diploblastic plans to coelomate plans?

Increasing levels of complexity

What crucial anatomical structure develops uniquely from the mesoderm layer?

Muscles

What is radial symmetry?

A body plan that can be divided into matching halves by multiple planes through a central axis

What type of symmetry is visually represented by a simple clay flowerpot or a sea anemone?

Radial symmetry

What is bilateral symmetry?

A body plan that can be divided into mirror-image left and right sides by only one unique plane

What type of symmetry is visually represented by a hand shovel or a lobster?

Bilateral symmetry Section 3: Core Flatworm Traits & Nervous ArchitectureWhat morphological feature is the most distinguishing characteristic of Platyhelminthes?

What evolutionary status do flatworms hold regarding bilateral symmetry?

They are the simplest animals with bilateral symmetry

Approximately how many total species are found within the Phylum Platyhelminthes?

25,000 species

What two physiological/ecological changes occur as flatworms diverge from simpler phyla?

An increase in physiological and ecological complexity

What two broad behavioral life-history strategies are present across flatworms?

Free-living forms and parasitic forms

What two groups comprise the vast majority of flatworm parasites?

Blood flukes and tapeworms

What is the scientific name of the flatworm found at San Miguel Island, California?

Prostheceraeus bellostriatus

Phylum Platyhelminthes stands as the first animal lineage to evolve what specific layer?

A true mesoderm

What structural question do biologists ask regarding the acoelomate nature of flatworms?

Whether it represents a primitive ancestral character or a secondary derived character

What term describes the concentration of sensory organs and nerve controls at the head?

Cephalization

What type of digestive tract or gut do flatworms possess?

A primitive gut

What structural component do certain tiny, free-living flatworm forms completely lack?

A gut

What distinct digestive exit tract is entirely missing in a flatworm's anatomy?

An anus

How many pharyngeal openings exist for food entry and waste elimination?

One pharyngeal opening

What specific structure allows flatworms to recognize light levels in their environment?

Eyespots

What sensory sensors allow flatworms to identify environmental chemical gradients?

Chemoreceptors

What sensory sensors allow flatworms to detect tactile touch or aquatic vibrations?

Mechanoreceptors

What specialized primitive organs provide flatworms with equilibrium and gravity sensing?

Statocysts

What is the general developmental status of a flatworm's nervous system?

A primitive nervous system

What represents the distinct brain center in a flatworm's anterior head region?

A central ganglion

What nerve structures track posteriorly down the body length from the central ganglion?

Longitudinal nerve cords

In what two broad aquatic habitats can flatworms be found?

Freshwater and marine environments

What complex reproductive trait characterizes a large portion of the flatworm phylum?

They are often hermaphroditic

What are the primary dietary habits of free-living flatworm species?

They are active carnivores or scavengers of dead matter

What specific structure coordinates the movement and locomotion of free-living flatworms?

Cilia bands on their ventral surface

What biological process drives the exchange of respiratory gases and nutrients in flatworms?

Direct diffusion

Where is digestion fully completed inside a generalized flatworm's cell structure?

By cells lining the gastrovascular cavity

What is the directional placement of the longitudinal nerve cords in a flatworm?

Ventral nerve cords (located on the belly side)

What muscular organ extends outward from the middle section of a flatworm to gather food?

The pharynx

What chemical substance does the pharynx release onto prey items to begin digestion?

Digestive juices

What single opening serves as both the entry point and exit point for the flatworm pharynx?

The mouth Section 4: Surface Area Calculations & Class TurbellariaWhat primary anatomical goal is achieved by changing body shapes to maximize surface area?

What is the calculated surface area (SA) of a solid 3cm x 3cm x 3cm cube?

54 cm²

What is the calculated total volume (V) of a solid 3cm x 3cm x 3cm cube?

27 cm³

If a 27 cm³ volume is flattened into a 1cm x 3cm x 9cm rectangle, what is its new surface area?

78 cm²

What are four structural adaptations used by organisms to increase surface area?

Flattening, branching, folding, and projections

What folded photosynthetic structure inside a 1-micrometer chloroplast increases surface area?

A thylakoid

What internal organ system represents the "branching" strategy inside a flatworm?

The gastrovascular cavity

What are the four primary taxonomic classes of flatworms discussed in the lecture?

Turbellaria, Trematoda, Monogenea, and Cestoda

What percentage of Phylum Platyhelminthes is composed of Class Turbellaria?

They comprise only 16% of the phylum

What baseline structural status separates Class Turbellaria from the other three classes?

They are the simplest flatworms and are mostly free-living

What is an example genus of Class Turbellaria shown in stained laboratory slides?

Syndesmis sp.

What group represents the most familiar, widely recognized freshwater free-living Turbellarians?

Planarians

What specific genus name identifies the standard experimental planarian?

Dugesia

What is the typical physical length of a standard free-living planarian?

Most are small, measuring less than 1 centimeter (<1cm)

What specialized cell structures act as excretory organs in free-living planarians?

Flame bulbs

What behavioral memory experiments were famously conducted using planarians?

The Thompson & McConnell biochemical memory experiments

What specific cellular structure lines the underside epidermis of a Turbellarian?

Cilia Section 5: Symbiosis & The Parasitic Classes (Trematoda, Cestoda, Monogenea)What category of symbionts establishes an intimate, durable relationship that directly costs the host?

What is the ecological difference between a typical parasite and a strict predator?

A parasite feeds continuously on a single host item without killing it

What positive system-level function do modern biologists assign to parasites?

They play critical ecological roles and serve as signs or signals of ecosystem health

Which university research lab studies parasite ecology in marine and freshwater systems?

The Wood Lab at the University of Washington (led by Dr. Chelsea Wood)

What is the common tracking name used to identify the Class Trematoda?

The blood flukes

What is the universal dietary status of all species within the Class Trematoda?

They are all obligate parasites

What anatomical structures do Trematodes use to ingest host fluids?

A mouth and a blind, one-way gut

What targets do Trematodes systematically ingest from inside their chosen host?

Host blood and tissue

What type of life cycle pathway is required for a standard Trematode to reach maturity?

A complex life cycle involving multiple host species

What massive neglected tropical disease is caused directly by human blood flukes?

Schistosomiasis (also called bilharzia)

How many people worldwide required active preventive chemotherapy for Schistosomiasis in 2023?

253.9 million people

In what specific tropical and sub-tropical environments is Schistosomiasis most prevalent?

Poor communities without potable water and adequate sanitation

What total number of individuals are currently affected by Schistosomiasis globally?

Almost 240 million people

Where does Schistosomiasis rank in public health importance among human parasitic conditions?

It ranks second behind malaria in socio-economic and public health importance

What organism serves as the definitive host where Schistosoma mansoni undergoes sexual reproduction?

Humans

What aquatic snail genus serves as the first intermediate host for Schistosoma mansoni?

Biomphalaria sp. snail

What aquatic snail genus serves as the intermediate host for Schistosoma haematobium?

Bulinus sp. snail

What ciliated larval stage hatches from a Schistosoma egg to locate and penetrate snail tissues?

Miracidia

What developmental stage reproduces asexually inside the intermediate snail host tissue?

Sporocysts

What free-swimming, fork-tailed larval stage is released by snails to infect humans?

Cercariae

What structural modification happens to a cercaria larva immediately after skin penetration?

It loses its tail and transforms into a schistosomulae

Where do paired adult Schistosoma worms migrate to live and mature inside human portal systems?

The liver and portal blood stream