Platyhelminthes, Rotifers, Turbellaria, Trematoda & Cestoda

• Taxonomy terms in bold require specific knowledge of Phyla, Subphyla, Classes, and Genera.
• Animal groups distinguishing characteristics are essential for identifying them.

Phyla Platyhelminthes and Rotifers

• Bilateral symmetry features a distinct left and right or top and bottom.

• Radial symmetry allows division into similar halves along a central axis.

• Radial symmetry benefits regeneration and omnidirectional threat detection/food capture.

• Bilateral symmetry facilitates directional movement and agility.

• Cephalization enhances sensing, response, movement, feeding, and survival.

Class Turbellaria, Trematoda, and Cestoda

• Class Turbellaria possess a pharynx for food ingestion through a single opening.
• Turbellaria are typically free-living flatworms.
• Class Trematoda consist of unsegmented, leaf-shaped parasitic flatworms with two suckers.
• Trematoda's digestive system lacks an anus.
• Class Cestoda includes parasitic worms with tape-like bodies, scolices, and proglottids.

Platyhelminthes Complexity

• Platyhelminthes have bilateral symmetry and three tissue layers which allows them to become more complex.

• These layers are the endoderm, ectoderm, and mesodermal differentiation.

• Turbellaria’s common name is Free-Living Planaria.

• Class Trematoda are called Parasitic Flukes.

• Class Cestoda's name is Parasitic Tapeworms.

• Flatworms cause diseases like schistosomiasis, fascioliasis, clonorchiasis, paragonimiasis, and cysticercosis.

• Proglottids are tapeworm segments with complete reproductive systems.

• The scolex is a tapeworm's anterior end with suckers and hooks for attachment.

• Parasitism involves one organism benefiting at the host's expense.

• Adaptations for parasites include high reproduction, reduced organ systems, and protective cuticles.

• Fluke life cycles involve egg, larval (snail-intermediate host), and adult (vertebrate-primary host) stages.

• Miracidia actively seek out and infect freshwater snails.

• Final hosts get infected by eating metacercariae-containing vegetation or undercooked fish.

Body Cavities

• Acoelomates lack a true body cavity.
• Pseudocoelomates have a false cavity not fully lined by mesoderm.
• Coelomates possess a true body cavity.
• Flatworms and ribbon worms are Acoelomates.
• Rotifers or nematodes are Pseudocoelomates
• Earthworms, humans, and most other vertebrates are Coelomates

Phylum Rotifera

• Rotifera is microscopic, aquatic, planktonic filter feeders.
• Rotifers mostly reproduce asexually with females producing diploid clone eggs.

Phylum Mollusca

• Protostomes develop a mouth from the blastopore.
• Annelids, mollusks, arthropods, and flatworms are protostomes.
• Deuterostomes develop an anus from the blastopore.
• Echinoderms(starfish, sea urchins) and chordates are deuterostomes.
• Mollusks have bilateral symmetry, cephalization, protostome and are coelomates.
• Mollusks are soft-bodied with or without shells including; a ventral muscular foot, a mantle, protective shell, and a radula.
• The radula is for scraping or cutting food.
• The mantle secretes shells.

Mollusca Classes

• Polyplacophora(bearing many shells).
• Bivalvia(two-shelled molluscs with no head).
• Gastropoda(stomach-foot, snailsm slugs, some have shells, broad foot, well-developed).
• Cephalopoda(a completely merged head and foot, with a ring of arms and/or tentacles surrounding the head).
• Chitons are Polyplacophora.
• Clams and Mussels are Bivalvia.
• Snails, slugs, conchs are Gastropoda.
• Cuttlefish, octopus, squids are Cephalopoda.
• Overharvesting threatens freshwater mussels.
• Convergent evolution is when unrelated species evolve similar traits.
• Cephalopod camera-like eyes exemplify convergent evolution.
• Chromatophores are pigmented cells in cephalopods for camouflage and communication.
• microscopic, larval glochidia of freshwater mussels attach to fish gills or fins.
• Zebra mussels are invasive bivalves causing ecological and economic damage in North America.

Phylum Annelida

• Annelida’s 3 classes are Polychaeta, Oligochaeta, Hirudinea.
• Polychaeta possess parapodia with setae commonly known as marine worms.
• Oligochaeta have citellum which forms an egg sac commonly known as earth worms and freshwater worms.
• Hirudinea have a clitellum at times, are carnivores and some parasitic commonly known as leeches.
• Setae are paired bristles preventing backsliding in locomotion mostly found in marine worm Polychaeta.
• Parapodia are paired, paddle-like appendages used for locomotion, respiration and sensing the environment in Polychaeta.
• Shared annelid characteristics include: segmentation, bilateral symmetry, protostome coelomates, paired setae, elongation, cephalization, cuticles, and a hydrostatic skeleton.
• Nematodes move via sinusoidal, thrashing motions.
• Annelids use coordinated peristaltic movements.
• Earthworms improve soil structure, aeration, and nutrients through tunneling, mixing, and castings.
• Invasive earthworms degrade ecosystems by altering soil, reducing leaf litter, and promoting invasive plants.
• The clitellum secretes mucus cocoons for egg storage in Oligochaeta and Hirudinea.
• Leeches are used surgically to relieve venous congestion and improve blood flow.

Phylum Nemertea

• Ribbon worms are soft-bodied segmented characterized by a unique eversible proboscis, a complete digestive tract, and a closed circulatory system.
• Nemerteans use their proboscis to capture prey or defend themselves.
• Proboscis lies in the rhynchocoel when inactive
• Nemerteans are unsegmented with a proboscis, while annelids are segmented with a muscular pharynx.

Phylum Nematoda

• Nematodes have an elongated, cylindrical body shape, with a complete digestive system.
• Nematodes bodies are covered by a collagenous cuticle that they periodically molt.
• Nematodes move by contracting longitudinal muscles.
• Nematodes thrash or wiggle.
• Nematodes are commonly called roundworms, threadworms, hookworms, pinworms, whipworms, and eelworms.
• Nematodes cause diseases like ascariasis, trichuriasis, hookworm disease, filariasis, trichinosis, and strongyloidiasis.
• Ecdysis is shedding an outer layer, seen in arthropods, nematodes, ecdysozoans, and others.

Phylum Onychophora

• Onychophora are also known as velvet worms.
• Onychophora live in rainforests and leaf litter, primarily in tropical and temperate regions.
• Onychophora link annelids and arthropods.
• Annelid characteristics of Onychophora: unjointed appendages, hydrostatic, some internal segmentation.
• Arthopod characteristics: of Onychophora - Chitinous cuticles, mandible mouthparts, ventro-lateral appendages, open circulatory system

Phylum Tardigrada

• Tardigrada are also known as water bears.
• Tardigrades habitats include mountaintops, the deep sea, and ranging from icy Antarctica to bubbling hot springs.
• Tuns are a state of cryptobiosis, also known as suspended animation, where it shrivels into a dry, seemingly lifeless ball to survive harsh conditions like desiccation, extreme temperatures, or radiation.
• Cryptobiosis is a state of reduced metabolic activity.
• Anhydrobiosis allows organisms to survive near-complete water loss.
• Meiofauna are small benthic invertebrates in marine and freshwater.
• Nematodes are a meiofauna phylum.
• Meiofauna have small size, elongate shapes, and ability to move through sediment.

Phylum Arthropoda

• Arthropoda feature a chitinous exoskeleton, jointed appendages, complex behaviors, complex sensory organs, and segmentation.
• Arthropods successful due to adaptable body plans, including their exoskeletons.
• Arthropod segments are characterized by a distinct head, thorax, and abdomen with jointed appendages.
• Arthropods typically have 3 body segments which are the head, thorax, and an abdomen.
• Insects are the most diverse group of arthropods in the subphylum Hexapoda.
• Chelicerata have 4 walking legs and 1 pair of palps
• Arachnida have spiders, mites, ticks, daddy longlegs, scorpions and all appendages on the thorax
• Chelicerata have 2 segments (cephalothorax and abdomen)
• Hexapoda have unbranched appendages, 1 pair of antennae, and mandibles
• Hexapoda are insecta for example bees, beetles, flies, fleas, butterflies, moths, comprised of 3 pairs of walking legs, 3 body parts & wings
• Myriapoda features unbranched appendages with mandibles
• Chilopoda are centipedes which have 1 pair of legs per segment
• Diplopoda are millipedes features 2 pairs of legs per segment
• Crustacea are crayfish, lobsters, shrimp, crab, isopods (terrestrial), Daphnia which have branched appendages, 2 pair of antennae, 2 body parts with mandibles, compound eyes which lie on all segments
• Black widow spiders and brown recluse spiders are venomous in the US.
• Metamorphosis is a dramatic physical transformation during an animal's life/ development.
• Complete metamorphosis (holometabolous) or incomplete metamorphosis (hemimetabolous).
• Insects show simple aggregations to complex eusocial societies, with ants, bees, and termites.
• Stridulation is the method some insects use to produce noise by rubbing body parts together.