Ecdysozoa and Nematodes

Ecdysozoa Overview

• Protostomes characterized by molting (ecdysis) of a non-living cuticle.
• Molting is regulated by the hormone ecdysone.
• Includes nematodes, arthropods, tardigrades, and others.
• Ecdysozoans lack a consistent body plan.
• Nematodes, Nematomorpha, and Kinorhyncha are pseudocoelomates.
• Panarthropoda (arthropods, onychophorans, tardigrades) are coelomate, but the body cavity is reduced.

Nematodes: Key Features

• Most important pseudocoelomate animals, abundant, and impactful.
• Found worldwide in various habitats: soil, oceans, freshwater, plants, and animals.
• Roughly 25,000 described species; possibly up to 500,000.
• Topsoil may contain billions of nematodes per hectare.
• Nematode parasites infest nearly all animal and plant species.
• Study of nematode infestations is important in agriculture and biomedical sciences.
• Cylindrical, bilaterally symmetrical, and unsegmented.
• Collagenous cuticle shed during growth (ecdysis).
• Lack cilia/flagella (except one species) and circulatory/respiratory systems.
• Only longitudinal muscles, no circular muscles.
• Muscle contractions create sinusoidal waves; aided by pseudocoelomic fluid.
• Complete gut: mouth, muscular pharynx, intestine, and anus.
• Pharynx sucks in food via triradiate lumen contractions.
• Free-living nematodes decompose in soil/water, recycling nutrients.
• Decomposers feed on bacteria and fungi.
• Critical in soil food webs as prey for mites and insects.
• Parasitic nematodes infect plants, animals, and humans, causing diseases (e.g., Ascaris, hookworms).
• High reproductive capacity; Ascaris females lay ~200,000 eggs/day.
• Direct life cycle involves a single host, such as Ascaris lumbricoides.
• Eggs are ingested, hatch in intestines, juveniles migrate to lungs, get coughed/swallowed, and mature in intestines.
• Hookworms burrow through skin, travel to bloodstream and lungs, then to intestines, causing anemia.
• Trichinella spiralis encysts in muscle from undercooked meat and reprograms host cells into nurse cells.
• Filarial worms block lymphatics, causing elephantiasis, and are transmitted by mosquitoes.
• The cuticle resists desiccation, chemicals, and host immune responses.
• Ascaris eggs can survive years in soil, tolerating extreme conditions.
• Public health measures include sanitation to avoid fecal contamination and thoroughly cooking meat.
• Prevention and control involve washing hands/vegetables and using anthelmintic drugs for infections.
• Ecologically vital as decomposers and economically significant as parasites.
• Unique hydrostatic skeleton, longitudinal muscle antagonism, and cuticle molting enable diverse lifestyles.
• Understanding life cycles (direct/indirect) and parasitic strategies is critical for agriculture and medicine.

Arthropoda: Introduction

• Represents over 75% of all described animal species, with approximately 1.1 million recorded species.
• Inhabit terrestrial, aquatic, and aerial environments, including parasitic forms.
• Negative impacts include disease vectors (e.g., Zika virus via Aedes mosquitoes) and agricultural pests.
• Positive roles include pollination (bees), food sources, and economic products (honey, silk, wax).
• The exoskeleton (cuticle) is made of chitin and proteins hardened via sclerotization.
• The outer waterproof layer is the epicuticle (lipids/waxes).
• The inner layer is the procuticle with exocuticle (pre-molt) and endocuticle (post-molt) layers.
• The exoskeleton protects against predators, desiccation, and mechanical stress.
• Apodemes (internal ridges) anchor muscles for movement.
• Tagmatization involves ancestral repeated segments fused/modified into specialized tagmata (e.g., head, thorax, abdomen).
• Jointed appendages are adapted for locomotion (legs, wings), feeding (mandibles), and sensing (antennae).
• Molting (ecdysis) sheds the exoskeleton to grow and is hormonally regulated.
• Exoskeletal mass and molting energy costs limit body size.
• Terrestrial arthropods have a tracheal system for direct air delivery to tissues.
• Aquatic arthropods have gills (e.g., crustaceans).
• An open circulatory system has hemolymph circulating in a hemocoel via a tubular heart.
• Nervous and sensory systems feature a dorsal brain with a ventral nerve cord.
• Advanced sensory organs include compound eyes and chemoreceptors.
• The exoskeleton enables terrestrial colonization.
• Metamorphosis reduces resource competition between larvae and adults.
• Efficient locomotion comes from jointed limbs and plate-like exoskeletal segments (tergum, sternum, pleuron).
• Behavioral complexity includes eusociality in bees/ants.
• Chelicerata includes spiders, scorpions, and horseshoe crabs.
• Crustacea includes crabs, lobsters, and barnacles.
• Myriapoda includes centipedes and millipedes.
• Hexapoda includes insects.
• Vector-borne diseases include Zika virus, dengue, and chikungunya (Aedes mosquitoes).
• Other disease vectors include malaria (Anopheles) and West Nile virus.
• Economically beneficial arthropods include silkworms, honeybees, and fisheries (crustaceans).
• Dominant ecosystems are related to the versatile exoskeleton, segmented bodies, and adaptive life cycles.
• Their ecological roles—both beneficial and harmful—highlight evolutionary success and interactions with humans.

Subphylum Chelicerata

• Diverse arthropods with ancient origins, dating back over 445 million years.
• Have two body regions (tagmata): cephalothorax (fused head and thorax) and abdomen.
• Six pairs of cephalothoracic appendages: chelicerae, pedipalps, and four pairs of walking legs.
• Chelicerae are pincer-like or fang-like mouthparts for feeding.
• Pedipalps have sensory or reproductive functions (e.g., sperm transfer in spiders).
• Lack mandibles or antennae.
• Most species suck liquefied prey tissues.
• Pycnogonida are marine arthropods with thin bodies and leg spans up to 0.75 meters.
• Pycnogonida use proboscis mouthparts for sucking fluids from soft-bodied prey.
• They have simple circulatory and respiratory systems; rely on diffusion.
• Merostomata includes living fossils like horseshoe crabs and extinct eurypterids.
• Merostomata use book gills for respiration and their telson (tail) is for steering.
• Unsegmented carapace covers the cephalothorax.
• Arachnida includes spiders, scorpions, ticks, and mites with 80,000+ species, primarily terrestrial.
• Arachnida have predatory adaptations: fangs, venom glands (spiders), stingers (scorpions).
• Have no antennae.
• They respire via book lungs (spiders, scorpions) or tracheae (mites).
• Excrete via Malpighian tubules (water conservation).
• Spiders produce silk (5x stronger than steel) for webs, prey capture, and reproduction.
• Ticks and mites transmit diseases and act as agricultural pests.

Subphylum Myriapoda

• Myriapods are terrestrial mandibulates with: head and multi-segmented trunk tagmata.
• Tracheal respiration and Malpighian tubules (evolved independently from Chelicerata).
• Chilopoda (centipedes) are carnivorous, with 1 pair of legs per segment and venom claws.
• Diplopoda (millipedes) are herbivorous/detritivorous, with 2 pairs of legs per segment and calcium carbonate-reinforced exoskeleton.
• Chelicerates use chelicerae and lack mandibles/antennae, have book lungs/tracheae.
• Myriapods use mandibles and have antennae, use trachea.
• Ticks transmit Lyme disease (Ixodes) and Rocky Mountain spotted fever (Dermacentor).
• Centipedes are carnivorous and fast, with venom, while millipedes are herbivorous, slow, and use chemical defenses.
• Chelicerates thrive as predators and parasites (e.g., spiders, ticks).
• Myriapods dominate decomposer and predator niches in soil ecosystems.
• Their innovations include silk production, venom, and tracheal systems.

Introduction to Crustaceans

• Often referred to as the "insects of the sea,” it is a diverse subphylum of arthropods.
• They primarily live in marine environments but also occupy freshwater and a few terrestrial habitats.
• There are over 67,000 named species, contributing to over 80% of all named animal species when combined with insects.
• Copepods (genus Calanus) are among the most abundant animals globally.
• Their exoskeleton comprises chitin, protein, and calcareous material.
• They have three tagmata - head, thorax, abdomen - with the head fused with some thoracic segments (cephalothorax).
• The thorax typically has 8 segments, while the abdomen has 6.
• Appendages are ancestrally biramous (two-branched), with exceptions like first antennae.
• Includes mandibles, maxillae, and antennae.
• Carapace: Dorsal covering over the cephalothorax.
• The tail structure is composed of the telson and uropods.
• Gas exchange occurs across thin cuticle areas in small crustaceans.
• The bailer mechanism (second maxilla) circulates water in decapods.
• The open circulatory (lacunar) system: Hemolymph flows freely in hemocoel.
• The single-chambered dorsal heart heart pumps heart → Arteries → Hemocoel → Gills (oxygenation) → Heart.
• Antennal/maxillary glands regulate osmoregulation of salt/water balance.
• Freshwater crustaceans excrete excess water.
• Marine crustaceans excrete excess salts and nitrogen waste via gills.
• Nervous system comprises paired ganglia for each segment (double ventral nerve cord).
• The compound eyes have ommatidia.
• Tactile and chemosensory hairs cover the antennae, mouthparts, and chelae.
• Modes of reproduction are mostly dioecious, but barnacles are monoecious.
• Some species (e.g., ostracods) reproduce via parthenogenesis.
• Larval stages entail a free-swimming nauplius larva that undergoes metamorphosis.
• Some (e.g., crayfish) show direct development.
• Parental care involves brooding eggs in chambers/attaching them to abdominal appendages.
• Molting allows for growth because the exoskeleton does not grow.
• During the premolt phase, the epidermis secretes a new cuticle.
• During ecdysis, the old cuticle sheds; the animal absorbs water to expand.
• In the postmolt phase, the new cuticle hardens from calcium deposits.
• The X-organ inhibits molting.
• The Y-organ (mandibles) releases ecdysone.
• Suspension feeders (e.g., copepods) filter plankton using setae.
• Predators (e.g., mantis shrimp) use chelipeds to capture prey.
• Scavengers (e.g., crabs) consume dead organic matter.
• Ostracoda are small (0.25–8 mm), have a bivalve carapace, and inhabit marine/freshwater environments.
• Copepoda are dominant zooplankton and dominant zooplankton and a key food source.
• Barnacles (Thecostraca) are sessile adults with calcareous plates; nauplius → cyprid → adult during development.
• Malacostraca is the most diverse with Isopoda (e.g., pill bugs) and Amphipoda (e.g., beach hoppers).
• Krill (Euphausiacea) is bioluminescent, is critical whale food, and crabs/lobsters/shrimp (decapoda) have 5 walking legs.
• Copepods form the base of marine food webs and krill sustain whales.
• Human culinary use includes crabs and shrimp.
• Commercial aquaculture and fisheries include shrimp, prawns, and crabs.
• Their biramous appendages, molting process, and osmoregulatory adaptations make them uniquely suited to aquatic life.
• They play vital roles in aquatic ecology and human economies.

Introduction to Hexapoda

• Hexapoda, a subphylum of Arthropoda, is characterized by six legs (uniramous), and a body divided into three segments: head, thorax, and abdomen.
• Consists of 2 major classes.
• Entomobryomorpha: Small, soil-dwelling arthropods with mouthparts enclosed within the head (e.g., springtails).
• Insecta: The most diverse class, with mouthparts outside the head (ectognathous), wings (in most), and adaptations for nearly all terrestrial habitats.
• The cuticle plates comprise the tergum (dorsal), sternum (ventral), and pleura (lateral).
• The head has compound eyes, antennae, and specialized mouthparts.
• Legs are modified for jumping, grasping, or swimming.
• Insects use a tripod gait for walking.
• Wing structures include outgrowths of thoracic cuticle.
• Most have two pairs, except Diptera (one pair and halteres for balance).
• Direct muscles attach to wings for precise control.
• Indirect muscles use thoracic cuticle elasticity for rapid wingbeats (up to 1000/sec in midges).
• Wing shape, load, and tilt determine speed (e.g., dragonflies: 48 km/h; monarch butterflies migrate).
• Gas exchange occurs through the tracheal system, a network of tubes delivering oxygen directly to tissues.
• Spiracle valves prevent water loss; aquatic insects use air bubbles or gills.
• Hemolymph circulates oxygen, but not oxygen, is carried through a tubular heart alone.
• The foregut grinds food (crop, gizzard).
• The midgut performs primary digestion/absorption (ceca increase surface area).
• The hindgut performs water/nutrient reabsorption, which is critical in arid habitats.
• Ametabolous: No metamorphosis (e.g., silverfish).
• Hemimetabolous: Gradual change (nymphs resemble adults; e.g., grasshoppers).
• Holometabolous: Complete metamorphosis (larva → pupa → adult; e.g., butterflies).
• Diapause is a genetically programmed dormancy.
• Chemoreception entails pheromones for mating and trail-marking (e.g., ants).
• Mechanoreception: Hair-like sensilla detect movement/airflow.
• Auditory organs (e.g., cricket legs) are used to detect sound frequencies.
• Vision includes compound eyes that detect motion/UV light and ocelli for flight orientation.
• Benefits include pollination, pest control, and decomposition.
• Drawbacks include crop damage and vector-borne diseases.
• Control methods include Bacillus thuringiensis (B.t.) toxin and integrated pest management (IPM).
• Water conservation is achieved with Malpighian tubules to excrete uric acid.
• Sensory acuity includes advanced chemoreception, vision, and auditory systems.
• Hexapoda exemplify evolutionary success through specialized locomotion.
• They have efficient respiration, and complex life cycles.
• Harmful ecological roles underscore their global significance.

Deuterostome Characteristics

• Echinoderms and hemichordates belong to the deuterostome clade, sharing key developmental traits.
• The blastopore forms the anus (mouth develops secondarily).
• Cleavage is radial and indeterminate (cells retain totipotency early).
• Coelom formation is enterocoelous (mesodermal pouches bud off the archenteron).

Phylum Echinodermata

• Show pentaradial symmetry (adults) derived from bilateral ancestors (larvae).
• Have a calcareous endoskeleton (ossicles/plates) often with spines.
• The water vascular system enables hydraulic locomotion in tube feet, while also aiding in gas exchange and predation.
• Lack a brain or cephalization; sensory organs are decentralized.
• Exclusively marine organisms (lack osmoregulation; avoid brackish water).
• Eleutherozoa includes Asteroidea, Ophiuroidea, Echinoidea, and Holothuroidea.
• Asteroidea (starfish) have open ambulacral grooves and tube feet with suckers.
• They are carnivorous and can evert the stomach to digest prey externally.
• Ophiuroidea (brittle stars) have slender, flexible arms and closed ambulacral grooves.
• They lack suckers and pedicellariae; move via arm pairs. Also known as basket stars.
• Echinoidea (sea urchins/sand dollars) feature a compact “test” with movable spines and closed ambulacral system.
• Holothuroidea (sea cucumbers) have elongated bodies and respiratory trees.
• Pelmatozoa contain the class Crinoidea (sea lilies/feather stars).
• Crinoidea are stalked or free-living with feather-like arms for filter-feeding.
• They have open ambulacral grooves but no madreporite.
• Pedicellariae are pincer-like structures for debris removal/prey capture.
• Dermal branchiae are respiratory projections from the coelom.
• Autotomy and regeneration allow sea stars to regenerate entire arms.

Phylum Hemichordata

• Share traits with chordates like gill slits.
• The tornaria larva resembles echinoderm larvae but has a stomochord, a buccal diverticulum.
• Enteropneusta (acorn worms) are worm-like, with proboscis/collar/trunk body divisions.
• They filter-feed using a mucus-covered proboscis.
• Pterobranchia are colonial animals with tentacled arms and reproduce asexually via budding.
• Synapomorphies are radial cleavage, enterocoely, and anus-from-blastopore.
• Hemichordates bridge the gap between echinoderms and chordates.
• Echinoderms diversified into benthic niches (e.g., starfish predation, sea cucumber detritivory).
• Water vascular system and the hemichordate stomochord underscore the phyla’s transitional role in deuterostome evolution.

Chordate Hallmarks

• All chordates exhibit the following features at some life stage: a notochord, dorsal tubular nerve cord, pharyngeal pouches/slits, an endostyle/thyroid gland, and postanal tail.
• A flexible, rod-like notochord provides axial support functions in muscle attachment and undulatory movement.
• In vertebrates, the notochord is replaced by vertebrae but persists in protochordates like lancelets and tunicate larvae.
• The dorsal tubular nerve cord develops into the central nervous system.
• Pharyngeal pouches/slits form gills in aquatic species or evolve into structures like the Eustachian tube in tetrapods.
• An endostyle/thyroid gland is a mucus-secreting organ for filter-feeding in protochordates, evolving into the thyroid gland in vertebrates.
• The postanal tail aids propulsion in water but is reduced or vestigial in some vertebrates.

Subphyla of Chordata

• Urochordata: Marine, sessile adults with a protective tunic and only larvae displaying all chordate traits (e.g., notochord).
• They filter-feed using pharyngeal slits (stigmata) and an endostyle.
• Cephalochordata retain all chordate traits into adulthood.
• They have segmented musculature and lack true vertebrae, a tripartite brain, and a chambered heart.
• Vertebrata have key innovations like an endoskeleton, a tripartite brain, neural crest, ectodermal placodes, and four Hox gene clusters.
• Pisces have jawless fish (Agnatha), cartilaginous fish (Chondrichthyes), and bony fish (Osteichthyes).
• Tetrapoda involves amphibians, reptiles, birds, and mammals.
• Vertebrates dominate due to a musculoskeletal system and physiological and sensory adaptations.

Definition and Diversity of Fishes

• “Fish” refers to individuals of a single species, while “fishes” denotes multiple species.
• Includes aquatic vertebrates that possess gills, fins, and dermal scales.
• Fishes are paraphyletic and exclude tetrapods.
• There are roughly 36,400 living species that exhibit diversity in morphology, habitat, and physiology.
• Jawless fishes have two classes: Myxini and Petromyzontida.
• Myxini (Hagfishes) are eel-like in body shape with degenerate eyes and 3 pairs of barbels.
• They lack jaws, paired fins, and true vertebrae.
• Marine scavengers/predators are osmoconformers.
• Petromyzontida (Lampreys) use an oral disk with keratinized teeth for suction.
• Anadromous species require osmoregulation in saltwater and freshwater.
• Invasive in Great Lakes, they devastated native fish via parasitism.
• Key innovations include jaws, paired fins, semicircular canals, and vertebral centra.
• Chondrichthyes has Elasmobranchii (sharks, skates, rays) and Holocephali (chimeras).
• Have a cartilaginous skeleton, placoid scales, and a heterocercal tail.
• Osmoregulation involves urea retention and excreting excess salt.
• Internal fertilization, oviparous, ovoviviparous, or viviparous.
• Ampullae of Lorenzini detect electric fields.
• Osteichthyes has Actinopterygii (ray-finned fish) and Sarcopterygii (lobe-finned fish).
• Agnathans represent early vertebrate evolution; hagfishes retain primitive traits.
• Gnathostomes: Jaws and fins spurred adaptive radiation.
• Human impacts threaten fish biodiversity.

General Characteristics of Fishes

• Aquatic vertebrates with gills, fins, and often dermal scales.
• "Fish" = one or more individuals of a single species.
• There are roughly 36,400 adapted species to varying salinity levels.
• Key features of Myxini are no jaws, paired fins, true vertebrae, and degenerate eyes.
• Slime production is key for defense in Myxini.
• Key features of Petromyzontida are well-developed eyes, an oral disk with keratinized teeth, and ammocoete larvae.
• Having jaws and paired fins also enhances feeding and locomotion.
• Vertebral centra provide a partial or complete replacement of the notochord.
• Heterocercal tails are asymmetrical for lift and homocercal tails are symmetrical for agility.
• Adaptations from Chondrichthyes are a cartilaginous skeleton, placoid scales, osmoregulation from urea retention. Hagfish retains unique slime for defense, which is studied for biomaterials.
• Lamprey has an ammocoete lifecycle that highlights evolutionary convergence (ammocoetes vs. lancelets).
• The lamprey invasion altered the ecosystem of the Great Lakes, leading to control measures.

Overview of Amphibians

• Belong to Chordata and are the first vertebrates to transition from water to land.
• They have modern amphibians under Lissamphibia, which includes Gymnophiona (caecilians), Urodela (salamanders), and Anura (frogs and toads).
• Terrestrial challenges include oxygen availability, support against gravity, and temperature fluctuations.
• Lungs have developed from modified swim bladders, which are supplemented by cutaneous and buccal breathing.
• Appendages have evolved into weight-bearing limbs.
• Sensory adaptations include tympanic membranes for airborne sound detection and redesigned olfactory systems for air molecules.
• Metamorphosis includes eggs laid in water, aquatic gill-breathing larvae, and terrestrial adults with lungs.
• Tailed Urodela are some fully aquatic, some terrestrial.
• Terrestrial amphibians require moist habitats, are ectothermic, and have declining populations.
• Adaptations such as limbs, lungs, and sensory modifications paved the way for reptiles and other land-dwelling vertebrates.
• Indicator of ecological changes is tied to water and permeable skin.

Overview of Reptiles

• Reptiles fully transitioned to life on land approximately 310 million years ago.
• This transition was driven by increased competition in aquatic environments.
• A self-contained amniotic egg has protective membranes and is waterproof.
• Reptiles possess thick skin composed of keratinized scales that reduce water loss.
• They breathe using rib ventilation, where lungs become more efficient.
• Reptiles have stronger jaws for terrestrial feeding and enhanced musculature.
• The rib ventilation system facilitates efficient negative pressure.
• They expend waste as uric acid to minimize water loss.
• Reptiles have expanded brains from enhanced vision.
• Lizards and snakes make up most non-avian reptiles, while turtles are oviparous.
• Snakes and lizards make up most non-avian reptiles and contain rear-fanged or hemotoxic venom.
• TSD means temperature-dependent sex determination, where climate change may skew these ratios.
• Reptiles were the first terrestrial vertebrates, where birds are technically considered part of this lineage.

Overview of Birds

• ~9,700 extant species divided into 30 orders.
• Characterized by feathers, beaks, and flight adaptations.
• Paleognathae subclasses include flightless birds with a flat sternum like ostriches.
• Neognathae encompasses most flying birds with keeled sternums.
• Contour feathers are lightweight with asymmetrical vanes for lift.
• Down feathers lack barbule hooks and provide insulation.
• Molting is a gradual replacement.
• The skeleton is lightweight with pneumatized bones.
• Fused vertebrae, synsacrum, and pygostyle bring stability.
• The respiratory system flows air unidirectionally through parabronchi.
• Circulatory systems contain the largest heart relative to body size.
• Digestive traits consist of a crop and a gizzard.
• Behavioral mating systems include nesting and altricial or precocial young.
• Behavioral features encompass migration, landmarks, and magnetic fields.
• Behavioral flocking involves cues and organized interactions.

Introduction to Mammalia

• Mammalia is a diverse class of vertebrates with approximately 5,400 living species.
• They are highly differentiated and domesticated for food, clothing, and research.
• Monotremata consists of egg-laying mammals, marsupials are pouched, and eutherians are placental.
• • Mammals show mammary glands and specialized teeth with an endothermic system.
• The integumentary system contains the waterproofing process in the skin and involves hair.
• Adaptations include nails, claws, and horns.
• Diet is reflected through digestive tracts (short for protein and long for fermentation).
• Lungs facilitate ventilation and gas exchange.
• Kidneys help with excretion in urine.
• Unique traits consist of flight and rare migration.
• Mammals show domesticated health links to zoonotic diseases.
• These specialized traits underscore the evolutionary process from natural selection.

Ecdysozoa

• Ecdysozoans molt cuticle as they grow.
• The Biochemical steps in molting are assumed to be similar among Ecdysozoans.
• The antifreeze protein is used for freeze resistance in some insects.
• The pseudocoelom is used as a hydrostatic skeleton in nematodes, kinorhynchs, and priapulids.
• The coelomate bodies panarthropoda contain arthropods of reduced size.

World of Nematodes

• Nematodes parasitize species and make nematode studies important to agriculture and science.

Nematoda: Roundworms

• Nematodes consist of 25,000 species.
• Nematodes can inflict infections.
• Hookworms consists of these with hook-like curves with blood sucking components in the intestinal system.
• Infected juveniles travel in the blood to the lungs, are coughed up then to be swallowed and goes to stomach and intestines.
• Juveniles mature in the intestine much like those of Ascaris sp.
• When poorly cooked meats are consumbed that contains the worms they mature in the intestines.
• Cause inflammation and blood blockage from mosquitoes containing diseases.
• They are decomposers who then make nutrients available to other organisms, which in turn support Fungal and Bacterial colonies.
• Nutrient cyclers occur through longitudinal muscle that allows pairings of the hydrostatic skeleton.

Arthropoda

• Silk is 5xStronger than steel and twice as elastic as nylon.
• High tensile strength (stretch without breaking) allows durable flexibility.
• Silk producing spools allows protection from outside elements.
• The venom is highly neurotoxic in species like spiders and scorpions.
• Important mites like chiggers feed on the dermal, causing skin irritation.
• Disease vectors tick the species of Ixodes which Carry Lyme disease (bacteria); the most harmful bacteria in the arthropod world.
• Arthropods have an open circulatory system where blood bathes internal organs directly.
• Contractions of hearts pump blood out to allow pores through vessels in the sinuses.
• Terrestrial arthropods use a tracheal system for direct oxygen transport.
• Malpighian tubules are the excretory glands found in arthropods.
• Arthropoda have specialized sensory organs and show complex behavioral patterns.
• Eyes vary from simple light sensitive which allows insects a wider occurrence of social organization. Larvae in arthropoda Avoid intraspecific competition by metamorphosis.
• Myriapods has shared related in the arthopod world for their mouth parts.
• Support is based on molecular evidence.

Chelicerata and Myriapods

• Chilopoda (centipedes) is the group that centipedes fall under.
• Diplopoda (millipedes) is the group that millipedes fall under.
• Myriapods has head and trunk tagmata that uses trachea to transport gasses.

Crustaceans

• Resemble sessile compound eyes with maxillipeds.
• Development is direct with little metamorphosis.
• They exploit aquatic resources and share dominance in freshwater environments with limited invasions into terrestrial area. Malacostraca is the most diverse with members of Copepods and Ostracods being the most abundant.
• Green gland excretory system - osmoregulation allows Thin cuticle to flow though the respiratory track.
• Ecdysis (molting) with direct development allows serial homology.

Animals In The News

• initial thought to be Cymothoa exigua tongue-eating louse. However, lab results indicate Megalopa, a type of tiny crab

Hexapoda

• Subphylum Hexapoda are named for the presence of six legs which are all uniramous. Have three body segments (tagmata) these include the head-thorax and the abdomen. Appendages attach to head and thorax while abdominal appendages may be greatly reduced or totally absent, this contributes to their stability over 1. 1 million classifed species. Waterproof and lighter weight allows for easier flight when compared to crustaceans.

Echinodermata

• Chordates were once referred to echinodermata because they were marine and bottom dwellers with bottom bodies.
• Water will enter the body through radiation and contraction of muscles known as inhalation and exhalation in several iterations.
• A link between echinoderms includes the tornarian larvae.
• Vertebrates musculoskeletal modifications were present early in the chordate process with segmented muscles acting as a framework inside the structured body that promotes better function.
• Fin rays dermis aided in swimming