Ecdysozoa and Nematoda

Ecdysozoa

• Many protostomes have a cuticle, a non-living outer layer secreted by the epidermis.
• Ecdysozoans undergo ecdysis, shedding their cuticle as they grow, regulated by the hormone ecdysone.
• Nematoda, Nematomorpha, and Kinorhyncha are pseudocoelomates.
• Panarthropoda (arthropods, onychophorans, and tardigrades) have coelomate bodies with reduced body cavity size.

Nematoda (Roundworms)

• Most are parasites in both humans and domesticated animals.
• Approximately 25,000 species have been described; may be as many as half a million species.
• Nematodes are found in virtually all habitats in all biomes.
• Nematode parasitism is important in agriculture and biomedical sciences.

Parasitic Nematodes

• Hookworms are small worms with hook-like curves at their anterior ends causing anemia in hosts.
• Hookworm eggs pass out in feces, juveniles hatch in soil, and infective juveniles burrow through skin to blood vessels.
• Infective hookworm juveniles travel to the lungs, are coughed up and swallowed, then mature in the intestine.
• Trichinella spiralis causes trichinosis; juveniles penetrate skeletal muscle cells, redirecting gene expression of host cell musculature.
• Trichinella sp. infects humans, hogs, rats, cats, and dogs through poorly cooked meat containing encysted juveniles.
• Eight species of filarial nematodes infect humans causing diseases, such as elephantiasis.
• Microfilariae are released into blood and lymph, ingested by mosquitoes, and transmitted to new hosts.
• Free-living nematodes recycle nutrients in the environment, acting as decomposers.

Arthropoda

• Web-spinning spiders have spinnerets with microscopic tubes connected to silk glands in the abdomen.
• Spider silk is stronger than steel and more elastic than nylon, composed of fibrous protein and different glands produce different kinds of silk.
• Black widow spiders have neurotoxic venom, while brown recluse spiders have hemolytic venom that destroys tissue.
• Scorpions detect prey using leg sensillae to detect surface waves and perform complex mating dances.
• Scorpions have appendages (chelicerae, pedipalps, and four pairs of walking legs) attached to cephalothorax.
• Ticks and mites (Order Acari) and are medically and economically important arachnids, with about 30,000 described species.
• Adult mites and ticks have four pairs of legs ( ticks may range up to 3 cm due to distension from feeding) along with a complete fusion of cephalothorax and abdomen
• House dust mites are free-living and cause allergies.
• Spider mites are agricultural pests that suck out plant nutrients.
• Chiggers are larval Trombicula mites that feed on dermal tissues.
• Human itch mites burrow into skin and cause scabies.
• Tick species of Ixodes carry Lyme disease, and Dermacentor transmit Rocky Mountain spotted fever, cattle tick transmits Texas cattle fever.

Arthropoda: Systems

• Arthropods have an open circulatory system, where hemolymph bathes organs directly in a hemocoel.
• Terrestrial arthropods use a tracheal system for direct oxygen transport; aquatic arthropods respire with gills. Paired excretory glands, coxal, antennal, or maxillary glands are present in some.
• Others excrete with Malpighian tubules.
• The nervous system is similar to annelids, with a dorsal brain connected to a ventral nerve chain.
• Sensory organs are well-developed for touch, smell, hearing, balancing, and chemical reception.
• Reproduction is usually sexual with internal fertilization; arthropods can be oviparous, ovoviviparous, or viviparous.

Arthropoda: Metamorphosis & Classification

• Many arthropods undergo metamorphic changes, where larvae and adults feed on different organisms.
• Molecular evidence divides Uniramia, where insects are in subphylum Hexapoda and others are in subphylum Myriapoda.
• The "Mandibulate hypothesis" suggests myriapods, hexapods, and crustaceans are closely related due to mandibles.

Myriapoda

• Myriapods have mandibles for feeding, two tagmata (head and trunk), and paired appendages along most segments.
• Chilopoda (centipedes) are agile carnivores that kill prey with venom claws.
• Diplopoda (millipedes) have cylindrical bodies with segments reinforced with calcium carbonate exoskeleton and are herbivores.

Chelicerata vs Mandibulata

• Spiders, scorpions, and ticks are chelicerates with a cephalothorax and abdomen.
• Chelicerates have chelicerae and may use spider silk but ticks and mites, rather than spiders, have a greater economic impact.
• Mandibulates, comprise millipedes and centipedes, and have antennae.

Crustacea

• Crustaceans are dominant arthropods in marine environments and share dominance in freshwater with insects.
• Malacostraca is the most diverse, while Copepods and Ostracods are most abundant and important in marine food webs.
• Crustaceans have two pairs of antennae, biramous appendages, and undergo ecdysis.

Crustacea Characteristics

• Crustaceans have cuticles composed of chitin, protein, and calcareous material and three tagmata: head, thorax, abdomen.
• One or more thoracic segments fused with the head form a cephalothorax.
• The head has a pair of mandibles, two pairs of maxillae, and two pairs of antennae.
• Appendages, except the first antennae, are ancestrally biramous.
• The dorsal covering is carapace.
• Malacostraca have paired appendages on the abdomen (swimmerets), while other classes typically do not.
• Crustaceans have an open circulatory system; hemolymph exits the heart through arteries.
• Antennal or maxillary glands (green glands) regulate ionic and osmotic composition, while nitrogenous wastes are excreted across the cuticle in the gills.
• Double ventral nerve cord has a pair of ganglia for each segment to control appendages.

Crustacea: Reproduction and Molting

• Some ostracods reproduce via parthenogenesis.
• Most crustaceans brood eggs in brood chambers, sacs, or attached to abdominal appendages.
• Nauplius larvae undergo metamorphosis, while crayfishes develop directly.
• Hormones control Ecdysis which is needed for crustaceans to increase in size because the exoskeleton doesn't grow.
• Environmental factors trigger the central nervous system to decrease molt-inhibiting hormone, promoting release of molting hormone.

Crustacea: Feeding Habits

• Mouthparts are adapted to wide range of feeding habits and food sources.
• Suspension feeders generate water currents to feed on plankton, detritus, and bacteria, using setae on legs to strain food.
• Predators consume larvae, worms, crustaceans, snails, and fishes.

Hexapoda (Insects)

• Hexapods are named for having six uniramous legs and three tagmata (head, thorax, and abdomen).
• Appendages attach to the head and thorax, while abdominal appendages may be reduced/absent.
• Class Insecta has ectognathous mouthparts (bases lie outside the head capsule).
• Insects live in nearly all habitats except the sea and entomology is the study of insects.

Insecta: Characteristics

• Exoskeleton is composed of complex plates (sclerites) connected by flexible hinge joints.
• Rigidity is due to scleroproteins, waterproof and lighter weight therefore important for flight.
• The cuticle of a body segment has a dorsal tergum, ventral sternum, and lateral pleura.
• The head has compound eyes, antennae (for touch, taste, or hearing), and mouthparts.

Deuterostomes

• Blastopore becomes the anus.
• Enterocoelous coelom formation.
• Radial cleavage.
• Indeterminant development.

Echinodermata

• Pentaradial as adults (bilateral as larvae).
• Water vascular system.

Hemichordata

• Marine worms.
• Contain gill slits.
• Includes Tornarian larvae.

Vertebrata: Characteristics

• Living endoskeleton.
• Segmented muscles, modified from V-shaped to W-shaped.
• Pharynx modified into a muscular pump passing water across internal gills.
• Accessory digestive glands.
• Paired, glomerular kidneys.

Vertebrata: Sensory, Innovations and Development

• Sense organs designed for distance reception, such as eyes, pressure receptors, chemical receptors, lateral-line receptors, and electrical receptors.
• Embryonic innovations: neural crest and ectodermal placodes.
• Four clusters of Hox genes due to genome duplication events.
• Gene duplication could be the primary mechanism for the evolution of complexity in higher organisms.

Chordate Characteristics

• Notochord and dorsal nerve cord.
• Pharyngeal pouches.
• Endostyle /thyroid gland derived from the endostyle.
• Postanal tail.

Vertebrate Characteristics

• Endoskeleton of vertebral column and cranium.
• Muscularized digestive tract with liver and pancreas.
• Closed circulatory system with multichambered ventral heart.
• Paired, glomerular kidneys.
• Tripartite brain.

Gnathostomata

• Three pairs of semicircular canals.
• Notochord replaced by centra of the vertebrae.
• Thrust generation comes from the caudal fins.
• Armor help fish avoid predators and improved feeding efficiency with scales.
• Have light, thin, flexible cycloid and ctenoid scales.

Chondrichthyes (Cartilaginous Fishes)

• There are approximately 970 living species, mostly marine.
• Cartilaginous endoskeleton.
• Placoid scales. -Chondrichthyes use urea as an osmolyte and have a rectal gland for salt secretion.

Teleosts: The "Swimbladder"

• Many fish use gas bladders to achieve neutral buoyancy and some fish use gas bladders to adjust density of fish to equal surrounding water.
• Physostomous fishes have a swim bladder connected to GI tract via a pneumatic duct, regulate bladder gas volume via blood.
• Physoclistous fishes have no connection to GI tract allowing exposure of swimbladder gas to ovale can be regulated by constrictor muscles.

Teleosts: Gas Exchange

• Gills are aquatic gas exchange organs.
• counter current exchange maintains stable gas (O2, CO2) diffusion gradients.

Teleosts: Osmoregulation

• Marine Teleosts must replenish water lost to the environment and secrete excess NaCl.
• Freshwater Teleosts replace salts lost to the environment.
• Euryhaline undergo Migration in Teleosts meaning Adult Freshwater; Larvae- Juvenile Seawater or Adult Seawater; Larvae-Juvenile Freshwater
• Anadromous (Salmon) and Catadromous (Freshwater Eels)

Teleosts: Reproduction, Development and Living Out of Water

• Most fishes are dioecious with external fertilization and external development but fish can be sequential hermaphrodites.
• Dramatic changes from larva to adult can be significant with most fish continuing to grow throughout life.
• Have been many adaptations for Fishes to live out of the water.

Amphibia

• Transition from water to land in ontogeny and phylogeny.
• Have four limbs (quadrapedal).
• Have a double circuit circulatory system.
• Respiration occurs by skin, gills and/or lungs.
• Hearing in air.
• Water is needed especially for reproduction.
• Amphibians can be Ectotherms.
• Apoda (caecilians): Dermal scales are present in skin.
• Salamanders (Urodela) have two pairs of equal limbs and some aquatic or terrestrial sp. have- direct development (no metamorphosis).
• Axolotl (Mexican salamander) undergo Paedomorphosis [Gk. pais, child; morphosis, form] resulting in embryonic/larval structures appearing in adult animals.

Amphibia: Anura (Frogs and Toads)

• Possess sophisticated vocalizations for communication.
• Frogs and toads plan is considerably modified from basic ancestral form with a fused head & trunk and a large mouth.

Reptillia

• Reptiles were the first vertebrates to have a complete transition to life on land.
• Have a thicker and more waterproof skin than Amphibia.
• Reduce water loss and Rib ventilation along the lungs and possess Stronger jaws.
• Reptiles are a paraphyletic grouping excluding birds.
• Major groups are Snakes, lizards, turtles, and crocodiles.

Reptilia: Order Testudines (Turtles)

• The body resides in a bony case of dorsal carapace and ventral plastron.
• All turtles are Oviparous and can exhibit TSD and GSD species (Temperature Dependent Sex Determination) and (Genetic Sex Determination).

Reptilia: Order Squamata (Snakes and Lizards)

• Account for up 95% of living nonavian reptiles who have keratinized epidermal scales or plates, which is shed and Vertebrae that are usually concave in front

Reptilia:Snake Venom

• Venom may be neurotoxic; blocking nerve transmission or hemorrhagic; breakdown blood cells and vessels.
• Venom can be injected into the victim by with a variety of fang setups.

Reptilia: Order Crocodilia (crocodilians)

• The skull is elongate with a massive Secondary palate allowing them to breathe with mouth full of water and/or food.
• Have a Four-chambered heart exhibiting Advanced social behavior where temperature determines sex.

Reptilia: Order Sphenodonta (tuataras)

• Found only in New Zealand with the slowest rate of morphological evolution in the vertebrates while exhibiting TSD.

Aves

• Birds display a Great Uniformity and flight is an extreme form of exercise that occurs in a monophyletic group displaying wings, beak, feathers.

Aves: Migration and Navigation

• Some aquatic species make rapid journeys
• Smaller species migrate at night
• Experiments suggest birds navigate chiefly by sight and a highly accurate sense of time with most migratory birds following established north-south routes.

Aves: Social Behavior and Reproduction

• Organized social interactions often occur during breeding season when many birds stake out territory, select mates, build nests, incubate and hatch eggs, and rear young
• Cuckoos and cowbirds are nest parasites exhibit No parental care whereas other precocial birds are able to feed and run or swim as soon as they are hatched.
• Altricial birds are naked and helpless at birth and must be fed in the nest for a week or more.

Aves: Features and Endothermy

• Light weight skelton (air cavities)
• Circulatory sytem with largest heart in the animal kingdom relative to their body size
• They Reduce excess baggage such as a smaller genome and exhibiting an Excretory system with loop of Henle (concentrated urine), uric acid, lack a bladder

Mammalia

• Exhibit Hair, mammary glands and homothermic endothermy.
• Advanced nervous system, alveolar respiratory system and loop of Henle concentration.

Mammalia: Reproductive Patterns

• Most mammals have mating seasons timed to coincide with the most favorable time to give birth and rear young during the estrous cycle.
• Animals with only one breeding season a year are monestrous and with Recurrent breeding is polyestrous.
• Pouched Marsupials give birth to tiny young that are still embryos nourished by milk lapped off mother’s fur near mammary glands.
• Platypus milk has protein with potential to fight superbugs and Placentals give birth to Eutherian young inside the body.