Lecture 18 Arthropods 1 Flashcards
Ecdysozoans are
a group of protostome animals, including Arthropoda, Nematoda, and several smaller phyla. The group was defined mainly based on phylogenetic reconstructions using 18S ribosomal RNA genes. Includes animals that grow by ecdysis, moulting their exoskeleton.
Tagmosis is
the evolutionary process that creates tagma by modifying and fusing segments
Cryptobiosis is
a physiological state in which metabolic activity is reduced to an undetectable level without disappearing altogether. It is known in certain plant and animal groups adapted to survive long periods of extremely dry conditions.
Ecdysozoa on phygenetic tree
What word could be used to describe relation between Lophotrochozoa and Ecdysozoa?
Two “clades” under Protostome animals
Four phyla or divisions in Ecdysozoa (ecdysis, “to slip out or escape”)
- Nematoda (round worms)
- Tardigrada (water bears)
- Onychophora (velvet worms)
- Arthropods
Describe Nematoda (Round worms)
- ~25,000 described species and ~ one million total species estimated
- Pseudocoelomates, unsegmented, elongated, circular in cross-section, limbless;
- Body protected by an elastic cuticle that is molted;
- Distributed in all possible habitats (marine, freshwater, terrestrial, extreme temperature, pressure);
- Feed on detritus, bacteria, fungi (free form); many are parasites (>50%, non-free form)
Describe Tardigrada (water bears or moss piglets)
- ~1000 described tardigrad species
- Small (0.05 – 1.5 mm long), segmented, eight short legs (with claws or sucking disks);
- Live in marine, freshwater and semi-terrestrial (moist areas) that will kill most other animals
- Not considered extremophiles (not extreme environments)
- Feed by sucking fluids from plants and animals, some are detritivores.
- Cryptobiosis (suspending metabolism for more than 30 years)
Describe Onychophora (claw bearing, velvet worms)
- ~200 described species
- Segmented animals with lobe like appendages
- Terrestrial, humid environments
- Nocturnal, ambush predators; Champion spitters of the animal kingdom. Spit immobilize prey, and toxic saliva kills it.
Describe Arthropoda “jointed foot”
- ~1,160,000 described species, 3/4 of all animals, and more than half of all
- Segmented animals with jointed appendages (tagma) and an exoskeleton (reduced segmentation)
- Process of fusion into tagmata called tagmosis
- All environments (Crustaceans aquatic, other terrestrial)
- Use specialized mouth parts to consume a variety of foods
Four classes under Anthropoda
Myriapods, Insects, Crustaceans, Chelicerates
Chara. features of Arthropods
- Segmented body plan
* Body segments
* Segments are specialized and fused to form tagma (diversified through number and function)
* The number of segments varies from fewer than 20 (insects and crustaceans) to over 100 in centipedes and millipedes - Jointed appendages
* biramous (branched) or uniramous (unbranched)
* specialized functions - Highly developed sense organs
* highly cephalized
* elaborate sensory organs including statocysts, antennae, simple or compound eyes (each called a ommatidia, low resolution, detect shape), sensitive hairs, etc - Rigid exoskeleton (ecdysozoan)
* secreted by epidermis
* covers all external surfaces, digestive tract, & tracheae
* non-living
* composed of layers (multi-layered)
* chitin, protein (insects) + CaCO3 (mineralized in crustaceans)
Advantages of rigid exoskeleton
- physical support and protection (from abrasion, predation, parasite entry or from desiccation)
- place for muscle attachment
- jointed appendages & exoskeleton allow faster locomotion
- opportunity to change morphology between larval and adult stages (metamorphosis)
- location of pigments (camouflage, warning colouration, mating signal)
Disadvantages of rigid exoskeleton
- inflexible and heavy (if thick and protective)
- continuous growth in size is not possible must be periodically shed (moulted)
- requires energy to form and shed
- crustaceans also use ambient calcium to build exoskeleton, so hard waters, ex. Daphnia, which is impacted by calcium erosion in Canadian lakes, “osteoporosis of lakes”
- respiration through skin in most cases is not possible; the need for spiracles (pores) & tracheae (tubes)
Describe discontinuous growth in size for arthropods
Mass grows continuously, but size changes in stepwise fashion, each step is called an instar
Describe complete metamorphosis
- Abrupt changes in form
- Often major habitat changes
- Includes four stages, one of which is a resting stage (pupa)
- Butterflies, moths, beetles, bees, ants, fleas, mosquitoes
Describe incomplete metamorphosis
- Gradual changes in form
- Three stages with no “resting” stage.
- Often no habitat change
- Grasshoppers, crickets, termites, mites
Describe hormones
- Chemical messengers
- Secreted by endocrine cells
- Hormones are distributed by blood, bind to target cell receptors (target specificity).
- Some animals endocrine cells directly respond to environmental stimulus
Describe Integration between nervous system and endocrine system
CNS after neural signal releases neurohormone
Describe Multi-level integration (e.g., hypothalamus – pituitary – peripheral hormone glands)
Describe Arthropod moulting hormones
- PTTH brain hormone (pro-thoracico-tropic hormone)
* Produced and stored by the brain (neurohormone)
* Production influenced by environmental cues
* Controls activity of prothoracic gland - Ecdysone
* produced by prothoracic gland
* secreted into blood
* target cells = epidermis
* response = ecdysis
* brain responds by shutting off PTTH hormone (negative feedback) - Juvenile hormone secreted by non-neural endocrine cells to control metamorphosis.
Describe Circulatory systems in Arthropods
- open system (the hemolymph fills the body cavity)
- dorsal tubular heart (1 chamber) with pores (ostia); drives hemolymph into hemocoel spaces
- one-way valves
