Lecture 6 RH Flashcards
What is the diversity of chelicerates like?
2nd largest group of arthropods
98% of chelicerates are arachnids
Most arachnids are spiders
Diversity is related to numerous uses of silk
What are some common features of chelicerates?
No antennae or mandibles
2 tagmata:
Cephalothorax
Abdomen
6 pairs of uniramous appendages:
chelicerae
Pedipalps
4 pairs of walking legs
Spines at the base of their appendages that are called macrobases
What are some features that only chelicerates don’t have?
No mandibles
No antennae
What is the function of pedipalps?
for holding onto food or mates
What happens to book gills in spiders?
They are internalized and act like lungs
What are the classes of chelicerates?
Merostoma (horseshoe crabs)
Arachnia (spiders, scorpions, ticks, mites)
Pycnogonida (sea spiders)
What are the types of merostomatans?
Horseshoe crab: 4 living species (located on the East coast of US, S.E, Asia, Indonesia
Eurypterid (extinct for 230 million years and are successful predators in paleozoic seas, have reached almost 3m in length, likely ancestor of arachnids)
What are the orders of class arachnida?
Arachneae: True spiders
Opiliones (daddy longlegs; harvestmen)
Solpugida and amblypygi: Solifuges and whip spiders resemble spiders
Scorpionida: scorpions
pseudoscorpionida and uropygi
Acari: ticks and mites
What are the adaptations of class arachnida for terrestrial life?
Exoskeleton for support and protection
Waxy epicuticle
Book lungs and tracheae in spiders and scorpions and some spiracles can be closed
Internal fertilization and eggs are shelled
Several types of highly sensitive mechanoreceptors that detect air vibrations
What are the features of araneae?
40k species
Chelicerae have fangs for stabbing and tearing prey usually with venom glands
Predators with external digestion
1 pair of pedipalps for holding prey; 4 pairs of walking legs
Usually 4 pairs of eyes
Abdomen includes several fused segments No segmentation visible externally
Pedicel
Spinnerets
What is a pedicel?
Narrowing between abdomen and cephalothorax to allow more flexibility
What is a spinnerets?
Organs that produce silk to spin webs
What is the function of pedipalps?
Holding prey
What is spider silk made of?
Complex liquid-crystalline polymer which is a liquid of protein subunits which arrange into a crystalline matrix when pulled from secretory glands.
What are the features of spider silk?
Remarkably strong and elastic
7 types of glands produce silk of different properties for different functions
Glands are arranged in spools from which the spun silk emerges
Spools are arranged in spinnerets on abdomen that direct and place the silk
What are some uses of spider silk?
Locomotion
Feeding
Breathing under water by creating a balloon
Reproduction
How do spiders use their silk for locomotion?
Dragline for safety
Climbing or descent
Ballooning
How do spiders use silk for feeding?
They create a thread of sticky spiral with adhesive droplets
They use silk to immobilize prey while they digest it
What is the mechanism a spider uses for an abreviated orb web?
Spider sits between tension thread and attachment thread and senses vibrations
How do spiders use silk for reproduction?
Communication between mates
Wrapping mates
Wrapped food as offering
Transfer of spermatophore
Egg cocoons
What are the features of order opiliones?
AKA daddy long legs or harvestmen
Abdomen has external segmentation and lacks a pedicel
Do not produce silk or toxins. Feed more as scavengers but also as predators.
*The misnamed daddy longlegs in your house is a true spider
What are the features of order scorpionida?
Very ancient arachnids
Live in arid or humid habitats, often secretive and nocturnal
Small chelicerae with gnathobases
Large pedipalps with chelae to hold prey
No pedicel
Telson with a poison stinger
Detect vibrations from prey through air or substratum with several types of mechanoreceptors
What are the features of order acari?
cephalothorax and abdoman are fused but some mites might have a furrow
Mouthparts are on a short anterior projection
What are the features of ticks?
Larger and more triangular or rounded than mites
Blood-sucking parasites with short mouthparts that anchor into host
Can transmit a variety of pathogens
What are the features of mites?
Longer mouthparts for various feeding modes (herbivores, predators, scavengers and parasites)
Great economic impacts as crop pests and animal parasites
What do chigger larva feed on?
Skin
What are the features of class pycnogonida?
1000 species approx
Chelicerae and palps are on an extension of the cephalothorax. Abdomen is greatly reduced
Slow moving marine predators
Feed mainly on cidarians bryozoans and other soft bodied invertebrates with sucking proboscis
Body size up to 70 cm in the deep sea but most are less than 1 cm
What are Hox genes?
present in many invertebrate and vertebrate phyla
Some of these genes are homologous
They control the development of body regions bty regulating the activity of other genes
Order of genes on chromosomes matches the order in which they act on the anterior-posterior axis
What evidence suggests that insects evolved from crustaceans?
Significant modifications of segments and appendages can be created by simple evolutionary changes in developmental regulatory genes (eg hox genes)
What do studies of regulatory genes reveal about arthropod evolution to terrestrial life?
It evolved from biramous legs of ancestral taxa
The same regulatory genes are active during development in gill branches (exopod of crustacians), wing of insects, book gills of horseshoe crabs, and the book lungs, tracheae, and spinnarettes of spiders.
Serial repetition allows specialization to evolve by modifying particular regions in the body. Loss or modification of structures in certain segments converts a homonomous plan to a heternomous plan, producing specialized tagmata
What are the features of phylum onycophora?
Coelomates
Protostomes
Segmented
Like arthropods:
Cuticle is molted
Greatly reduced coelom
Tracheae
Like annelids:
Soft cuticle, noncalcified
Homonomous metamerism
Paired appendages that are fleshy and unjointed like parapodia
Where do onycophorans live?
In leaf litter of southern hemisphere rainforests
How do they eat?
They are predators that catch prey with sticky slime released from special glands.
What phyla are onychophorans similar to?
Annelids and arthropods
Which phyla are lophotrochozoa?
Platyhelminthes
Annelids
Molluscs
Which phyla are ecdysozoans?
nematoda
onycophora
arthropoda
What are the lophophorate phyla?
Ectoprocta (bryozoa)
Phoronida
Brachiopoda
What do lophophorates have in common?
They contain a lophophore which is a structure used for suspension feeding and gas exchange and is a ring of tentacles that are ciliated and gas exchange.
How do lophophores work?
Cilia move water through the tentacles and allows for food and gas exchange to take place
What are the traits that are common between lophophores?
Bilateral symmetry
Triploblastic
Complete gut (exception is one class of brachiopods)
Coelomate (3 separate compartments; protocoel, mesocoel, and metacoel)
Almost all are marine with the exception of a few freshwater ectoprocts
Benthic, sedentary or sessile
Uncephalised
Secrete a protective covering
U-shaped gut, anus is outside the lophophore
What are the 3 compartments of lophophore coeloms?
Protocoel
Mesocoel
Metacoel
What are bryozoans?
Moss-animals
What are the features of bryozoans?
Live in colonies
Each polypide lives in a zooecium with an orifice from which the lophophore extends above an extension called the introvert
No circulatory, gas-exchange, or excretory systems
What are the types of colonies that bryozoans can form?
Arborescent (branched colonies)
Encrusting (sheet structure)
How is the lophophore forced out of the body?
Coelom squeezed by contraction of parietal muscles forcing the introvert out releasing the lophophore.
How is the lophophore forced back in?
Retractor muscles pull on introvert
What is zooid polymorphism?
Among the colonies there are specialized individuals in the colony for each function.
What are the reproductive zooids of the colonies called?
Ovicell
What are the protective zooids of the colonies called?
Avicularium which contain mandibles that can “bite”
Vibraculum is a spiny zooid.
What are the features of phylum phoronida?
Only 2 genera and 14 species
Solitary worms
More organs than bryozoa (Blood-circulatory system, metanephridia)
Protective covering is a chitinous tube
Sedentary in sediments
What are the features of phylum brachiopoda?
All marine
Solitary
Calcareous bivalved shell (covers dorsal-ventral)
Pedicle may attach to substratum
Dominated over bivalve molluscs for several hundred million years but were eventually outcompeted
Important fossils for evolutionary studies
U shaped lophophore 2 arms
Blood-circulatory system, metanephridia
Adductor and abductor muscles
What are the types of larvae of bryozoans?
Coronate
Cyphonautes
What type of larvae do phoronids have?
Actinotroch
What do the larvae suggest about evolution of lophophorates?
Difference in larval forms give no evidence of a close relationship among phyla
Only the shared trait of a lophophore has been thought to unite these phyla as close relatives
Other aspects of their development are curious and fit neither protostomes nor deutrostomes
What are the features of rotiferans?
2000 species
What are the features of phylum chaetognatha?
100 species 1 - 12 cm in size
Coelomate
All are swift and voracious predators in marine plankton. Have teeth and grasping spines for this purpose
Phylogeny is highly debated: Protostomes or deutrostomes?! No simple morphological synapomorphy
What are the differences between protostomes and deutrostomes?
radial cleavage is seen in deutrostome
Spiral cleavage is typically seen in protostomes but not always
Method by which the coelom is
formed
Blastopore destination
What is the method by which a protostome coelom is formed?
Schizocoely whereby gut is separated from other pouches by early mesoderm cells forming pouches in the coelom..
What is the method by which the deutrostome coelom is formed?
Enterocoely whereby gut outpouchings form the coelom
