Exam 4 - Invert Zoology

Panarthropoda,

Panarthropoda

1,200,000 described arthropod species

1300 described tardigrade species

200 described onycophoran species

Phylum Tardigrada

Water bearers

Modified segmentation

Unjointed legs

Semi-aquatic

0.1-0.5 mm

Phylum Tardigrada - Anabiosis, Cryptobiosis, Anhydrobiosis

Terrestrial, freshwater

States of dormancy

“tun'“ stage

Anabiosis

Cryptobiosis

Anhydrobiosis

Phylum Tardigrada - Cyclomorphosis

Marine

Quick life cycle triggered by environment

Phylum Tardigrada - Body Plan

Weak cephalization

Reduced coelom

Four pairs of legs

Cuticle

• 3-6 molts

Phylum Tardigrada - Locomotion

Step by step gait

• antagonistic muscle sets

Phylum Tardigrada - Feeding/Digestion/Excretion

Oral stylets

• salivary glands

Bacteria, algae, decaying plant matter, small invertebrates

Complete gut

Malphighian tubules - excretion

Phylum Tardigrada - Circulation/Nervous system

No circulatory system

• diffusion

Metamerous nervous system

Sensory structures

• tactile: bristles/spines and cirri

• photo: eyespots

• chemo: clavae

Phylum Tardigrada - Reproduction

Gonochoristic

• internal or indirect fertilization

Parthenogenesis - extreme environments

Hermaphroditic - rare

Sculptured eggs - resist water loss

Indeterminate development - cell fate is unknown

Phylum Onychophora

Velvet worms

Completely terrestrial

Segmentation

Unjointed legs

5mm-15cm

Phylum Onychophora - Body Plan

Head appendages

• antennae

• jaws

• oral papillae

• beady eyes

Lobopodal walking legs - sac like

Cuticles

Phylum Onychophora - Locomotion

Legs filled with hemocoelic fluid

• extension and contraction of hydrostatic forces

Phylum Onychophora - Feeding/Digestion

Carnivorous

• small invertebrates

Slime glands - shoot slime to trap prey

Jaws

Phylum Onychophora - Circulation/Osmoregulation

Open circulatory system

Gas exchange

• tracheae - tubes inside of spiracles

• spiracles - hole on side

Excretion/Osmoregulation

• nephridia - each segment that bears legs

• vesicles

Phylum Onychophora - Nervous System

Ladder-like

• bilobed cerebral ganglion, two ventral nerve cords

Sensory structures

• tactile: sensillae

• photo: eye, but photophobic

• chemo: crural

Phylum Onychophora - Reproduction

Gonochoristic

• internal fertilization

• most viviparous

Arthropods Problems and Solutions

Life in a hard exoskeleton

• problem: locomotion

• solution: jointed appendages and regionalized muscles

• problem: circulation

• solution: hemocoel and heart

• problem: growth

• solution: ecdysis

• problem: so many habitats

• solution: tagmosis - specialized body segments

Arthropods - Body Plan

Cuticle

• sclerites

Appendages

• biramous - two rami on the leg

• uniramous - one rami on the leg

• articulations - places they can bend

Arthropods - Ecdysis

Ecdysis

• ecdysone form Y organ

• Instars or Intermolts

• MIH from X organ

Arthropods - Digestive system

Complete gut

Regional specialization

• foregut

• midgut

• hindgut

Arthropods - Circulation/Gas exchange

Circulation

• open

• heart - vessels - hemocoel - heart

• hemolymph

Gas exchange

• gills

• book lungs - modified gills

• tracheae and spricales

Arthropods - Excretion/Osmoregulation

Excretion

• nephridia - nitrogenous waste

• malpighian tubules - other waste

Osmoregulation

• gut absorbs water

• marine crustaceans: 70-90% ammonia

• terrestrial arachnids: uric acid

Arthropods - Nervous System

Nervous system

• Cerebral ganglion

• Ventral nerve cords

Sensory Structures

• tactile

• chemo

• proprio

• photo - “eyes”

Arthropods - Reproduction

Gonochoristic

Internal fertilization

Brooding/mixed development

Homoplasy

• rigid exoskeleton

• hox genes