MFWB_A - Arthropods

beginning of phylum

panarthropoda

tardigrades

1150 species, 0.5 mm long, mosses, lichens, algae, can be cryobiotic to survive extreme colds, metabolic rate to 0.01% of normal, water content decreases

arthropoda

most diverse of animal groups due to versatile body plan (80% of known animals), exoskeleton, segmented body, paired jointed appendages,

tagmatisation

grouping of multiple segments - some can completely fuses

segments

head (sensory organs), thorax (locomotion), abdomen (digestion, reproduction)

subphylum chelicerata

sea spiders, horseshoes crabs, arachnids, first marine 525 mya, then colonised land, 2 marine groups left, over 100,000 species

chelicerata characteristics

cephalothorax (fused head and thorax for easier eating), chelicerata instead of antennae (clawlike structures to catch prey), 4 pairs of eyes, pedipalp (pincers), book lungs, malphigian tubules

book lungs

modified gills, gaps for air flow, lamellae (thin, plate-like structures) - highly vascularised, allowing for efficient exchange of carbon dioxide and oxygen between air and haemolymph, spiracles (not covered by exoskeleton, allows for air intake) - 4 pairs in scorpions, 2 in spiders

malphigian tubules

osmoregulatory, in the hind gut, control processing of water and retain/filter nutrients, haemolymph brings salt, uric acid and water into tubules, salt and water recycled, uric acid and faeces out

horseshoe crab

4 species, prosoma (head and thorax) covered by carapace, compound dorsal eyes, less likely to be flipped due to aerodynamic, telson if it is, opisthosoma (fused segments, telson, bears gills), pedipalps, gills closer to lobsters and crabs

arachnids

arancae at end of abdomen - modified appendage, spinneret to spigot then open to environment (silk production, can control the wetness/state of it), chelicerae - fangs, connected to the venom glands

scorpiones

pectins (sensory organs on underside for texture of surface, smell pheromones), prosoma (cephalothorax), opisthosoma (abdomen), pedipalps, venomous segmented tail, exoskeleton of chitin

myriapoda

4 well defined classes, damp areas or where water is drawn out

Chilopoda

centipedes, venemous forceps, uneven number of segments, paired legs per segment so would fall over if even

diplopoda

millipedes, slow moving, detritus eating, each segment has two pairs of legs, domed to push through debris (legs underneath), thought to be the first animals on land