An Overview of Arthropods and Their Ecological Roles
Water Vascular System
Group of fluid-filled canals connected to tube feet
Involved in feeding, respiration, internal transport, waste removal, and movement
Same larval type as chordates
Internal skeleton
Radial symmetry
No anterior or posterior end and no brain
Two-sided
Mouth on oral (top) opposite side = aboral
WVS: Open via madreporite
Starfish > Mad > ring
Tube feet on each canal
System operates like a series of hydraulic pumps (suction cups)
Water pushed in tube feet, it expands
Water pulled, cup on end shrinks making a vacuum
One foot can’t do much but many can make enormous force
Carnivorous > Opens bivalve shells via tube feet
Flips stomach from mouth, releases enzymes on food, and digestion occurs in prey’s shell. Digestion finished, pulls stomach back
Herbivorous > scrapes algae with 5-jaw
Filter feeders: Use tube feet to catch food floating by
Detritus feeders: Move like a bulldozer eating everything
Most use tube feet for respiration
Others use skin gills
Respiration done through tube feet and skin gills
Nutrient distribution done by digestive glands and fluid in body cavity
Solid waste removed via anus
Ammonia excreted by tube feet and skin gills
Most echinoderms use nerve ring surrounding mouth and radial nerves that connect the ring
Sensory cells detect food chemicals
Starfish have clusters of up to 200 sensitive cells called eyespots at arm tips
Statocyst = tells if organism is right side up
Male or female
Eggs and sperm released in water when other eggs and sperms are detected so fertilization occurs in open water
Larvae swim to plankton community till mature and go through metamorphosis into adults at the bottom of the ocean
Not found in freshwater or on land
Starfish = 5+ arms spiny
Sea urchin = oval
Sea cucumber: soft cucumber
Important carnivores control populations of other animals
Sea urchin control algae (can overeat)
Used by humans for food and potential drug against cancer and viruses
Sea urchin used to study embryological development because larvae are similar
6 million+ species
80% animals = arthropods, 76% insects
Subphylas:
Trilobita = oldest subphylum, ancient seas, now extinct
Used to have appendages on each segment
Chelicerata = Spiders, ticks, mites, scorpions, horseshoe crabs
Crustacea = Edible organisms, crabs, and shrimp
Uniramia = Most arthropods and all insects
Tough exoskeleton, jointed appendages, segmented body
Ventral nerve cord and open circulatory system
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Exoskeleton = supporting structure made of chitin, insect exoskeletons are leathery and flexible while lobsters/ticks are hard
Protection from physical damage
Many terrestrial arthropods have waterproof exoskeletons, restricting water loss
Possible to inhabit dry environments
Exoskeleton is a solid coating
Cannot grow (shed to enlarge)
Movement only occurs at joints of exoskeleton
Arthropod = joint and pod = foot
Appendage enables movement
Adapted to many environments
Arthropod appendages include antennae, claws, legs, and wings
All arthropods have segmented bodies
Three regions (Head, thorax, abdomen)
Some have many segments such as centipedes
Insects, spiders, and crabs have lost some segments or fused
Locusts = anything green
Herbivores = selective plant parts
Some carnivores like spiders, king crabs, catch and eat other animals
Other carnivores such as many crabs and crustaceans feed on dead animals
Parasitic arthropods can be external or internal
External parasites like ticks, fleas, and lice drink blood and nibble on the skin of animals
Some internal parasites absorb nutrients passively, while others eat at the host from the inside
Many marine arthropods are filter feeders that use bristles on mouth/legs to filter plants/animals from water
Three types of respiratory structures: Gills, book gills and book lungs, tracheal tubes
When the heart contracts, it pumps blood through arteries which branch into smaller vessels and enter tissues. Blood moves through space in tissue called sinuses. Blood collects in a large cavity surrounding the heart, from which it re-enters the heart through a small opening
Undigested food becomes solid waste and leaves via anus
Nitrogen-containing wastes result of cell metabolism are removed in other ways
More terrestrial arthropods use Malpighian tubules which are bathed in blood in body sinuses
Malpighian tubules remove waste from blood, concentrate and add to undigested food before leaving the anus
Some terrestrial arthropods have excretory glands at the base of legs in addition to Malpighian tubules
Many aquatic arthropods eliminate nitrogen wastes through green glands
All arthropods have well-developed nervous systems. They have a brain of a pair of ganglia in the head which receives incoming info and provides outgoing instructions to muscles
Ventral nerve cord connects the brain with the rest of the body and connects to several more ganglia (1 at each segment). These ganglia serve as local communication centers to control movement of wings and legs. Arthropods have simple sense organs like statocysts and chemoreceptors. Most arthropods have sophisticated sense organs like compound eyes for gathering info on the environment (bad resolution but good field of view)
Simple eyes = single lens dispersing image for many receptors (light intensity and direction)
Crustaceans and insects have well-developed sense of taste
Chemoreceptors associated with taste and smell are on mouthparts, antennae, and legs
Many insects have well-developed ears that hear sounds above human range
Insect ears are often in odd places
Grasshopper has a tympanum (eardrum) behind legs
Arthropods have well-developed muscle systems. Coordinated by the nervous system. Pull of muscles against exoskeleton allows arthropods to beat wings, walk, or swim
Reproduction is simple, males produce sperm, females produce eggs, fertilization occurs inside the female body
Dioecious: internal fertilization
In spiders and some crustaceans, males deposit a small packet of sperm that the female picks up
In most insects and crustaceans, the male uses a special reproductive organ to deposit sperm inside the female
Ecological roles: Pollination, production of honey, wax, silk, recycling of biomaterials to aid in producing topsoil, Form symbiotic relations, part of the food chain
Grasshopper = head has sensory antennae, eyes, and mouth segments. Thorax has 3 pairs of legs, adults may have 1-2 pairs of wings
Abdomen contains most internal organs
Exoskeleton is light with less chitin
Front wings are leathery, to protect broad flying hind wings
Third pair of legs suited to jumping
Tympanum on the side of the first abdomen segment for sound reception
Chewing mouth segments harvest food; stored in crop; gastric mill grinds food before the stomach digests
Malpighian tubules extend into coelom
Spiracles = opening in exoskeleton, lead to tubules called tracheae that diffuse gases for respiration
Circulation involves a tubular heart that pumps clear hemolymph through open coelom
Insects reproduce by copulation; female stores sperm in seminal receptacle; female grasshopper deposits fertilized eggs in the ground by ovipositor to overwinter
Metamorphosis = insects as with most arthropods molt many times between hatchling and adulthood
Grasshoppers undergo incomplete metamorphosis
Insect egg hatches into larva that looks like an adult, but smaller and has no sex organs and wings
As they molt they will grow and acquire adult characteristics
Organism always resembles adult
Larva to adult
Butterflies and some others go through complete metamorphosis
4 stage process = eggs hatch into larva (nothing like parent) > larva molts and grows continuously > at a certain age larva undergoes one last molt and becomes pupa (body is rearranged) and adult structures grow from tiny buds and use the larva structures as raw materials. When metamorphosis is complete the adult emerges
Crustaceans = Largely marine group includes lobsters, shrimp, barnacles, crabs
Exoskeleton is calcified; body forms diverse
Head has a pair of compound eyes, two pairs of antennae, and 3 pairs of mouth parts: mandibles
In crabs, head and thorax (bearing pair of claws (chelipeds) and four pairs of walking legs) are fused into cephalothorax covered by a carapace (shell) that covers the gills
Abdomen segment equipped with swimmerets (aid in swimming); first pair enlarged in males for passing sperm to female
Fan-shaped tail ends in uropods and telson = swimming
Crabs feed food to the stomach through a gastric mill that grinds and filters before absorption
Pair of green glands (filters blood) excretes wastes at the base of antennae
Coelom reduced to a cavity around the reproductive system; hemolymph washes respiratory pigment (hemocyanin) through coelom sinuses (open circulatory system)
Ventral nerve cord and ganglia system similar to earthworm
Sexes are separate, gonads are ventral to pericardial cavity and sperm exit at the base of the 5th leg; ovaries open at the base of the 3rd walking leg; eggs are attached to swimmerets of the female
Gills > Tracheal Tubes
Ammonia > Uric Acid
Respiratory Pigments > Simple Diffusion
Contrasting locomotor and nervous systems
Antenna = touch + taste
Cheliped = Grabbing food + protection
Antennule = balance, touch + taste
Rostrum + head + thorax = cephalothorax
Mandible crush + chew food // Maxillae hold/pass food to move // maxilliped hold/pass food to mouth
Palps = hairs on mouth parts for touch + taste