Transcript Phylum Arthropoda - University of Evansville

Phylum Arthropoda
Similarities between Annelids and Arthropods
• Arthropods are metameric and their segments have appendages
• Nervous system with ventral nerve cords
Phylum Onychophora
Annelid-like
• Segmented; unjointed
appendages; similarity in structure
of the body wall; segmentally
arranged nephridia; pigment-cup
ocelli
Arthropod-like
• Reduced coelom, open
circulatory system, tracheal
system; soft cuticle composed of
chitin
Peripatus, a small, nocturnal form found
among the leaf-litter of tropical forests of
South America.
The fossil record indicates that onychophorans have not
changed much in 500 million years.
The Onychophoran Aysheaia from the Cambrian.
A lobe-limbed, segmented animal. Also note the spines on the legs.
The head end has a pair of tapering limbs with spines, and three small
projections near the mouth. Traces of the digestive tract can also be
seen.
Phylum Tardigrada or “water bears” also have features in common
with both annelids and arthropods
Annelid-like
• Unjointed (8) legs; annelid-type
nervous system
Arthropod-like
• Presence of a cuticle
(nonchitinous) that is periodically
molted; similar attachment of
muscle fibers to exoskeleton
• One of the most interesting features of tardigrads is their
ability to undergo cryptobiosis
Arthropod Taxonomy: Overview
The arthropods evolved along four main lines, which most
zoologists recognize as 4 distinct subphyla
1. Trilobita - extinct trilobites
2. Chelicerata - horseshoe crabs, spiders, ticks, mites, and some
extinct groups
3. Crustacea - crabs, lobsters, shrimps, barnacles
4. Uniramia - insects, centipedes, millipedes
The Arthropod Exoskeleton
• Epidermis secretes an external skeleton called the exoskeleton
• Advantages of possessing an exoskeleton:
– provides strong support
– provides rigid levers that muscles can attach to and pull
against
– offers protection
– serves as a barrier to prevent internal tissues from drying out;
important because many arthropods live on land
– serves as a barrier to prevent infection
Structure of the Exoskeleton
• Composed of the polysaccharide chitin and protein - glycoprotein
• Outer surface called the epicuticle; contains waxes
• The thicker portion is called the procuticle:
• exocuticle
• endocuticle
• In the exocuticle, the glycoprotein chains are cross linked;
process is called tanning
epicuticle
exocuticle
procuticle
endocuticle
epidermis
Molting
• In order to grow the arthropod must shed its exoskeleton,
and secrete a new and larger one - molting or ecdysis.
Jointed Appendages
• Exoskeleton divided into a number of plates and cylinders
• At the junction point between plates and cylinders, the exoskeleton remains
thin and flexible; these are the joints
• Jointed appendages allows arthropods to move efficiently and quickly
• Muscles are integral to arthropod movement; they attach to the inner side of
the exoskeleton; they often function as a lever system
Arthropod joint
Vertebrate joint
Specialized Arthropod Segments: Reduction in Metamerism
• The evolution of the arthropods witnessed a reduction in
metamerism
• The arthropods evolved modified groups of segments (e.g.,
segments became lost, some fused together
•The fusion of groups of segments into functional groups is called
tagmatization
• In so doing, various appendages on segments became specialized
for functions other than locomotion, e.g. prey capture, filter feeding,
sensing various kinds of stimuli, gas exchange, copulation, etc.
Arthropod Respiratory Advances
• Special respiratory structures allow the arthropods to
metabolize more efficiently and thus move rapidly
• High metabolic rates require rapid oxygen delivery, and
arthropods can accomplish this with respiratory organs
that have a large surface area for collecting oxygen
quickly
Gills
• Many aquatic arthropods (crabs and lobsters) have gills, which are
typically modifications of appendages or outgrowths of the body wall
- folds of tissue with a large surface area
Tracheae
• Gas exchange organs among terrestrial arthropods is usually
internal; invaginations of the integument
• Insects have
tracheae, branching
networks of hollow air
conducting tubes such
that air is sent to every
cell in every tissue
Book Lungs
• Spiders have book lungs, chambers with leaf-like plates for
exchanging gases; air flows over the plates and blood flows through
them
Acute Senses
• Arthropods have a well-developed nervous system that is of the
same overall design as the annelids; anterior brain and a double,
ventral hollow nerve cord.
• The sensory receptors of arthropods are usually associated with
modifications of the chitinous exoskeleton
• The head usually bears various kinds of sense organs (e.g.
antennae) with extreme sensitivity
Acute Senses cont.
•Many arthropods have compound eyes - eyes that are composed of
many visual units called facets (ommatidia); capable of color vision
and detecting the slightest movements of prey or predators
• Some eyes are simple eyes with only a few photoreceptors; however,
they are capable of forming crude images
Digestive System
Divided into 3 main regions: foregut, midgut, and hindgut
• Foregut and the hindgut are lined with chitin
• Foregut is involved with ingestion, mechanical breakdown, and
storage
• Hindgut is involved with water absorption and formation of the feces
• Midgut is not lined with chitin; involved with digestion and
absorption
• Outpockets (e.g. digestive glands) increase the surface area for
digestion and absorption
Internal Transport and Excretion
• Open circulatory system
• Many crustaceans possess an excretory organ
called the green gland (antennal gland), which
filters fluid from the blood
• Most insects and spiders have a excretory
system called malpighian tubules
Reproduction
• Sexes are separate; fertilization is external in aquatic forms,
internal among the terrestrial forms
Arthropod Diversity
Subphylum Trilobita
• A group of extinct marine arthropods.
• Ranged in size from a few millimeters
up to 75 centimeters.
• Body divided into three parts:
– cephalon (head), a single plate
made up of several fused segments
– thorax, consists of a number of
segments hinged together
– pygidium (tail), also segmented,
but like the head, fused together
into a single plate.
• Compound eye, composed of radially
arranged visual units
Subphylum Chelicerata
• Lack antennae
• Body is usually composed of two regions: cephalothorax and
abdomen
• Cephalothorax is usually covered dorsally by the carapace
• Six pairs of appendages: first pair are modified feeding structures chelicerae
• Second pair are called pedipalps
• Four additional pairs of
appendages are walking legs
• No abdominal appendages
• Some have compound eyes,
usually have simple eyes
capable of forming crude
images.
Class Meristomata (e.g., Horeshoe crabs)
• Marine chelicerates, common off of the Atlantic and Gulf coasts
• Large dorsal carapace bearing compound eyes
• Possess chelicerae, pedipalps, and 4 pair of walking legs (all but
the last pair are chelate
• Abdomen terminates in a long tail called the telson; used to turn
the animal right side up
• Possess a series of gill plates called book gills
Class Arachnida
• Among spiders, the cephalothorax and abdomen shows no external
segmentation; tagma are joined by a narrow pedicel
• Respiration is accomplished via book lungs, tracheae, or both
• Usually have 8 simple eyes; at the very least they detect motion; for some of
the predatory forms, they are capable of forming crude images
• Many species have evolved poison glands associated with the chelicerae
Black widow
Brown recluse
Class Arachnida cont.
• Many of the spiders and mites
are capable of producing silk;
produced by silk glands that
open to the exterior part of the
abdomen through spinnerets
• Silk is used to build webs for
trapping prey, nests which serve
as retreats, and egg cases; it is
also used to form a dragline
• Most spiders are predaceous
and have all kinds of sensory
hairs and relatively welldeveloped eyes for motion
detection
Orb web construction
Prey capture among the spiders
• Some species are cursorial predators, those
that stalk and ambush their prey; they usually
have well-developed eyes
•Others are web building spiders, those
that construct various kinds of webs made
of silk to trap their prey
• Eyes are not as well developed as cursorial
predators, but they have a battery of sensory
hairs for detecting vibrations
Jumping spider
Grass spider
SubPhylum Crustacea
• Possess 2 pair of antennae: First pair is homologous to those of
insects; second pair is unique to the crustaceans
• Second antennae have various functions, including sensory,
locomotion or feeding.
• The head bears a pair of compound eyes and 3 pairs of mouthparts: a
pair of mandibles, and 2 pairs of maxillae; used for food handling
• Trunk varies considerably among
classes
• Primitively, the first three pairs of
thoracic segments are maxillipeds;
function in handling food
• Also, there are usually 5 pairs of
appendages strengthened for
walking (walking legs) and
protection (chelipeds, pincer-like
claws)
SubPhylum Crustacea cont.
•Abdomen is also highly variable, but it is primitively large
• Groups with a well-developed abdomen usually possess six pairs
of appendages: Five pairs of structures called swimmerets
(=pleopods); one pair of structures called uropods,
• Uropods together with the terminal telson form a tail fan than can
serve as rudders during locomotion
SubPhylum Crustacea cont.
•Primitively many of the appendages of the crustaceans are
biramous: there is an outer exopod and an inner endopod
• They usually have an extremely hardened exoskeleton, which is
impregnated with calcium carbonate - carapace
SubPhylum Crustacea cont.
• The primitive larva of the crustaceans is called the nauplius larva
• It has an unsegmented body, a frontal eye, and 3 pairs of
appendages, representing the 2 pairs of antennae and the mandibles
Crustacean Diversity
Ostracod
Copepod
Fairy shrimp
Water flea
Fish louse
Barnacles are Crustaceans!
SubPhylum Uniramia
• Single pair of antennae
• First pair of feeding appendages are mandibles
• There are one or 2 pairs of maxillae
• Number of legs vary from 3 pair to many pairs; they are unbranched
or uniramous
SubPhylum Uniramia cont.
Class Chilopoda (Centipedes)
• Serial segmented, flattened body and each segment has a pair of jointed
appendages
• Active predators, killing their prey with poison claws, which are
modified legs on first segment
SubPhylum Uniramia cont.
Class Diplopoda (Millipedes)
• Serially segmented, rounded body with 2 smaller pairs of legs per
segment
• Slow moving; feed on decaying plants
Class Insecta
• Body is divided into 3 parts: the head, thorax and the abdomen.
• Head has one pair of antennae, a pair of compound eyes and
several sets of simple eyes
• Mouthparts: a pair of mandibles, and two pairs of maxillae
• One pair of maxillae are fused together to form a lower lip labium
• An upper lip - labrum - formed from an extension of the head
Class Insecta cont.
• Mouthparts are highly modified depending on the group you are
discussing
• Mosquitoes have pointed mouthparts for piercing and sucking;
grasshoppers have mouthparts that are well adapted for chewing;
butterflies for siphoning; flies for sponging
Class Insecta con’t
• Thorax is composed of 3 segments and each one has a pair of legs;
the last two segments also have a pair of wings.
• Wings of insects are modified portions of the exoskeleton
• 1st pair is usually tough and leathery and fold over the inner pair for
protection.
• Abdomen does not have appendages; terminal portions do harbor the
reproductive structures
Most insects undergo metamorphosis
Incomplete Metamorphosis (Hemimetabolous)
• Early developmental stages are very similar to the adults; only the
wings and the reproductive structures gradually develop
• The immature stages are called nymphs
• Thus development is egg----> nymphs ----> adult
Complete Metamorphosis (Holometabolous)
• Each of the
developmental stages is
structurally and
functionally very
different
• The egg develops into
an immature larva; eats
voraciously
• Followed by a
transitional stage pupa, contained within
cocoon
• Metamorphosis occurs
within the pupal
exoskeleton, yielding a
sexually mature adult