Phylum Arthropoda: Part 1

The brain is formed by fusion of ganglia from the first 3 segments. Leaving the brain are numerous nerve tracts leading to the ___, ___, and ___ ___, which gives the brain a stellate appearance. TWO large nerves exit the posterior margin of the ___ encircling the ___; hence their name circumesophageal nerves. These two nerves come together behind the esophagus on the floor of the cephalothorax to form the ___ ___. This large ganglion is the result of the embryonic fusion of ___ pairs of thoracic and head ganglia. After the nerve cord leaves the ___ ___, it resembles the annelid nerve cord with its repetitive, ___ appearance.

antennae, antennules, compound eyes brain - esophagus subesophageal ganglion five subesophageal ganglion - segmented

crayfish- mandibular muscle

control motion of mandibles

What is a disadvantage of having a skeleton on the outside of the body?

limits body size

What do you suppose is the purpose/function of the telson?

locomotion/escape

crayfish- intestine

long tube passing through abdominal region in which nutrients are absorbed into the bloodstream for delivery to the body tissues

crayfish- antennae

longer, paired appendages on head modified for chemosensory and tactile reception

crayfish branching

most appendages exhibit some degree of branching - biramous nature of appendages - characteristic of Subphylum Crustacea

crayfish- gastric muscles

move cardiac chamber of stomach

What type of circulatory system does the crayfish have, open or closed? What anatomical evidence is present to support your answer?

o.c.s. - no veins/artery

arthropod circulatory system

open

crayfish- mouth

opening to digestive tract located on ventral surface of body

Although arthropod bodies are ___ like those of annelids, the ___ ___ often exist ONLY during ___ ___, and many eventually ___ into functional groups.

segmented; individual segments; embryological development; fuse

crayfish- antennules

shorter, paired appendages on head modified for chemosensory, tactile, and equilibrium reception

ovaries (crayfish- female)

site of egg production

testes (crayfish- male)

site of sperm production --> travel along each vas deferens to a sperm duct (located on animal's ventral surface at base of 5th pair of walking legs, which is @ 4th pair of periopods) --> sperm transferred to + held in seminal receptacle of female, and fertilization occurs externally as she releases eggs from her oviducts

crayfish- compound eyes

small, dark sense organs for detecting light + forming visual images

chelicerae

small, inward-folding ___ used to hold and chew food

crayfish- brain

small, radiate structure lying dorsal to the green glands; houses the majority of neural ganglia in the crayfish from the 1st 3 segments

crayfish- heart

specialized, muscular chamber (that is small, white, and angular) containing ostia (holes) to allow passive uptake of blood, which is delivered to the body tissues through arteries situated medially among the lobes of digestive gland tissue

How many compound eyes do horseshoe crabs have? simple eyes?

4. 2 simple eyes - 2 compound eyes

Subphylum Chelicerata

Class Merostomata (horseshoe crabs) Class Arachnida (spiders, daddy longlegs, scorpions, ticks, mites, tarantulas, chiggers)

Subphylum Crustacea, Class Malacostraca

(crayfish, lobster, crab, shrimp, pill bugs, barnacles, copepods, krill, isopod) -2 pairs of antennae -biramous appendages -1 pair of mandibles -2 pairs of maxillae -marine, freshwater, or terrestrial

Subphylum Trilobitomorpha *

-Class Trilobita (trilobites) -ALL extinct -(one of most prominent marine arthropod of Paleozoic era) -Cambrian explosion -> Permian period -distinct head, thorax, and tail -body divided into 3 lobes by 2 longitudinal furrows -biramous appendages -jointed appendages - chitinous exoskeleton - complex n.s. - highly flexible, segmented bodies divided into distinct regions - complete d.s. with specialized internal organs - compound eyes - single pairs of antennae - reproduce sexually -crawl along seafloor or within reefs, scavenging on organic debris or preying on smaller invertebrates -dug into ocean sediments to hunt for food and to conceal themselves from predators

Limulus (horseshoe crab)

-Subphylum Chelicerata, Class Merostomata -leathery, horseshoe-shaped exoskeleton divided into a cephalothorax (fused head/thorax) + an abdomen -on DORSAL side of cephalothorax - where lateral compound eyes and the simple eyes located -along its edge the abdomen has 6 pairs of spines + a long, spiked telson extending from posterior edge ventral surfaces of cephalothorax and abdomen: -cephalothorax (several pairs of modified appendages: chelicerae, pedipalps, walking legs)... -abdomen (numerous pairs of highly modified appendages- platelike structures called gill opercula that conceal book gills underneath)

Cambarus (freshwater crayfish)

-Subphylum Crustacea, Class Malacostraca -body divided into 2 main regions: cephalothorax + abdomen... + appendages present on both body regions -fusion of segments occurring during embryonic development -appendages modified for various functions -extending anteriorly from cephalothorax (pointed rostrum) -under rostrum are a pair of stalked, compound eyes + 2 pairs of antennae

Arthropod features:

-bilateral symmetry -triploblastic -true coelom -segmentation in many groups -jointed appendages * -exoskeleton *

male crayfish: copulatory swimmerets

-first 2 pairs of swimmerets modified for transferring sperm to female during copulation -larger club-shaped swimmerets than the other swimmerets + called copulatory swimmerets -sperm ducts visible at base of 5th pair of walking legs

crayfish- uropod + telson (tail)

-for swimming backwards -broad, fan-shaped region of body used for rapid movement and for directional control during leisurely locomotion -pair of appendages on last segment flattened into 2 uropods

arthropod exoskeleton?

-hard exoskeleton (chitin + protein secreted by and remains fused to epidermis) -though the segments appear to be separate, the ___ is a continuous structure with overlapping folds -___ is rigid in certain spots and flexible in others, allowing the body to bend and the appendages to move -___ provides support for body; provides an anchor for muscle attachment; protects animal from predators; impedes water loss

jointed appendages

-highly specialized -their numbers often are reduced in more advanced members of this phylum

Subphylum Chelicerata- Class Arachnida

-lack antennae + mandibles -cephalothorax bears first (single) pair of appendages called chelicerae; second (single) pair of appendages are pedipalps; + 4 pairs of walking legs -NO abdominal appendages or telson -most are carnivorous (except mites) - feed on liquefied food, which they digest externally by injecting enzymes into prey with fangs (modified chelicerae) -bite out of defense, + then usually after provocation -primarily terrestrial - book lungs (breathing) -small slits along ventral surface of abdomen (allow air to enter hollow compartment filled w/ numerous thin folds of body wall that resemble book pages) --- one side of each "page" exposed to air + inner layer of page (bathed in hemolymph, blood, to allow gas exchange across thin, moist surface)

Subphylum Chelicerata- Class Merostomata

-living relic... -lack antennae + mandibles -first pair of appendages are chelicerae -second pair of appendages are pedipalps -4 pairs of walking legs (scurry along ocean floor + nestle in sand for hiding) -spiked telson + platelike gill opercula present on the abdomen -marine -primarily nocturnal + swim on their backs in search of small mollusks/worms upon which to feed -2 protruding compound eyes above sediment (watching for danger) -example: horseshoe crab (Limulus)

hemocoel

-main body cavity of arthropod -consisting of blood-filled sinuses in the tissues -comprising part of "open circulatory system"

arthropod nervous system

-resembles that of Annelids, consisting of a dorsal brain + a single v.n.c. -as in Annelids, the ventral ganglia control much of the animal's behavior, any many arthropods can continue to carry out functions such as eating, moving, and copulation with brain removed from body.

crayfish- gills

-respiration -actually external -reside b/w 2 protective pieces of exoskeleton (the outer lateral side of carapace + a thinner/inner chitinous membrane) -___ attached to walking legs @ their proximal juncture

What are the TWO KEY CHARACTERISTICS that ALL ARTHROPODS share?

1. Segmented bodies 2. Jointed appendages

How many pairs of chelicerae do horseshoe crabs possess? How many pairs of pedipalps? How many pairs of walking legs?

1st pair of appendages is called chelicerae - 2 pairs of chelicerae + 2 pairs of pedipalps + 4 walking legs

crayfish- maxillae

2 sets of short, paired appendages located on ventral surface near mouth used to hold food while mandibles grind off bits/pieces to ingest bailing h2o from gill chamber

crayfish- maxillipeds

3 sets of paired appendages located on ventral surface near mouth used to manipulate food; holding/tasting/manipulating food

what 3 classes male up 95%+ of all arthropod species?

Arachnida, Insecta, Malacostraca

crayfish- Circumesophageal nerves

Branches of the ventral nerve cord that bifurcate at the base of the brain and encircle the esophagus before merging along the ventral surface of the crayfish just posterior to the esophagus

crayfish- walking legs (periopods)

Locomotion (walking on land and crawling across stream bottom)

crayfish- ventral nerve cord

Long, white "cord" located along the ventral surface of the body; contains large swellings of ganglia that handle the majority of coordination without intervention by the brain

crayfish- dorsal abdominal artery

Longitudinal blood vessel that distributes blood to the dorsal aspect of the abdomen

Limulus - horseshoe crab: a) compound eyes vs. b) simple eyes

a) true, image-forming eyes b) detect only shadows and differentiate b/w light and dark areas

crayfish- swimmerets (pleopods)

abdominal appendages modified for swimming; distal end of each swimmeret is biramous (has two branches)

crayfish- digestive glands

accessory digestive organs that secrete enzymes into the pyloric stomach to facilitate chemical breakdown of food

ecdysis (molting)

as the body grows larger inside, the old exoskeleton is shed periodically --> the soft, new exoskeleton is secreted and fixed in place before the old shell is shed -having a larger exoskeleton inside a smaller one --> the soft, new exoskeleton folds upon itself as it's being produced --> -after old shell is shed and the body is free of its former constraints...the new, larger shell slowly expands to its final size and harden in place

female crayfish: swimmerets

develop long, hairlike setae on edges that attach eggs to swimmerets during the egg-laying season after eggs laid (via the oviducts at base of 3rd pair of walking legs) and are attached to swimmerets, they are brooded by the female until they hatch the female's seminal receptacle located b/w the fifth pair of walking legs, often obscured from view by the ends of the folded swimmeret

The crayfish uses the chitinous teeth of the ___ ___ to grind food mechanically into smaller pieces for digestive enzymes secreted by the ___ ___ to act upon as the food moves into the ___ ___ of the stomach and then empties into the ___, where nutrient absorption occurs.

gastric mill - digestive glands - pyloric chamber - intestine

crayfish-mandibles

hard, chitinous mouthparts used to grind food into mouth

Arthropod excretory system

have specialized excretory organs for eliminating waste = malpighian tubules found in insects

Arthropod respiratory system

have specialized respiratory organs: gills (crustaceans), book lungs (arachnids), tracheae/spiracles (insects)

arthropods (grasshoppers + crayfish)

jointed appendages modified into: legs, pinchers (chelipeds), swimmerets, antennae, wings, + complex arrays of mouthparts

Crayfish - Chelipeds

large pinchers used for grasping food and for defense; "1st pair of walking legs" even though not used for this function

green glands (crayfish)

paired excretory organs (round glands that are highly folded tubule systems) found along the ventral margin of the head region; they release waste out of the crayfish through small pores in the ventral body wall sit in hemocoel hemolymph filtered by the tubules, and concentrated urine is stored in small bladders + released to outside through openings (nephropores)

crayfish- esophagus

passageway b/w mouth + cardiac portion of stomach

crayfish- rostrum

pointed region b/w eyes demarcating anterior end of body

exoskeleton: function

protection, support, an anchor for muscles, + a barrier to minimize water loss

How do the relative positions of the brain and the nerve cord in crayfish compare to the positions of the brain and the nerve cord in the earthworm? Is this evidence of common ancestry?

same positioning - after the nerve cord leaves subesophageal ganglion, it resembles the annelid nerve cord with its repetitive, segmented appearance

beating of gill opercula aids in

swimming + aerating book gills in horseshoe crabs

crayfish- anus

terminal point of digestive system located on ventral surface of telson

crayfish- cardiac chamber of stomach

thick-walled, anterior portion of the stomach containing gastric mill-chitinous teeth that grind food into a liquefied mush

The larger the body inside, the ___ and ___ the exoskeleton must be to support the body weight + bear the strain of muscular contractions.

thicker + heavier

crayfish- Pyloric chamber of stomach

thin-walled chamber where chemical digestion of food occurs

T/F: *Arthropods are grouped w/ roundworms in the lineage Ecdysozoa, due to this shared trait (ecdysis)*

true

T/F: Arthropods are first animal group to evolve the ability to fly, giving them access to 3-D terrestrial landscape devoid of any other competitors.

true

T/F: During the evolution of arthropods, departure from the ancestral aquatic lifestyle favored the development of characteristics that permitted successful adaptations to the many ecological hurdles associated with terrestrial living, such as the need for stronger support systems, smaller body size, and reproductive/skeletal/digestive/excretory/respiratory systems that conserved water.

true

T/F: In an animal encased in such a rigid suit of armor, the coelom can play no major role in locomotion, and in the course of arthropod evolution, the coelom has become greatly reduced.

true

T/F: Phylum Arthropoda is the LARGEST in the animal kingdom.

true

T/F: HOWEVER, large exoskeletons are simply too heavy to move around. -terrestrial arthropods -aquatic arthropods

true -terrestrial: rarely larger than a few inches long -aquatic: gain some relief from this constraint b/c of the buoyancy of water, + rarely grow larger than a few feet

jointed appendages: function

used for walking, flying, feeding, reproducing, sensing the environment

Where on the body surface of the crayfish are the external openings for the excretory organs (green glands) located?

ventral to the cardiac stomach + situated on each side of it

Arthropods have an open circulatory system similar to bivalves...

when the heart contracts, special valves prevent blood (hemolymph) from escaping through ostia, and blood is directed out of heart along arteries - once the hemolymph reaches tissues, it leaves the vessels and percolates through open spaces in hemocoel - the blood returns to heart by flowing to the pericardial space surrounding the heart and re-enters the heart through pores/ostia on its surface

Are the crayfish antennae biramous? Are the antennules biramous?

yes - no