L5 - Arthropods Flashcards
What are the subphylum of arthropoda?
Crustacea, Hexapoda, Myriapoda, Cheliriformes
What is the abundance phylum Arthropoda?
Estimated that there are approximately 1.5 million, 5.5 million, and 7 million species of beetles, insects, and terrestrial arthropods. Crustaceans estimated at over 50k, but as they are mostly aquatic this is almost an underestimate. Between 75-80% of all other animals are arthropods.
What is the phylum Arthropoda?
Bilaterally symmetric, triploblastic protostomes. Each body segment has a pair of segmented, jointed, ventrally attached appendages ; some have evolved into mouthparts. Trend is towards reduction in number of segments. Cephalon (head) usually has a pair of compound eyes. Size - microscopic up to 4m long. Cuticle forms an exoskeleton of plates (sclerites)
What is the phylum Arthropoda? pt 2
No true hydrostatic skeleton, no repeating organs in each segment, no cilia. Seperate sexes (usually), immature stages represented by varying numbers of larval forms. Tagmatisation (tagmosis). Body divided into functional groups of segments called tagma (pl. tagmata). Minimally divided into head (cephalon) and trunk, which is usually subdivided e.g. crustacean trunk divided into peraeon (thorax) and pleon (abdomen)
What is the phylum Arthropoda? What is the Bauplan?
The arthropods are taxonomically joined together by a single body plan, which is the end result of a process known as arthropodisation. Previously, people thought that this body plan evolved independently in each of the subphyla, and that the similarities were due to the presence of an exoskeleton. Current evidence points to a single common ancestor to all the arthropods, and that single common ancestor had an exoskeleton. The arthropod exoskeleton provided good protection from attackers, but is also relatively inflexible and heavy.
What is the phylum Arthropoda? How is the arthropod cuticle hardened and what are some of the consequences?
Hardened by sclerotisation (tanning) - crossbonded protein molecules. In some (e.g. Crustaceans) hardening taken further by mineralisation - depositing of calcium carbonate into outer regions of procuticle.
Consequences
- Very strong and protective against predation & water loss
- Must be in sections to allow movement.
- Restricts growth, therefore have to moult
-Relatively heavy which restricts locomotion on land.
- Unless it is very thin, respiration, excretion and osmoregulation are restricted
- New methods of sensing the external environment are needed
What is the phylum Arthropoda? What does each somite (body segment) have?
A large dorsal sclerite called a tergite (tergum)
A large ventral sclerite called a sternite (sternum)
Side regions are unsclerotised & flexible, called pleura (pleuron) where limbs articulate.
Body cavity is open haemocoel, organs bathed in haemocoelic fluid or blood
What is the phylum Arthropoda? What is the cuticle divided into?
Cuticle is divided into epicuticle and procuticle. Procuticle (layers of protein and chitin) subdivided into exocuticle and endocuticle. Endocuticle can be calcified or uncalcified ; secreted by epidermis. Cement layer : lipoprotein protects against bacteria. Waxy layer : best developed in insects and arachnids ; prevents water loss. These two layers isolate remainder of the cuticle from external environment ; critical in terrestrial arthropods. Remainder called cuticulin layer ; mainly protein.
What is the phylum Arthropoda? What is the arthropod limb joint?
Sclerites are joined at articulation points by thin and flexible cuticle to allow for movement ; called articular membranes. Usually, each articulation is bridged by one or more pairs of antagonistic muscles. Muscles may be attached to inward projections of sclerites called apodemes. There may be points of contact or bearing surfaces between sclerites called condyles
What is the phylum Arthropoda? Growth?
Exoskeleton is rigid so no gradual growth possible. Occurs in steps after shedding exoskeleton ; known as moulting. Controlled by the hormone ecdysone. Moulting is therefore known as ecydsis (final shedding of old cuticle). Intermolt stages known as instars.
What is the phylum Arthropoda? What is the process of moulting?
Enzymes digest old endocuticle, separating exoskeleton from epidermis. Epidermis secretes new, soft cuticle beneath existing exoskeleton. Old cuticle splits along pre-determined lines. Animal takes in air or water and body swells, enlarging the new cuticle. Cuticle then hardened by sclerotisation. All cuticular linings are lost during ecdysis, including surfaces such as foregut, hindgut, eyesurfaces etc. Dangers include difficulty withdrawing from old cuticle, prone to predation before new cuticle hardens
What is the phylum Arthropoda? What specific thing are arthropods and what does this mean?
They are ecdysozoans, and ecdysis is a complex process that is regulated by hormones, but here is a simplified outline of the main features. Tissue growth, intermoult (instar), digestion of old endocuticle, secretion of new cuticle, old cuticle splits and sheds, moult, body swells (air/water), new cuticle hardens, new exoskeleton.
What is the phylum Arthropoda? What are they made up of?
7 articles, or podites
What is the phylum Arthropoda? What are the two processes called?
Uniramous, biramous
What is the phylum Arthropoda? What is uniramous?
Single process : endopod only, usually associated with walking
What is the phylum Arthropoda? What is biramous?
Two processes : endopod and exopod (can occur in crustaceans and trilobites) ; usually associated with swimming
What is the phylum Arthropoda? How does respiration occur?
Most arthropods have specialised systems, for gas exchange, which all function on the same two priniciples, which is to produce a high surface area to volume ratio, whilst also keeping the gas exchange organ moist. This is particularly challenging for the terrestrially adapted arthropods, such as insects, arachnids, and woodlice
What is the phylum Arthropoda? Excretion?
There are two methods of excreting waste and osmoregulation : nephridia and malphigian tubules. Nephridia take waste from the coelom and excrete it via special glands. Crustacea - antennal/maxillary glands, Arachnids - coaxal glands. Malphigian tubules, which are attached to the stomach and lie inside the body cavity. Arachnids, myriapods, insects, tardigrades.
What is the phylum Arthropoda? Vision?
Arthropods eyes are very different to the camera eyes of vertebrates and some molluscs. The simplest kind of eye is known as an ocelli, which is composed of a single lens and does not have a retina. More complex eyes are known as compound eyes, as they are composed of thousands of repeating ommatidia, each of which is a self-contained photoreception unit, consisting of a cornea, lens and photoreceptor cells.
What is the phylum Arthropoda? Summary?
Everything in the arthropods is defined by the exoskeleton. There are 4 subphyla within the arthropoda. Specialised physiological adaptations allow this phylum to colonise the aerial, aquatic, and terrestrial environment.
What is the phylum Arthropoda? What is the Subphylum Crustacea?
70,000 described species, maybe 500,000 undescribed. Crabs, lobsters, shrimps, prawns, barnacles, krill. Body usually of 3 tagmata - head (cephalon), thorax and abdomen - Cephalic shield or carapace usually present. 5 pairs of cephalic appendages 1. Mandibles, 2. 1st maxillae (maxillules), 3. & 4. 2 pairs of antennae, 5. 2nd maxilla. Usually compound eyes or simple ocelli, marine, freshwater and terrestrial, dominate marine environment. Size - from 100um to crabs with 4m legs
What is the phylum Arthropoda? What is the Subphylum Crustacea? What is the class Remipedia?
Only 12 species discovered since 1970s, found in tropical sea caves
What is the phylum Arthropoda? What is the Subphylum Crustacea? What is the class Cephalocarida?
Only 10 species, living in benthic marine sediments
What is the phylum Arthropoda? What is the Subphylum Crustacea? What is the class Branchiopoda?
1000 spp in 3 orders, Anostraca, Nostraca, Diplostraca. Mostly small freshwater shrimp - like animals ; often short lived. Produce drought resistant eggs