Origins

Question 1

Impact on humans

Answer 1

Provides food and ecosystem services such as pollination. They do however also spread disease and damage crops.

Question 2

Why so many arthropods?

Answer 2

Success is probably due to small size allowing them to occupy a greater variety of ecological niches and smaller actual physical niches. Also due to water conservation techniques, water conserving excretory system and tracheal breathing.

Question 3

Diversity of Arthropoda

Answer 3

Non insect arthropods make up around 20% of all arthropods. Arthropods mainly consists of beetles, flies, butterflies, moths, bees, wasps, spiders and crustaceans.

Question 4

Six Arthropoda Phyla

Answer 4

Tardigrada
Pentastoma
Onychophora
Chelicerata 
Uniramia 
Crustacea

Question 5

Lobopod arthropods

Answer 5

Soft bodied, non jointed legs with no exoskeleton. Have fleshy appendages along their bodies.
Consists of the phyla tardigrada, pentagonal, Onychophora.

Question 6

Tardigrada and Onychophora

Answer 6

May be survivors of the lobopod proto arthropods of the Cambrium.
Onychophora have bits of chitin embedded in their skin, and Tardigrades have external cuticular plates.

Question 7

Pentastoma

Answer 7

Lobe limbs may be secondary, and they have been considered a degenerate Crustacea.

Question 8

Controversy of the phylogeny of Arthropoda

Answer 8

The worms and arthropods shared a common ancestor in Cambrian. Both bodies would have had a number of serially repeated legs.
At one stage Onychophora were thought to be and intermediate form between the worms and the Arthropoda, but molecular evidence suggests that they are a sister group to Arthropods.

Question 9

Cambrian

Answer 9

550 million years ago

Question 10

Onychophora Features

Answer 10

It has a segmented body, with a soft cuticle and chitin similar to that of arthropods. It moult and has tarsal claws, antennas, a haemocoel, mandibles and a trachea which are all common in arthropods as well. However the features it shares with annelids are a segmented body, soft cuticle and paired nephridia.

Question 11

Nephridia

Answer 11

A tubule open to the exterior which acts a s an organ of excretion or osmoregulation. It typically has ciliated or flagellated cells and absorptive walls.

Question 12

True Arthropods

Answer 12

Chelicerata
Uniramia
Crustacea

Question 13

Panarthropods (True Arthropods and Lobopods)

Answer 13

Mostly a monomeric body plan, haemocoelic body cavity, but with serially repeated legs ending in claws, and usually a hard exoskeleton and ventral nerve cord. Onychophora and Tardigrada have body designs intermediate to that of Annelids and true Arthropods.

Question 14

Metameric

Answer 14

Consisting of several similar segments.

Question 15

Monomeric

Answer 15

Comprising of a single segment.

Question 16

Basic body design of an arthropod

Answer 16

The metameric part of the body contains segmental arrangement of all of the organ systems associated with the limbs. Non leg associated organs (excretion, and reproduction) are not segmentally arranged or repeated. This basic pattern has undergone considerable change in the various groups, by means of fusion of segment, specialization of segments and loss of appendages etc. Apart from the cuticle, arthropods have few common features (compound eyes absence of cilia). This suggests that the arthropod condition might represent a type of body design achieved by unrelated organisms, not a monophyletic assemblage.

Question 17

Jointed hard exoskeleton and moulting

Answer 17

Characteristic of true arthropods. Exoskeleton is made of chitin and protein and sometimes impregnated with calcium carbonate. It restricts growth, thus moulting is required, with rapid growth in between. From a phylogenetic perspective the exoskeleton probably arose as bands of chitin across a body in an organism which had a hydrostatic skeleton such as in Tardigrades. Some arthropods still use a haemocoel to extend the legs.

Question 18

Moulting in true Arthropods

Answer 18

The old exoskeleton is partially reabsorbed before the moult, then is shed. A soft animal emerges which is vulnerable and thus grows a new exoskeleton beneath the old one. The new skeleton takes a while to harden allowing the organism to grow in size.

Question 19

Ancient arthropods

Answer 19

In the Cambrian there were many diverse Lobopods and a range of bizarre Arthropods. Few of these survived that period, and only five major groups survived beyond the Devonian.

Question 20

Devonian

Answer 20

350 million years ago.

Question 21

Hallucinogenia

Answer 21

One of the strangest animals to have existed, only known from Cambrian fossils that are missing heads. Reconstruction was made after event discovery of fossils with heads.

Question 22

Trilobita

Answer 22

Survived for 300 million years, but went extinct in the Permian.

Question 23

Classes of Chelicerata

Answer 23

Merostomata
Arachnida
Pycnogona

Question 24

Orders of Arachnida

Answer 24

Scorpiones
Solpugida
Opiliones 
Acariformes
Araneae

Question 25

Phylum Chelicerata

Answer 25

The body is divided into the anterior prosoma, which is covered by a dorsal carapace. The posterior opisthosoma lacks legs, and generally also any appendages. Appendages are uniramous, and compound eyes acre typically absent. Chelicerae form mouthparts but parts of other limbs bases near mouth may assist in crushing food. It has a non calcareous exoskeleton.

Question 26

Opisthosoma

Answer 26

Abdomen

Question 27

Prosoma of Chelicerates

Answer 27

Acron and six appendage bearing segments.

Question 28

Horseshoe Crabs

Answer 28

Probably the ancestors of the remaining Chelicerata. They have external gills on appendages of the opisthosoma.

Question 29

Chelicerata Book lungs

Answer 29

Resembles external gills that have been invaginated. Resembles a stack of plates, but in some they are tube like and form sieve like/tube trachea.

Question 30

Debate on the evolutionary relationships between the Hexapoda, Myriapoda, Crustacea and Chelicerata

Answer 30

Many do not support the phylum uniramia, and the most recent evidence suggests that Hexapoda and Crustacea may be sister groups and form the Pancrustacea. In this system, the Myriapoda are either related to the Pancrustacea or the Chelicerata.

Question 31

Mandibulata model vs Paradoxopod model

Answer 31

Both the Mandibulata and paradoxopoda models propose a pancrustacean Claude consisting of Hexapods and Crustaceans as closely related sister groups. They differ in their treatment of the Myriapods and Chelicerates. Paradoxopoda has Myriapods and Chelicerates as closely related sister groups whilst Mandibulata has Myriapoads as a sister group to the Pancrustaceans and the Chelicerates as a distant, early branching Claude of arthropods. While the Mandibulata is supported by taxonomy (crustaceans, Hexapods, Myriapods have mandibles and Chelicerates have chelicerae), Paradoxopodia is primarily supported by recent mitochondrial molecular phylogenetics. Also under contention is the relationship between crustaceans and Hexapods within the increasingly well supported Pancrustacean clade. It has not yet been settled if the two are distinct sister groups or if the Hexapods are nested wishing the Crustaceans. The latest studies which used a wider number of species in the analysis, plus a greater number of genes supports the hypothesis that Hexapoda are nested within Crustacea.