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# BIOL 108 Introduction to Biological Diversity
## Topic 24: Arthropoda
> Lecture A2
> Yan-yin Wang
Introduction to Arthropoda
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
Phylogeny of animals with characteristics mapped.
True tissues
(1) Bilateral
symmetry
(2) Triploblastic germ layer
Radial
symmetry
Clade Ecdysozoa contains Nematoda and Antrhopoda.
Arthropoda
Most animal species belong to Arthropoda.
~ 1 million extant species documented and ~ 3 to ~ 30 million species estimated to exist.
Vast body forms and adaptations across terrestrial, freshwater, marine, and aerial environments.
Many taxa are ecologically important decomposers and pollinators. Arthropod Origin and Evolution
> https://www.flickr.com/photos/jsjgeology/15270893371
> # Trilobite Asaphus kowalewski (top) and anatomy of the honeybee (bottom).
Arthropods originated in the Cambrian explosion event.
Arthropod body plan:
A segmented body
Jointed appendages
A hard exoskeleton
Evolutionary themes of arthropods
A decrease in the number of body segments
An increase in appendage specialisation
Evolutionary transitions may be enabled by altering Hox gene expression.
> https://hbrc.ca/honey-bee-anatomy/
Arthropod Characteristics
Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
# Segmented body of grasshopper (top) and surface anatomy of the lobster (bottom).
1. Segmented body
All arthropod embryos are segmented.
The last common ancestor of all arthropods likely had numerous undifferentiated segment with functional limbs.
Body segments and limbs are arranged into functional units called tagmata with specialised functions.
Tagmatisation : Fusion of body segments. Abdomen
Briggs, D. E. (2005). Evolving form and function: fossils and development . Peabody Museum of Natural History, Yale University. Arthropod Characteristics
Vasconcelos, P., Carvalho, A. N., Pil, D., Pereira, F., Encarnao, J., Gaspar, M. B., & Teodsio, M. A. (2019). Recent and consecutive records of the Atlantic blue crab (Callinectes sapidus Rathbun, 1896): rapid westward expansion and confirmed establishment along the Southern Coast of Portugal. Thalassas: An International Journal of Marine Sciences , 35 , 485-494.
# Jointed paired appendages in the Atlantic blue crab (top) and the mouth part of mosquitos (bottom).
2. Jointed paired appendages
Jointed appendages are versatile anatomical parts with specialised functions.
Functional specialisation likely originated from long, evolutionary modifications.
Examples of specialised appendages:
Head appendages: feeding, sensory.
Thoracic appendages: locomotion.
Abdominal appendages serve a variety of functions, e.g. swimming or reproduction.
Dixon, A. R., & Vondra, I. (2022). Biting innovations of mosquito-based biomaterials and medical devices. Materials , 15 (13), 4587. Arthropod Characteristics
https://marine-freshwater.fandom.com/wiki/Coconut_Crab
# Exoskeleton in the coconut crab (top) and Zn/Mn biomineralization in arthropods (bottom).
3. Sclerotised cuticle composed of chitin.
Cuticle forms hard, lightweighted, external skeleton (i.e., exoskeleton).
Protective structure.
Rigid surface for muscle attachment.
Cuticle sclerotization sometimes involves biomineralisation.
Incorporation of minerals such as calcium carbonate in the exoskeleton.
Schofield, R. M. S., Bailey, J., Coon, J. J., Devaraj, A., Garrett, R. W., Goggans, M. S., ... & Nesson, M. H. (2021). The homogenous alternative to biomineralization: Zn-and Mn-rich materials enable sharp organismal tools that reduce force requirements. Scientific Reports , 11 (1), 17481. Arthropod Characteristics
Daly, I. M., How, M. J., Partridge, J. C., Temple, S. E., Marshall, N. J., Cronin, T. W., & Roberts, N. W. (2016). Dynamic polarization vision in mantis shrimps. Nature communications , 7(1), 12140.
# Cephalisation in the mantis shrimp.
4. Prominent cephalisation
The head is formed by fusion of several body segments.
Neural ganglia are centralised.
Complex organs (e.g., compound eyes, antennae). Arthropod Characteristics
> https://islandtutors.co/private-interactivecontent/adaptations-breathing/
# Gills in crab (top) and book lung in arachnids (bottom).
5. Reduced coelom
Primary internal cavity is the haemocoel, which supports internal organs and functions as a hydrostatic skeleton.
6. Open circulatory system
The circulatory fluid called haemolymph is circulated in haemocoel.
Presence of various respiratory systems.
Diffusion in small, aquatic arthropods
Gills in crustaceans
Book lung in arachnids
> https://www.asianarachnology.com/glossary/book-lung/
> Kamenz, C., Dunlop, J. A., & Scholtz, G. (2005). Characters in the book lungs of Scorpiones (Chelicerata, Arachnida) revealed by scanning electron microscopy. Zoomorphology ,124 , 101-109.
Diversity of Arthropoda
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
> # Phylogeny of Arthropoda.
Three lineages are supported by morphological and molecular evidence:
Subphylum Chelicerata
Subphylum Myriapoda
Clade Pancrustaceans
The phylogeny of arthropods is an ongoing debate:
Shared morphological characters suggest a close relationship between myriapods and hexapods.
Molecular evidence suggests crustaceans to be a paraphyletic group, and hexapods are closely related to crustaceans. Arthropoda Chelicerata
> https://peabody.yale.edu/explore/collections/invertebrate-paleontology/eurypterids-sea-scorpions
# A fossil eurypterid (top) and juvenile horseshoe crab (bottom).
Chelicerates include taxa such as spiders, scorpions, and mites.
Chelicerata likely originated as marine animals in the Early Paleozoic Era.
Early chelicerates in the fossil record were large, widespread eurypterids (water scorpions).
Only small portions of marine chelicerate taxa survive now, including the horseshoe crabs.
> https://sccf.org/blog/2024/08/02/report-horseshoe-crab-sightings/
Arthropoda Chelicerata
> https://www.peacockspider.org/undescribed-peacock-spiders#/maratus-sp-unnamed-wa-87/
Peacock spider (top) and anatomy of a typical spider (bottom).
Characteristics of chelicerates
1. Presence of two main tagmata
Anterior cephalothorax
Covered by a dorsal exoskeleton section called carapace.
Six pairs of appendages
Chelicerae, pedipalps, and four pairs of legs
Absence of antennae
Uniramous appendages
Posterior abdomen
Absence of appendage
Houses digestive and reproductive organs.
> https://australian.museum/learn/species-identification/ask-an-expert/what-is-a-spiders/
Arthropoda Chelicerata
Cabra-Garca, J., & Hormiga, G. (2020). Exploring the impact of morphology, multiple sequence alignment and choice of optimality criteria in phylogenetic inference: a case study with the Neotropical orb-weaving spider genus Wagneriana (Araneae: Araneidae). Zoological Journal of the Linnean Society , 188 (4), 976-1151.
# Diversity of chelicerae in spider.
Characteristics of chelicerates
2. Presence of chelicerae as mouthparts
Chelicerae are modified appendages positioned before the mouth.
Chelicerae are homologous to antennae in other arthropods.
Chelicerae are composed of two or three segmented fangs or pincers.
Chelicerae function for predation and defence. Arthropoda Myriapoda
Myriapods include millipedes and centipedes.
Only terrestrial myriapods are known.
Myriapods likely originated in the Cambrian Period.
Myriapods were likely one of the earliest, terrestrial animal groups.
> Fernndez, R., Edgecombe, G. D., & Giribet, G. (2018). Phylogenomics illuminates the backbone of the Myriapoda Tree of Life and reconciles morphological and molecular phylogenies. Scientific Reports ,8(1), 83.
# Examples of extant myriapods. Arthropoda Myriapoda # head of the giant centipede in anteroventral view (top) and the tracheal lung in centipede (bottom).
Characteristics of myriapods
1. Body plan is less tagmatised than chelicerates.
Head has simple eyes (ocelli), three pairs of mouth parts, and one pair of antennae.
Presence of numerous pairs of jointed, uniramous legs.
2. Respiration via tracheal system
Air enters the trachea via opening called spiracles.
Air circulate through the body via tracheoles and haemolymph without oxygen transporter (O 2).
3. Direct development without larval stage
> https://www.stancsmith.com/blog/awesome-animal-giant-centipede
> Hilken, G., Rosenberg, J., Edgecombe, G. D., Blml, V., Hammel, J. U., Hasenberg, A., & Sombke, A. (2021). The tracheal system of scutigeromorph centipedes and the evolution of respiratory systems of myriapods. Arthropod structure & development ,60 , 101006.
Arthropoda Pancrustacea
Following molecular evidence, Pancrustacea includes the paraphyletic Crustacea and the monophyletic Hexapoda.
Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
# Phylogeny of Arthropoda.
# Hermit crabs (left) and Asian lady beetle (right).
https://www.burroughspestcontrolcompany.com/pest-control/other-pests/lady-bug.html
https://winnebagoanimals.org/hermit-crabs-the-basics/ Pancrustacea Crustacea
> https://www.bettafish.com/threads/harpacticoid-copepods-in-my-aquarium.615242/
# Isopod (top), copepod (middle), and decapod (bottom).
Crustaceans include ~ 40,000 to ~ 50,000 extant species of crabs, lobsters, shrimps, and their close relatives.
Variations in body size are huge.
Crustaceans are mostly marine, but freshwater and terrestrial taxa are also known.
Some notable examples:
Isopods including parasitic taxa in fish such as the tongue-eating louse.
Small, mostly planktonic copepods
Prey on diatoms
Relatively large decapods such as lobsters and crabs
> https://www.nationalgeographic.com/science/article/tongue-eating-fish-parasites-never-cease-to-amaze
> Parasites in the Fossil Record: A Cretaceous Fauna with Isopod-Infested Decapod Crustaceans, Infestation Patterns through Time, and a New Ichnotaxon
Pancrustacea Crustacea
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
Anatomy of the lobster (top) and # compound eye in the fiddle crab Uca vomeris (bottom).
Crustacean characteristics (body plan)
1. Three tagmata with head, thorax, and abdomen.
Head and thorax are often merged into cephalothorax.
2. Head, thorax, and cephalothorax are usually covered by a carapace.
Carapace covers dorsal and lateral aspects
3. Presence of compound eyes
Compound eyes are often supported by stalks.
> Abdomen
> Zeil, J., & Hemmi, J. M. (2006). The visual ecology of fiddler crabs. Journal of Comparative Physiology A ,192 , 1-25.
Pancrustacea Crustacea
> https://thehaul.wordpress.com/terms-of-art/lobster-anatomy-diagrams/
Anatomy of a typical crustacean (top), rusty crayfish (bottom left), and pleopod (bottom right).
Crustacean characteristics (body plan)
4. Presence of biramous appendages specialised for various functions
Two pairs of antennae
At least two pairs of maxillae
Paired segmented mandibles
Thoracic limbs for locomotion.
More than four pairs in crustaceans
Abdominal limbs for locomotion, respiration, filter-feeding, and holding eggs
> By Image by User:Uwe kils - from Wikisource, made by Uwe Kils., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=225284
> https://www.invasivespeciesva.org/species/rusty-crayfish
Pancrustacea Crustacea
> Wootton, E. C., Pope, E. C., Vogan, C. L., Roberts, E. C., Davies, C. E., & Rowley, A. F. (2011). Morphology and pathology of the ectoparasitic copepod, Nicotho astaci (lobster louse) in the European lobster, Homarus gammarus. Parasitology ,138 (10), 1285-1295.
# Gills of the European lobster (top) and lung in isopods (bottom).
Crustacean characteristics (body plan)
5. Exoskeleton is often strengthened by biomineralisation.
Calcium carbonate is incorporated into cuticle.
Cuticle is hardened into shell in sessile crustaceans such as barnacles.
Temporary storage of calcium carbonate (gastroliths) in the wall of stomach.
6. Oxygen (O 2) is transported by the respiratory protein haemocyanin.
Aquatic crustaceans have gills modified from unsclerotised appendages.
Terrestrial crustaceans have branched tracheae.
> https://www.wikiwand.com/en/articles/Pleopodal_lungs
Pancrustacea Hexapoda
> Tihelka, E., Cai, C., Giacomelli, M., Lozano-Fernandez, J., Rota-Stabelli, O., Huang, D., ... & Pisani, D. (2021). The evolution of insect biodiversity. Current Biology ,31 (19), R1299-R1311.
> # Phylogeny of Hexapoda.
Hexapoda is a clade with enormous number of species, most of which are insects.
Class Insecta contains over 1 million known, extant species in freshwater, terrestrial, and aerial habitats.
Insects are the only group of invertebrates capable of flight.
Several adaptive radiations likely occurred in the evolutionary history of insects.
Adaptation of flight, of feeding on gymnosperms, and pollinating angiosperms.
Other small groups of wingless hexapods
Protura, Collumbola, and Diplura. Pancrustacea Hexapoda
https://www.lcfpd.org/education/cicadas/
# Surface anatomy of the cicadas (top) and the diabolical ironclad beetle (bottom).
Hexapod characteristics
1. Consistent tagmatisation
Head with one pair of antennae and three pairs of mouth pars (including mandibles).
Thorax with three pairs of jointed, uniramous legs.
Wings may be present.
Abdomen lacking paired, jointed appendage.
https://www.cbc.ca/radio/quirks/oct-24-ironclad-beetle-s-uncrushable-shell-extinction-made-us-upright-and-warm-blooded-and-more-1.5773387/the-diabolical-ironclad-beetle-s-super-tough-shell-can-even-resist-being-run-over-by-a-car-1.5774066 Pancrustacea Hexapoda
https://www.britannica.com/animal/insect/Circulatory-system
# Respiratory systems in the grasshopper (top) and the beetle (bottom).
Hexapod characteristics
2. Gas exchange via a tracheal system
Spiracles on the lateral aspects of the tagmata are openings into the tracheal system.
Branched, cuticle-lined tubes distribute oxygen to tissues.
Most hexapods lack Oxygen (O 2) carrier.
Kaiser, A., Klok, C. J., Socha, J. J., Lee, W. K., Quinlan, M. C., & Harrison, J. F. (2007). Increase in tracheal investment with beetle size supports hypothesis of oxygen limitation on insect gigantism. Proceedings of the National Academy of Sciences , 104 (32), 13198-13203. Insect Wings
> https://www.smcmvcd.org/fleas
# Wings in cicadas (top), the fossil dragonfly Meganeuropsis (bottom left), and the wingless but not witless fleas (bottom right).
Wings represent a pivotal evolutionary transition in insects.
Several basal insect groups lack wing, such as the paraphyletic Apterygota.
Most insects belong to Pterygota
Presence of wing is a synapomorphy
Wing only evolved once in this clade.
Some taxa such as bed bugs and fleas have lost wings secondarily (e.g., fleas).
One to two pairs of wings on the thorax
Insect wings are extension of cuticle with various degrees of sclerotisation.
How and why wing evolved is not well understood.
Flight is a key factor in adaptive radiation of insects.
Adults typically have wings
> Saito, K., Nagai, H., Suto, K., Ogawa, N., Seong, Y. A., Tachi, T., ... & Kawahara, Y. (2021). Insect wing 3D printing. Scientific reports ,11 (1), 18631.
> https://uk.pinterest.com/pin/486177722260270490/
Some Reflective Questions (Not an Exhaustive List for Exam!)
Name the characteristics of arthropods.
Of the arthropod characteristics, which support their phylogenetic placement under Bilateria?
Among the arthropod groups introduced in this topic, which are evidence supporting the evolutionary themes of arthropods?
How may we distinguish major groups of arthropods?
Close phylogenetic relationship between Crustacea and Hexapoda is recovered by molecular evidence. Can we find some shared, morphological traits as supporting evidence as well?