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# BIOL 108 Introduction to Biological Diversity
## Topic 22: Lophotrochozoa
> Lecture A2
> Yan-yin Wang
Introduction to Clade Bilateria
> 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
Pro
Deu
The majority of animals belong to the clade Bilateria.
Bilateria contains two main groups:
Protostomes.
Deuterostomes.
Characteristics:
Bilaterally symmetrical body plan
Triploblastic animals.
Most bilaterians have a coelom and a digestive tract.
Muscles and internal organs are derived from mesoderm. Bilaterial Symmetry
> 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 Bilateria (right) and a bilaterally symmetrical dog (bottom).
Bilaterally symmetrical bodies are strongly differentiated along the anteroposterior axis.
Implications:
Directional mobility.
Cephalisation (formation of the head) for sensory and feeding structures.
Concentration of neural ganglia (i.e., a rudimentary brain).
Taxa secondarily lost bilateral symmetry also have reduced cephalisation.
Digestive and reproductive structures are typically positioned posteriorly.
> Aspinall, V., & Cappello, M. (2015). Introduction to veterinary anatomy and physiology textbook . Elsevier Health Sciences.
Basal Bilaterians
Phylum Acoela is basal to other bilaterians based on molecular evidence.
Divergence of Acoela before origin of three main bilaterian clades.
Characteristics:
Small, flattened body.
Minimal cephalisation and simple nerve net (lack a brain).
Absence of a body cavity or complex organ.
Presence of simple digestive system with a mouth but lack gut cavity or anus.
Digestion takes place within individual cells (endocellular digestion).
> 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 Bilateria (right) and # two acoelan taxa (bottom).
> Egger, B., Steinke, D., Tarui, H., De Mulder, K., Arendt, D., Borgonie, G., ... & Ladurner, P. (2009). To be or not to be a flatworm: the acoel controversy. PLoS One ,4(5), e5502.
Introduction to Lophotrochozoa
> 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 Lophotrochozoa (right), lophophore structure (bottom left), and a trochophore lava (bottom right).
Clade Lophotrochozoa includes about half of animal phyla (17 /35 ).
Recovered from molecular phylogenetics with unclear basal relationships.
Absence of unifying synapomorphy.
Common characteristics:
Presence of lophophore for feeding in some taxa.
Presence of trochophore larval stage.
Some taxa lack either.
Most diverse body plans, from simple flat worms to behaviourally complex octopuses. Lophotrochozoan - Platyhelminthes
> 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.
Flatworms include ~ 20,000 extant species.
Inhabitants of marine, freshwater, and damp terrestrial environment.
Characteristics:
Triploblastic animals lacking fluid-filled body cavity.
Digestive tract is incomplete.
Presence of mouth and gut, but an anus is absent.
Mouth and gut may be absent in parasitic taxa.
Absence of circulatory or gas exchange systems.
Flatworm body plan (left), phylogeny of Lophotrochozoa (right) and diversity of flatworms (bottom).
> Collins, J. J. (2017). Platyhelminthes. Current Biology ,27 (7), R252-R256.
Lophotrochozoan - Platyhelminthes
> Fields, C., & Levin, M. (2018). Are planaria individuals? What regenerative biology is telling us about the nature of multicellularity. Evolutionary Biology ,45 (3), 237-247.
> # Basic anatomy of free-living planarians.
Rhabditophorans form the more diverse lineage of Platyhelminthes (~20,000 extant taxa).
Free-living predators.
Parasites.
Planarians are the most well known.
Characteristics of free-living planarians:
Presence of anterior cephalisation.
Presence of light-sensitive eyespots.
Presence of a pair of ganglia connected to a pair of ventral nerve cord.
Gastrovascular cavity with one opening.
Hermaphrodites with capacity to reproduce both sexually and asexually. Lophotrochozoan - Platyhelminthes
> Collins, J. J. (2017). Platyhelminthes. Current Biology ,27 (7), R252-R256.
> # Life cycle of a typical trematodes.
Parasitic rhabditophorans live in or on other animals.
Characteristics:
Presence of suckers or hooks for attachment.
Tough outer layer composed of mostly proteins and collagens.
Protection against host immune system and digestive enzymes.
Complex life cycle involving at least two hosts.
Intermediate host for asexual reproduction.
Definitive host for sexual reproduction.
Two groups of parasitic rhabditophorans:
Trematodes (flukes) and tapeworms. Lophotrochozoan - Platyhelminthes # Anatomy of a tapeworm (top) and a tapeworm from fish (bottom).
Tapeworms are endoparasites in the digestive tract of host animals.
Characteristics of tapeworms:
Complex life cycle involving at least two hosts.
Absence of a digestive system.
Presence of scolex with suckers and hosts.
Hermaphrodites with long chain of segments called proglottids, which contains male and female sex organs.
> 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.
> https://www.zipcodezoo.com/bear-tapeworm/
Lophotrochozoan - Lophophorata
> 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.
Lophophorates are known for the feeding structure called lophophore.
Lophophore : A fan of ciliated tentacles surrounding the mouth.
Lophophorata includes Ectoprocta and Brachiopoda.
Both contains aquatic animals with planktonic larval stage and sessile adult stage.
Phylogeny of Lophotrochozoa (top) and lophophore (bottom). Lophophorata Ectoprocta
> 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.
Ectoprocts are sessile, colonial animals, with ~ 4,500 extant mostly marine species.
They superficially resemble corals.
Characteristics:
Presence of a hard exoskeleton in most marine taxa by secreting calcium carbonate.
Exoskeletons in freshwater taxa are gelatinous or chitinous.
Suspension feeding using a retractable lophophore.
Presence of a U-shaped digestive tract.
Both sexual and asexual (budding) reproductions are known.
# Anatomy of ectoproct (top left), phylogeny of Lophotrochozoa (top right), colony of freshwater ectoprocts (bottom left) and marine colony of ectoprocts (bottom right).
> https://www.digitalatlasofancientlife.org/learn/bryozoa/
> https://earthlife.net/phylum-bryozoa-ectoprocta/
Lophophorata Brachiopoda
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.
Brachiopods are sessile, suspension feeders in marine habitats.
Once highly diverse in Palaeozoic Era.
Characteristics:
Most taxa are attached to the seafloor by a stalk (pedicle).
Suspension feeding using a retractable lophophore.
Presence of a digestive tract with, or without an anus.
# Anatomy of a brachiopd (top left), phylogeny of Lophotrochozoa (top right), Extant brachiopods (bottom left) and a fossil brachiopod (bottom right).
https://www.steinkern.de/steinkern-de-galerie/givetische-massenkalke-sauerland/stringocephalus-sp-12900.html
Topper, T. P., Strotz, L. C., Holmer, L. E., Zhang, Z., Tait, N. N., & Caron, J. B. (2015). Competition and mimicry: the curious case of chaetae in brachiopods from the middle Cambrian Burgess Shale. BMC Evolutionary Biology , 15 ,1-16.
Harper, D. A., Popov, L. E., & Holmer, L. E. (2017). Brachiopods: origin and early history. Palaeontology , 60 (5), 609-631. Lophophorata Trochozoa
> 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 Lophotrochozoa (top), # anatomy of trochophore (bottom left), and SEM image of a trochophore (bottom right).
Trochozoa includes Phylum Annelida (e.g., segmented worms) and Phylum Mollusca (e.g., snails).
Adult annelids and molluscs do not resemble each other.
Trochozoans share
Patterns of early embryonic development.
Presence of microscopic, motile, trochophore larvae.
Trochophore larvae are planktonic larvae with two bands of cilia for movement and feeding.
A sensory plate with a simple eyespot above the cilia bands.
> Levin, S. A. (2013). Encyclopedia of biodiversity .Academic Press. https://simple.wikipedia.org/wiki/Trochophore#/me dia/File:Haliotis_asinina_trochophore.jpg
Trochozoa Mollusca
> 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.
Phylum Mollusca includes more than 100,000 extant species of snails, slugs, oysters, calms, octopuses, and squids.
Predominantly marine taxa but also inhabit freshwater and terrestrial environment.
Molluscs are soft-bodied animals, and they are often protected by hard calcareous shells.
The shell is reduced or lost in some taxa.
Phylogeny of Lophotrochozoa (top), # anatomy of trochophore (bottom left), and SEM image of a trochophore (bottom right).
Fig 33.17 A chiton
Fig 33.18 A gastropod (land snail)
A bivalve (scallop)
Fig 33.18 A Gastropod (sea slug) Characteristics of Mollusca
> 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 a typical body plan in molluscs.
1. Common, unsegmented body plan:
Muscular ventral foot for locomotion.
Visceral mass dorsal to foot, containing internal organs.
Coelom is reduced and visceral mass is within the haemocoel.
Thin layer of tissues called the mantle.
Calcareous shell is secreted from the mantle.
The mantle is often involved in respiration and excretion by forming a water-filled mantle cavity. Characteristics of Mollusca
> 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.
2. Body typically has gills in the mantle cavity for gas exchange.
Gills are sometimes used for feeding (e.g., scallops).
3. Feeding in molluscs is achieved by a rasp-like radula (cutting food).
4. Presence of an open circulatory system.
Haemolymph fluid is circulated into and out of the haemocoel by the heart.
5. Presence of dioecious and hermaphrodite taxa.
6. Presence of trochophore larval stage.
# Anatomy of a typical body plan in molluscs (top), a snail (bottom left), and the radula in snail (bottom right).
> https://www.reddit.com/r/Awwducational/comments/25jir2/snails_and_other_mollusks_eat_with_an_apparatus/?rd t=42679
Phylogeny of Mollusca
> Kocot, K. M., Cannon, J. T., Todt, C., Citarella, M. R., Kohn, A. B., Meyer, A., ... & Halanych, K. M. (2011). Phylogenomics reveals deep molluscan relationships. Nature ,477 (7365), 452-456.
Phylogeny of Mollusca.
Four major classes in Molusca:
Polyplacophora (chitons).
Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses).
Bivalvia (clams, oysters, and other bivalves).
Gastropoda (snails and slugs). Mollusca Polyplacophora
Ibez, C. M., Waldisperg, M., Torres, F. I., Carrasco, S. A., Sellanes, J., Pardo-Gandarillas, M. C., & Sigwart, J. D. (2019). Environmental and ecological factors mediate taxonomic composition and body size of polyplacophoran assemblages along the Peruvian Province. Scientific Reports , 9(1), 15934.
Phylogeny of animals with characteristics mapped.
Chitons are oval-shaped marine animals with ~ 1,000 species.
Muscular foot functions like a suction cup, such that chitons are adhered to rocks.
Characteristic:
Body is protected by eight dorsal plates. Mollusca Cephalopoda
> https://www.scienceinschool.org/article/2023/squid-dissection-activity-to-teach-cephalopod-anatomy/
Phylogeny of animals with characteristics mapped.
Cephalopods include ~900 predatory species of squids, octopuses, cuttlefish, and chambered nautiluses.
Characteristics:
Absence of external shell (except in nautiluses).
Presence of a siphon fused from the tubes of mantle.
Fire a jet of water to propel itself.
Presence of long tentacles around the mouth.
Radula is modified into a beak.
Presence of venom gland to immobolise the preys.
Presence of a closed circulatory system.
Presence of complex brains and sensory organs.
Absence of trochophore larvae.
> Pena-Francesch, A., Domeradzka, N. E., Jung, H., Barbu, B., Vural, M., Kikuchi, Y., ... & Demirel, M. C. (2018). Research update: programmable tandem repeat proteins inspired by squid ring teeth. APL Materials ,6(1).
Mollusca Bivalvia
> https://swaggology.weebly.com/class-bivalvia.html
# Bivalves (top) and adductor in a scallop (bottom).
Bivalves are aquatic, mostly marine animals with ~ 20,000 extant species.
Some taxa are sessile (e.g., marine mussels) and some other taxa are sedentary (e.g., scallops).
Some bivalves can dig with muscular foot or can swim by clapping their shells.
Characteristics:
Presence of a shell divided into two halves connected by adductor muscles.
Some taxa have eyes or sensory tentacles along the margin of the mantle.
Absence of cephalisation.
Absence of radula.
> Sun, X., Liu, Z., Wu, B., Zhou, L., Wang, Q., Wu, W., & Yang, A. (2018). Differences between fast and slow muscles in scallops revealed through proteomics and transcriptomics. BMC genomics ,19 , 1-13.
Mollusca Bivalvia
> 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 a clam.
Bivalves are suspension feeders, using the gills in the mantle cavity.
Gills are also used for gas exchange.
Some bivalves are invasive pests (e.g., zebra mussels). Mollusca Gastropoda
> Lw , P., Molnr, K., Kriska, G., Lw , P., Molnr, K., & Kriska, G. (2016). Dissection of a Snail (Helix pomatia). Atlas of Animal Anatomy and Histology , 49-77.
# terrestrial snail (top left), sea hare (top right), and dissection of terrestrial snail (bottom).
Gastropods form a diverse group of snails and slugs, which contains ~ 75% of extant molluscs.
Most gastropods are marine animals with others inhabit freshwater or terrestrial environment.
Aquatic gastropods have trochophore larvae.
Terrestrial gastropods have direct development.
Some terrestrial taxa evolved a simple lung from the mantle cavity (e.g., terrestrial snails).
Characteristics:
Presence of a single, coiled, tubular shell.
Shell is reduced or lost in some taxa (e.g., sea hare , slug).
Strong cephalisation. https://www.plantasiaswansea.co.uk/blog/giant-african-land-snails-alien-invaders/
> https://www.reefcleaners.org/the-store-1/all-products-1/out-of-season/freckled-white-spotted-sea-hare-detail
Trochozoa Annelida
Capa, M., & Hutchings, P. (2021). Annelid diversity: historical overview and future perspectives. Diversity , 13 (3), 129.
Annelids include a wide array of marine and freshwater species (over 22,000 species).
Two major clades are recovered from molecular phylogenetics:
Errantia
Sedentaria
# Diversity of annelids.
Phylogeny of Lophotrochozoa.
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. Trochozoa Annelida
> https://www.opentextbooks.org.hk/ditatopic/35138
Annelids include a wide array of marine and freshwater species (over 22,000 species).
Characteristics:
Presence of segmented bodies separated by internal partitions called septa.
External and internal anatomies are similar between segments.
Presence of a coelom as a hydrostatic skeleton.
Cephalisation with well-developed mouth and brain.
Presence of a complete digestive system.
Presence of a closed circulatory system.
# segmented body of annelids (top) and evolution of nervous systems (bottom).
> Parry, L., & Caron, J. B. (2019). Canadia spinosa and the early evolution of the annelid nervous system. Science advances ,5(9), eaax5858.
Annelida - Errantia
> 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.
# The errantian, Nereimyra punctata (top), and chaetae in Eurythoe complanate
(bottom).
Errantians are mobile, often predatory, marine organisms.
Characteristics:
Presence of a pair of parapodia per body segment.
Parapodium is the paddle-like or ridge-like structure on the side of the body segment.
Parapodium has numerous chaetae and bristles composed of chitin.
Parapodia are often associated with external gills.
Cephalisation with head, antennae, and eyes.
Sexual reproduction is typical:
Gametes are released into water.
External fertilisation leads to development of trochophore larvae.
> Tilic, E., Pauli, B., & Bartolomaeus, T. (2017). Getting to the root of fireworms' stinging chaetae chaetal arrangement and ultrastructure of Eurythoe complanata (Pallas, 1766)(Amphinomida). Journal of morphology ,278 (6), 865-876.
Annelida - Sedentaria
https://www.amnh.org/explore/ology/zoology/whats-this-leeches
# leeches (top left), the oral apparatus of leeches (top right), and the earthworm
Perionyx excavatus (bottom).
Sedentarians include leeches and earthworms.
They are generally less mobile than errantians.
Some taxa burrow into substrates (e.g., earth worms), and others live in protective tubes.
Tube-dwelling sedentarians often have elaborate gills or tentacles used for suspension feeding.
Characteristics:
Parapodium is not always present (e.g., earth worms).
Cephalisation with head, antennae, and eyes.
Some taxa lack a trochophore larval stage (e.g., leeches). https://navaneetham.in/specialities/medicinal-leech-therapy-mlt/
Subbiahanadar Chelladurai, K., Selvan Christyraj, J. D., Azhagesan, A., Paulraj, V. D., Jothimani, M., Yesudhason, B. V., ... & Selvan Christyraj, J. R. S. (2020). Exploring the effect of UV-C radiation on earthworm and understanding its genomic integrity in the context of H2AX expression. Scientific Reports , 10 (1), 21005. Some Reflective Questions (Not an Exhaustive List for Exam!)
What are the characteristics of major groups within Lophotrochozoa?
Based on the characteristics of lophotrochozoans, how would you resolve the polytomy?
Acoela and Platyhelminthes do not form sister group relationship on the phylogeny. Why is it?
Trochophore larvae are present in some lophotrochozoan taxa, how can we interpret this observation?