6-8, 10, 12: Ecdysozoa (inc. Arthropoda, Insecta) + Lophotrochozoa Flashcards
Describe the Priapulida in terms of their basic features and taxonomic position
Priapulida = “Penis Worms,” marine worms, most are burrowers which capture prey by waiting upright at the surface of mud or sand
Their introvert/trunk can retract using muscles, and usually ends with curved spines (scalids) around the mouth which capture food and then retract
Simple worm-like anatomy - circular nerve ring around gut, whole body covered by chitinous cuticle
Describe the Nematoda in terms of their basic features and taxonomic position
Ecdysozoans -> Nematoia (alongside Nematomorpha)
Pseudocoelomate, parasitic “roundworms” - all environments and types of animals - cause diseases eg Ascariasis, Elephantiasis and Trichinosis
Circular nerve ring around gut, specialised “oral stylets” i.e. mouthparts (some for herbivory, some for predation) - retracted piercing device
Name three Nematode-caused diseases and the associated species
ASCARIASIS (Ascaris lumbricoides) -> spread via faeces by contaminating soil, causing pneumonia, abdominal symptoms and occasionally intestinal blockage
TRICHINOSIS - caused by Trichinella, adult worms bury into small intestines, then juveniles enter blood vessels, then skeletal muscle cells. Can be lethal but drugs are available
ELEPHANTIASIS - caused by filarial worms e.g. Wuchereria or Brugia; inflammation and lymphatic obstruction, swelling, often spread by mosquitos
Name the groups contained within PANARTHROPODA and the defining characteristics from other ecdysozoans
Tardigrada, Onychophora (Velvet Worms) and Arthropoda
All have paired walking appendages with claws and show segmentation (though difficult to find a “good” synapomorph)
*share some patterns of gene expression and brain structure, but also some key differences and some features only shared between 2 of the three phyla
*Tardigrada slightly debatable - show some features of Cycloneuralia
Describe the Onychophora in terms of their basic features and ecology
VELVET WORMS - They appear like “worms with chunky, fleshy, lobed legs,”
Have a ventral nerve chord - NOT circular around the gut
They use slimy webs to trap prey (e.g., cockroaches) then eat using mandibles and mouth
Describe the Tardigrada in terms of their basic features and ecology
“Water bears/Moss Piglets” -aquatic but most live on land, often in thin water layer on moss
Have 8 non-jointed appendages, limited circulatory and respiratory systems, complex worm-like nervous system
They have a piercing stylet mouth and sucking pharynx, evolved either for predation (e.g., of nematodes and rotifers) or for herbivory
Once thought to show major HGT with bacteria - mostly just contamination
Can undergo prolonged Cryptobiosis in response to stress (anoxybiosis, anhydrobiosis, crybiosis, etc.) and form Tuns - small sacs, evolved to survive harsh conditions
BONUS - unlike trehalose used by nematodes etc. in dehydration, Tardigrades use unique intrinsically disordered proteins (TDPs) which become rigid when dessicated
Describe the general current outlook on Ecdysozoan phylogeny
Monophyly of Ecdysozoa now generally accepted, despite prior dissent from morphologists
Difficult to resolve internal phylogeny due to Long Branches of Nematoda and Tardigrada, and limited developmental/morphological data for others
Decent evidence for Panarthropoda as a clade, but other placements within Ecdysozoa still largely debated - microRNAs may soon prove useful in resolving this due to their deep homology
Current Leading Hypothesis:
- Scalidiphora (Priapulida, Kinorhyncha and Loricifera)
- Nematoida (Nematoda and Nematophora)
- Panarthropoda (Tardigrada, Onychophora and Euarthropoda)
Describe what is understood about Lobopodia (and name some examples)
“Worms with legs” - many seen in NOT a monophyly -> probably plesiomorphic ancestor state of MANY panarthropods - may resemble Panarthropod Common Ancestor
Many had an armoured and arthropod-like digestive system
Hallucigenia, Megadictyon, Diania, Xenusion, Jianshanopodia
Describe Opabinia and its significance
Opabinia is a possible stem-Arthropod from the Cambrian Period (probably between Megadictyon and Anomalocaridids on the tree)
Appears like a lobopodian but with swimming appendages and euarthropod-like compound eyes
Describe Megadictyon and its significance
A possible stem-Arthropod, probably more “stemward” than Opabinia and Anomalocaris
Appears like a lobopodian, considered a stem-Arthropod as it is armoured and has an Arthropod-like digestive system
Describe Anomalocaridids (e.g., Anomalocaris) and their significance
A possible Euarthropod stem group with arthropod-like jointed raptorial oral/feeding and swimming appendages
Describe the Bivalved Arthropods (e.g., Canadaspis)
Complex and specialised biramous appendages (like many euarthropods)
Describe the Megacheirans (Great Appendage Arthropods)
Have biramous swimming AND walking appendages along the whole body
Great appendages at front (crab/lobster like) - may be homologous with those of euarthropods - but hard to be sure
(e.g., genus Leanchoilia)
Some hypothesise that we can prove homology using fossilised brains -> debatable whether nerve tissue can be this well preserved?
Summarise the general trend(s) seen in Arthropod evolution
Along the stem lineage of Euarthropoda, we see a step-wise acquisition of arthropod-like traits:
- Compound eyes
- Arthropodised cephalic and trunk limbs
- Arthrodisation (appeared AFTER arthropodisation)
- Sternites and tergites
Probable order of key players:
Megadictyon -> Opabinia -> Anomalocaridids -> Bivalved Arhropods -> Great Appendage Arthropods -> Euarthropods
What is the main evidence for Lophotrochozoan monophyly?
Genetic Data - 18S ribosomal gene data, ESTs, 28S nuclear ribosomal gene, myosin II heavy chain
BUT no single synapomorphic morphological trait
Summarise our current understanding of Lophotrochozoan phylogeny
Lophotrochozoa are a reasonably well-established clade of around 13 phyla, named after the Lophophore (a feeding structure) and the Trochophore (larval morphology)
However, there is no common morphological trait across all their groups, and the internal resolution of this group’s phylogeny is controversial
Generally thought to be two major groups within Lophotrochozoa:
- one includes Mollusca, Annelida, Ribbon Worms (Nemertea), Phoronida and Brachiopoda
- one includes Bryozoa, Entoprocta, Cycliophora, the three Gnathiferan phyla (Gnathostomalida, Rotifera and Micrognathozoa), Gastrotricha and Platyhelminthes
Name and describe the “first” three Lophotrochozoan phyla within the non-Trochozoan group
BRYOZOA - ectoprocts, sessile, live in colonies, mainly marine
ENTOPROCTA - similar lifestyle to Bryozoa but different anus position [note: no proper lophophore]
CYCLIOPHORA - live on lobsters’ feeding parts (very limited niche)
Name the group of 3 Phyla grouped together in lecture, but limited evidence for monophyly in literature
Gnathifera (Gnathostomulida, Rotifera, Micrognathozoa)
Name and describe the 5 Phyla in the Platyzoa group
Gnathostomulida “jaw worms”
Rotifera - tiny, thorny-headed worms, some are parasitic
Micrognathozoans “jaw animals”
Gastrotricha “hairybacks” - worm-like
Platyhelminthes (includes flatworms, flukes and tapeworms)
-> most are parasitic
-> had a coelom but lost over time, so not as primitive as thought
-> eyespots and nervous tissue clusters at anterior, two nerve cords along body
Name and describe the three phylogenetically closest Lophotrochozoan species to the Annelids and Molluscs
Phoronida - Horseshoe worms - another sessile filter feeder
Brachiopoda - resemble bivalve molluscs (but this is purely convergent, different phyla!)
Nemertea - ribbon worms, can be very long, no segmentation, proboscis/stylet - often used in conjunction with neurotoxin
Describe the ecology of Annelida
Annelida (eg. earthworms and Hirundidae/leeches) can be marine or terrestrial, and can be sessile, predatory or take more bizarre forms
They are ecologically vital for fertilisation, aeration, drainage and preventing compaction
Describe the key feature of Annelida mentioned in the lecture
METAMERISM - segmentation in which morphological features are repeated in each segment - allows larger size while still moving efficiently
Describe the ecology of Mollusca
Most are herbivorous, though some (e.g., squids) are predatory
Includes Gastropods, Bivalves, Cephalopods and many more obscure ones
Second most speciose phylum in Animalia!
Describe the Gastropods
- Includes Snails, Slugs, Sea Angels and Nudibranch
- Often have an enlarged locomotive foot
- Most (but not all) have a radula on top of the odontophore - buccal mass houses the protractor/retractor muscles
- Most have a calcium carbonate shell
Describe the cephalopoda
Includes squid, octopus and others (e.g. pharaoh cuttlefish)
Many convergent traits with other aquatic animals, also with human eye
Octopuses highly intelligent - surprising given their ecology
What are the three main subphyla of arthropods?
Trilobites (extinct)
Chelicerates
Mandibulates
Describe the key features of arthropods
- A segmented body with jointed appendages
- Tagmatisation - segments fused together into functional regions (e.g. head, thorax, abdomen)
- Highly cephalized (concentration of sensory organs at anterior end of body - often sophisticated mouthparts and sensory organs)
- Open circulatory system
- Chitinous exoskeleton that moults (ecdysis)
Describe the features that allowed Arthropods to be so successful
- Segmented body allows efficient locomotion
- Highly developed sense organs
- Exoskeleton versatility
- Complex learned AND unlearned behaviours
- Tracheal system pumps air directly to cells
- Metamorphosis allows exploitation of multiple niches by one species
Briefly describe the trilobites and their presence in the fossil record
The trilobites are an extinct subphylum of arthropods, with an exoskeleton divided into three lobes
They were extremely successful for hundreds of millions of years following the Cambrian Explosion, but disappeared relatively quickly in the Devonian
Describe the anatomy of chelicerates
- They have segments (though these are not always obvious in adults)
- Body is divided into two main regions (prosoma at front, opisthosoma at back)
- Six appendage pairs on prosoma: chelicerae, pedipalps (unique to chelicerates!) and 4 walking limb pairs
- The chelicerae can be scissor-like (e.g. Opiliones, Scorpiones, Xiphosura) OR highly specialised (e.g., fangs and venome in Aranae)
