Invertebrates Flashcards
What are Bilateria?
Protostomes and Deuterostomes.
What are Deuterostomes?
Cephalochordates. Urochordates. Hemichordates. Echinoderms. Vertebrates.
Spiral cleavage in eggs.
Blastopore -/-> mouth (as in protostomes).
Coelom forms by budding not splitting.
Nerve cords not ventral.
What are Protostomes?
Lophotrochozoans and Ecdysozoans.
What are Lophotrochozoans?
Bryozoans. Entoprocts. Platyhelminthes. Pogonophorans. Brachiopods. Phoronids. Nemerteans. Annelids. Echiurans. Molluscs. Sipunculans. Gnathostomulids. Rotifers.
What are ecdysozoans?
They have an additional surface layer - the cuticle which is shed and replaced as they grow: Gastrotrichs. Nematodes. Priapulids. Kinorhynchs. Onychophorans. Tardigrades. Arthropods.
Which 3 phyla have their own groups in the tree?
Ctenophores.
Cnidarians.
Poriferans.
How many living phyla are there?
About 35.
How many species are there per phylum?
15 - >1,000,000.
What are the largest phyla?
- Arthropoda.
- Mollusca.
- Nematoda.
What evidence is the phylogenetic tree most based on?
Fossils:
Oldest metazoan fossils 570mya (controversial - may be protoctists or fungi).
Ediacaran fossils 564-543 mya (may be ancestral forms or dead-ends).
Cnidarian fossils (?) 560 mya.
Cambrian explosion 543-525 mya (Burgess shale fossils most well known - some unique and some related to extant groups).
What lead to the Cambrian explosion?
Increased oxygen levels allowed the evolution of larger animals, Hox genes (body patterning) and ecological competition (exoskeletons).
Why is the fossil record biased?
Soft bodied organisms not preserved, so can’t find ancestors pre-exoskeleton.
When did most groups appear in the fossil record?
540-520 mya - evolving independently since.
What are the 5 main challenges of being a metazoan?
- Locomotion/support.
- Feeding.
- Excretion/osmoregulation.
- Gas exchange/circulation.
- Reproduction.
Why are Porifera a separate branch on the phylogenetic tree?
- Parazoan organisation - no tissues/organs, just specialised cells.
- No inherent symmetry.
- Unique aquariferous system.
Why are sponges important?
- Highly species rich (~5500).
- Dominant biomass in much of the marine zone.
- Have diverse forms.
- Produce a huge variety of toxins (useful - anti-inflammatory, antibacterial, anti-tumour…).
- Form complex symbioses eg. Spongicola shrimp live as monogamous pairs in Euplectella (cannot get out when they grow too large).
What is the basic sponge bauplan?
3 body layers:
- Pinacoderm (one cell thick protective surface).
- Mesophyl (skeleton and wandering amoebocytes).
- Choanoderm (single layer of specialised choanocytes.
Body is perforated by ostia leading into the spongocoel (atrium). There is one exit hole - the osculum.
What are the 3 sponge body grades?
- Asconoid - simple.
- Syconoid - more complex (choanocyte layer divided into chambers opening into spongocoel).
- Leuconoid - most complex (choanocyte chambers within mesophyl, connected to each other, the spongocoel and the outside by incurrent canals).
How do sponges feed?
Suspension feeding: Generate a flow of water - in through body perforations (ostia) to spongocoel then out through the osculum.
Can also trap, grow over and digest small crustaceans.
Can also obtain food through symbiotic relationships w. bacteria and algae - sponge provides home, symbiont provides food.
How are poriferan choanocytes specialised for suspension feeding?
A choanocyte has a flagellum which beats to generate the flow of water, drawing it in through the ostia. It also has a collar of microvilli to trap food particles. These are then phagocytosed by the cell body to form food vacuoles, which can be passed to the rest of the sponge.
How are larger food particles captured in sponges?
By archaeocytes wandering along the lining of the incurrent canals.
What is the sponge skeleton made from?
Organic collagen and/or inorganic silica or calcite.
Collagen fibrils can be dispersed in the mesophyl or organised in a network. Inorganic spicules can be separate (held together by collagen) or in an organised skeleton.
How do sponges reproduce?
Asexual:
Fragmentation.
Budding.
Producing reduction bodies (resistant to harsh environmental conditions).
Sexual:
Most species sequential hermaphrodites but some dioecious (and some have both).
Choanocytes -> sperm (shot out osculum).
Choanocytes and archaeocytes -> eggs (shot out or retained - fertilisation can be either internal or external).
What are the 3 sponge larval forms?
- Parenchymulan larvae (sponges with internal fertilisation) - released and swim for a few days before settling and metamorphosing to adult form.
2 and 3. Coeloblastulan and amphiblastulan larvae - have longer free swimming time before metamorphosis.
What are the 3 main sponge classes?
- Calcareae (calcareous sponges) - calcite skeleton, marine, all body grades.
- Demospongiae (silicaceous sponges) - silica skeleton, marine/freshwater, leuconoid.
- Hexactinellidae (glass sponges) - silica skeleton, marine, unique body form.
Used to be more - extinct.
Which metazoa are diploblastic?
Cnidaria and Ctenophora.
What does the ectoderm produce?
- Epidermis.
- Nerve cells (in diploblasts).
- Muscle-like cells (in diploblasts).
What does the mesoderm produce?
- Muscles.
2. Some organs.
What does the endoderm produce?
- Digestive lining.
- Muscle-like cells (in diploblasts).
- Some organs (in triploblasts).
What type of skeleton do Platyhelminthes have?
Hydrostatic.
Cheap but low power generation and easily damaged.
How many living species are in the phylum Platyhelminthes (flat worms)?
~20,000.
What are Platyhelminthes?
Lophotrochozoan, acoelomate flat worms (dorso-ventrally flattened), cephalised, bilaterally symmetrical, triploblastic.
Which of the main classes of Platyhelminthes is mostly free-living?
The Turbellaria.
Mostly marine but some freshwater and very few terrestrial (damp/humid environments only as high SA low V = water loss).
Mostly carnivores or scavengers, but some grazing herbivores.
How do Turbellaria (platyhelminthes) move?
Circular, longitudinal and dorsoventral muscles (under the epidermis) relax and contract against the hydrostatic skeleton to change body shape. This allows large species to move using peristaltic waves. Small species use cilia for locomotion.
How do Platyhelminthes reproduce?
They are usually hermaphrodites (have testicles and ovaries).
What is the digestive tract like in the Turbellaria (Platyhelminthes)?
The pharynx runs from the mouth (ventral) into the gut/intestine, which has a single entrance/exit (no anus). There is a pharyngeal cavity separating the pharynx from the rest of the body so that the muscles of the pharynx can work independently of the worm’s other muscles (so the movements of the rest of the body such as squeezing don’t affect the digestive tract).
What sensory systems do Turbellaria (Platyhelminthes) have?
Auricles - chemosensory areas to translate chemical -> nervous signals.
Ocellus - for seeing, signals carried by an optic nerve. Can only sense changes in light, rather than images.
A concentration of nerves in the head end forms the cerebral ganglia (acts as the brain).
What is the Turbellaria (Platyhelminthes) osmoregulatory system?
Response to SA:V problem. A network around the body emptying at pores on the body surface. May do some excretion, but most excretion products are exchanged across the body wall.
How do Turbellaria (Platyhelminthes) flame bulbs work?
Osmoregulation. Have cilia which collect ions and pump them into the nephridial canals, then they are passed to nephridiopores.
What are the ancestral Platyhelminthes and how did the classes evolve from there?
Free-living.
Parasitic forms are specialised Platyhelminthes.
Free-living as ancestral form supported by mtDNA phylogeny.
Ectoparasitic monogenea evolving next, first epithelial feeding then blood feeding (attachment structures, tegument, reduced body complexity).
Next endoparasitic digenea (initially blood living then spreading into other niches).
Lastly cestodes (loss of gut).
What are the 3 classes of parasitic Platyhelminthes?
- The monogeneans - mostly ectoparasites, usually 1 host species.
- The digeneans - mostly endoparasites, usually 2/3 hosts in life cycle.
^^Both of these groups are flukes. - Cestodes/tapeworms - always endoparasites, usually multiple hosts in life cycle, contains the largest flatworms.
What is an example of a medically important Platyhelminth?
Schistosoma- causes schistosomiasis which affects 200 million people worldwide.
What are the evolutionary challenges for ectoparasites?
- Finding a host.
- Attaching/holding on to host.
- Extracting resources.
What are the evolutionary challenges for endoparasites?
- Finding a host.
- Getting into the host.
- Extracting resources.
What are the evolutionary advantages to becoming a parasite?
Can lose a lot of expensive anatomy/physiology/behaviour.
Once a host is found, only need systems for feeding and reproduction.
How are monogenean flukes adapted for attachment to a host?
They have 2 attachment areas. The opisthaptor is the main attachment organ including suckers with hooks/claws and the prohaptor is a pair of adhesive structures either side of the mouth with suckers/pads.
How do monogenean flukes feed?
By external digestion of host tissue - release enzymes and then suck the digested material into the pharynx.
How do monogenean flukes reproduce?
They are hermaphrodites like Turbellarians but produce many more offspring - finding hosts is difficult/dangerous so more offspring = more likely some will survive.
How are schistosomes different reproductively to other digenea and Platyhelminthes?
They are dioecious (and mate for life).
How do the digenea compare to the monogenea?
The majority of digenea are similar to the monogenean flukes, but have complex life cycles involving more than 1 host species. Schistosomes have snail and human hosts and multiple reproductive stages, including sporocysts produced by asexual reproduction.
What is the body structure of cestodes/tapeworms?
- Scolex - complex head end with hooks and suckers evolved for attaching (suckers) and embedding (hooks) into host’s gut wall.
- Neck.
- Proglottids - repeated segments containing male and female reproductive systems.
Why do cestodes have no digestive system?
They can absorb nutrients (digested food) from their host through their body wall.
How do cestodes reproduce?
Non-fertilised proglottids have male and female reproductive systems. They can self fertilise (different or same proglottid) or mate with other tapeworms. After a proglottid is fertilised, both reproductive systems degrade and the uterus expands with developing eggs until the proglottid is filled with embryos. Proglottids are then released.
Why are flukes and cestodes not destroyed by the host’s immune system/digestive enzymes from the host’s intestine?
They have a tegument - an external covering providing protection, a membrane for gas exchange and excretion as well as for food absorption in cestodes (highly folded for SA). Surface proteins allow evasion of the the host’s immune system and in cestodes enzyme inhibitors may be produced to neutralise host digestive enzymes.
What are protonephridia and metanephridia?
Osmoregulation and excretory systems.
What are the features of protonephridia?
- Flame bulbs or solenocytes.
- Nephridiopores.
Found in acoelomates and some annelids.
What are the features of metanephridia?
- Multicellular.
- Open at both ends.
Found in annelids, molluscs, sipunculans, echiurans etc.
Why are there many different worms?
Convergent evolution. Worm-like forms are effective and so have evolved numerous times.
How many species in phylum Nemertea (ribbon worms)?
About 900.
Mainly marine, wide range of lengths, contains the longest animals (60m).
Majority are active predators.
What are some anatomical differences between Nemerteans and Platyhelminthes?
Nemerteans:
1. Coelomate (rhyncocoel).
2. Circulatory system - contains analogues of RBCs and WBCs and transports nutrients, gases, excretion products. Flow can be in any direction.
3. Complete digestive tract - one way flow from mouth to anus = potential for specialisation and more efficient digestion.
Platyhelminthes:
1. Acoelomate.
2. No circulatory system.
3. Incomplete digestive tract - single entrance/exit.
How do nemertea move?
Like Platyhelminthes - large species using peristaltic waves, small using cilia.
How do nemertea reproduce?
Mostly dioecious.
Can produce asexually by fragmentation.
Can be protandric or simultaneous hermaphrodites.
How is the head end clearly defined in nemertea?
The mouth and proboscis are in the head area and nervous tissue is more concentrated in the head.
What is the Nemertean proboscis?
A chemosensory organ everted when prey is detected to wrap around them and bring them to the mouth. May contain toxins to paralyse or kill or be armed to puncture prey’s hydrostatic skeleton. Held inside the rhyncocoel at rest by the proboscis retractor muscle and exits through the proboscis pore (in some species mouth) when the muscles surrounding the rhyncocoel contract, increasing the hydrostatic pressure and relaxing the retractor muscle. In some species eversion/inversion are solely by changes in hydrostatic pressure.
How many species of sipunculids (peanut worms) are there?
About 250.
All marine detritivores.
Live in burrows/crevices and large range in length.
Can be quite abundant in some coral reefs.
Why do nemertean worms have a closed circulatory system but sipunculids do not?
Nemerteans are predators and fast moving but sipunculids are relatively slow so don’t need it.
What is the body structure of sipunculids?
- The trunk - normally in burrow or crevice.
- Introvert - moves tentacles.
- Tentacles - sweep across substrate and bring food particles to the mouth.
How do sipunculids move the introvert?
Dorsal retractor muscles pull introvert and tentacles into the body.
Longitudinal and circular muscles in the body wall contract to increase pressure of coelomic fluid in the trunk and push out the introvert and tentacles.
How do burrow-dwelling sipunculids remove waste?
They have a U-shaped digestive system.
What is the body structure of the rotifers (wheel animals)?
- Head - with ciliated corona.
- Trunk.
- Foot.
Where do rotifers live?
Mostly fresh-water.
How do rotifers feed?
Suspension feeding using ciliated corona.
What are the acanthocephala (thorny-headed worms)?
Parasites. Thought now to be descended from rotifers rather than a separate phylum, with the rotifer body reduced to attachment (proboscis - controlled by retractor muscles) and reproductive organs (no digestive or circulatory systems), also hydrostatic skeleton. They have however evolved complex life cycles.
How do acanthocephala reproduce?
Dioecious and can hormonally manipulate host behaviour to maximise reproduction. Cause low harm in their definitive vertebrate hosts as in best interest of the parasite for that host to live as long as possible (this is where they reproduce). Eggs pass out of the definitive host and are eaten by intermediate hosts (eg insects or crustaceans) where they develop, but their intermediate hosts must be eaten by the definitive host to complete the life cycle. Acanthocephala therefore manipulate their intermediate hosts to increase their predation risk. Eg infected amphipods (crustacean) prefer light to dark, so are more likely to be eaten by foraging ducks.
How do acanthocephala feed?
They absorb nutrients from the host’s gut across their body surface.
What do predatory nemertea, detritivore sipunculids and parasitic acanthocephala have in common?
- Same basic body form - vermiform.
- Coelomate.
- Some form of eversible proboscis (convergent evolution).
- Hydrostatic skeleton (and related muscular system).
Which group of annelids has the majority of species?
The polychaetes.
Which 3 lophotrochozoa phyla may actually be annelids?
Echiura, pogonaphora (both polychaete) and sipunculida.
What are the 3 annelid classes?
- Polychaetes.
- Oligochaetes.
- Hirudinoidea.
Where do the polychaetes live?
Mostly marine with a few fresh water species.
Where do the oligochaetes live?
Mostly terrestrial with many fresh water and few marine species.
Where do hirudinoidea live?
Mostly fresh water or terrestrial.
How do polychaetes feed?
Hunters or deposit/suspension feeders. Exception is chaetopterids, which are true filter feeders. Hunters are generally homonomous (segments not differentiated) and fast moving. They typically catch prey by everting their pharynx (body wall muscles contract to increase pressure on coelom to push it out). Prey (small worms, crustaceans) are caught on the sticky surface or between 2 jaws which close when the pharynx is pulled back in. Deposit feeders draw water into their burrows to liquefy the substrate and then ingest it. Any organic matter is digested and the rest is defecated at the surface in castings. Suspension feeders (marine) are the most heteronomous with specialised segments and parapodia. A tentacular crown is used where radioles beat to draw water up into the crown and cilia create a flow of water over the tentacles, so particles can be trapped by mucous and moved to the mouth.
How do oligochaetes feed?
Hunters, deposit feeders or detritivores.
Hunters suck prey (small worms, crustaceans) into their pharynx.
Deposit feeding similar to polychaetes (ingesting substrate along with organic matter), earthworms are a good example, and very important in improving soil fertility.
