• Anterior (head) to Posterior (anus if applicable) 
• Homologous from radial symmetry - same genes involved. 
• Only a single plane of symmetry 
• Extremely efficient for locomotion 
• Cephalization - CNS structures, sensory structures, and feeding structures localized on the anterior or head. 

• Most have complete gut = tube within a tube 
• Foregut (stomodeum) = Mouth
• Midgut  
• Hindgut (proctodeum) = anus 

Problem

• Tissues within tissues 
• Must supply O_2, C (energy), N (protein), etc 
• Must remove CO₂, wastes, etc. 
• For a given shape, SA/V ratio is always 2/3

Solutions?

• Increase Surface Area
• Stay small
• Flatten 
• Use fluid circulation 
• Grow in modules 

Triploblasts with spongy parenchyma, circumferential and longitudinal muscles arrising from mesoderm. 

No anus

No circulatory or respiratory systems.

Incomplete gut  

Has excretory and nervous systems. 

• Can get long and skinny, or short and fat. 
• Spongy Parenchyma acts sort of like a hydrostatic skeleton. 
• Circum muscles extend
• Long muscles shorten 
• Can also swim with undulatory body waves. 

Pharynx in middle with no anus. 

type of cladidia's correlate or possibly decides the size. 

• Rhabdocoels - smallest with a simple straight gut and bulbous pharynx. 
• Tricladida - litle bit bigger with a three lobed gut and a tubular protrusible pharynx. 
• Polycladida - Largest (way so) with a many lobed gut and protrusible pharynx. 

A protonephridial system 

EPITHELIUM BECOMES FILTER

Flame cells contain a "head" in which flagellum beats forcing water down into the tubules

   This creates a negative pressure within the flame cell so that waste water enters the cell.

   Once inside tubules there is then a positive pressure and reabsorption of amino acids, sugars, ions, etc takes place before the final urine is released through the excretory pores. 

Rhynchocoel and Proboscis are derived, shared characters. 

Rhynchocoel wall is lined by peritoneum suggesting that it evolved from coelomic space. 

The Pseudocoeloem is derived from the blastocoel, not mesoderm. 

Protonephridial system with flame cells coupled to circulatory system (no pump)

Blood vessels are also lined by peritoneum and shared derived characters. 

Apart of Ecdysozoa - molt cuticle 

Pseudocoelomates (from coelomates) 

Only longitudinal muscle - sinosoidal waves

Ph. Annelida

Cl. Polychaetae 

External Features 

Anterior and posterior differentiation. 

Coelomic compartmentation: partitioned coelome

• Parts of Trochophore Larva
• Prostomium: Anterior = Not truly segmented and without internal coelome 
• Pygidium: Posterior = Same 

Cuticle can stretch and grow unlike Nematoda  

Heavily Cephalized 

• many sensory structures and "hard parts" (jaws and teeth: formed from cuticle which have crosslinked = Sclerotization 

Parapodia - First true appendages for locomotion 

• Consists of many chetae (setae) 
• Stiffened by Aciculae fromed through sclerotization 
• Chetae and Setae are homologous structures 

Gills might be seen on those that live in anoxic environments.  

Ph. Annelida

Cl. Polychaetae 

Internal Features

Complete gut runs through septae.

Well defined circulatory system and nervous system with ganglia in every segment. 

Spacious soelomic space 

Peritoneum seperates left and right halves. 

• Blood vessels form between two basal lamina of peritoneum. 
• Large blood cavity surrounds gut. 

Nephrostome - connects septae 

Ph. Annelida

Cl. Polychaetae 

Blood Vascular System 

Contracting blood vessels 

Flow goes from around gut --> ventral vessels --> Parapodium (respiration) --> Dorsal Vessels

Ph. Annelida

Cl. Polychaetae 

Locomotion 

Uses coelome to move in to ways. 

   1) Synoisoidal - oppiste longitudinal muscles contracting on each side of a relaxed septae. 

   2) Peristaltic - A bulbous wave (think of earth worm) 

Those that swim have very large wavelength. 

Segmentation allows for better presuure control for more efficient burrowing (Peristaltic) 

Ph. Annelida

Cl. Polychaetae 

Excretory systems 

Metanephridia 

Use the blood vascular system. 

Podocyted protrude as irregular epithelium and acts as a filter - the pumping of blood drives the filter (opposed to flagella in flatworms and nemerteans) 

Urine is collected in the Coelomic space 

Active secretion

Coelomoduct - where gametes leave the body that are produced between peritenium and released into coelomic cavity where they mature with urine! 

Ph. Annelida

larval biology and development 

Trochophore-type larva have 3 "trochs" or sets of cilia 

   1) Prototroch 2) metatroch 3) telotroch 

Growth begins at prostomium (anterior portion) 

This larvae type determines closely related phyla 

• Molluscs 
• Sipunculans 
• nemerteans 

Ph. Annelida

Cl. Polychaetae 

F. Siboglinidae 

Extremophiles -> thermal vents or shallow, cold methane seeps 

Use bacteria to gain energy from chemosynthesis 

Vestimentiferans - large gutless worms at thermal vents

Pogonophrans - Long thin gutless worms that live in anoxic basins. 

• Tentacles are used to greatly increase surface area to capture HSulfide which it delivers to the Trophosome where the bacteria live. 
• Trophosome - is homologous from gut, but it is quite different

Clear segmentation only observed at the posterior end

Median mesentary  

Ph. Annelida

Cl. Echiura

Spoon worms now nested within Polychaetes

Very long proboscis 

Environment determines sex - if no females are present where the larva lands, it becomes female. If female is present, it becomes male

Homologous metanephridia organ = Egg collecting organ - dwarf male lives inside the female. 

Ph. Annelida

Cl.(?) Sipuncula 

Introvert - invert into body cavity 

Can be suspension or deposit feeders using tentacles 

Recently placed as class wthin Annelida 

Ph. Cnidaria

Subcl. Hexacorallia (Zooanthallae) 

Scleractinian corals = Calcium Carbonate 

Can be hermatypic - Reef forming scleractinians 

Ph. Cnidaria

Subcl. Hexacorallia (Zooanthallae) 

Importance 

• High primary productivity 
• Provides habitat - especially nursuries 
• Oceanic Buffer - CO₂ uptake with symbionts 
• Coastline barrier and Ecotourism

The phytoplankton and other nutrients (which normally scatter light) are held within the coral tissue. 

Zooanthellae live within coral tissue in gastrodermal cells. 

The 20 degree celcius isotherm borders areas where hermatypic corals live. = temp plays a role. 

Ph. Cnidaria

Subcl. Hexacorallia (Zooantharia) 

Nutrition 

Corals are carnivours 

Zooanthellae provide them with fixed carbon in exchange for nitrogen 

Ph. Cnidaria

Subcl. Hexacorallia (Zooantharia) 

Reef Building

Ca⁺⁺ + 2HCO₃ <--> CO₂ + H₂O + CaCO₃ (insoluble) 

As zooanthellae take in CO₂ for photosynthesis, it drives the reaction to the right allowing for more CaCO₃ so that the coral can build large reefs. 

Ph. Cnidaria

Subcl. Hexacorallia (Zooantharia) 

Bleaching

Occurs when Zooanthallae are expelled from the coral. 

Symbionts create O₂, but when temperature increases, oxygen radicals are produced which destroy cell tissue. 

• 25% of humans infected 
• 50% of Nematoda are Parasitic 
• Live in intestines & not always debilitating 
• Feed on chyme 
• Mal nutrition and migration 
• Spread from eggs in feces 
• Sperm whale placenta RW is 9m long!

• 10% of Humans infected with 100,000 d/yr
• Gastrointestinal blood feeders 
• Malnutrition 
• Get from contaminated food or water

• 1% of humans infected 
• Migrate to muscles so that it is eaten

• 300 million infections / year 
• Mosquito vector - therefore debilitating 
• River blindness and elephantiasis

• 1990: 3.5 million cases 
• 2013: only 148 cases (Carter foundaiton) 
• Intermediate host is Copepod.
• Egg released at skin wound. 

• Mild effects - not that debilitating (tradeoff - doesn't reproduce to that point) 
• Transmission through itching and retroinfection 

• 20-25% of Humans 
• gastrointestinal blood feeders 
• Embryos in feces 
• Larae emerge on soil 
• Penetrate skin and enter circulatory system 
• Travels to heart, then to lungs where it is coughed up and swallowed! 

Platy's are 80% parasitic and really shows the evolution of parasitism. 

• Monogeneans: ectoparasites - single host
• Digeneans: two or more hosts (human liver fluke)
• Schistasome worms: distended belly from gas buildup by peritineum infection 
• Lifecycle: feces - Hatch in Water - Snail - Sporocysts - Water - Human Host 
• Asexual amplification (over 1 million times total) 
• Miracidium contain 100 sporocysts which contain 100 cercaria 
• Liver fluke infected by raw fish consumption (its in the muscle) Snail - fish - Human

• 2.5% population 
• Tapeworms - intestinal but do not feed - they lack a true gut and absorb through skin 
• Proglotids to increase SA (body is essentially like an intestine itself) 
• Become very debilitating when they migrate to other tissues (the brain for example) 

Annelida

Subcl. Hirudinea (100%)

• Land or water based ectoparasites (leeches)
• Engorge on blood meals 
• Must be able to expand = changes in coelome locomotion 
• One large space inside 
• Move like inchworms using anterior and posterior suckers. 
• Used in medicine 

• holoparasitic - only vertebrates - strong specialization 
• Loss of digestive system - absorb nutrients within vertebrate intestines 
• Microcrustacean and snail are intermediate hosts 
• Alter the behavior of hosts 
• 3 Host lifecycle - turtle, ostracod, snail

Holoparasitic horse hair worms 

• Adult stage is free living and does not feed = no digestive system 
• Juvenille stage infects arthropods 
• ingestion of tissue & adsorption => fatal 
• Alters state of hosts 
• Stylets used to introduce sperm 
• Sister group to nematodes 
• Move like nematodes