Flashcards in Lecture 5 Deck (16):
What are the lophophorate phyla?
The bryozoa, Phoronia and brachiopoda
What are the features of the bryozoa?
There are only about 5000 living species but 15000 fossil species are known
Colinal animals that look a bit like mosses
Most are marine and sessile but a few are freshwater
The colony is usually encased by a hard exoskeleton
They are filter feeders
They are important in reef building
What are the features of the Phoronia?
There are only about 15 species
They are worm-like, range in length of 1mm to 50cm
All are marine and live in tubes
What are the features of the brachiopoda?
There are 330 living species but 30 000 known as fossils
In terms of numbers of the fossil remains they are the most numerous of any paleozoic organism
All are marine
Live in clam shells but shell halves are dorsal and ventral (rather than the lateral of clams)
Attached to substrate by pedicel (stalk)
What are the important shared features of the lophophorate phyla?
They are all coelomate as they contain a true coelom (have a body cavity completely lined by mesodermally derived tissues)
They all have a lophophore (a horseshoe shaped structure surrounding the mouth which bears ciliated tentacles and are used to trap food)
All have a U shaped alimentary tract with the mouth and anus close together but the anus is outside the lophophore and cilia which cause water to flow over the lophphore and into the mouth
What are the consequences of having a true coelom?
Allows the gut to develop its own set of mesodermally derived muscles allowing independent movement of the gut
Gut can develop more complex set of associated tissues (blood vessels and nerves)
Inner and outer layers can connect forming mesenteries which suspend organs
Inner and outer layers of muscles allow better use of hydrostatic skeleton and greater control over movement
What are the evolutionary features of mollusca?
They are a successful group with 150,000 known living species
Appeared early in the fossil record, pre-cambrian (570 mya) but this could be due to the hard shell fossilising well
Nautilus is a living fossil which has changed little in 500 million years
What type of larva do molluscs have?
They have a trochophore larva
What are the ecological features of molluscs?
They are highly diverse living in marine, freshwater and terrestrial environments, they can be sessile, swimmers or glide on mucous
They can also be carnivores, herbivores or scavengers
What is the general mollusc body plan?
They all have a true coloem (like lophophorates- though in molluscs it is reduced to make it a small site surrounding the heart)
A shell which is hard and made of calcium carbonate (some species have lost this)
Radula which is a strap like organs used in feeding to scrape food into the mouth
A foot which is a muscular structure for movement
Two nerve cords from the brain
Visceral mass containing most body organs and a mantle
What is commonly held in the visceral mass of molluscs?
Heart, gonads a gut consisting of a mouth, radula, digestive gland, stomach, intestine and anus, as well as nephridia which are specialised excretory organs
What is the mantle?
A fold of tissue that drapes over the visceral mass and secretes the shell and often extends beyond the visceral mass to form a water filled mantle cavity
The mantle cavity houses excretory pores, Anus, and gills structures attached to circulatory system which are specialized for gas exchange and may be single, paired, or multiple and can have cilia to aid water flow and special filaments to increase surface area
What type of blood system do molluscs have?
An open blood system where the blood is pumped around the body by the heart but is not kept in blood vessels and instead occupies a series of sinuses which are separately derived from the coelom and from a haemocoel
What are the features of the gastropoda class of molluscs?
Largest class of mollusca, mostly marine though a few freshwater snails and terrestrial snails like garden snails
The terrestrial forms have lost their gills using the lining of the mantle cavity as a lung
Most have a single spiralled shell used for protection and to avoid destruction
Group contains herbivores and carnivores
What are the features of the bivalva class of molluscs?
Contains clams, oysters, mussels and scallops
These have shells divided into two halves which are lateral (on the sides of the body) rather than dorsal and ventral as in the brachiopods
The shell is hinged at the mid-dorsal line and drawn together through powerful adductor muscles
Most are filter feeders