Saturday, May 06, 2006


The order Anura is an order in the class Amphibia that is comprised of toads and frogs which are referred to as tailless amphibians1. The word Anura is derived from a Greek an-without oura-tail hence tailless2. Frogs have no tails except for their larval stages called the tadpoles. They exhibit both terrestrial and aquatic lifestyles and depend on water for reproduction2. They are distributed in tropic and temperate areas of the world occupying diverse habitats. By evolving to live on land the frogs have adapted to escape the predation of their egg in the aquatic environment where they are more vulnerable than on land. On land they have also enemies which include invertebrates (especially ants and spiders) which feed on their eggs vertebrates like snakes and small mammals which feed on the young1.

Various methods have been adopted by anurans in order to protect their young and eggs predation and enhance chances of survival in terrestrial environments. This is a form of parental care exercised by the anurans. The Families Rhacophoridae, Hylidae, Hyperoliidae, Leptodactylidae and Myobatrachidae build foam nests that are used to harbour their young4. The genus Chiromantis which is found in Africa is an example, which builds nests on tree branches near water, by the female excreting a liquid which is beaten into a froth ball by the male. Eggs are laid in the froth which hardens to retain moisture. The eggs hatch into tadpoles and have moisture constantly added by the female. Later the tadpoles drop from the froth ball when it softens and drop into water4.

Others like Pipa carvoelhi (a toad) after mating have fertilised eggs picked by the male frog on the hind legs and spread on the female’s back where they are embedded and a membrane forms to cover them. The tadpoles hatch and develop and break from the skin. Others of the Genus Afrixalus (leaf folding frogs) lay eggs in leaves where they are fertilised and then the frogs fold the leave and sometimes grasses with a sticky substance which keeps them trapped till they hatch and the glue loosens and they are released into water3.

The Nectophrynoides of Western Africa have internal fertilisation and the eggs develop in the female’s oviduct to maturity and the frog gives “birth” to froglets. The Chilean frog Rhinoderma buries her eggs on moist ground and is guarded by the males who later take them into their mouths (vocal sacs) till they mature into little frogs. One of the poisonous Phyllobatids of South America lay eggs near males who guard them till they hatch. They later take the tadpoles on their backs and produce mucous which covers the eggs till they mature. An interesting method of parenting is practised by the Australian frogs Rheobatrachus silus and Rheobatrachus vitellinus. The female swallows the eggs after fertilization brooding them in her stomach for six weeks. To avoid the eggs being digested by the digestive juices it’s thought a substance (prostaglandin E2) is secreted by the egg capsules and then by the tadpoles which stops digestion. They feed from the york of the eggs and mature to adults where they ‘born’ in a process to mammalian birth because of the contractions but through the mouth4.

Europe’s midwife toad (Family Discoglossidae) lives in holes close to water but mates on land. The eggs are in strands are fertilised and are twisted on the males hind legs till they are about to hatch and they are taken to water to continue their life there4. Another form of parenting is practised by a small frog in Brazil which builds its own pond with mud to lay eggs and the tadpoles mature in the ponds. As the rains persist the ponds are flooded and the tadpoles swim into other bigger water bodies4. Whereas the above mentioned anurans only need to utilise water that’s readily available their counterparts in desert areas had to evolve and adapt to survive with little not readily available water. They had two problems to handle escaping predators (together with the young) and also be able to utilise the scarcely available water.

The African Breviceps is a burrowing group of frog which lives in arid areas but mate when there’s a heavy rain where also the female takes in a lot of water. They have bigger females and smaller males, and fertilisation occurs with the males gluing on the females back1, 4. In this position the female burrows and lays the eggs which are fertilised by the male. Constantly the female sprays moisture onto the eggs from her bladder till the froglets hatch4. The spade foot toads in the Western Deserts of USA have tadpoles developing within two weeks or less to small frogs. The water-holding frog, Cyclorana of the central desert regions of Australia mate and lay their eggs in tepid shallow pools of water. They rapidly develop from egg, tadpole and into froglets then take as much water before burrowing deep into the sand and secrete a membrane around them to prevent them from water loss4. This way they are able to survive long dry spells in the desert.


1. Duellman, W. E. and Trueb, L. 1986. Biology of Amphibians Philippines: McGraw-Hill, Inc..

2. Wikipedia contributors. Frog [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 4, 14:56 UTC [cited 2006 May 6]. Available from:

3. Carruthers V. 2001. Frogs and Frogging in Southern Africa. Cape Town: Struik Publishers (Pty) Ltd

4. Knight, R. BCB Biodiversity chapter 2 The Invasion of the Land (Cited 2006 May 6)


Biodiversity and Conservation Biology

University of the Western Cape

Private Bag X17 Bellville

TEL: +27825103190




Hi Everyone

Vincent spotted that some text went missing on page 83 of Chapter 2 - see his posting

I will try and sort this out shortly, but I think it is best to explain how this chapter was generated. It started off as a 450 page MS Word document that we add hidden code (called XML) using third parties (Connected Learning). I use CSS (cascading style sheets) to control the final look and feel of the site. The advantage of this is it automatically creates your Page and Chapter navigation - otherwise you would have to keep renumbering pages each time you inserted a new page (Weblogs get over this by only reporting in chronological order so there is no problem). In using this approach I have noticed a couple of bugs - the worst being when two hyperlinked words to different sites follow each other they get joined together as a single word losing their space. Please just bear with this while I contact the developer on this part of the project.

There is a second issue when inserting the code we can sometimes forget to close tags for the formatting and this is what Vincent has found - a missing classification or text caused by human error of not closing a tag. When you start your HTML - you will find that it is very easy to do a mistake like this.

There is also potential for a third issue/problem, when the material was prepared I did not have access to Wikipedia and its classification concepts for species classification - and therefore the classifications could vary slightly (similar to the Homo erectus and Homo ergaster problem identified earlier in the year). It is also possibly the Wikipedia can also be wrong or inconsistent. To illustrate this the lobe-finned fish http:// called the Coelacanth Latimeria chalumnae (order Crossopterygii), if you search Wikipedia for "Crossopterygii" it will re-direct you to "Sarcopterygii". Sarcopterygii is actually the Class, and the main Wikipedia has directed you to this site and reports a different classification order "Coelacanthiformes" for the Coelacanth, but in its Wikibooks
1 Chordates
... and vindicates what I have put into the text.
A fourth point issue, I am aware of is the putting of species into italics is inconsistent - the actually scripting is tedious and we used students for the job, and well mistakes were made - but please remember there were 450 pages and more than 102 000 words, so inevitably mistakes will creep in (and we had literally a few weeks to develop the course).
If you find a mistake that is not a font-based italics or joining of two words that have independent hyperlinks (we know these are issue), then identify the page e.g. page_93.htm where there is a problem and attach as a comment to this BUG Page and in due course it will get fixed. Since when putting a change in - we have to re-compile the whole site which can potentiall change a pages url (and is literally an overnight computing task) these will not be done immediately.

Dr Richard Knight
Co-ordinator: National Information Society Learnerships - Ecological Informatics
Department of Biodiversity and Conservation Biology
University of the Western Cape
Private Bag X17
Bellville 7535

Phone 27 + 21 + 959 3940
Fax 27 + 21 + 959 1237


The phylum is a grouping of organisms used in the classification of life. The mollusca are large and varied group of organism that includes a variety of recognizable creatures well-known for their attractive shells or seafood. The common name for mollusca is mollusc or molluscs. The molluscs are triploblastic protostomes. It has thin shell, muscular foot that is used for movement and round mantle shell (1).

These range from tiny snails, clams and abalone to the octopus, cuttlefish and squid. The snail applies to most members of the mollusca class Gastropoda that have coiled shells. These snails are of herbivorous nature, found in fresh water, marine and terrestrial environment. The snails are also grouped in to, Pulmonata group (snails with lungs) and the Praphyletic group (snails with gills form). The snails move like earthworms by alternating body reductions with stretching, with proverbially low speed. They use mucus to reduce friction and chance of being injured. The mucus helps them to prevent dangerous insects like ants (1).

Mollusc are classified into nine classes of which eight of them are still living, these classes make up the 250 000 and more species of mollusc (2).Class Pelecypoda (Bivalvia) are compacted animals with two shells hinged on the animal’s dorsal surface. This class species are found in just about every marine environment. The clams are shelled marine of freshwater molluscs belonging to the class Bivalvia. They can live for 150 years old or longer. They can be hard shelled or soft shelled, according to the degree of calcification of their shells, according to species (1).

The abalone belongs to the large class of gastropods and the Haliotidae family. The shell is rounded to oval, with two to three whorls and the last one auriform, grown in to a large ‘ear’ giving rise to the common name ‘ear-shell’. ‘The cuttlefish are the animals of the order Sepiida, and are marine cephalopods, small relatives of squids and nautilus. They are having the internal shell, large eyes, and eight arms and two tentacles furnished with denticulate suckers’ (1). The squid are the large, varied group of marine cephalopods accepted as food in cuisines as widely separated as Korean and Italian. Class Caudofoveta are small (1 – 30 mm) class of the phylum mollusca, primitive deep sea molluscs. They are worm – like molluscs that live buried head down in the floor, lacking shells or distinct muscular feet (1).

Class Monoplacophora have a single cap-like shell and they superficially resemble limpets. The class Polyplacophora, usually known as chitons, have seven or eight dorsal shell plates. Class Scaphopoda or Tusk shells have a tapered, tubular shell that is unlock at both ends (1). Class Gastropoda are the largest most successful class of molluscs. Most of the approximately 40 000 living species of this class have shells; there are few groups that have either reduced or internal shells or no shell at all. The shelled forms are generally called ‘snails’ and the forms without shells are called ‘slugs’ (1).

“The slugs and snails move by contracting and relaxing their foot muscles. They are having two types of muscles fibres that are performing different work. When they are going forward they use one set, which is pulling the snail from the front and pushing it off towards the back. While the second pair pulls the outer surface of the sole forward. Usually the sole is not divided in the snails. There are some of the snails which their sole are splited lengthwise and are known as Pomatias elegans. They can both move separately, creating a sort of pedal like locomotion” (3).


1. Wikipedia contributor, Mollusca [internet]. Wikipedia, the free encyclopaedia, 2006 May 03, 08:00 UTC cited, available [].

2. Wikipedia contributors, Phylum [internet]. Wikipedia, The Free Encyclopaedia, 2006 May 03, 12:50, UTC. Available from [].

3. Arno Brosi. 2000. The biology of snail. [Internet]. Available from [, accessed 16/05/2006, 14:34].

Ms Evelyn Maleka
P.O. Box 395
Pretoria 0001
Tel: (012) 841 2133
Fax: 012 842 7024


Chordates (Phylum Chordata) are animals that have a notochord which is a stiffened cartilage rod or a back bone1 Cartilage is a dense connective tissue made of Chondrocytes (cells) embedded within a firm gel-like matrix with no blood vessels.2

Bone is a “hard endoskeletal connective tissue” which has a bone marrow and both the bone and cartilage the derived from the mesoderm.3

Chondrichthyes are cartilaginous fish which include sharks, rays and skates7, 4. They have a large brain which is less dense than the one of bony fish in comparison to their bodies4. Cartilaginous fish don’t have a bone marrow as they don’t have a bone. They produce the red blood cells in the spleen, a specialized Heydig’s organ and the specialized tissue around the gonads4. In comparison the bony fish have a bone marrow where the red blood cells are produced. They also have a special organ called Epigonal organ which is responsible for their immunity needs as their counterparts immune system is taken care of from the bone marrow 4.

Bony fish have external fertilization whereby they lay eggs that are later fertilized outside the body. The fertilized eggs later hatch to young fish, though many of which don’t reach maturity level6. Cartilaginous fish have internal fertilization like mammals and give rise to live small fish (e.g. the ray) or lay eggs (some sharks and skate). 4, 5 Sharks produce either by oviparity (lay eggs), vivparity (born alive) or oviviparity (eggs mature within mother without being fed by the mother) 6. This means of fertilization ensures that all eggs are fertilized as compared to external fertilization where sperm is sprayed on the eggs and can be washed off. The eggs also can be easily predated on6. Also the process of keeping young one in the body enhances their chances for survival of the young. Though internal fertilization has an advantage as compared to the external in terms of security of the young it also makes the Chondrichythes heavy. This makes an advantage to the bony fishes allowing them to move fast.

Bony fishes have an internal organ called a swim bladder that helps them to float5. They used to move to the water surface and gulp air and fill a pouch which served as the first lungs and were used for buoyancy, later developed into a swim bladder. Cartilaginous fish rely on oil stores in their body and have to keep swimming to remain afloat. 6 Bony have the ability to float in one position by the ability to absorb oxygen through their blood system from the gills which fills the swim bladder and this gas can be regulated to determine the height the fish wants to float. This frees the fins and tail for movements other than staying afloat making them fast.

Some sharks like the sand tiger shark normally gulp air from the surface and store it the stomach to maintain buoyancy6. Due to their somehow heavy head they have pectoral fin which helps them maintain balance and also propels them by beating in water.

The bodies of cartilaginous fish are covered by a tough skin covered with dermal teeth which feels like a sand paper called the placoid scales. This helps them reduce turbulence as they move .6 Bony fish have smaller tightly fitting scales overlapping like roof tiles and covered by mucous making more it smooth and slippery7. This makes them agile and move fast. Bonyfish have the ability to float in one position by the ability to absorb oxygen through their blood system from the gills which fills the swim bladder and this gas can be regulated to determine the height the fish wants to float.

Osteichthyes have adapted well and are able to occupy various niches as compared to Chondrichthyes who are restricted to only being either mobile hunters (sharks) or sea bed feeders7.


1. Wikipedia contributors. Chordate [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 15:22 UTC [cited 2006 May 5]. Available from:

2. Wikipedia contributors. Cartilage [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 21:28 UTC [cited 2006 May 5]. Available from:

3. Wikipedia contributors. Bone [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 24, 16:15 UTC [cited 2006 May 5]. Available from:

4. Wikipedia contributors. Chondrichthyes [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 5, 20:22 UTC [cited 2006 May 5]. Available from:

5. Wikipedia contributors. Fish [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 5, 18:29 UTC [cited 2006 May 5]. Available from:

6. Wikipedia contributors. Shark [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 4, 20:53 UTC [cited 2006 May 5]. Available from:

7. Knight, R. BCB Biodiversity chapter 2 The Conquest of the Water and the Birth of the Vertebrates (Cited 2006 May 5)


Biodiversity and Conservation Biology

University of the Western Cape

Private Bag X17 Bellville

TEL: +27825103190