Toad dissection

I decided to photograph and talk about a toad dissection I did this week. Some people (Lorelei?) might not want to see these pictures. A few of the Queenslanders amongst you are likely to have done a toad dissection at school. I wish I could preface this entry with some illuminating comment on the ethics of dissection, but in order to do this sort of thing I try not to think too hard about the morals of what I'm doing. Sometimes I feel a sympathetic pain in the same body part as the part of the animal I'm cutting. I am a hypocrite. But enough of my moral flabbiness, and on with the toad.



Here's my toad. I picked it out of the other toads in the tub because it was a very pretty shade of pale yellow. It's illegal to breed cane toads, so the toads we used were captured in Northern Queensland and crated down.



This is always the saddest part of the dissection.




Once I've made the first cut it's easier to think of the toad as a specimen, and not an animal. Here (above) I've cut through the skin to reveal the abdominal muscles. Toads have no external genitalia (both sexes have a multi-purpose cloaca), so it's only once you get inside that you can tell what sex it is. This is a male toad, because it has a vocal sac. You can see the vocal sac in the photo immediately above. It's the black-and-white flecked section of skin beneath the lower jaw.



These pictures were taken after I cut through the muscle layer. The internal organs are known collectively as the viscera. In the above picture, where the chest muscles and vocal sac have been severed, you can see the white roof of the toad's mouth.


Here's a close-up of the viscera. The following organs are visible:

Lungs: the pale yellow, honey-comb sacs on either side of the body. As well as breathing with their lungs, toads can breathe and absorb water through their skin.

Heart: dark red, in the centre of the chest.

Stomach: pale pink tube on the lower right hand side of the photo. It is attached the small intestine, which is the thinner, coiled tube.

As it turned out, there was something wrong with my toad. The large grey ball in the middle of the viscera is the gall bladder, which is abnormally enlarged. Normally the toad's liver would be dark brown-red and cover a large portion of the viscera. However, this toad's liver is visible as the two shrunken, pale brown masses on either side of the gall bladder. Humans with poor liver function can have a yellow complection. Maybe the yellow colouring I initially took to be the sign of a particularly beautiful toad was actually a result of liver disease. The demonstrator told me that if my toad was a human, it would be an alcoholic.

At this point my camera ran out out of batteries, so I can't show you the toad's kidneys, which were located under the rest of the viscera, or its internal testes, which are small yellow things that sit above the kidneys. Neither can I show you inside its heart, which I had to remove, slice through and put in a petri dish. Underneath the viscera I could see the toad's backbone sitting against its skin. I ran out of time to draw the nervous system, so I wanted to take the toad home in my lunchbox to finish the prac, but the demonstrator wouldn't let me.

Next week I'm doing a pigeon.

To Pea or not to Pea

Here are the names of some plants we had to identify on our ecology excursion. I like a good latin name, but sometimes you can't beat a common name for whimsy.

screw fern
pithy sword sedge
wire rapier sedge
red beaks
milky beauty-heads
common billy-buttons
creeping cudweed
button everlasting
honey-pots
twin-flower beard-heath
common raspwort
slender dodder-laurel
coarse dodder-laurel
love creeper
horny conebush

It's nice to know, though, that even scientific names are not above being a wee bit twee. Note the obtuse angles in the leaves of this plant, the common flat-pea. The plant's scientific name is Platylobium obtusangulum.

Having the Slime of my Life: defensive reflexes in Myxiniformes

Some animals have unfortunate names.

The dik dik, for example.











Or the nudibranch.

Other animals not only have a funny name, but remind us that nature is not always beautiful. The naked mole rat springs to mind.

But my favourite animal in the aforementioned category is the hagfish. Hagfish resemble the earliest fish in that they have no lower jaw. Instead, they tear pieces off polychaete worms and dead fish. I am not sure whether it's their gummy, left-my false-teeth-out style of eating that gives them the name 'hags', but it seems appropriate.

Hagfish are also known, charmingly, as slime hags, due to their numerous mucus glands. This is what my textbook has to say about hagfish:

"A disturbed hagfish can produce enormous volumes of protective mucus; once released from the body, the mucus expands very rapidly and can completely fill a bucket containing the hagfish within minutes."

Disappointingly, it seems that there is no such creature as a fagfish, with whom these slimy, disturbed hags would presumably form a symbiotic relationship.

Rhesus monkey skeletons, Melbourne Uni zoology museum

Fish fingers: Acanthostega and tetrapod evolution

This handsome devil is Acanthostega. One of my lecturers refers to him as 'friend Acanthostega', and, for reasons I will explain, I have come to think of Acanthostega as a friend.
There are no photos to show you, because Acanthostega has been dead for approximately 365 million years.

A cultural theory enthusiast might say that Acanthostega inhabited the liminal zone. A normal person might say that he was a half-fish, half reptile who lived in a swamp. When you hear about creatures crawling out of the primeval soup, it's Acanthostega who did the crawling.


As you can see, Acanthostega's limbs sit a little awkwardly on his body. This is because limbs have only just been invented. Acanthostega's predecessors were fish with fins. He was probably not mobile on land, but could use his legs to brace himself against aquatic plants, and push up out of the mud.

Early limb-bearing creatures like Acanthostega usually had six to eight digits on each hand. It was only later in evolutionary history that most animals settled on five digits as the optimal number.

Of all the species that have ever existed, it is estimated that 99% are extinct. It's sad to think of the last Acanthostega sinking lifelessly into the Upper Devonian mud. However, there is a happy ending. Limbs proved to be a very successful evolutionary strategy. Acanthostega is not just a friend, but a relative. It seems (my textbook is not explicit on this) that his descendants include ourselves!

If an animal mates with another species of animal, is it still bestiality?: Onychophorans and outbreeding depression.

I promised more obscure invertebrates, so here is an onychophoran. Onychophorans are forest leaf litter dwellers. I have never seen one, but I live in hope. Their common-or-garden name, velvet worms, seems to suggest that holding one would feel like being stroked with a piece of velvet. As a presumptive scientist, I have qualms about using a word like 'cute', but look at those little antennae. I'm only human!

Onychophorans are also wonderful because they are freaks. I have a soft spot for animals who exist in distant, unclassifiable, evolutionary backwaters. Onychophorans appear to be related to both insects and annelid worms, but cannot be classified as either. They exist in a phylum all of their own. To put this in perspective, human beings are in the phylum Chordata, along with (more or less) everything else that has a backbone. The phylum Onychophora contains only onychophorans. 

Germaine Greer reputedly remarked the other day that she was an animal. Perhaps Germaine should consider becoming an invertebrate. In the tradition of female-dominated ant, bee and termite societies, and female praying mantises who devour their mates after sex, some onychophorans live under a rigid matriarchal hierarchy. 

The Australian species Euperipatoides rowelli commonly lives in a social group of up to 15 females, males and young. They hunt as a pack, immobilising their prey with a sticky secretion of mucus. The group observes a strict hierarchy in the order in which they feed. The dominant female feeds first, followed by other females, then the males and young. According to biologists who made this discovery, 'hierarchy within the group is established by aggressive-dominant and passive-subordinate behaviours'. At least there are no passive-aggressive onychophorans. 

Aggressive behaviour consists of kicking, biting, chasing and climbing on other individuals. Passive behaviour involves running away or allowing oneself to be climbed on. Females are commonly larger than males, and this may explain their higher status. Onychophorans of this species have been observed running their antennae over others' backs, perhaps to estimate their size and social status. 

However, while it's a dog-eat-dog world inside the onychophoran pack, they close ranks against outsiders. To quote the aforementioned biologists, 'E. rowelli from different groups, ie. from different logs, are met with intense agression'. Perhaps Germaine is right. It seems all too easy to draw parallels with the human condition. Personally, when I see someone from a different log, I can barely contain myself. But first I run my antennae over their back, just in case. 

Unfortunately for onychophorans, fragmentation of their habitat means it's sometimes difficult to find a mate, so they resort not to inbreeding, but to outbreeding. To explain by way of analogy, onychophorans are not like the hillbilly who marries his cousin, but the hillbilly who marries his goat. Unable to find a mate of the same species, they will breed with a different species of onychophoran. As with many cross-species matings, the resulting offspring often have fertility problems, as well as unusual numbers of legs. 

God scribbled a penis on the ocean floor: the discovery of Riftia pachyptila

Invertebrates are animals that have no backbone. (Actually, to be technically correct, they have no dorsal notochord, but I want this blog to be intellectually light weight, so let's say the first definition is okay.)

Some invertebrates have captured the popular imagination. There are childrens' films featuring ants and bees. There are no childrens' films that feature cute, talking digenean flukes. You might dress your kid in a T-shirt with a picture of a butterfly. You would not dress her in a shirt with a picture of a tapeworm. Or, for that matter, a nematode, a nemertean, or a nudibranch.

Pycogonids are related to spiders, but Incy Wincy pycogonid never climbed up the water spout. A vestimentiferan never flew away home to find her children missing and her house on fire.

Maybe this is because having your house on fire is a pretty normal state of affairs for vestimentiferans. These animals live around hydrothermal vents on the ocean floor. At great depths, molten rock released below the earth's surface causes hot water to flow up into the ocean.




Before 1977, no one knew vestimentiferans existed. Scientists who were conducting an oceanographic survey from a navy submarine unexpectedly discovered unfamiliar worm-like creatures living around vents at a depth of 2500 metres.

Vestimentiferans live inside a hard tube. They have no mouth or gut. Instead, they are filled with bacteria. The hydrothermal vents release sulphur, which the bacteria digest to produce energy. (This is highly unusual, as most living things have to obtain energy either from eating someone else or from photosynthesis.) The vestimentiferan can then digest the bacteria.

In the words of our normally serious and world-weary lecturer, they are 'easy to remember for the exam because they're the ones that look like a giant penis'. Giant is the right word. Vestimentiferans grow to be 2.5 metres long.

More deeply unpopular invertebrate friends to come!