biology zoology blog benno meyer rochow lamprey parasitism

Something Terribly Fishy

But unquestionably true

Speak with a non-zoologist about “parasitic fishes” and the conversation will inevitably come to “murderous” piranhas. Yet, in spite of their reputation these South American freshwater fish are not parasitic, but represent predators with razor sharp teeth and a healthy appetite, which can indeed kill, but aren’t murderous. Predators, by definition, finish off their prey; yes, but parasites are animals that obtain nourishment from another living animal without killing it, like for instance blood-sucking hagfishes and lampreys. —>—>

roundworms insect science biology

Wriggling to Success

Who could beat the roundworms?

When zoologists mention the term “successful” in connection with animal species, they mean something different from the success that a sportsperson, a business manager or a movie star might be talking about. A successful animal species or animal group, referred to as a “taxon”, is one that is widespread and has been able to exploit a variety of different habitats. Clearly, insects are very successful as a group, for they occur in virtually all terrestrial habitats. But the emphasis has to be on “terrestrial”, because there are almost no marine species, yet more than 70% of the Earth is covered by oceans!

One of the truly most successful animal groups are the roundworms, i.e. nematodes as they are known to the zoologist. All of them in contrast to, for example, the earthworm have an unsegmented round body and the vast majority of them are microscopically small, though Ascaris, the horse roundworm, can grow to pocket ruler length and the giant amongst the roundworms, which lives in the placenta of whales, may reach more than a metre in length.

Roundworms exist in and on the soil, in and on other animals as well as plants and I have recently found several species inside the gut of millipedes. Some species occur in the deep sea, others call the desert home; some thrive in vinegar and even in the soggy, circular beer coasters of Bavaria roundworms have been found. Humans, especially children, may be hosts of the pinworm Enterobius vermicularis (a rather harmless parasite), but hook worms, Trichinella species and the horrible Wucheria bancrofti, the latter causing a disfiguring disease known as ‘elephantiasis’, are roundworm species one had better not encounter.

Nematodes are champion survivors and some species may enter a state known as cryptobiosis, during which totally dry and extremely low temperatures can be tolerated. Under optimal conditions, however, they can be prolific reproducers. They possess, of course, muscles for their characteristic whip-like propulsive movements, a mouth, a gut, a nervous system etc., but unlike most animals their nerves don’t send projections to the muscles: the muscles instead have long outgrowths to contact the nervous system.

If that is not peculiar enough, roundworm bodies are made up of a precise number of cells, so that the researcher can determine exactly how many cells the entire animal and its organs consist of and, even better still, what each embryonic cell will differentiate into during the animal’s development. No wonder that such cell-constancy displaying species (and especially the tiny Caenorhabditis elegans) have become celebrated ‘laboratory pets’ for geneticists, who take an interest in unravelling the fundamental processes of cell fates. The worm’s main disadvantage is that its behavioural repertoire is rather limited and morphologically Caenorhabditis elegans and other roundworms also exhibit far fewer interesting features than, for instance, the hundreds of fruit fly mutants (another ‘pet animal’ of the molecular geneticists) that researchers have access to for study.

Final advice: if by chance you should have become a roundworm’s unwilling host some day, don’t panic, for even the most successful creep (worm or otherwise) can be defeated.

parasite manipulation biology science

For more reading about parasites : click for another story : “Parasitic manipulations”

© Dr V.B. Meyer-Rochow and, 2016.
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parasite manipulation biology science

Parasitic manipulations

Who’s in control ?

Having a dog forces us to walk more frequently, finding a cockroach in a meal makes us lose our appetite, and having ticks or lice makes us scratch (and perhaps wash) more often: Animals can cause us to change our behaviour. But those changes are nothing compared with what some animals (especially small ones) do to others.

Nematode worms of the genus Mermithia castrate their insect hosts. A worm, known as Acanthocephala, matures in freshwater fish, but has larval forms that attack small crustaceans. Following an infection, the latter turn bright red and become easy targets for the predatory fish. Unusually red abdomens in some tropical ants, filled with nematode eggs, are also a consequence of a parasite attack, causing ants to resemble tropical fruits and to get eaten by birds. Thus, the nematodes reach their target. Continue reading