Schistosomatidae

Key takeaways

Schistosomatidae belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Schistosomatidae to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Schistosomatidae from memory before moving on to harder problems.

Reference excerpt

Schistosomatidae is a family of digenetic trematodes with complex parasitic life cycles. Immature developmental stages of schistosomes are found in molluscs and adults occur in vertebrates. The best studied group, the blood flukes of the genus Schistosoma, infect and cause disease in humans. Other genera which are infective to non-human vertebrates can cause mild rashes in humans. Schistosomatids are dioecious (individuals are of separate sexes) which is exceptional with regard to their phylum, Platyhelminthes, in which most species are hermaphroditic (individuals possess both male and female reproductive systems).

History The eggs of these parasites were first described by Theodor Bilharz, a German pathologist working in Egypt in 1851 who found the eggs during the course of an autopsy. He wrote two letters to his former teacher Karl Theodor Ernst von Siebold in May and August 1851 describing his findings. von Siebold wrote a paper (published in 1852) summarizing Bilharz's findings. Bilhart's wrote a paper in 1856 describing the worms more fully and he named them Distoma haematobium. Their unusual morphology meant that they could not be comfortably included in Distoma so in 1856 Meckel von Helmsback created the genus Bilharzia for them. In 1858 Weinland proposed the name Schistosoma (Greek: 'split body') after the male worms' morphology. Despite Bilharzia having precedence the genus name Schistosoma was officially adopted by the International Commission on Zoological Nomenclature. In 1898 all the then known species were placed in a subfamily by Stiles and Hassel. This was then elevated to family status by Looss in 1899. Poche in 1907 corrected a grammatical error in the family name. The life cycle was determined by da Silva in 1908.

Evolution There are a number of different families of blood fluke including the Schistosomatidae. The others include the spirorchiids (turtle parasites) and the sanguinicolids (fish parasites). The Schistosomatidae are considered venous system specialists and their sister group are vascular system generalists - the Spirorchiidae. Schistosomatidae differ from other blood flukes in having separate sexes and homeothermic hosts. They have compensated for the reduction in potential reproductive partners by

an increased overdispersion in the vertebrate host the reduced egg hatching time in the external environment the formation of permanent pairs mimicking the hermaphroditic condition the increased longevity in the definitive host increased fecundity. Colonization of the venous system was made possible by

the evolutionary radiation into terrestrial vertebrates the increased immunopathology associated with the high, constant body temperature of homeothermic vertebrates. The arterial-dwelling spirorchiids release eggs in the direction of blood flow, resulting in a wide dissemination of eggs within the host. The lower body temperature of poikilotherms is accompanied by a seasonal nature of the immune response in these hosts resulting in a quantitatively reduced pathogenesis. Hosts that did succumb to the infection would most likely die in water where eggs could be released by predation, scavengers, or decomposition and develop successfully. Colonization of the venous system by schistosomes required precise egg placement because their eggs are released against the blood flow. Eggs are then sequestered within the portal system (or perivesicular plexus in some species) of homeotherms which restricts egg dispersal but limits the resulting pathology to less sensitive organs. A significant number of eggs may escape into the external environment before a heavily infected host is incapacitated by, or dies from, the infection. The first hosts of the schistosome were birds. Based on their current geographical spread the most likely place of origin of this family is Asia with subsequent spread to India and Africa. Only one species is known to infect crocodiles - Griphobilharzia amoena. This species infects the freshwater crocodile Crocodylus johnstoni. Phylogenetic analysis shows that the genus Griphobilharzia rather than being a basal schistosome is a relation of the spirorchiids that infect freshwater turtles. It has also shown that the spirorchiids are the closest relations of the schistosoma. An outline of the evolution of the schistosoma is now possible. The ancestral species infected freshwater turtles and the life cycle included gastropod hosts. Some of these species in their turn infected the marine turtles. At some point members of species infecting marine turtles developed the ability to infect birds – most likely waterfowl. This probably occurred somewhere in the Asian continent presumably at or near the coast. The bird species eventually developed the ability to infect mammals. This last development seems to have occurred in Gondwana between 120 million years ago and 70 million years ago.

Taxonomy The family was created in 1926 by Stiles and Hassel for the Schistosoma, the Sanguinicolidae and the Spirorchiidae. It has since been divided into four subfamilies: Schistosomatinae, Bilharziellinae, Denrobilharziinae and Gigantobilharziinae. In the Gigantobilharziinae the ventral sucker is absent and the female genital pore is medial near the anterior end of the body. In the Bilharziellinae the ventral pore in the female is always posterior to the ventral sucker. Both the Bilharziellinae and the Gigantobilharziinae are found exclusively in birds while the Schistosomatinae are found in both mammals and birds. In the Denrobilharziinae both suckers are absent and the caecum has numerous branches. In this latter family there is one genus (Denrdobilharina) with two species (Dendrobilharzina purvulenta and Dendrobilharzina asicaticus). There are 12 genera in this family. Of these, seven infect birds: the others infect mammals including humans. There are about 100 known species in this family. The largest genus within the family Schistosomatidae is Trichobilharzia with over 40 species. The genera are:

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Illustrations

Worked examples

Example 1 — a first encounter with Schistosomatidae

Start with the simplest possible case. Write down what Schistosomatidae claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Schistosomatidae before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Schistosomatidae ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Schistosomatidae

In research: Schistosomatidae appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Schistosomatidae in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Schistosomatidae is common in secondary-school and first-year university syllabi. It links to neighbouring topics Diplostomida, Trematoda families, Waterborne diseases, so understanding it makes those chapters shorter.
In everyday life: Look for Schistosomatidae outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Schistosomatidae in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Schistosomatidae means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Schistosomatidae out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Schistosomatidae in simple terms?

Schistosomatidae is a family of digenetic trematodes with complex parasitic life cycles. Immature developmental stages of schistosomes are found in molluscs and adults occur in vertebrates.

Why does Schistosomatidae matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Schistosomatidae?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Schistosomatidae.