science

Prosobranchia

Prosobranchia is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Prosobranchia rather than just read about it. In short: Prosobranchia was a large taxonomic subclass of gastropods, which included sea snails, land snails and freshwater snails. This taxon dates back to the 1920s, but has since been proven to be polyphyletic (consisting of more than one lineage of descent).

Key takeaways

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

Reference excerpt

Prosobranchia was a large taxonomic subclass of gastropods, which included sea snails, land snails and freshwater snails. This taxon dates back to the 1920s, but has since been proven to be polyphyletic (consisting of more than one lineage of descent). In biology taxonomy must reflect phylogeny and monophyletic groups are preferred; in other words, the classification of a group must reflect its evolutionary descent as far as that is known through studies of Morphology (biology) and genetic analysis, and must include a common ancestor and all of its descendants. Therefore, the taxon Prosobranchia with its multiple evolutionary origins is no longer considered suitable to be used. One can still encounter this subclass used as if it is still valid in many texts and websites. Although Prosobranchia is no longer generally accepted as a taxon by malacologists, the term prosobranch is legitimately used as an anatomically descriptive adjective or noun, and the taxon Prosobranchia is still sometimes used by paleontologists. The majority of marine gastropods are prosobranch, as are a few land snails and freshwater snails. The prosobranch gastropods include the majority of marine snails, among them conches, cones, cowries, limpets, murexes, periwinkles, volutes and whelks, as well as numerous freshwater groups, and some land snails with an operculum. Prosobranchs have their gills, mantle cavity and anus situated in front of their heart. Most prosobranchs have separate sexes.

Description The majority of prosobranchs have an operculum, a corneous or calcareous plate situated on the dorsal surface of the foot. In many prosobranchs, the animal can completely close the aperture with the operculum. The nervous system of prosobranchs is twisted into a figure 8 due to a developmental process known as torsion. The eyes are situated at the base of the tentacles.

Taxonomic context The taxonomy of the gastropods is changing rapidly. The old classification (Johannes Thiele) divided Gastropoda into three subclasses: Prosobranchia, Opisthobranchia and Pulmonata. The subclass Prosobranchia (Henri Milne-Edwards) was further divided into the orders Archaeogastropoda, Mesogastropoda and Neogastropoda. The new version of the gastropod classification is explained in Taxonomy of the Gastropoda (Ponder & Lindberg, 1997).

References

Thiele, J., 1929–1935. Handbuch der Systematischen Weichtierkunde. 2 vols. 1154 p., 584 figs. Bieler, R. & P. M. Mikkelsen (eds.), 1992. Handbook of Systematic Malacology, Part 1 (Loricata [Polyplacophora]; Gastropoda: Prosobranchia). Smithsonian Institution and National Science Foundation, xviii + 625 pp., 470+1 text-fig. (Annotated English-language edition of: Thiele, J., Handbuch der systematischen Weichtierkunde, Teil 1). Also published, in 1993, by Gustav Fischer Verlag, Stuttgart/Jena/New York. Bieler, R. (1992). "Gastropod phylogeny and systematics". Annual Review of Ecology and Systematics. 23 (1): 311–338. Bibcode:1992AnRES..23..311B. doi:10.1146/annurev.es.23.110192.001523. Haszprunar, G. (1988). "On the origin and evolution of major gastropod groups, with special reference to the Streptoneura". Journal of Molluscan Studies. 54 (4): 367–441. doi:10.1093/mollus/54.4.367. Bieler, R. (1990). "Haszprunar's "clado-evolutionary" classification of the Gastropoda - a critique". Malacologia. 31 (2): 371–380.

Illustrations

Worked examples

Example 1 — a first encounter with Prosobranchia

Start with the simplest possible case. Write down what Prosobranchia claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Prosobranchia 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 Prosobranchia 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 Prosobranchia

In research: Prosobranchia appears in science 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 Prosobranchia 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: Prosobranchia is common in secondary-school and first-year university syllabi. It links to neighbouring topics Gastropod taxonomy, Mollusc subclasses, Obsolete gastropod taxa, so understanding it makes those chapters shorter.
In everyday life: Look for Prosobranchia 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.

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How to study Prosobranchia in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Prosobranchia 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 Prosobranchia out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Prosobranchia in simple terms?

Why does Prosobranchia matter?

Because it connects several science 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 Prosobranchia?

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 Prosobranchia.