science

Holonema

Holonema 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 Holonema rather than just read about it. In short: Holonema is an extinct genus of relatively large, barrel-shaped arthrodire placoderms that were found in oceans throughout the world from the Mid to Late Devonian, when the last species perished in the Frasnian-Fammian extinction event. Most species of the genus are known from fragments of their armor, but the Gogo Reef species, H. westolli, is known from whole, articulated specimens.

Key takeaways

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

Reference excerpt

Holonema is an extinct genus of relatively large, barrel-shaped arthrodire placoderms that were found in oceans throughout the world from the Mid to Late Devonian, when the last species perished in the Frasnian-Fammian extinction event. Most species of the genus are known from fragments of their armor, but the Gogo Reef species, H. westolli, is known from whole, articulated specimens.

Description Holonema is thought to have been a benthic-dwelling fish, based on its cambered body shape, which performs better hydrodynamically when closer to the sea bed. Although previously thought to have fed in the bottom seafloor mud, more recent morphological studies of the jaw and toothplates suggest a more planktivorous lifestyle. Holonema fossil individuals have small stones in the trunk shield, and pieces of feldspar in the abdominal region, suggesting Holonema used these as gastroliths for processing food.

Species

H. rugosum H. rugosum is the type species. It was originally described as a species of the antiarch genus, Pterichthys. Fossils are found in Frasnian strata of New York and Pennsylvania, and Givetian strata of Wisconsin and Michigan. It is a fairly large species, though the type specimen is of an 18 centimeter long median dorsal plate belonging to a small individual. Fossils of H. horridum and Glyptaspis eastmani may be this species. Fossils from Frasnian Iran (H. cf. rugosum) may also belong to this species.

H. arcticum A large species from Givetian-aged strata in Novaya Zemlya, Russia, known only from two plates from one individual's trunk shield.

H. bruehni H. bruehni is a recently discovered species from the Middle Eifelian-aged Brandenberg stratum of Sauerland, Northwestern Germany. Juveniles had a dermal ornamentation of irregularly spaced tubercles, while the dermal surface of adults' armor were smooth.

H. farrowi Known from fragments from the Givetian-aged "Traverse Group" stratum in Michigan. The median dorsal plates range up to 20 cm in length. The median dorsal plate is fairly broad at the posterior end, but narrows as one approaches the anterior end.

H. haiti Known from fragments from the Givetian section of the Jefferson formation in Idaho. The median dorsal plate is estimated to be about 28 cm in length, and is very narrow compared to those of other species.

H. harmae Found in the Givetian-aged Burtnieki beds of Estonia. It is distinguished from other species in that the spinal and subpectoral margins of the anterior-ventral plates meet at almost a right angle.

H. obrutshevi Found in the Eifelian-aged Aruküla beds of Estonia. The median dorsal plate has a small, horn-like process, and the trunkshield is somewhat circular when viewed from the top or bottom.

H. ornatum From the Givetian-aged Bressay flags of the Shetland Islands. Imperfectly known. Denison 1978 suggests that it may not belong to Holonema.

H. radiatum This species is known primarily from the Frasnian-aged Shelon beds of the Baltic, and the Donetz Basin of Russia. Specimens and fragments from the Frasnian-aged Holy Cross Mountain of Poland, and the Givetian sections of the Fiskekløfta formation in Spitzbergen. It is a fairly large species with a moderately narrow median dorsal plate. The median dorsal plate averages about 30 cm in length.

H. westolli This is the best-known species of the genus, known from numerous, often articulated specimens from the Frasnian-aged Gogo Reef. The species is very similar to H. rugosum, but the trunk shield is comparatively more narrow. This species reached around 60.6 cm (23.9 in) long.

References

Further reading Case, Gerald Ramon. A Pictorial Guide to Fossils Long, John. Swimming In Stone

Illustrations

Worked examples

Example 1 — a first encounter with Holonema

Start with the simplest possible case. Write down what Holonema 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 Holonema 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 Holonema 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 Holonema

In research: Holonema 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 Holonema 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: Holonema is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fossil taxa described in 1889, Fossils of Australia, Fossils of Estonia, so understanding it makes those chapters shorter.
In everyday life: Look for Holonema 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 Holonema in 20 minutes

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

Frequently asked questions

What is Holonema in simple terms?

Why does Holonema 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 Holonema?

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 Holonema.