Macroctopus

Key takeaways

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

Reference excerpt

Macroctopus is a monospecific genus of cephalopod belonging to the family Octopodidae, the "typical octopuses". The only species in the genus is Macroctopus maorum, the Māori octopus or the New Zealand octopus (wheke in Māori). It is found in the waters around New Zealand and southern Australia. M. maorum is one of the largest octopus species living in the New Zealand and Australian waters. They feed mainly on crustaceans and fish. Although they have a short life span, the females lay thousands of eggs and are very protective of them. This taxon is regarded as a synonym of Pinnoctopus cordiformis by some authorities.

Taxonomy Macroctopus was first proposed as a new subgenus of Octopus in 1928 by Guy Coburn Robson with Octopus maorum as its type species. This species was first formally described in 1880 by Frederick Hutton with its type locality given as Dunedin. This taxon is regarded, by some authorities, as being regarded as conspecific with Pinnoctopus cordiformis, with M. maorum being treated as the junior synonym of P. cordiformis. Yet other authorities do not regard P. cordiformis as conspecific with M. maorum and suggest that P. cordiformis is a synonym of Enteroctopus zealandicus.

Identification Macroctopus maorum is a large octopus and it is regularly described as a ‘robust’ species, it is a member of the Octopus macropus species complex. The morphological traits characteristic of this complex are a high number of gill lamellae, a robust conical copulatory organ and arms of varying length with long unequal dorsal arms generally four to six times longer than the mantle. Although being unequal, their arms are said to be long and evenly tapering and Macroctopus maorum are even known to regrow arms when one has been lost. Being the largest member of its complex arm span is said to exceed 3 metres (9.8 ft). They have four to six suckers on the first and second arm pairs which are usually about 40 millimetres (1.6 in) in size. Suckers are arranged in two rows down the arm length. There is thought to be no correlation between sexes and size of suckers; however, there was an increase in sucker size with body mass increase. Coloration of this species can vary Macroctopus maorum can be distinguished from other species by the colour, they will be either orange-brown or dark purple-grey. The octopus has numerous small iridescent white spots on the web, arms and dorsal arm crown but there are no spots present on the mantle. Macroctopus maorum has 12–14 gill lamella per demibranch, the mantle is described as broadly ovoid and exhibits a skin pattern of longitudinal ridges. Along the dorsum there are five rows of unbranched papillae and two more papillae appear individually above the eyes. Octopus papillae are camouflage specialised with the ability to change shape, such as by extending in and out from the body. Male M. maorum have a small ligula, the ligula is a specialised arm tip on the hectocotylized arm which grips to allow the transfer of spermatophores. Within the complex O. macropus, Macroctopus maorum is thought to be the largest member. In a study estimating M. maorum size based on a sample of 90 beaks, the largest individual found had a body length of 2.0 metres (6 ft 7 in) and body mass of 12 kilograms (26 lb). Macroctopus maorum has an upper beak and lower beak, the upper beak can be used to differentiate Macroctopus maorum and Enteroctpus zealandicus as it has a lack of overlap in the ratio of upper hood length and upper chest length. Macroctopus maorum hatchlings are usually about 5.06 millimetres (0.199 in) in size, they have 7–8 suckers per arm and each dorsal arm will have 6–11 chromatophores.

Life cycle/Phenology

Sexual maturity

Female Grubert and Wadley assigned 5 maturity stages for the egg development of Macroctopus maorum:

Newly formed primary oogonia which has a small, distinct nucleus is visible and Follucular cells attach to the ovum and forming follicular epithelium. Follicular epithelium has completely filled the ova and nucleus is no longer visible. There are no yolk present and cuboidal follicular cells become distinct and closely packed. First granular yolk appears in the ova. Epithelial convolution still occupying much of the interval volume. Only periphery of the ova found and been forced out by the expanding yolk. Nuclei of epithelium has now become indistinct. Mature ova which have thin walls and are replete with yolk. Follicular epithelium produced the chorion and degenerated. Ova is free in the ovary, oviduct or oviducal glands. Female that undergoes stage 4 oocytes were caught throughout the month of April to October, while those females that undergo stage 3 were caught only in April and July. However, females with stage 5 oocytes were caught every month except May and August.

Male In the male, the position of testis from juvenile to adult is different. The position of testis moved backward until it reached the final position at the hinder end of the body during the adult stage. Fully mature male octopus consist of fully-formed spermatophores in the Needham’s sac. They usually had up to 13 spermatophores in the Needham’s sac. Furthermore, their reproductive organ will increase in size over the lifetime.

Mating During mating, the male Macroctopus maorum will be on top pinning down the female and usually overpowering the female physically or pouncing on them. The male will inserts a sperm packet by passing it along the arms to the oviduct of the female. When it gets near the oviduct, the end of the spermatophore burst open and release the sperm. Male octopus will then become senescent and die after mating. Female Macroctopus maorum mature and mate during March and October.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Macroctopus

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

In research: Macroctopus appears in earth 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 Macroctopus 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: Macroctopus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cephalopods of Oceania, Molluscs described in 1880, Molluscs of New Zealand, so understanding it makes those chapters shorter.
In everyday life: Look for Macroctopus 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 Macroctopus in 20 minutes

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

Frequently asked questions

What is Macroctopus in simple terms?

Macroctopus is a monospecific genus of cephalopod belonging to the family Octopodidae, the "typical octopuses". The only species in the genus is Macroctopus maorum, the Māori octopus or the New Zealand octopus (wheke in Māori).

Why does Macroctopus matter?

Because it connects several earth 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 Macroctopus?

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 Macroctopus.