the-french-artist/wikipedia_20220301.simple_sentence_split huggingface dataset:
In species where the hectocotylus is missing, the penis is long and able to extend beyond the mantle cavity and transfers the spermatophores directly to the female.
The females lay many small eggs in one batch, and die afterwards.
The Nautiloidea, on the other hand make a few large eggs in each batch, and live for a long time.
The class developed during the late Cambrian and were the most common and varied marine life forms during the Palaeozoic and Mesozoic eras.
Tommotia, an early cephalopod, had squid-like tentacles but also a snail-like foot it used to move across the sea floor.
Early cephalopods were at the top of the food chain.
The old (cohort Belemnoidea) and modern (cohort Neocoleoidea) coleoids, as well as the ammonoids, all diverged (evolved away from) from the external shelled nautiloids during the middle Paleozoic Era, between 450 and 300 million years ago.
Most ancient varieties had protective shells.
These shells at first were conical but later developed into the curved shapes seen in modern nautilus species.
Shells inside the body still exist in many living cephalopod groups, such as cuttlefish.
The most famous group with external shells, the ammonites, became extinct at the end of the Cretaceous period.
Berthold, Thomas, & Engeser, Theo.
Phylogenetic analysis and systematization of the Cephalopoda (Mollusca).
Verhandlungen Naturwissenschaftlichen Vereins in Hamburg. (
NF) 29: 187-220.
Engeser, Theo.
Fossil Nautiloidea page.
<http://userpage.fu-berlin.de/~palaeont/fossilnautiloidea/fossnautcontent.htm>
Felley J. Vecchione M. Roper C.F.E. Sweeney M. & Christensen T. 2001-2003: Current classification of Recent Cephalopoda.
internet: National Museum of Natural History: Department of Systematic Biology: Invertebrate Zoology: http://www.mnh.si.edu/cephs/
Shevyrev A.A. 2005.
The Cephalopod macrosystem: a historical review, the present state of knowledge, and unsolved problems: 1.
Major features and overall classification of cephalopod molluscs.
Paleontological Journal.
39: 606-614.
Translated from Paleontologicheskii Zhurnal #6, 2005, 33-42.
CephBase - cephalopod database
TONMO.COM - The Octopus News Magazine Online - cephalopod articles and discussion
Tree of Life Web Project - Cephalopoda
Mikko's Phylogeny Tree
Articles on various fossil cephalopod topics for non-specialists
Fish vs. Cephalopods
Will Fast Growing Squid Replace Slow Growing Fish?
Bipedal Octopuses with links to video and original paper
Palcephalopoda/Neocephalopoda Hypothesis
Biomineralisation in modern and fossil cephalopods
Cuttlefish are marine Cephalopod molluscs.
They belong to the same class as squid, octopodes and the nautilus.
Cuttlefish eat small molluscs, crabs, shrimp, fish and other cuttlefish.
Various sharks and fish prey on them.
They live about 1 to 2 years.
Cuttlefish have an internal cuttlebone, made of calcium carbonate.
It is porous, full of small holes, The buoyancy of the cuttlebone can change, allowing the cuttlefish to go lower or higher by changing the amount of gas and liquid in its chambers.
The cuttlebone of each species has a distinct shape, size, and pattern of ridges or texture.
Cuttlebones are used by jewellers and silversmiths as moulds for casting small objects.
They are probably better known today as the material given to pet birds as a source of calcium.
The cuttlebone is only found in cuttlefish, and is one of the features that makes them different from squid and other molluscs.
Cuttlefish are sometimes called the chameleon of the sea because they are able to change their skin color.
Their skin can flash a colorful pattern in order to communicate with other cuttlefish and to camouflage them from predators.
This color-changing function is produced by groups of red, yellow, brown, and black pigmented chromatophores above a layer of reflective iridophores and leucophores.
These are all in the cuttlefish's skin, and work together to change its colour.
There are up to 200 of these special pigment cells per square millimeter.
The pigmented chromatophores have a sac of pigment and a large membrane that is folded when retracted.
There are 6-20 small muscle cells on the sides which can contract to squash the elastic sac into a disc against the skin.
Iridophores are plates of chitin or protein, which can reflect light.
They are responsible for the metallic blues, greens, golds, and silvers often seen on cuttlefish.
All of these cells can be used in combinations.
As well as being able to influence the colour of the light that reflects off their skin, cuttlefish can also affect the light's polarization, which can be used to signal to other animals which sense polarization.
Cuttlefish eyes are among the most developed in the animal kingdom.
The way cephalopod eyes develop is fundamentally different from that of vertebrates like humans, but the way they work is rather similar.
The similarity between cephalopod and vertebrate eyes is an examples of convergent evolution.
Although they cannot see color, they can perceive the polarization of light, which improves their ability to see contrast.
They have two spots of concentrated sensor cells on their retina (known as fovea), one to look more forward, and one to look more backwards.
The lenses, instead of being reshaped as they are in humans, are instead pulled around by reshaping the entire eye in order to change focus.
The blood of a cuttlefish is an unusual shade of green-blue because it uses the copper-containing protein haemocyanin to carry oxygen instead of the red iron-containing protein haemoglobin that is found in vertebrates.
This is similar to the blood of arthropods.
Haemocyanin is not as good at carrying oxygen as haemoglobin.
The blood is pumped by three separate 'hearts'.
Two of these are used for pumping blood to the cuttlefish's pair of gills (one heart for each gill), and the third for pumping blood around the rest of the body.
Human interest
Cuttlefish have inks like squid and octopuses.
As with squid, the ink is a defensive tool, squirted out to cover its retreat in the case of danger.
This ink was formerly an important dye, called sepia.
Today artificial (not natural) dyes have replaced natural sepia.
Cuttlefish as food
Cuttlefish are caught for food in Mediterranean, and East Asian cultures.
Although squid is more popular as a restaurant dish all over the world, in East Asia dried cuttlefish is highly popular.
Cuttlefish is popular in Italy and Croatia, where it is used in Risotto Nero. "
Nero" means 'black', which is the colour the rice turns because of the cuttlefish ink.
Spanish cuisine often uses cuttlefish and squid ink for cooking due to the marine flavor and smoothness that it provides to the meals and it is included in dishes such as rice, pasta and fish stews.
Cuttlefish in literature
Cuttlefish made their most important literary appearance in the title of Eugenio Montale's collection of poetry called Cuttlefish Bones (Ossi di seppia), published in Turin in 1925.
Montale was awarded the Nobel Prize for Literature in 1975.
There are over 120 species of living cuttlefish, in 5 genera.
Sepiadariidae contains seven species and two genera; all the rest are in the Sepiidae.
CLASS CEPHALOPODA
Subclass Nautiloidea: nautilus
Subclass Coleoidea: squid, octopus, cuttlefish
Superorder Octopodiformes
Superorder Decapodiformes
Order Spirulida: Ram's Horn Squid
Order Sepiolida: bobtail squid
Order Teuthida: giant squid
Order Sepiida: cuttlefish
Suborder Sepiina
Family Sepiadariidae
Family Sepiidae
Scientific Database with photos and videos of cuttlefish and other cephalopods
TONMO.com offers articles and forum discussion on cuttlefish care
YouTube video of a cuttlefish harassing a diver
YouTube video of cuttlefish hovering about.
You can see colour changes and movement.
Amazing cuttlefish – Cephalopods with natural camouflage and sepia ink
Diving with cuttlefish
Nautilus is the common name for cephalopods of the family Nautilidae.
They are the only living members of the subclass Nautiloidea.
In appearance, they have not changed much in millions of years.
The term chambered nautilus is also used for any species of the Nautilidae.
Today, there are six living species in two genera.
The species Nautilus pompilius, from Western Australia is the largest and best known.
It get up to 27 cm in diameter.
However, most other nautiluses never exceed 20 cm.
The Bellybutton nautilus, Nautilus macromphalus, is the smallest species, usually measuring only 16 cm.
The radula is wide and has exactly nine teeth.
There are two pairs of gills.
The shell
Nautiluses are the only cephalopods who have an external shell.
This is an ancestral or basal, feature.
The animal can withdraw completely into its shell.
It can the close the opening with a leathery hood formed from two specially folded tentacles.
The shell is coiled and calcareous, with mother-of-pearl lining.
It is pressure resistant, but will implode at a depth of about 800 m. The nautilus shell is made of two layers: the outer layer is a dull white, while the inner layer is a striking white with iridescence.
The innermost portion of the shell is pearlescent, blue-gray.
A osmena pearl is not a pearl, but a jewellery product got from this part of the shell.
The shell is internally divided into chambers.
All the walls between chambers ('septa') are pierced in the middle by a duct, the siphuncle.
Through this the animal can change the air pressure in the chambers.
As the nautilus matures its body moves forward, sealing each chamber in turn with a new septum (wall).
The last fully open chamber, the largest one, is used as the living chamber.
The number of chambers increases from around four at the moment of hatching to thirty or more in adults.
The shell colour keeps the animal hidden in the water.
When seen from the top, the shell is darker in color and marked with irregular stripes, which makes it blend into the darkness of the water below.
The underside is almost completely white, making the animal indistinguishable from brighter waters near the ocean surface.
This mode of camouflage is called countershading.
Buoyancy and movement
In order to swim, the nautilus draws water into and out of the living chamber and makes use of jet propulsion.
When water is inside the chamber, the siphuncle extracts salt from it and diffuses it into the blood.
When water is pumped out, the animal adjusts its buoyancy with the gas contained in the chamber.
Buoyancy can be controlled by the  pumping of gas and fluid into or from the chambers using the siphuncle.
The control of buoyancy like this limits the nautilus; they cannot operate under extreme pressure.
In the wild, nautilus usually lives in depths of about 300 m, rising to around 100 m at night for feeding, mating and egg laying.
The shell of the nautilus cannot withstand depths greater than approximately 800 m.
Diet and sensory system
Nautiluses are predators and feed mainly on shrimp, small fish and crustaceans, which are captured by the tentacles.
However, due to the very little energy they devote to swimming, they need only eat once a month.
Unlike other cephalopods, they do not have good vision; their eye structure is highly developed but lacks a solid lens.
They have a simple "pinhole" lens through which water can pass.
Instead of vision, the animal is thought to use olfaction as the primary sensory means during foraging, locating or identifying potential mates.
Fossil records indicate that nautiloids have not changed much (at least in their body form) for the last 500 million years.
Nautiloids were much more common and varied 200 million years ago.
Many of the early ones were straight-shelled, as in the extinct genus Lituites.
They developed in the Cambrian and became a significant sea predator in the Ordovician period.
Some species reached over 2.5 meters in size.
The other cephalopod subclass, Coleoidea, diverged from the Nautilidae long ago and the nautilus has remained relatively unchanged since.
Extinct relatives of the nautilus include ammonites, which were very important for many millions of years.
Other groups were the baculites and goniatites.
Reproduction and lifespan
Nautiluses are sexually dimorphic and reproduce by laying eggs.
Attached to rocks in shallow waters, the eggs take twelve months to develop before hatching out at around 30 mm long.
Females spawn once per year and regenerate their gonads, making nautiluses the only cephalopods to repeat reproduction.
The lifespan of nautiluses is about 20 years, which is exceptionally long for a cephalopod.
Nautiluses are only found in the tropical Indian and Pacific Oceans, from 30° N to 30° S latitude and 90° to 185° W longitude.
They live on the deep slopes of coral reefs.
Ward, P.D. 1988.
In search of Nautilus.
Simon and Schuster.
Nautilus pompilius at ARKive
Nautilidae discussion forum at TONMO.com
Waikïkï Aquarium: Marine Life Profile: Chambered Nautilus
A molecular and karyological approach to the taxonomy of Nautilus
A logarithmic spiral, equiangular spiral or growth spiral is a special kind of spiral curve which often appears in nature.
The logarithmic spiral was first described by Descartes and later extensively investigated by Jakob Bernoulli, who called it Spira mirabilis, "the marvelous spiral".
In polar coordinates (r, θ) the curve can be written as
hence the name "logarithmic".
In parametric form, the curve is
with real numbers a and b.
The spiral has the property that the angle ɸ between the tangent and radial line at the point (r,θ) is constant.
This property can be expressed in differential geometric terms as
The derivative r'(θ) is proportional to the parameter b.  In other words, it controls how "tightly" and in which direction the spiral spirals.
In the extreme case that b = 0 (ɸ = π/2) the spiral becomes a circle of radius a.  Conversely, in the limit that b approaches infinity (ɸ → 0) the spiral tends toward a straight line.
The complement of ɸ is called the pitch.
Spira mirabilis and Jakob Bernoulli
While this curve had already been named by other mathematicians, the name "miraculous" or "marvelous" spiral was given to this curve by Jakob Bernoulli, because he was fascinated by one of its unique mathematical properties: the size of the spiral increases, but the shape stays the same with each added curve.
Maybe because of this property, the spira mirabilis has evolved in nature, seen in some living beings, such as nautilus shells and sunflower heads.
Jakob Bernoulli wanted the shape on his headstone, but, by error, an Archimedean spiral was placed there instead.
Logarithmic spirals are self-similar in that they are self-congruent under all similarity transformations (scaling them gives the same result as rotating them).
Scaling by a factor  gives the same as the original, without rotation.
They are also congruent to their own involutes, evolutes, and the pedal curves based on their centers.
Starting at a point P and moving inwards along the spiral, one has to circle the origin infinitely often before reaching it; yet, the total distance covered on this path is finite.
This was first realized by Evangelista Torricelli even before calculus had been invented.
The total distance covered is r/cos(α), where r is the straight-line distance from P to the origin.
One can construct approximate logarithmic spirals with pitch about 17.03239 degrees using Fibonacci numbers or the golden ratio as is explained in those articles.
Similarly, the exponential function exactly maps all lines not parallel with the real or imaginary axis in the complex plane, to all logarithmic spirals in the complex plane with centre at 0. (
Up to adding integer multiples of 2πi to the lines, the mapping of all lines to all logarithmic spirals is onto.)
The pitch angle of the logarithmic spiral is the angle between the line and the imaginary axis.
Logarithmic spirals in nature
In several natural phenomena one may find curves that are close to being logarithmic spirals.
Here follows some examples and reasons:
The approach of a hawk to its prey.
Their sharpest view is at an angle to their direction of flight; this angle is the same as the spiral's pitch.
The approach of an insect to a light source.
They are used to having the light source at a constant angle to their flight path.
Usually the sun is the only light source and flying that way will result in a practically straight line.
The arms of spiral galaxies.
Our own galaxy, the Milky Way, is believed to have four major spiral arms, each of which is roughly a logarithmic spiral with pitch of about 12 degrees, an unusually small pitch angle for a galaxy such as the Milky Way.
In general, arms in spiral galaxies have pitch angles ranging from about 10 to 40 degrees.
The arms of tropical cyclones, such as hurricanes.
Many biological structures including spider webs and the shells of mollusks.
In these cases, the reason is the following: Start with any irregularly shaped two-dimensional figure F0.
Expand F0 by a certain factor to get F1, and place F1 next to F0, so that two sides touch.
Now expand F1 by the same factor to get F2, and place it next to F1 as before.
Repeating this will produce an approximate logarithmic spiral whose pitch is determined by the expansion factor and the angle with which the figures were placed next to each other.
This is shown for polygonal figures in the accompanying graphic.
Spring Loaded Camming Device
Jim Wilson, Equiangular Spiral (or Logarithmic Spiral) and Its Related Curves, University of Georgia (1999)
Alexander Bogomolny, Spira Mirabilis - Wonderful Spiral, at cut-the-knot
Spira mirabilis history and math
Logorithms
The small white (Pieris rapae) is a small to mid-sized butterfly of the 'yellows' & 'whites' Pieridae family.
It is also commonly known as the small cabbage white or just the cabbage white.
It looks like a smaller version of the Large White.
The upperside is creamy white with black tips to the forewings.
Females also have two black spots in the center of the forewings.
Its underwings are yellowish with black .
Like its close relative the large white this is a strong flyer and the British population is increased by continental immigrants in most years.
Like other 'white' butterflies it hibernates as a pupa.
Like the large white, it is sometimes known as the cabbage white' or cabbage butterfly.
Its caterpillars can be a pest on cultivated cabbages. .
It also lays eggs on wild members of the cabbage family such as the charlock Sinapis arvensis and hedge mustard Sisybrium officinale.
The eggs are laid singly on foodplant leaves.
Known in the United States as "imported cabbage worms", the caterpillars are green and well camouflaged.
Unlike the large white they do not store the mustard oils from their foodplants and so are not distastful to predators like birds.
Asher J. et al.
The millennium atlas of Britain and Ireland Oxford University Press
Evans W.H. 1932.
The identification of Indian butterflies.
2nd ed, Bombay Natural History Society, Mumbai, India.
Argonauta, the argonauts, is the only living genus in the Argonautidae family.
They are a group of pelagic octopods.
They are also called paper nautiluses, because of the paper-thin eggcase that females make.
This structure does not have the gas-filled chambers of nautilus shells, and is not a true cephalopod shell.
It is an evolutionary innovation unique to the genus Argonauta.
Argonauts are found in tropical and subtropical waters worldwide: they live in open ocean.
Like most octopods, they have a rounded body, eight arms and no fins.
However, unlike octopuses, argonauts live close to the sea surface rather than on the seabed.
Argonauta species have very large eyes and small distal webs.
They have a mantle-funnel locking apparatus, which is a way to identify the genus.
It consists of knob-like cartilages in the mantle and corresponding depressions in the funnel.
Unlike the closely related genera Ocythoe and Tremoctopus, Argonauta species lack water pores.
Sexual dimorphism and reproduction
In Argonauts, males and females are quite different in size and lifespan.
Females grow up to 10 cm and make shells up to 30 cm, while males rarely grow larger than 2 cm.
The males only mate once in their short lifetime, but the females can get pregnant repeatedly.
The females have been known since ancient times while the males were only described in the late 19th Century.
The males use a modified arm, the hectocotylus, to transfer sperm to the female.
For fertilization, the arm is inserted into the female's pallial cavity, then is detached from the male.
The hectocotylus was originally described as a parasitic worm.
The hectocotyl arm and its correct function were described by Aristotle.
His account was disbelieved for over 2000 years, but was rediscovered in the early 19th century.
Eggcase
Female argonauts make a laterally compressed, calcareous eggcase in which they live.
It is secreted by the tips of the female's two greatly expanded dorsal tentacles (third left arms) before egg laying.
After she deposits her eggs in the floating eggcase, the female herself takes shelter in it, often along with the male's detached hectocotylus.
She is usually found with her head and tentacles protruding from the opening, but she retreats deeper inside if disturbed.
These ornate, curved white eggcases are occasionally found floating on the sea surface, sometimes with the female argonaut still clinging to it.
It is made of calcite, with a 3-layered structure The argonauts may have evolved to use ammonite shells for their egg laying, eventually becoming able to mend the shells and perhaps even make their own.
Argonauta argo is the largest species in the genus and also produces the largest eggcase, which may reach a length of 300 mm.
The smallest species is Argonauta bottgeri, with a maximum recorded size of 67 mm.
The beaks of Argonauta species are distinctive.
They  are characterised by a very small rostrum and a fold that runs to the lower edge or near the free corner.
The rostrum is 'pinched in' at the sides.
This makes it much narrower than in other octopuses, with the exception of the closely allied monotypic genera Ocythoe and Vitreledonella.
Argonaut beaks are most similar to those of Ocythoe tuberculata and Vitreledonella richardi.
They differ in 'leaning back' to a greater degree than the former and because they have a more curved jaw angle than the latter.
Feeding and defense
Feeding mostly occurs during the day.
Argonauts use tentacles to grab prey and drag it toward the mouth.
It then bites the prey to inject it with poison from the salivary gland.
They feed on small crustaceans, molluscs, but also jellyfish and salps.
If the prey is shelled, the argonaut uses its radula to drill into the organism, then inject the poison.
Argonauts are capable of changing their color.
They can blend in with their surroundings to avoid predators.
They also produce ink, which is ejected when the animal is being attacked.
This ink paralyzes the olfaction of the attacker, providing time for the argonaut to escape.
The female is also able to pull back the web covering of her shell, making a silvery flash, which may deter a predator from attacking.
Argonauts are preyed upon by tunas, billfishes, and dolphins.
Shells and remains of argonauts have been recorded from the stomachs of Alepisaurus ferox and Coryphaena hippurus.
Male argonauts have been seen living inside salps, which are planktonic tunicates.
Little is known about this relationship.
The genus Argonauta contains up to seven existing species.
Several extinct species are also known.
The extinct species Obinautilus awaensis was originally assigned to Argonauta, but has since been transferred to the genus Obinautilus.
Tree of Life web project: Argonauta
Protection means when any group of people or things try to defend the people or things that they care about (so that they would not get hurt).
Protection can also mean other things, for example:
Civil protection, or civil defense, protecting life, health, property and environment of citizens
Environmental protection, is a political action that is to do with protecting nature by preservation (keeping them), and restoration (making something that was lost to come back)
Contraception (euphemism)
Protectionism, in world trade, making people stop buying what other countries make, so they must buy things made in their own country
Protective clothing, clothing that protect the body from danger
A protectorate, in politics and history, is the protector (the person who protects), for example:
A Lord protector, guarding as the country like a minor Monarch or during The Protectorate as a British republic
The protectorate between a strong power (the protector) and a weaker one, who can ask for help when needed, or are obliged to agree
Protection (album), a 1994 album by the group Massive Attack
Protection (song), a song by trip-hop band Massive Attack.
It was released in 1995
Protection (band) is an American band, based in San Francisco
The Protection of the Mother of God, a feast day in the Eastern Orthodox Church
Minor (law), a young person who has not yet reached the age of majority or some other legal age
Minor scale, a minor key in music
Camouflage is a visual disguise.
Without it, an animal would be recognised easily.
If the natural colour of an animal makes it look like its surroundings, that is camouflage.
A tiger's stripes in the long grass, and the battledress of a modern soldier are examples.
Camouflage is a form of deception.
The word camouflage comes from the French word camoufler, which means "to disguise".
Natural camouflage
In nature, most animals blend into their environment or conceal their shape.
They are very hard to see.
This way they survive, and if they survive, then they can reproduce.
There are exceptions: animals which are dangerous to eat (e.g. wasps) advertise with warning colouration.
Prey animals hide from predators.
Predators must search for prey without being seen.
Natural camouflage is one way to do this: an animal can blend in with its surroundings.
Another way is for the animal to disguise itself as something harmless.
Some camouflaged animals also copy movements in nature, e.g., of a leaf blowing in the wind.
Other animals attach natural materials to their body for concealment.
A few animals change color in changing environments.
Seasonally: (many Arctic animals, such as the arctic fox, or arctic hare).
Or quickly, like the chameleon and the cuttlefish.
Some herd animals, like zebra, have a pattern which makes it difficult for the predator when they are running.
Most animals are dark on top and light underneath.
With light coming from the sky, this countershading makes them less visible.
That this is the correct explanation is proved by cases where the animal lives upside down.
A famous example is the Nile catfish, which swims belly uppermost.
In this case, the belly is dark, and the back is light in colour.p43
Transparency and silvering
Transparent or partly transparent animals are common in the pelagic layer of the sea.
These are the layers into which light penetrates.
The effect of transparency or silvering works is better under water than above it.
This is because the amount of light which penetrates is less and less as the depth increases.
Also, the proportion of the light reflected is much less under water (0.001–0.6%) than in air (2–5%).
Warning colouration: the opposite of camouflage
Ferrari, Mareo 1992.
Colors for survival: mimicry and camouflage in nature.
NY: Barnes & Noble.
Behrens, Roy R. 2002.
False colors: art, design and modern camouflage.
Bobolink Books.
Wolf, Art 2005.
Vanishing act.
Text by Barbara Sleeper.
NY: Bullfinch Press.
Purser, Bruce 2003.
Jungle bugs: masters of camouflage & mimicry.
Toronto: Firefly.
Forbes, Peter 2009.
Dazzled and deceived: mimicry and camouflage.
Harris, Tom.
How animal camouflage works.
How Stuff Works.
Roy R. Behrens.
Art and camouflage: an annotated bibliography
Roy R. Behrens 2006.
The thinking eye: a chronology of camouflage
An informal study into camoflage
BBC/Attenborough: Octopus hides in shells, from Blue Planet II.
In biology, an extant group is one which has survived to the present day, and so it is a living group.
This distinguishes it from an extinct group.
Echinoderms  are a successful phylum of marine animals.
They include sea stars, brittle stars, sea urchins, sea cucumbers and their relatives.
A skeleton of plates.
These are formed from calcite, a mineral made of calcium carbonate.
The plates are usually spiny, and the skeleton is covered outside and in by a layer of skin.
Five-rayed (pentameral) symmetry.
A water-vascular system.
This is an internal system of tubes and bladders filled with water.
Tube feet.
These are extensions of the water-vascular system.
The tube feet poke out from the skeleton, and are used in walking, respiration and feeding.
The animal handles the world outside by using its tube feet.
Stenohaline.
They can't handle big changes in the salinity of the water.
No doubt this is why they are:
Entirely marine.
Echinoderms live in all parts of the ocean, but mostly on the sea floor.
Some are filter feeders, and others (starfish) are important predators of molluscs and other shell-fish.
They are extremely common near the shore, and on reefs.
They have a long and abundant fossil record.
This phylum appeared in the early Cambrian period; it contains about 7,000 living  and 13,000 extinct species.
The four or five main groups are called sub-phyla by some authorities, and classes by others.
A modern classification
Asterozoa: about 1,500 species that catch prey for their food.
Asteroidea: the starfish.
Sea daisies, notable for their unusual water vascular system.
Only two species, now merged into Asteroidea.
Ophiuroidea (brittle stars and basket stars), the largest echinoderms; about 1,500 species.
Crinozoa (crinoids: the feather stars or sea lilies): about 600 species that are suspension feeders.
Originally these were stalked echinoderms with long arms, rather plant-like in appearance.
In this form they are called 'sea lilies'.
The P/Tr extinction event almost eliminated them.
Now they are reduced to a few deep-water species.
The free-living 'feather stars' in shallow water are quite successful today.
Blastozoa: the cystoids, an extinct group.
They were mostly sessile and lived in shallow waters.
Sometimes put together with crinoids in the subphylum Pelmatozoa.
Echinozoa: echinoids and sea cucumbers.
Echinoidea: sea urchins and sand dollars, notable for their movable spines.
There are about 1,000 species.
Holothuroidea (sea cucumbers).
Relatively soft-bodied animals with a tube-like shape; about 1,500 species.
The usual calcareous elements in the skin are much reduced, but the skin is quite tough, and covered in slime.
They have good defences against predators.
Homalozoa: an extinct group of strange early echinoderms.
Some put them in the phylum Chordata, and call them calcichordates.
A simplified classification
For many purposes it is better to use the following classification.
It is easier to learn and understand, and is based more on the living forms.p19
Ophiuroidea: the brittle-stars
Echinoidea: the sea-urchins
Holothuroidea: the sea-cucumbers
Crinoidea: the sea-lilies and feather-stars.
General account
All echinoderms have fivefold radial symmetry in their body at some stage of life.
The holothurians have bilateral symmetry as adults, and do not have so much of a skeleton as other groups.
Echinoderms have a hydraulic water vascular system.
This network of fluid-filled canals moves and feeds the animal, and allows gas exchange.
There is also a complete digestive tube.
They have a simple radial nervous system that consists of a modified nerve net.
There are nerve rings with radiating nerves around the mouth extending into each arm.
The branches of these nerves coordinate the movements of the animal.
Echinoderms have no brain, although some do have ganglia.
They usually move with their tube feet, but brittle stars use their arms to pull against rocks.
Some feather stars and sea cucumbers can swim.
The sexes are usually separate.
Sexual reproduction typically consists of releasing eggs and sperm into the water, with fertilization taking place externally.
Their larvae are planktonic.
Many echinoderms have remarkable powers of regeneration.
A starfish arm cut off will regenerate.
A section as small as a single arm, with some central disk and neural tissue, can regenerate the whole organism.
Echinoderm larvae
Most of the adults have radial symmetry.
If they are not sessile or attached, they are at least benthic (bottom-dwellers).
In contrast, echinoderm larvae are planktonic, and have bilateral symmetry.p119 Echinoderm larvae are ciliated free-swimming organisms that have a bilaterally symmetry rather like embryonic chordates.
The first stage in all groups except the crinoids is the dipleurula, which has a row of cilia winding round its body.
All the groups have second and third stage larvae.
The larvae grow, and are carried away from their parents.
Later, the adult body grows into a radial form, with the body arranged in five parts around a central axis.
This means they often have a star-shaped pattern.
There is no geological evidence about the origin of echinoderms.
The first undoubted fossils in the Lower Cambrian are already well developed, and fall into five or six different groups.
Arkarua, from the Ediacaran, is thought to be an echinoderm.
Tribrachidium is another possible, from the same period.
On general biological grounds, it seems that echinoderms, and some related phyla, may have been derived from worm-like ancestors.p311
Of all invertebrate phyla, the echinoderms are the closest relatives to the chordata, that is, animals who have spinal cord, such as vertebrates.
With the chordates and hemichordates, echinoderms are deuterostomes, one of the two major divisions of the animal kingdom.
Clark A.M. 1968.
Starfishes and their relations, 2nd edition.
Paul C.R.C & Smith A.B. (eds) 1988.
Echinoderm phylogeny and evolutionary biology.
Echinodermata from the Tree of Life website.
Argonauta, a genus of octopus
Jason and the Argonauts, a tale from Greek mythology
Argonaute (protein), a kind of protein
The Toronto Argonauts, a Canadian Football League team that plays in Toronto, Ontario
Das Rheingold (The Rhinegold) is an opera by Richard Wagner.
It is the first of the four operas that together tell a story called Der Ring des Nibelungen (The Ring of the Nibelung).
Das Rheingold is an opera in one act, divided into four scenes.
It is a very long act, lasting 2 ½ hours, but it is normally played without an interval as the music is continuous, even between the scenes.
The characters in the opera are Gods, Giants, Nibelungs and the Rhinedaughters.
The Nibelungs are a race of dwarfs.
They are cunning and evil and live underneath the surface of the earth.
The first scene takes place in the river Rhine where the three Rhinemaidens: Woglinde, Wellgunde and Flosshilde, are guarding the precious Rhine gold.
Alberich, an evil Nibelung dwarf, arrives and tries to catch the Rhinemaidens.
From what they say Alberich learns that the gold they are guarding gives the person who owns it the power to rule the world.
Alberich wants the gold, but the Rhinemaidens say that anyone who wants to have it has to renounce (give up) love.
They think that Alberich will not do that because he is very fond of girls, but Alberich does renounce love and so he gets the gold.
The second scene takes place in Valhalla, which is where the gods live.
Wotan, the chief god, is there with his wife Fricka.
Two giants have been building an enormous castle for the gods.
Wotan has promised them that he would pay them for their work by giving them Freia, the Goddess of Youth and Beauty.
Fricka is worried about the promise that Wotan has made, but Wotan tells his wife that he is not going to keep his promise.
He thinks he can find a way of tricking the giants.
Freia enters.
She is frightened because the giants are coming for her.
The giants, Fasolt and Fafner, enter.
They want to have Freia in payment for having built the castle.
The problem for the gods is that Freia has a garden in which she grows golden apples.
If the gods no longer have these golden apples they will grow old and die.
Wotan does not know what to do.
Loge, the god of fire, enters.
Wotan is cross with Loge for not having found something else to pay the giants with.
Loge says he has been all over the world looking for something.
He tells everyone that the gold from the Rhine has magic power, and how Alberich renounced love so that he could steal it from the Rhinemaidens.
He tells them that a ring can be made from the gold, and that whoever has the ring will have power over all the world.
The giants hear what Loge is saying and decide that they want the gold instead of Freia.
They take Freia as hostage, saying that they will be back later to collect the gold.
If they do not get it then they will keep Freia forever.
Wotan asks Loge how they are going to get the gold.
Loge tells them that they should steal it from Alberich.
After all, Alberich stole it from the Rhinemaidens, so it does not belong to him.
Wotan and Loge go down below the earth to the Nibelungs.
Scene 3
Underneath the earth Alberich is forcing the Nibelungs to work for him.
They are hammering at the anvil.
Mime, who is Alberich’s brother, has used some of the gold to make a helmet.
This helmet is called the Tarn helmet.
Anyone who wears it can change their shape or become invisible.
Alberich treats his brother very cruelly.
Wotan and Loge tell Alberich that they have heard how clever he is.
They ask him to show them what he can do with the Tarn helmet.
Alberich puts on the helmet and changes himself into a huge dragon.
Wotan and Loge pretend to be impressed.
They ask him whether he can change himself into something small.
Alberich show off again, changing himself into a frog.
Wotan immediately puts his foot on him and catches him.
Wotan and Loge take all the gold and go back to Valhalla.
Wotan and Loge tease Alberich.
Alberich asks them what they want so that he can be free.
Wotan demands the gold.
The Nibelungs pile the gold up.
Alberich is not too worried, because he still has the ring which gives him magic power.
He thinks he can use this power later to get the gold back.
Wotan sees the ring on Alberich’s finger.
He tells him to give him the ring.
Alberich is terrified, but Wotan tears it from his finger.
Before Alberich goes he puts a curse on the ring.
Whoever has had the ring will die.
This is very important to the whole story of the four operas.
The two giants appear with Freia.
The gods have become very weak, but once Freia returns they start to become stronger again.
Wotan tells the giants they can have their gold.
The giants say that they must pile up the gold in front of Freia until they cannot see her.
They do this, but the giants say there is still a tiny hole through which they can see Freia’s eye.
They see the ring on Wotan’s finger and tell him to put it in the hole.
Wotan says they can have anything they want but not the ring.
Erda appears.
Erda is the Earth Goddess.
She reminds Wotan that there is a curse on the ring and that he should quickly give the ring to the giants.
Wotan has no choice.
He puts the ring in the hole.
Now the giants are happy.
Immediately, however, the giants start to argue with one another and Fafner kills Fasolt.
The curse on the ring is working.
Loge tells Wotan he was wise to give up the ring.
However, Fricka is still worried because Wotan did have the ring.
Donner, the god of Thunder, enters and swings his hammer.
There is a flash of lightning and a crash of thunder.
The clouds vanish, a rainbow makes a bridge to Valhalla and the gods enter Valhalla.
The Rhinemaidens are heard crying out to Wotan to give the gold back, but Wotan takes no notice.
The gods are now at the height of their glory.
We shall see, at the end of the fourth opera, that the curse will catch up with them and that they, too, will die.
The music of Das Rheingold is beautifully written to fit every person and every situation.
The famous opening starts with a low chord of E flat which describes the bottom of the river Rhine.
At first the notes of the chords are held on, then gradually a ripple of broken chords and arpeggios suggest the ripples of the water.
The harps make a sound like the waves.
The harmony just consists of the same E flat chord for the first 136 bars until the Rhine Maidens start to sing.
Each character in the opera has his own musical leitmotif which can change and combine to show their changing moods and situations.
There are big, heavy chords for the giants, creepy chromatic winding music for Loge, the god of fire, who is supposed to be very crafty, dignified music for the Earth Goddess Erda etc.
There is a special leitmotif for the curse, which is heard at various times in all four operas.
The other operas
The second opera in the cycle is Die Walküre.
The third opera in the cycle is Siegfried.
The fourth opera in the cycle is Götterdämmerung.
The whole cycle is called Der Ring des Nibelungen.
Compositions by Richard Wagner
Die Walküre (The Valkyrie) is an opera by Richard Wagner.
It is the second of the four operas that together tell a story called Der Ring des Nibelungen (The Ring of the Nibelung).
The story continues from the first opera which was called Das Rheingold.
It is a very beautiful piece.
Die Walküre was first performed on 26 June 1870 in Munich.
The first performance that was part of the whole Ring cycle took place on 14 August 1876.
The opera starts with a storm.
The young man Siegmund is out in the storm and comes to a house.
The house belongs to Hunding who lives there with his wife Sieglinde.
An ash tree is growing in the middle of the house.
Siegmund and Sieglinde are twins who were separated as children, so neither of them knows who the other one is.
Their father is Wotan, the chief god, but they don’t know this either.
Their mother was a mortal (an ordinary person, not a goddess) or perhaps a she-wolf, which is how the goddess Fricka refers to her.
Sieglinde lets Siegmund into the house and gives him a drink of mead.
They start to fall in love.
Hunding arrives and asks Siegmund who he is.
Siegmund says that his name ought to be Woeful because he has had an unhappy life.
When he was small he came home once and found his house burned down, his mother murdered and his twin sister had been abducted (taken away).
He then remembers that some years later he went to help a young lady who had been forced to marry a cruel man.
He had killed some of the man’s friends.
Hunding realizes that he himself was this man, so that he is Siegmund’s enemy.
He says to Siegmund that he can sleep in his house tonight because this is a law of hospitality, but in the morning he will have to fight him.
Sieglinde goes to prepare a drink for her husband.
She puts a drug in it which will make Hunding sleep deeply.
Siegmund meanwhile is thinking about something his father had promised him.
He had told him that he would thrust a magic sword called “Nothung” into a tree.
No one would get that sword until, one day, when Siegmund found himself in great difficulty, he would be able to pull it from the tree and use it.
Sieglinde enters and tells Siegmund a story about how, on the day she was forced to marry Hunding, an old man had come into the house and thrust a sword into the ash tree in the middle of the room.
They start to realize that they are brother and sister,  but it does not stop them from falling in love and they sing passionately about their love for one another.
Siegmund pulls the sword from the tree and the two lovers embrace.
Wotan is the chief god, whom we heard in Das Rheingold.
He is trying to get rid of the curse of the Rheingold, and has built a grand plan around Siegmund.
Wotan tells his daughter Brünnhilde that she must make sure that Siegmund wins the fight with Hunding.
Brünnhilde (the out-of-wedlock daughter of Wotan and Erda, the Earth-Mother goddess) has the power to do this.
She is one of eight daughters of Wotan who are Valkyries (German: Walküren).
Their job is to collect the dead bodies of brave heroes who have died in battle and take them back to Valhalla, the house of the gods.
Wotan’s wife Fricka arrives in a chariot pulled by a ram.
Brünnhilde disappears, and there follows a big argument between husband and wife.
Fricka says to Wotan that Siegmund and Sieglinde must be punished for breaking Hunding's marriage, and for loving one another because brothers and sisters are not allowed to be lovers (this is called “incest”).
She says that she herself is the goddess of marriage and must make sure that marriage laws are obeyed.
Fricka says that the gods will all be disgraced.
Wotan says that he went to the world to have children with mortal women because the gods needed a race of heroes who would protect them.
But Fricka says to Wotan that he is wrong: Siegmund cannot be a free hero if he is being protected by Wotan.
Giving in, Wotan now tells Brünnhilde that she must leave Siegmund to his fate.
Sieglinde tells Siegmund that she feels guilty and that he ought to leave her, but they are desperately in love.
When she hears Hunding’s horn she imagines that Siegmund will be torn apart by the dogs and she faints.
Brünnhilde pities Siegmund.
She tells Siegmund that he must follow her to Valhalla.
When Siegmund asks whether he can take Sieglinde with her Brünnhilde says that he cannot do this.
Siegmund refuses to go.
Brünnhilde tells him that he cannot escape his fate.
Siegmund continues to plead with Brünnhilde, and in the end she is so moved that she changes her mind.
She breaks Wotan's order, and says that she will protect Siegmund in battle.
Hunding appears and the two men fight.
Brünnhilde protects Siegmund with her shield.
Siegmund is nearly winning when suddenly Wotan appears and smashes Siegmund’s sword into pieces.
Hunding kills Siegmund.
The other Valkyries are wondering where Brünnhilde is.
They see her coming on her horse, but instead of a hero she is carrying a woman (it is Sieglinde).
The Valkyries are angry with Brünnhilde because she disobeyed Wotan.
Sieglinde wants to die, but when she is told that she has a baby in her womb she asks Brünnhilde to save her.
She escapes into the forest with bits of Siegmund’s sword.
One day the baby she is now bearing will grow up, become a hero, and use the bits to make another sword.
Wotan goes to the Valkyries.
He is furious with Brünnhilde because she disobeyed him.
He punishes her.
He tells her that she is no longer a Valkyrie.
She will fall asleep on a rock and any man who finds her can have her.
Brünnhilde pleads with Wotan.
She asks him whether he could, at least, put a fire round her so that the only man who could get her would be a hero.
In the end Wotan agrees.
Loge, the god of fire, arrives and lights the fire.
At the end of the opera Brünnhilde is asleep on the rock, surrounded by the fire.
There she will stay until, one day, a hero comes to rescue her.
The music of the opera
The music contains many wonderful moments.
The most famous bit is the beginning of Act Three where the Valkyries are riding on their horses.
This music is known as The Ride of the Valkyries.
It is very dramatic music.
The very beginning of Act One is also very dramatic.
The music describes a storm.
The orchestra is a very large one, including special tubas which are known as “Wagner tubas”.
There are no separate arias in these operas: all the sections flows into one another.
Sometimes a character has a section when they are telling a story.
There are beautiful sections like the one in Act One where  Siegmund is remembering about his father and the sword, or the love music between Siegmund and Sieglinde.
By using leitmotifs (music which goes with certain ideas or characters) he gets many subtle effects.
When Siegmund looks at the ash tree we hear the sword motive because the sword is in the tree, although at that moment he does not know about it.
We also hear Wotan’s theme when Siegmund talks about his father.
We (the listener) know who his father is, but Siegmund does not.
The music tells us lots of things that the characters in the story may not understand.
This makes the music very powerful and exciting.
The first opera in the cycle is Das Rheingold.
Siegfried is an opera by Richard Wagner.
It is the third of the four operas that together tell a story called Der Ring des Nibelungen (The Ring of the Nibelung).
The story continues from the end of the second opera which was called Die Walküre.
The first performance of Siegfried took place when the whole Ring cycle (all four operas) were performed in the Festspielhaus in Bayreuth on 16 August 1876.
The first part of the opera takes place in a forest where the giant Fafner lives.