Sources : Sea-urchin

Aristotle [ca. 350 BCE] (De animalibus, Book 4, 4.1-6): [Book 4, 4.1] The echini contain no flesh, but this part is peculiar, for they are all of them void of flesh, and are filled with a black substance. There are many kinds of echinus, one of which is eatable; in this one the ova are large and eatable, both in the greater and the less. [Book 4, 4.2] And there are two other kinds, the spatangus and that called bryttus; these are inhabitants of the sea, and rare. Those which are called echinometrse are the largest of all. Besides this, there is another small species, which has long and sharp spines; this is procured from the sea, in many fathoms water, and some persons use it for stranguary [a disease]. [Book 4, 4.3] Around Torona there are white marine echini, which have shells, and prickles, and ova, and are longer than others but the prickle is neither large nor strong, but soft, and the black parts from the mouth are more in number, and united to the outward passage, but distinct among themselves, and by these the animal is as it were divided. The eatable kinds are particularly and especially active, and it is a sign of them; for they have always something adhering to their spines. [Book 4, 4.4] They all contain ova, but in some they are very small, and not eatable : that which is called the head and mouth in the echinus is downwards, and the anus placed upwards. The same thing occurs in the turbinated shells, and the patella; for their food is placed below them, so that the mouth is towards the food, and the anus at or on the upper part of the shell. [Book 4, 4.5] The echinus has five hollow internal teeth, in the midst of these a portion of flesh like a tongue ; next to this is the oesophagus; then the stomach, in five divisions, full of seculent matter: all its cavities unite in one, near the anus, where the shell is perforated. Beneath the stomach, in another membrane, are the ova, the same number in all, there are five in number, and uneven. [Book 4, 4.6] The black substance is joined above to the origin of the teeth, this black substance is bitter and not eatable; in many animals there is either this substance or its analogue, for it is found in tortoises, toads, frogs, turbinated shells, and in the malacia; these parts differ in color, but are entirely or nearly uneatable. The body of the echinus is undivided from beginning to end, but the shell is not so when seen through, for it is like a lantern, with no skin around it. The echinus uses its spines as feet, for it moves along by leaning upon them and moving them. - [Cresswell translation, 1887]

Pliny the Elder [1st century CE] (Natural History, Book 9, 51) The sea-urchin, which has spines instead of feet, belongs to the same genus [as the crab]. These creatures can only go forward by rolling over and over, and consequently they are often found with their prickles worn off. Those of them with the longest spines are called echinus cidaris, and the smallest are called cups. They have not all the same transparent color: in the district of Torone some are born white, with a small spine. The eggs of all have a bitter taste; they are laid in clutches of five. Their mouths are in the middle of their body, on the under side. It is said that they can forecast a rough sea and that they take the precaution of clutching stones and steadying their mobility by the weight: they do not want to wear away their spines by rolling about. When sailors see them doing this they at once secure their vessels with more anchors. - [Rackham translation]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:57): The sea-urchin [echinus] has taken its name from the land echinus [hedgehog], which is commonly called iricius [ericius]. The sea urchin’s shell is two-fold, sharp with spines like chestnuts when they fall from the tree still covered. Its flesh is soft and like vermilion... - [Barney, Lewis, et. al. translation]

Saint Ambrose [4th century CE] (Hexameron, Book 5, 9): The urchin, a tiny, common and despicable animal (I refer to the sea variety) is frequently used by navigators as a sign of a threatening storm or as a harbinger of clear weather. The reason for this lies in the fact that at the approach of a wind storm this little creature takes hold of a fairly large pebble and uses it as a sort of ballast or anchor so as to avoid being carried out of the water. Thus it balances and directs itself by means of an alien weight, not by its innate strength. This sign gives an indication to the sailor that a storm is brewing. Accordingly, he takes precautions lest the sudden approach of a hurricane may find him unprepared. - [Savage translation, 1961]

Alexander Neckam [1147-1217 CE] (De naturis rerum, Book 2.34): The sea-urchin, which has no confidence in swimming because of the lightness of its body, takes hold of a stone which is equal to it in weight, to be balanced as if by a kind of anchor, so it is not disturbed by the waves. - [Wright/Badke]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.33; 7.35): [Thomas mistakenly appended his main account of the sea-urchin to the end of his account on the echeneis. It has been moved here for consistency.] [Fish 7.33] According to Pliny, they are of the genus of crabs, which have spines for feet in a similar manner. Around the crown they grow white. Their eggs are bitter, produced in large number. They have a mouth in the middle of their body, and are the color of glass, almost the image of a scorpion. Instead of teeth they have heavy stings in their mouths. Many people use this fish to damage their enemies. But this fish cannot be eaten, because when eaten it brings death to man, by dissolving the state of his disposition. Under the belly of this fish are the spines, which are similar to feet. As the blessed Ambrose and Pliny and the great Basill write: Echinus is usually an indicator of future storm or calm, and in these is usually a message to sailors. When it feels that a storm is coming, it seizes a strong stone and uses it like an anchor and drags it like an anchor, so that it is not shaken by the waves. And so it does not liberate himself by its own strength, but it establishes and governs itself by the weight of another. When the sailors see this they anchor their ships by the example of a sea urchin. [Fish 7.35] Ericius is a marine fish, having a head and mouth below, as Aristotle says, and a superfluous exit above; and this against other animals. It uses spines instead of feet. Its anterior parts are separated and the lower parts are continuous. It is a terror to the other fish of the sea, because it is full of thorns; hence it does not become an easy prey for any fish. Its flesh is intensely red, similar to the color of a minnow, as Pliny says. - [Badke translation/paraphrase]