Why does abalone shell have holes

The organs of the abalone are in a circle surrounding the muscular foot. These are organs of the digestive, respiratory, circulatory and reproductive systems. The head and mouth of the abalone is right near the most recently formed open hole on the shell. The digestive tract bends to the left when viewed from the top , back to the apex under the spiral where it turns and comes back along the left side ending in the anus. The anus is right under the last open hole and at the end of a slit in the mantle on the left side of the animal.

Abalone head with central mouth, flanked by a pair of oral tentacles and a pair of eyes. Abalone heads have a mouth, pair of oral tentacles, pair of eyes, and an internal radula. The oral tentacles can be extended out, under the shell to sense the surrounding area. The eyes of the abalone are sensitive to light. The mouth of the abalone is pressed down on its food algae when feeding, and the radula is used to scrape pieces of the food.

All abalone are herbivores, feeding primarily on various species of marine algae. Abalone radula from a four inch maricultured abalone. Note the brown area that is the area in use stained by brown algae.

Abalone radula close up left showing rows of sharp teeth. Microscopic view of abalone radular teeth right. GA images. Abalone radula and odontophore. The odontophore is what presses the radula against the food while the animal is eating. It is made of cartilage. The radula is like a mini chain saw with a constant sharpening mechanism. Radulae are a characteristic of many mollusks. These unique organs are flexible bands with rows of sharp hooked teeth.

A hard material is located under the radula and is used to press the radular teeth against the food. As radular teeth become broken this outer area of the radula is shed and new sharp teeth are moved up. The mollusks continue to form new radular teeth their entire life. The part of the radula in the abalone that is used is often stained due to the pigments in their preferred algal food.

The hard material used to press the radula in the abalone is called the odontophore and is a pair of cartilaginous-like structures operated by red muscle. Abalone reproductive organ greenish is seen on the right side of the abalone. The foot and epipodium of the abalone is on the hand under the animal, it is stretching out so you can see the foot muscle and how it goes up and attaches to the center of the shell.

The thin mantle is visible under the shell with the greenish reproductive organ in a pocket of the mantle. The animal is a female males have a beige reproductive organ.

The head of the animal is visible on the right just under the thumb with an eye raised up. Abalone reproductive organs are on their right side. These are large, horned-shaped organs located on the side of the animal opposite from the open holes.

The organ is located in a pocket of the mantle and gets larger and swollen just before spawning. As abalone grow, they eat larger types of algae and seaweed.

Abalone live by clinging to rocks in intertidal oceanic zones. Base abalone shell colors vary and include a mixture of whites, pinks, purples, blues, greens, yellows and browns. Colors of the outer shell layers vary depending on the type of algae the abalone feed on.

Abalone, along with oyster shells and some mussels , produce a substance called nacre that gives them their iridescence.

Nacre is a durable substance made from calcium carbonate. Nacre is also known as mother of pearl. When light shines on the thick nacre shell layer, the reflected light on the inner layer interferes with the reflections of light on the outer layer, causing the iridescent effect. As abalone grow, they add new layers to their shell, increasing their shell's size and thickness. Different species of Haliotis grow to different sizes. This is a very unusual species of abalone, rarely observed.

It has a smooth, mottled grey shell and is small, only growing up to 9cm. All abalone species eat algae, and mature adults prefer scraps of kelp. Abalone are quite lazy and prefer to remain in a small area and wait for scraps of kelp to drift by. However, they will move when there is a change in season or water quality, or when food is scarce - a change in their shell colour usually indicates a new food source. Juvenile abalone cannot grip the scraps of kelp, so they rely on films of bacteria, algae and micro-organisms on rocks for nourishment.

In nature, abalone are at risk of predation at all stages of their life. Their eggs and planktonic larvae are fed on by filter-feeders like barnacles, bivalves and shrimps.

Juvenile abalone hide in cracks or under the spines of Cape sea urchins during the day but need to forage at night - putting them at risk of predation by octopuses , sea stars , crustaceans, snails and durophagous shell-swallowing fish.

Adult abalone are at risk of predation by a few large predators, such as rays with crushing jaws and sea otters. However, humans pose the greatest threat to mature abalone and are responsible for its current population decline. Abalone are "broadcast spawners", meaning their eggs and sperm are released into the ocean and fertilisation takes place in the water column. This spawning is synchronised by temperature, season or a full moon - different species use different indicators.

A fully grown abalone can release tens of millions of eggs in a single spawn. Eggs hatch into tiny larvae that swim freely in the water for a few weeks, using tiny hairs to propel themselves.

Eventually, these larvae settle on the sea floor and shed these hairs - immediately beginning the secretion of a shell. Survival rates are very low, and it is estimated that fewer than one in 10 abalone survive to maturity even before taking human threats into account. Perlemoen takes eight to 10 years to reach "legal" fishing size in designated commercial zones. However, abalone grow slowly and can take up to seven years to reach sexual maturity - the regulations are simply unable to ensure that abalone have sufficient time to reproduce in the wild before being harvested.

If a species cannot reproduce before being harvested, its numbers cannot recover. Additionally, abalone's small size and high value have led to prolific poaching. Fishing is poorly regulated and despite best efforts, there is little effective management of this species. Juvenile perlemoen depend on Cape sea urchins to survive - they follow the urchins around, hiding under their spines for protection from predators. An unprecedented influx of West Coast rock lobster to regions of the Cape has resulted in increased predation of these urchins , leaving the young perlemoen exposed.

This influx of rock lobsters, which previously only inhabited the West Coast and rarely rounded the Cape Peninsula, has not been thoroughly explained. However, increased pressure on the rock lobster population caused by water pollution and climate change is likely responsible for this migration, and is evident by the increasing numbers of " lobster walkouts ".

This relationship between kreef, urchins and perlemoen highlights the intricacies of ecosystems and how susceptible they are to damage by humans. There are many factors that go into the appearance, quality, and availability of abalone. Abalone only exists in a few areas of the world, typically where the ocean is cold.

The rarity stems from the fact that they have no holes in their shells at all. This is particularly bizarre when you consider the function of these holes. There are many ways to prepare — and eat — abalone. You can eat them cold, straight off the shell, or cook them in a number of ways. However, like some other species of seafood, abalone is almost always cooked alive.