Thorny Oyster – Shy, but Scary-Looking Clams
The thorny oyster, also known as spondylus, is a genus of clams, bivalve mollusks that are quite common in the waters of the Caribbean, especially between Brazil and the Carolinas. Spondylus species can also be found in the Indo-Pacific region, especially around Australia, China, Japan and the Philippines. They prefer coral reefs and rocky areas or places where there are wrecks with crevices to hide in and shallow waters not deeper than 40 meters.
The Appearance, Behavior and Biology of the Thorny Oyster
The spondylus genus includes many species that differ considerably in size – some species are only a few centimeters across, while others measure almost 30 cm in diameter –, but they all share a few features: they all have shells that are white, cream, brown, yellow or reddish-orange on the outside and they all have thorns and ribs and smooth, light-brown or orange on the inside. The two halves of the shell are joined with a hinge that resembles a ball-and-socket mechanism – a feature that distinguishes these oysters from other clams that usually have toothed hinges. The lower half of the shell is usually more convex, while the upper half is flat, with thorns protruding on the surface and around the edges as well. Thorny oysters have a well-developed nervous system as well as several eyes and many short tentacles distributed around the edge of the shell. They are shy animals that withdraw into their shell at the smallest sign of danger and they are sessile, too, but they don’t anchor themselves to the surface they want to stick to – they cement themselves to the substrate or to the corals. They are also able to move by flapping their shells, but they prefer to stay settled.
The Thorny Oyster and its Favorite Food
All spondylus species are filter-feeders, living on the food particles delivered to them by the water currents. They are omnivorous, but their favorite food is phytoplankton and food particles that contain calcium, absolutely necessary for shell growth. While eating, the animals opens its shell a little and draws in water through the gills that extract the nutrients, then the water is pumped out.
The Few Facts Known about the Reproduction of the Spondylus
Very little is known about the reproduction of thorny oysters; the only thing that seems to be sure is that the larvae are free-swimming and after birth they instantly start seeking for a suitable spot on the substrate to settle on. Young thorny oyster individuals look for areas where there is plenty of calcareous matter available to facilitate the development of the calcium-carbonate shell.
The Squamosa Clam – a Large, Colorful and Widespread Clam Species
The squamosa clam, also known as the scaly clam or the fluted giant clam is among the largest and hardiest species of clams known today. Common from the coasts of Africa, throughout the Indo-Pacific and all the way from the costs of Japan to Australia, squamosal clams are adaptable creatures, able to survive in various shallow water environments from coral reefs to walls, from reef flats to lagoons.
The Physical Features of the Squamosa Clam
Squamosa clams grow to measure up to 40 cm in diameter. One of the physical features that distinguishes them from other giant clam species is the fluted and fan-like appearance of the shell. The mantle is usually colorful, variations ranging from brown and green to purple and yellow, with spots or linear patterns, but there are individuals that have a mantel of a uniform or striped bright blue color. The mantle is thick, fleshy and large enough to cover the entire shell when fully extended. Squamosa clams have a special organ called a byssus that protrudes from the shell and is used by the animal to attach itself to rocks, corals or to the sandy substrate. The byssus secretes a liquid that hardens and fastens the clam securely.
The Diet of the Squamosa Clam
The clam lives in symbiosis with zooxanthellae algae that provide it with valuable nutrients such as carbs and glucose from the waste they produce during photosynthesis. If conditions are optimal, the algae multiply endlessly, which prompts the clam to consume some of them integrally, maintaining the algae population constant inside its tissues. In addition, squamosal clams obtain nutrients with the help of a specialized organ on the mantle that extracts phosphates, ammonia and nitrates from the water and they also filter the water with their gills, extracting food particles.
The Reproductive Behavior of Squamosa Clams
These creatures are protandry clams, meaning that they are all born male, some of them becoming female at a later stage of development. Fertilization happens externally, the males releasing their sperm and the females releasing their eggs into the water. The fertilized eggs hatch into trocophore larvae, swimming freely until they reach the next stage of development, the veliger stage when the larvae already look like tiny clams. It is at this stage that juvenile squamosa clam individuals start looking for a spot of substrate or a coral on the reef where they can anchor themselves to.
The Maxima Clam – Large, Sessile Bivalves of the Indo-Pacific
The maxima clam, also known as the small giant clam, is a species of sessile mollusks common across the Indo-Pacific region. Their preferred habitat is on coral reefs – they usually live in well-lit areas, attached to the upper part of corals or in the sandy substrate.
What Does the Maxima Clam Look Like?
Maxima clams are relatively large, reaching the length of 20-30 cm when they are fully developed. They are bivalves, meaning they have two valves, one on each side of their mantle. The valves are used for drawing in water for filtering it for food and oxygen. The shell of maxima clams is quite large and is attached to the substrate with long and strong filaments that protrude from inside the shell, through a hole next to the shell hinges. The mantle of the clam is green, bright blue or brown to provide optimal conditions for the symbiotic algae to carry on with the photosynthesis as well as to protect the clam against the harmful effects of strong solar radiations.
The Diet of the Maxima Clam
Maxima clams use the zooxanthellae algae they live in symbiosis with as a source of energy. While the symbiotic algae engage in photosynthesis, they also produce waste that is a valuable food source for the clam. Maxima clams are filter-feeders, too – they pump water, drawing it into their body and filtering it for phytoplankton and oxygen. Unlike many other members of the bivalvia phillum, maxima clams are not voracious, they feed regularly, but not all the time.
How Maxima Clams Proliferate
Maxima clams reproduce by means of broadcast spawning – when the water is sufficiently warm, usually at the end of spring, the clams release their gametes into the water. The process is started by the males, and then the females follow by releasing their reproductive fluids, usually between one hundred thousand and one million eggs at a time to increase chances of fertilization. The fertilization takes place in the water and results in eggs that hatch after about half a day into larvae called trochophores, tiny, saucer-like organisms that float in the water. The trochophores develop quickly – first, a pair of calcareous valves appear that later on transform into the shell, then the young clams continue their development for a few more weeks, during which they become able to host zooxanthellae algae. Afterwards, the now adult maxima clam individuals find a suitable spot of substrate and they attach themselves to their new home.
Derasa Clam – A Large and Colorful Mollusk with a Smooth Shell
The Derasa clam, also known as the Southern giant clam or the smooth giant clam, is one of the largest species of mollusks that live in the world’s seas and oceans and also among the longest-lived marine creatures, often living to over 200 years. Native to the shallow waters of the reefs that surround Indonesia, Australia, Papua New Guinea, Philippines, Solomon Island, Fiji and Cocos Island, these large and colorful clams are often seen lying on the sandy substrate of the open seabed or in lagoons and they can be noticed floating around freely as well.
Spotting a Derasa Clam – Physical Features of the Smooth Giant
Derasa clams grow to the length of around 60 cm, which ranks them among the largest clam species. Their shell lacks ribbing (hence the name smooth clam), but it comes in six or seven folds – a feature that distinguishes these clams from other giant clam species. The mantle is colorful, with wave-like, black, white, bright green, orange, yellow and blue stripes. Inside the hinged shell is the large and soft body of the clam, a body with no head, but with a thick and muscular foot that protrudes through the hinges of the shell and is used by the animal to attach itself to the coral reef or to the substrate.
Derasa Clams – The Circle of Life
All clams in the species are born male, but they become hermaphrodites over time. They reach sexual maturity when they reach the length of 30 cm, that is, between the age of 3-5. They proliferate by means of broadcast spawning, but each individual releases only one type of reproductive fluid at a time, either eggs or sperm, in order to prevent self-fertilization. Their mating season is usually in spring.
How Does the Derasa Clam Eat?
These giant clams satisfy their hunger through filter feeding as well as by using the nutrients produced for them by the microscopic algae that live in a symbiotic relationship with the clams. When filter feeding, the creaturel uses another muscular organ called the intake siphon that also protrudes from the shell to extract the phytoplankton and other microscopic organisms and food particles from the water column. The algae hosted by the clam engage in photosynthesis and they feed their host with the byproducts of the process, such as carboydrates and other nutrients. This combined method is very efficient – the growth rate of the Derasa clam exceeds 3 inches per year.
The Boring Clam or Crocea Clam – A Small Bivalve Species from the Indo-Pacific
The boring clam, crocea clam, crocus clam, or better known to scientists and marine biologists as the Tridacna crocea, is a small creature with thick valves that usually features dim, gray and white colors, sometimes also containing a hint of yellow, orange or red. This species is a bivalve that belongs to the Tridacninae subfamily associated with the family Cardiidae. This family has a limited number of genera, and the boring clam is in fact distinguishable as the smallest species in its entire subfamily. The clam is native to the Indo-Pacific, and has a wide range, but is also quite picky about the habitats it elects for itself.
The Crocea Clam – General Description and Physical Features Characteristic to the Species
While the genus that the boring clam belongs to contains mainly larger clams, the crocus clam itself has a shell size of only about 15 cm – that being considered the maximum size it can grow to. Its thick valves are joined together by a shorter but tough hinge. The shell is typically elongated, and the clam appears inflated, its upper valve in particular consisting of 6-10 folds that interlock to give the clam more consistency and ensure that it can lock more tightly.
How Does the Crocea Behave in Its Environment?
Crocea clam populations are similar in their behavior to most Tridacna species. The animal normally fastens itself securely to the seabed. This is obtained through the use of slits present on the lower valve, which ensure byssal threads can emerge to secure the clam to the bottom. The boring clam also has the habit of burrowing itself into the substrate. This action is the main reason why the exterior valves are smooth and shiny, as the substrate tends to polish them. The clam may also appear to be uneven when burrowing into harsh or uneven substrate and running into harder areas that are more difficult to dig through.
Where Can We Normally Find the Crocus Clam?
Commonly found in the Indo-Pacific, the boring clam prefers habitats that are rich in massive corals. This is why its preferred living space is usually located in tropical regions where the temperature is not only predominantly high all year round, but also stable. The clam’s range extends from Malaysia and Vietnam westward, to Palau, the Philippines, Vanuatu and the Solomon Islands.