Roper clam
A denizen of the oceans of Dadauar, the roper clam is not intentionally hostile to humans, but has led to many deaths nonetheless. Roper clams are enormous clams, varying widely in size but reaching up to three meters in diameter in extreme cases, that hunt prey with their long "tongues", long, sticky extensions of their feet that they can whip out with extreme rapidity and accuracy. The tongues wrap around their targets, holding them fast both by their gluey secretions and by the strength of their grip. Once a victim is caught, the clam pulls it in toward its mouth.
Anatomy
Like other clams, roper clams have two shells, joined by a ligamental hinge and by adductor muscles that can pull it closed. Within the shells is the mantle, a thick membrane that both secretes the shell material as the clam grows and encloses most of the clam's fleshy body within a mantle cavity. Extending partially outside the mantle cavity is the foot, a large muscular organ. The foot is able to secrete a growth of tough threads collectively called a byssus that can affix the clam to a hard surface. While the roper clam does spend most of its time so anchored, it is capable of movement. Dissolving the byssus when it wishes to relocate, it uses its foot for locomotion, recreating the byssus when it finds a congenial new site. Small roper clams can propel themselves above the substrate for short distances by expelling water at high speeds from their siphons, but this is a tiring ability that the clam seldom uses, and which becomes impossible for older, heavier ropers.
The roper has an open circulatory system: a three-chambered heart located near the hinge pumps the hemolymph through the clam's body, but most of the fluid bathes the clam's organs directly rather than being contained in vessels. To breathe, the roper clam takes in water through a tube called an incurrent siphon. The water passes through a comb-like gill structure called a ctenidium, where gas exchange takes place with the hemolymph, and then is expelled through the excurrent siphon back to the clam's surroundings. The roper clam's central nervous system comprises three pairs of ganglia distributed throughout its body.
Roper clams have two features that make them stand out strongly from other clams. One is the clam's mouth. Most clams are filter feeders, straining plankton and other food particles from the water with cilia on their gills. Their mouths are small holes, no bigger than they need to be to take in the tiny bits of food they ingest. Roper clams consume much larger prey, and their mouths can expand accordingly, big enough in the largest specimens if not to swallow a human, then at least to swallow something the size of a cat. The labial palps that in other clams sort the food and carry it toward the mouth have in the roper clams joined and adapted into a powerful sphincter that holds the mouth closed and prevents its prey from escaping. Aside from the mouth, the rest of the roper's digestive system is similar to that of other clams: the mouth opens almost directly to the stomach where the prey is digested, only a very short œsophagus in between. From there, what's left of the food passes through the intestine, where further digestion takes place, and waste is excreted through the anus into the excurrent siphon, where it is expelled along with the deoxygenated water.
The other unique feature of the roper clam is of course its "tongue", the appendage it uses to capture prey. Despite the name, the tongue is not located in the roper clam's mouth, and is no way homologous to the tongue of a tetrapod. Rather, the roper clam's tongue is a part of its foot, a long tentacle covered with gluey slime. The roper has considerable dexterity with its tongue, and moreover is able to shoot it out at remarkable speeds, using a complex mechanism of muscular "springs". Even after the tongue reaches its full extension, the clam can curl the end, and generally coils it about its prey to better hold it fast. The clam then pulls the prey in and transfers it into its mouth.
Roper clams have both compound eyes and pit eyes spaced around the margin of the mantle. While these eyes do not have an especially high resolution, they are sufficient to at least give the roper clam some notion of its surroundings, and to let it see potential prey at a distance.
Distribution
Roper clams are most comfortable in tropical climates, and are most common in the Veiled Ocean and the southeastern part of the Nubilous Ocean. They do have some tolerance for temperate temperatures, and are sometimes found farther northwest in the Nubilous Ocean and in the eastern Duhhian, but they do not do well in pageric waters. Roper clams are also found in the Restless Sea, although it's not entirely clear how they got there, given that there's no direct connection between that and the Veiled Ocean. The Green Isthmus is narrow enough that it's generally assumed that larval clams were conveyed across it at some point, but the details are unknown.
Although they do not seem to have been originally native to the area, since the construction of the Blue Canal roper clams have spread into the Serpentine Sea as well, having apparently got there through the canal. A few have also recently been seen in and near the Golden Sea, where they are an invasive species that was apparently brought there by traders or travelers, whether intentionally—perhaps for their culinary usage—or accidentally.
Description
The shells of roper clams have pronounced plications, with six deep folds running from the umbo to the outer margin and giving the shell's edges an undulous shape. This corrugation gives ropers an appearance much like the giant clams of the genus Tridacna, to which, however, they are not closely related, the similarity apparently being the result of convergent evolution. The base part of the shell is covered with a thick, fibrous, dark brown periostracum that gives it a furry appearance.
The inside of the roper clam is vividly colored, although the exact colors differ by population. Some are light blue; others vivid violet with yellow or blue spots; others orange with red striations; still others marbled royal blue and green. Many malacologists opine that the different colors mark distinct subspecies of clam, though others disagree. (There are minor differences between these clam populations besides the color, but none significant enough to unambiguously mark them as separate subspecies.) Those who do hold this view place the blue clams in the subspecies Linguifer magnus nubium (the "northern roper"), the violet and blue L. m. ianthinus (the "purple roper"), the violet and yellow L. m. perspicax (the "starry roper"), the red and orange L. m. carnatus (the "tomato roper"), and the blue and green L. m. caeruleus (the "smooth roper").
Reproduction
Like most bivalves, roper clams are diœcious, requiring a male and a female to reproduce. Fertilization is external; the female clam releases a few thousand eggs into the surrounding water, and the male releases the sperm. Over a few days, the eggs develop into tiny ciliated planktonic larvæ called trochophores, which over another few days grow rudimentary shells, metamorphosing into another stage called a veliger. After settling onto the sea floor, the veliger takes on its final, benthic form, now a smaller version of the adult clam called a spat. Roper clams grow quickly, and it takes only a few years for the spat to reach maturity and to be itself capable of reproduction. A newly mature roper is just under a meter in diameter, but ropers continue growing after reaching maturity, and can grow much larger if they live long enough.
Few roper larvæ survive to become mature clams. Perhaps one tenth of a percent actually live long enough to find a place on the seafloor. Even then, the small spats have a difficult time both finding enough to eat and avoiding predators set on eating them, and less than one spat in a hundred survives to attain sexual maturity. The mortality rates of mature clams, however, are much lower. Once a clam reaches a meter or two in diameter, there are few predators capable of breaking through its hard shell.
Ecology
Only a very few creatures, such as the xastre, are known to feed on adult ropers. Roper larvæ, however, are in an entirely different situation; while there are no known organisms that are adapted to feed on roper larvæ exclusively, their small size and free-floating nature makes them prey for all manner of planktonivore.
Roper clams are also subject to certain specialized parasites. The clam louse is a type of parasitic copepod that attaches itself to the roper's mantle and feeds on its hemolymph and mucus. Dinoflagellates of the genus Verrucifex live within the hemolymph of infected clams, and cause them to develop whitish pustules on their mantles. Cryptocreion mastigosimus is an unusual, highly modified horseshoe worm that has adapted to an endoparasitic lifestyle and resides in the roper clam's digestive tract.
Danger to humans
The roper clam's intended prey is small fish, and occasionally crustaceans. An unintelligent creature, however, it tends to lash out at anything nearby making similar motions, and may grab a human or other ellogous creature by accident. Humans are in little danger of being eaten by the clams—only the largest clams could fit an adult human inside their shells, and even they couldn't actually get them into their mouths—but may be in danger of drowning. After some time of trying and failing to ingest a too-large captive, the clam will eventually give up and let go, but this may take a few minutes to half an hour, and by then it may be too late.
Escaping from a roper clam, once grabbed, is a difficult proposition, given the clams' strength and the stickiness of their tongues. It's not impossible to break free, but it's beyond the capabilities of most humans. If the victim has a sharp instrument—or can reach a nearby rock or piece of coral—cutting through the tongue may be an option. A roper's severed tongue will grow back within about a week.
Uses
Roper clams are edible, and are considered something of a delicacy in the nations of Malchec and Niphachar. A sort of pie made from roper meat called a roper tart is considered the signature dish of the Niphachari city of Astanja. Roper shells, too, are valued for their size, and are often used to make items such as furniture and coffers. Like most shelled molluscs, roper clams can produce pearls, but roper pearls are lumpy and lusterless and are valueless unless they're exceptionally large, and even then they're valued more as curiosities than for beauty.