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Ammohead

INTRODUCTION

Ranging in size from coin to VW Bug, ammonoids (also called ammonites), form a great part of the world's marine fauna from their inception in the Devonian all the way through the Mesozoic.  In our home time-line, the story of the ammonoids ended there, at the end of the Cretaceous, but Spec, it seems, has more to tell.

Ammonoids, although they are outwardly similar to the coil-shelled nautiloids, and actually of a more advanced group, related to the squids and octopuses.  Formally, ammonoids are distinguished from nautiloids by the construction of their septa, the barriers between different chambers of their shell, which in nautiloids are simple sheets of calcium carbonate, but in ammonoids are intricately wrinkled and folded.  Ammonoids also distinguish themselves by possessing 12-8 sucker-laden tentacles, a squidlike beak composed of chitin (although in some species, the chitin is replaced by calcite later in life), and a toothed tongue or radula.  An ammonoid's nervous system is similarly advanced, with central brain-like nerve ganglion and complex eyes that allow some ammonoid species to distinguish shapes and colors with the same facility as a human.  

All ammonoids begin life as a planktonic ammonitella, a tiny swimming creature protected by a simple protoconch, the precursor of its parents' shells.  As the ammonitellae age, their protoconchs elongate, adding sections separated by increasing complex septa, producing a structure resembling a corckskrew.  The shell, itself, is composed of aragonite, or mother-of-pearl, the mineral form of the calcium carbonate an ammonoid injests in seawater.  The shell grows as the ammonoid lays down layer after layer of this material to a base of calcite (another compound of calcium carbonate) to form a hardened chamber, which it then walls off with a septum.  The living ammonite dwells in only the foremost chamber, the one still composed of calcite, but retains control over the other chambers by means of the siphuncle, a tube of living tissue that extends through the shell.  The ammonite uses the siphuncle to pump nitrogen gas and water around the chambers of its shell, altering its own buoyancy to ascend or sink through the water.  As the larval ammonite ages, the shell's coils tighten into the familiar ramshorn.  Depending upon the species, the ammonitellae then either descend to the bottom of the ocean, remain floating, or head for fresh water.  Ammonoids have adhered to this life cycle for millions of years, and indeed, the fossil protoconchs of the tiny ammonitellae form a signifigant part of the marine fossil record.

HISTORY

The history of the ammonoids is long and complex.  Originally evolving during the Silurian (420 million years ago), the ammonoids quickly supplanted the nautiloids that were their distant cousins (to this day, nautiloids are present in a meager handful of species).  These early ammonoids, the bactritids, sported straight, conical shells, like those of the belemnites , and it was not until the early Devonian (400 million year ago) that the familiar coiled shells evolved.  Ammonoids grew steadily in diversity through the remainder of the Paleozoic, up until the extinction blast of the end-Permian wiped out virtually all life on Earth, both in the seas and out of them.  For quite some time, it looked as if the ammonoids had been one of the casualties of the disaster; no ammonoid fossils exist in the early part of the Mesozoic.  However, it seems that at least some of the coiled-shell species survived, as the little ramshorns begin to turn up again in the late Triassic, and then explode in diversity through the Jurassic and Cretaceous.  By the end of the Mesozoic, the ammonoids were at the all-time height of their diversity.  It is difficult to determine what groups of ammonoids were present at the time without soft-tissue impressions, but their hard shells had certainly become variable.  Some ammonoids grew round, fat shells, others possessed flattened, frisbee-shaped shells, or straightened, conical shells.  Still others grew strange corckscrew shapes and hook-like structures that could never have floated through water and so must have belonged to bottom-feeders. This fantastic array of forms lasted through the Cretaceous, and ended, abruptly, at the end of the Mesozoic.

The ammoniods survived the tectonic irregularities at the Mesozoic's finale, but at great cost. For much of the early Tertiary, these shelled cephalopods were restricted to the poles, where their simple, rounded shells indicate a passive, filter-feeding lifestyle.  For several million years, the ammonites seemed stuck in this limited niche, while the fishes and squid of the lower latitudes furiously diversified.  Paradoxically, it was the great extinction at the end of the Eocene, far more severe than the hiccup at the end of the Mesozoic, that granted the ammonoids a second chance.  Climatic fluctuations having destroyed the ecosystems of the lower latitudes, the cold-water ammonoids were suddenly free to diversify.

Much of the rest of the Tertiary is a story of ammonoide renaissance.

These versatile cephalopods have expanded into a huge number of niches and have generally been quite successful, although their actual species count has never risen past their Cretaceous high.  From the simple coiled shell-types that survived the K-T transition, the modern ammonoids have re-evolved many of the shell-types of the Cretaceous heyday. Present-day ammonoids have descended to the greatest depths of the sea, migrated across its vast distances, and navigated rivers, a feat accomplished by no other cephalopods.

SPHAEROCONIDAE

Named for the rounded shape of their shells, the sphaeroconids (commonly called 'barrelfish') are widely regarded as the most primitive group of living ammonoids.  Barrelfish are distinguished from other ammonoids by their enlarged and complex siphuncles, which allow them to efficiently pump nitrogen and water through the chambers of their shells and thus have very fine control over their buoyancy.  Barrelfish can drop like stones or float like corks, according to the animals' preference.

While the siphuncle is expanded, however, sphaeroconids have had to part with other parts of their anatomy.  The eyes and nervous systems are reduced in most species (indeed, most spheroconids are almost entirely blind), and the siphon is often absent altogether.  Although some primitive members of this clade retain squid-like beaks and radulae, advanced barrelfish replace their chitinous beak with flattened plates of calcium carbonate as they age.  These plates, the opercula, and function as doors, behind which the animal may retreat when threatened.  In these species, the radula is flexible and strong, having become the principal food-gathering organ of the animal.

Sphaeroconids all possess 12 tentacles, and in most species, the suckers have been modified into flexible tendrils which coil around prey.  All extant spheroconids are passive feeders, floating like jellyfish just below the surface of the water, trailing their tentacles below them to snare fishes. It should be noted that some ammonoids of other groups (often the novammonids) have adapted to a similar lifestyle, and so sport spherocone shells.  These creatures are often called barrelfish, but are not true sphaeroconids.

A barrelfish begins its life as a planktonic ammonitella, a tiny creature floating in the upper layers of the ocean, catching and eating smaller particles of food. Barrelfish ammonitellae are far more aggressive than their parents, possessing functioning eyes, siphon and beak in order to locate, pursue, and dispatch their prey. As they age however, the ammonitellae become more sluggish. Their eyes and siphons gradually disappear as their shells swell. The suckers on their tentacles elongate into flexible tendrils, and their chitinous beaks transform into opercula, flat plates of calcium carbonate that protect the barrelfish from predators. Within a year, the minute, predatory ammonitella is gone, replaced by a passive, floating filter-feeder with a shell more than a meter in diameter. This shell grows steadily throughout the rest of the barrelfish's life, and some aged individuals exceed diameters of ten meters.

Supported by gasses trapped within their shells, the adult barrelfish dangle their long tentacles in the water below them, waiting patiently for water-borne food particles and clumsy sea creatures to be trapped by the sticky mucus coating each tendril. When the barrelfish feels its trapped prey tug on one of its tentacles, it coils the appendage toward its mouth. As the tentacle approaches the barrelfish's eating orifice, the great, plated opercula open, and the toothed radula snakes out, wraps itself about the tentacle and extracts the food particles stuck in the mucus. The barrelfish then swallows the mouthful- food, mucus and all- and slowly uncurls its tentacle, which gradually excretes enough mucus to catch the next crop of floating detritus.

Blue-Hooded Barrelfish (Sphaeroconus rotundus)

The great, round shell of the blue-hooded barrelfish (Sphaeroconus rotundus) is a common sight in the warm waters of the Gulf of Mexico. The great reef of the gulf supports many strange and beautiful animals, but this barrelfish is one of the most fascinating.
Blue-hooded barrelfish

Blue-hooded barrelfish (Sphaeroconus rotundus)

   

Blue-hooded barrelfish are most easily distinguished from the other barrelfish that live around them by their smooth, round shells and their bright blue hoods, the fleshy mantle extensions that protect their heads. The exact reason as for these hoods' color is a topic of some debate, since the blue-hood, like all true barrelfish, is blind. One theory holds that the hood is a visual clue for one of the barrelfish's many symbiotic partners. Studies have concluded that many Caribbean animals associated with these barrelfish, including bennies, shrimps, squids, and even larval tunicates, are attracted to the blue-and-red-striped pattern of the barrelfish's hood. Critics of this theory point out that the fact that certain marine animals are attracted to the pattern may simply be because they recognize the sign of a good home, and tout the barrelfish as a mimic of the similarly colored lollipop curly (Novammonites horrescens), another ammonoid of the Caribbean whose bite carries deadly neurotoxin.

Whether the creatures of the Caribbean seek out the blue-hood or whether it actively attracts them, these barrelfish are the basis of a large web of symbiosis. As any marine surface will, a barrelfish's shell becomes the anchor for barnacles and other sessile creatures of many species. Corals, tunicates, and seaweeds cement themselves to the shell's surface, and sea anemones may make a home there as well, fed by the scraps of food the barrelfish ignores. Soon, more mobile animals find a safe haven among the foliage decorating the shell, and the barrelfish is surrounded by a complete ecosystem, a miniature reef floating above the larger formations below.

Veiled Lady (Aulaeibrachium formosum)

Veiled lady

Veiled lady (Aulaeibrachium formosum)

    The veiled lady (Aulaeibrachium formosum) is another of the Caribbean's barrelfish. Smaller than the blue-hooded barrelfish, whose tentacles can stretch for 50 meters or more, the veiled lady favors shallower, calmer waters than its cousin.

Fighting Barrelfish (Doloritentaculum hostile)

The fighting barrelfish (Doloritentaculum hostile) is a medium-sized barrelfish of the southern Pacific that has evolved a peculiar defense against the mosarks that prey upon them, a defense that hinges upon the help of an unassuming little cnidarian.

Fighting barrelfish

Fighting barrelfish (Doloritentaculum hostile)

    Sea anemones, blobby, tentacled creatures related to jellyfishes and corals, often colonize barrelfish, and indeed, several barrelfish species actively collect the little creatures. Fighting barrelfish go a step further, relegating six of their tentacles to the solitary purpose of anemone nurturing. These "fighting tentacles" are short and club like, radiating out from around the barrelfish's beak while the other six feeding tentacles dangle below. The skin of a fighting tentacle is porous and wrinkled, forming an anchor site for the barrelfish anemone (paradamsia utilis). These little anemones, like all their kin, begin life as free-floating microscopic planula larvae, which are drawn by chemicals emitted by a growing barrelfish to colonize the porous flesh of the fighting tentacle. The medusae cement themselves to the barrelfish's fighting tentacle and then grow into fist-sized, highly poisonous adults. Through this behavior, the anemones gain a safe home and a steady food supply of scraps gleaned from the barrelfish's feeding tentacles. The barrelfish in turn, gains a powerful predator deterrent in the form of the anemones' extremely toxic stinking tentacles.

PLACENICERATIDAE (Curlies and pizzafish)

Pizzafish (Discus crustiformis)

Pizzafish

Pizzafish (Discus crustiformis)

This clade includes Spec's actively swimming ammonoids. It is rather species-poor but can be found throughout the uppermost few hundred meters of all oceans.

The pizzafish (Discus crustiformis) is a very common pelagic ammonoid of the open Pacific. The laterally flattened, keeled shell of a pizzafish is a hydrodynamic adaptation, enabling it to swim straight for large distances in search of food with little effort.

KOSSMATICERATIDAE (False barrelfish)

Crusty Barrelfish (Sphaeroconoides fallacis)

Crusty barrelfish

Crusty barrelfish

The crusty barrelfish (Sphaeroconoides fallacis) labors under a misnomer, since it is not a true sphaeroconid barrelfish. Crusty barrelfish possess functioning eyes and siphons and have only eight tentacles laden with suckers rather than finger like tendrils. The similarity of the crusty barrelfish to the true barrelfishes is due to convergence; both organisms live in much the same way, passively snatching food as they sit suspended in the water. Interestingly, the crusty barrelfish seems to be going through some of the same changes as the sphaeroconids in response to this lifestyle. Its eyes and siphon are small, while its siphuncle is large; traits independently evolved by both groups of ammonoids.

NOVAMMONIDAE

The most common and easily recognized of the ammonoid families, the creatures most people think of when they think "ammonoids", are the novammonids.  These creatures are outwardly similar to the ancestral Cretaceous ammonites, possessing none of strange specializations of the spheroconids.  Novammonids possess fully functional eyes and siphons and their beaks remain chitinous throughout their lives.  Most species possess only eight tentacles, but a few primitive species sport twelve.            

SCAPHITIDAE (Bulletfish, etc.)

Most ammonoids that are alive today belong to the Scaphitidae, a group that began its career on the sea floor (similar to the nostoceratids) but has since radiated into other niches as well.

Bulletfish (Escahamata sp.)

Arctic ammonites

The three most prevalent ammonoid species in the Arctic: Top: the planktonic Nanoneocephalus minimus. Mid: Cryoceras commune, a generalized predatory ammonite that is very common in arctic waters and are primary prey for sea-parrots. Bottom: Megaloscaphites ponderosus, another plankton-eating scaphitid, but rather large and very heavily shelled, occasionally prey to the walrooster; their young are intensively hunted by sea-parrots.

Bulletfish (Escahamata sp.) have revived the venerable ammonoid tradition of evolving straight shells. The advantages and disadvantages of this change are still not quite clear, but it seems safe to assume that the resulting streamlined shape increases swimming speed. Indeed, several species have been observed "bulletting" more or less vertically out of the water by means of their powerful jet propulsion to flee enemies such as mosarks or selkies.

Rapala (Escahamata piscatoria)

Rapala

Rapala

The rapala (E. piscatoria) is the most common bulletfish in the northern Atlantic Ocean, including the North Sea. Hanging with its head downwards, it uses its tentacles to dig for crustaceans and mussels. The eyespots on a rapala's shell confuse predators , which will attack the "head of the rapala only to find unpalatable shell (if the rapala can't flee fast enough, for example when the predator comes from above).

ONCORITEUTHIDAE (Salmonites)

Salmonites are a group of ammonoids that have adapted to living lives divided between the river and the sea.  The only known cephalopods that spend any time in fresh water, the salmonites are certainly strange.  Stranger still is the possibility that the transition from salt to fresh water may have happened more than once; several groups of the animals we call salmonites may be descended from completely different marine lines.  Most oncoriteuthids either belong to the genus Terroreptilis (like the Ryömäläinen ) or Escahamata (like the Rapala ), but there are few shared features between these two genera, other than the enlarged liver and thickened mantel, which may well be convergent.  Some biolgists state that the family Oncoriteuthidae is polyphyletic (composed to unrelated groups) and should be scrapped, while others cling to the origional taxonomy, citing many shared features in the egg and larval structures that both Terroreptilis and Escahamata share.  For the time being, we will side with the traditional format and place all fresh-water ammonoids in Oncoriteuthidae.

    Salmonites are not exclusive lake dwellers; they spend the first half of their lives as normal ammonoids plying the open ocean.  Salmonites spawn in salt water, cementing their egg-sacs to rocks and then leaving the newly-hatched ammonitellae to mature alone in the sea.  Once the larval salmonites have grown fat off of oceanic plankton and have begun to secrete a shell, they migrate toward fresher water.  After a little more time, the sub-adults make some last additions to their shells and swim upstream.  Here, the salmonites live out most of the rest of their lives, feeding upon insects, fish, and aquatic detritus.  During the mating season (usually in the earliest spring, soon after the ice has melted from the lakes and streams), the salmonites court, flashing dazzling patterns over their tentacular faces, and the males implant their sperm into the females.  At this point, some species (most often those of the genus Escahamata) immediately die, and allow their egg-laden shells to float back to sea, but other salmonites actively swim or crawl back down to the ocean to lay their eggs.  Most mate only once, but some salmonite species live several years as adults, making the harrowing journey to and from the sea each year.

Living in fresh water is a harrowing experience for a marine creature, and doubly so for an ammonoid.  Like any sea-dwelling animal living in fresh water, salmonites face the problem of osmotic pressure. While the ocean contains a large amount of salts and other minerals dissolved in the water, lakes and streams, of course, do not.  The upshot of this difference is that the osmotic pressure of salt-water is higher than that of fresh water; the dissolved minerals that are so closely packed together in salt water want to get out into freshwater and relieve the pressure.  The problem associated with the pressure becomes apparent when a cell adapted to living in saltwater is placed in fresh water.  High osmotic pressure within the cell seeks  release in the same way as high air pressure within a balloon seeks release---the cell explodes.

Salmonites and other fresh-water organisms have adapted to this problem by shielding their internal fluids from the water outside.  The water they drink does not enter the bloodstream until it has been passed through a large and active liver, where salts obtained from food are added to it.  Other dissolved minerals, such as calcium carbonate, the principal ingredient of the salmonites' shells, are in short supply in streams, as well and salmonties must either find these minerals within their food (several species have been known to eat clay) or do without for their adult lives.

These, and the other chemical and physical limitations of lakes and streams are probably the reason why cephalopods never invaded freshwater habitats in our home time-line.  Ammonoids, whose external support at least allows them to survive in a stream without being smashed, are still restricted chemically, and so cannot grow to very large sizes---no species grows larger than the Eurasian ryömäläinen , with a shell diameter of 50 centimeters.  On the other hand, salmonites are often the largest, or at least the most intelligent and aggressive predators in their habitat, and so can successfully compete with vertebrates for their niche.

Ryömäläinen (Terroreptilis crapulacorne)

Ryömäläinen

The ryömäläinen is a bottom-dwelling scavenger common to the fast-flowing streams of Fennoscandia.  As adults, these creatures rarely use  jet-propulsion or the bouyancy of their shells to swim, but instead rely on their powerful tentacles for locomotion. Because of their ability to crawl against the pull of a current, ryömäläinen are also able to climb against the pull of gravity, and so are often seen crawling though the soggy grass, on the way from one river to another.

The ryömäläinen (Terroreptilis crapulacorne), is a bottom-dwelling scavenger common to the shores of the Arctic Ocean and its surrounding seas as well as the fast-flowing streams of of Fennoscandia. Although like all ammonoids, a ryömäläinen ammonitella is a planktonic predator of the open ocean, their adult form is quite different. A mature ryömäläinen rarely uses jet-propulsion or buoyancy to swim, but instead relies on its powerful tentacles for locomotion. The shell is tightly coiled and almost helical, like a snail, which allows water (such as tidal currents or waves) to such past the animal without upsetting its grip. Because of their ability to crawl against the pull of a current, ryömäläinen are also able to climb against the pull of gravity, and so are often seen crawling though the soggy grass, on the way from one river to another.

Benthic Crawler (Helicornis benthicus)

Benthic crawler

Benthic crawler (Helicornis benthicus)

The benthic crawler, (Helicornis benthicus) is a large ammonoid that dwells below the waves on the sea floor. with only a limited ability to swim, crawlers mostly rely on their muscular tentacles for locomotion.

HOPLOTIDIDAE(Deep Sea Ammonoids)

Most deep sea ammonoids alive today belong to this group, one that has been around since the Cretaceous. Modern Hoplotidids have been driven into the deep seas of Spec either to avoid predators that live in shallower waters or to look for the abundant sources of food left alone by most animals. They have adapted thicker shell walls to deal with the extreme pressure in the deep sea. Some of them have evolved convergantly with RL's deep sea animals while others look like nothing else that has ever lived. Modern Hoplotidids have been divided into two major groups: Piscatorocephalinae and Flagellumocephalinae. This split occurred not long after Hoplotidids took to deeper waters, about 38 million years ago. At first there were little differences between the two groups, but today it is hard to believe that they ever belonged to the same group.

PISCATOROCEPHALINE

Piscatorocephalines are some of the wierdest animals ever to have evolved in Spec. When they first split off from the Hoplitididae about 35.5 million years ago they looked much like the typical ammonite. But 35.5 million years is a long time to evolve different traits from their relatives. And Piscatorocephalines are definatly different. They have evolved convergantly with RL Angler Fish, and are commonly known as Angler Ammonites. They have one specialized tentacle that is elongated and is tipped with an oval-shaped lure. This lure is filled with a biolominescent liquid which glows blue. The Smooth Angler Ammonite is the only species alive today.

Smooth Angler Ammonite, Piscatorocephalus smilorostrus The Smooth Angler Ammonite's name refers to the shell lacking ridges. One of it's tentacles has elongated and become tipped with a oval-shaped hollow lure, filled with bioluminescent liquid that creates a blue light dangling infront of it's razor-sharp beak. It's beak is cleaved into two points and the top designed for stabbing prey. It's throat is so large that it can still be seen even when the beak is closed. Smooth Angler Ammonites prefer to hunt small prey that they can swallow whole as their beaks are designed for stabbing not slicing.

FLAGELLUMOCEPHALINAE

Flagellumocephalinae is the most common group of deepwater ammonoids. Flagellumocephalines are well known for their two super-elongated tentacles, known as "whip-tenacles." These tentacles are what give this group their common name: whipsquids. Whipsquids are very diverse, they have done much better the Angler Ammonites due to their adaptobility. While many whipsquids are deadly carnivores, some are herbivores that feed on floating algae, and there is even one filter-feeder within the group. Their whip-tentacles commonly have some sort of extention to help them catch their food.

Bull-whip Ammonite (Flagellumocephalus giganteus)

By being red this whipsquid is perfectly camoflauged in the twilight zone of the deep sea. It's whip tentacles are tapered to the tip and have no extentions. They are used to grasp prey and pull it towards it's beak which will slice out chunks of flesh. It feeds primarily on small fish, squid, and occasionally jellyfish, this feeding behavior is unlike the angler ammonites who eat basicly anything they can catch. The Bull-whip Ammonite is 10 feet long with it's whip tentacles. It can also use its tentacles to constrict its prey, like a snake can.

Algae Squid (Flagellumocephalus torvas)

Possibly the most bad tempered and ferocious type of whipsquid lives at the bottom of the ocean and disguises itself with the wierd algae-like splotches on its skin. Its whip-tentacles are shorter than in most species and are used simply to lure its prey closer to its mouth. To get its prey's attention, the Algae Squid makes its whip-tentacles flash with color and waves them through the water. When prey comes close enough, it will grasp it with its other tentcles which are covered with hooks. Its shell is long and flattened to help disguise itself in the sand.

Spider-Trap Ammonite (Flagellumocephales casses)

This weirdest of the whipsquids can reach lengths of 30 feet. It's incredably long whip tentacles support strands of material similar to a far stronger version of spider silk, found in no other creature. These strands are used to trap any small invertabrates floating through the water including amphipods, copepods, and ostricods. Then the tentacles are brought to the beak which pulls these off the tentacles, but it also takes in water, this mixture is filtered through bristles in the throat and pushed out through a small hole on either side of the beak. Its beak is now straight and blunt, as its only use is to pull small invertabraes off of the whip-tentacles. Its remaining tentacles, as they are no longer needed, are short, stubby, and useless. 

There are also a few unnamed species which feed on algae that float through the water.

-All credit for these species goes to yahoo group.

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