The Snouters: Form and Life of the Rhinogrades

The Snouters: Form and Life of the Rhinogrades is a book originally published in 1957 in Germany (original title: Bau und Leben der Rhinogradentia) by Gerolf Steiner, which wrote most of the book with the pseudonym of Harald Stümpke.

This book describes in detail a previously unknown order of mammals, Rhinogradentia (literally: "nose-walkers"), or Snouters, that appear to live only in a remote archipelago in the southern Pacific Ocean. These mammals are distinguished by the nasarium, a structure derived from their nose that has been adapted for all sorts of purposes, from fighting to jumping, and most commonly walking.

The Hy-yi-yi Archipelago
According to Stümpke, the Hy-yi-yi Archipelago (or Hi-yi-yi, or Hi-iay) was discovered in 1941 by a Swedish explorer, Einar Petersson-Skamtkvist, escaped from Japanese imprisonment. They're mountainous islands of volcanic origin, with a mildly tropical climate. Besides Snouters, they host a characteristic endemic flora with archaic forms such as psilotales, primitive insects similar to cockroaches and unique six-winged dragonflies.

The archipelago was also home for the peaceful Hooakha-Hutchi tribe, that unfortunately quickly went extinct due to a common cold outbreak just after having met the Europeans. In the following years, the Darwin Institute of Hy-yi-yi was founded on the islands to promote research about the Snouters.

In the late 1950s, secret nuclear tests were conducted near the Hy-yi-yi Archipelago, and the earthquake triggered from the explosion completely submerged the island, conveniently destroying every evidence that the Snouters ever existed (but see below).

Nasarium
The distinguishing feature of Rhinogradentia is a structure called nasarium, a structure derivd from the snout or the nose. It's extremely developed and rich in nerves and muscles, making it extremely sensitive and finely motile. The main tissue of the nasarium is a corpus spongiosum, usually soft but stiffened by blood pressure when the need arises. In the suborder Polyrrhina, the proto-nasarium is cleft at an early stage of embryonic development, so that it develops into four or six nasaria - a condition unique among vertebrates. In the family Hopsorrhinidae (or "Snout Leapers") the nasarium is also powered by the longissimus dorsi, a muscle extending from the back. Since all Snouters except for Archirrhinos use their nasarium as a mean of locomotion, if they move at all, limbs have lost that function; the front limbs are modified as grasping appendages, while the hind limbs are reduced or disappeared.

Phylogeny of Rhinogradentia
Stümpke's original treatise included 151 species of Rhinogradentia, included in 28 genera, in 15 families.

Monorrhina
Monorrhina is a (probably paraphiletic) group of Snouters with only one nasarium. Most of them fall in the section Pedestria (those who walk with the nasarium), with the only exception of Archirrhinos haeckeli, or Primitive Snouter. It is the only species of the section Pedestria, as it's the only one that walk with its feet. It does, however, use the broad nasarium, held fast to the ground by viscous mucus, when it uses all the four legs to hold and eat the cockroaches it feed on.

The section Nasestria is then divided in two tribes: Asclerorrhina, with a soft, muscular nasarium, and Sclerorrhina, whose nasarium is stiffened by bones.

Asclerorrhina
The tribe Asclerorrhina comprises essenially two groups of Snouters: surface Snouters (Epigeonasida) and burrowing Snouters (Hypogeonasida and Georrhinidae). In Asclerorrhina the nasarium is still soft and not much developed, but it's already useful for locomotion.

Nasolimacidae (Nasolimacius and Rhinolimacius, on the right) have a nasarium similar in shape to a slug, which moves forward rippling its surface, carrying the rest of the body upside-down with a speed up to 10-13 m/min (30-40 ft/min). The family Rhinocolumnidae (Dulcicauda, Dulcidauca and Columnifax, on the left) have a strong pillar-like nasarium on which they stand relatively motionless; Dulcicauda and Dulcidauca secrete from their tail a sweet nectar used to attract insects which then they seize with their front limbs. Another Rhinocolumnidae, Emunctator sorbens (Snuffler) has a smaller and more primitive nasarium it uses to "fish" for aquatic invertebrates, catching them in strands of highly viscous mucus. Columnifax is similar to Dulcicauda; it has established a symbiotic relationship with a hopsorrhinid that brings it hunted preys in exchange for milk, which is produced by both sexes.

The subtribe Hypogeonasida comprehends a number of burrowing species that live in the mud of lakes and streams. They breathe through long nasaria that protrude from the mud like snorkels, and they show a strong reduction of external features such as hair, eyes and sometimes limbs. Members of the genus Rhinostentor (Trumpet Snouters) are more aquatic, and they have a wide siphon lined in hair that allow them to catch plankton.

Except for Rhinotalpa, which in overall aspect is similar to Hypogeonasida, the subtribe Georrhinidae shows a strong degeneration of most body structures in favor of the nasarium, unique among vertebrates. Rhinotalpa has a large, bristled and inflatable nasarium used to dig tunnels, while it shows reduction or disappearance of digestive tract, lung capacity, nostrils, hair, brain, eyes and homeothermy. In the more extreme Enterorrhinus and Holorrhinus, the nasarium accounts for most of the body length, while the digestive systems is a simple tube and the brain is a small ganglion. Finally, the diminutive Remanonasus menorrhinus completely lacks, blood vessels, anus and spine, so that some scientists believe that it's not actually a Snouter, or even a vertebrate, but rather a turbellarian (an aquatic worm).

Sclerorrhina
The tribe Sclerorrhina is distinguished by the presence of articulated bones in the nasarium that allow them to use it as a proper, leg-like limb for locomotion (see here about monopods). The most primitive family of Sclerorrhina (Amphihopsidae) are tree-dwelling Snouters with both the nasarium and the tail are turned in limbs to leap, both forward and backward, while the legs are still as developed as before.

True Snout Leapers (Hopsorrhinidae) have an extremely developed nasarium with two long sections, stiffened by the nasur  and the nasibia, and a "feet" formed by rhinanges; the hindlimbs have disappeared, while the front limbs and the forked tail still exist as grasping appendages. Hopsorrhinus consumes insects it captures by leaping backwards; Mercatorrhinus brings them to the rhinocolumnid Columnifax, receiving milk in exchange.

Among Hopsorrhinidae, Otopteryx volitans (shown on the book cover and on the right) deserves a special mention. Thanks to very long, narrow ears (stiffened by a bone, the os alae auris) that provide lift, each leap allow it to glide for a long distance, until it lands by spreading the ears wide.

Finally, Orchidiopsidae (on the left) do not use their prehensile tail and their ossified snout to leap after insects, but rather catch them by posing as flowers, like the orchid mantis or Flower-Faced Snouters. The nasarium has flat, broad section similar to the petals of an orchid (in Orchidiopsis) or a lily (in Liliopsis), while the forked tail holds fast on a branch. The petal-like sections also emit a viscous, flower-scented secretion; in Liliopsis thaumatonasus, such secretion is also luminescent thanks to symbiotic bacteria.

Polyrrhina
Polyrrhina are distinguished by the unique feature of multiple snouts: during embryonic development, the nasarium clefts and divides into four or six independent nasaria, each with its own muscles and nostrils. Since the nasaria are moved thanks to a pneumatic apparus, when moving it constantly emits a hissing noise. Most of the Polyrrhina species (Tetrarrhinida and Hexarrhinida) are found inside the phalanx Brachyproata (Short-nosed Snouters); they're detailed in the paragraphs below. The other phalanx, Dolichoproata, contains only one genus, Rhinochilopus, or the Tasselsnouter. Tasselsnouters have a nasarium branching in nineteen pairs of nasidi, slender appendages they use to root in the woods, searching and carrying food. They're quite large-sized, 1.5-2 m long (5-7 ft), and apparently more intelligent than any other Snouter; during courtship, they use channels in the nasarium (the ductuli musici) to produce musical sounds.

Tetrarrhinida
Tetrarrhinida are Polyrrhina with four nasaria. They're relatively unspecialized, as they all use the nasaria as tentacle-like legs; they also have a long tail and less developed limbs, though at least the front legs are always present.

Most species in this tribe are found in the family Nasobemidae, the true Snout Walkers. Their nasaria are very long, slender and fully flexible, while their long tail, albeit thin, can be used as a grasping appendage to hold fruit. While the tail is usually a flat ribbon, it can be controlled by pumping throw internal channel the gas derived from the digestion of plant matter. The type species, Nasobema lyricum, was, according to Stümpke, the inspiration for Christian Morgenstern's poem Das Nasobēm ("The Nasobame", 1895).

The most specialized species of the tribe, and only member of its family, is Tyrannosasus imperator, the Predacious Snouter. Though mostly similar to Nasobemidae, it's distinguished by strong hindlimbs, teeth apt to tear flesh and a relatively short tail, controlled by the same means, armed with a venomous claw at the tip. Because of the noise emitted from the nasaria, it's unable to stalk silently its preys, but rather it has to pursue them; often Nasobema defends itself by hanging with the tail from a branch and oscillating to confuse the predator.

Hexarrhinida
Hexarrhinida have six nasaria. One of the two families of Hexarrhinida, Anisorrhinidae, includes only one species, Mamontops (= Mammontops) ursulus, the Shaggyfaced Snouter. It's generally similar to Nasobemidae, though it's much larger (more than a meter high) and covered in thick fur, and, while it also walks on four nasaria, there other two which are thinner and used to uproot plants.

The other (possibly polyphiletic) family, Isorrhinidae, is distinguished by six very long and slender nasaria, somethimes lacking corpora spongiosa. The less specialized Isorrhinidae, Eledonopsis, lives in burrows with its thin nasaria, up to 30 cm long, crawling around the forest floor, from which it takes the name "Ribbon Snouter". The surface of the ribbons is covered in bristles and curls in a tube to bring captured springtails and barklice towards the mouth, while larger preys such as spiders are entangled in mucus and tied by several nasaria.

The other two genera of Isorrhinidae, Hexanthus (also called Ranunculonasus) and Cephalanthus (also called Corbulonasus) trap insects by posing as flowers, like Orchidiopsidae, but with very different methods. Hexanthus lies motionless on the ground, hidden by its greenish colour, while its nasaria creep up the stalk of flowers, while the end of each nasarium ends with a flower-shaped structures. These, coloured yellow, red and black, emit a vanilla-like scent, known to attract the six-winged insects. Cephalanthus brings its small body at the level of the flowers, standing on a long and rigid tail. The nasaria form six broad petal-like structures circling the mouth, and close around the insects pushing them towards the teeth. Cephalanthus never move from their spot; to mate, the males simply wait to be pushed by the breeze towards the females.

Recent discoveries
The Russian edition of the book (2000) adds an appendix where newly discovered species of aquatic Snouters are described, allegedly collected a decade before in the shallow sea off the Antarctic coast. They've been assigned to the Hydroidopsidae and Scyphoidopsida families as highly derived members of the tribe Hexarrhinida. All of them are only a few cm long.

The family Hydroidopsidae contains two new species: Rhizoidonasus euphorbiformis and Larvanasus haleciformis. Rhizoidonasus lives in colonies, with the parent individual attached to the seafloor through the six nasaria, each branching in rhizoid-like structures. The long tail is also branched, and younger organisms live attached to these branches while their nasaria develop.

Larvanasus is even more derived, with a smooth, curved, boneless, translucent body that contains 9-10 larvae in various stages of development. While the "root" of the adult individuals is still similar to a foot, and the "face" still shows traces of six haired noses and stalked eyes, the rest of the body doesn't even look like a vertebrate anymore. What remains of the skeleton forms a thin transparent external shell. The spawned larvae grow a fur cover during their swimming phase, and they look in fact like mammals, but they lose hair, limbs and internal bones when they settle down on the seafloor.

The last species, Nudirhinus medusiformis, is the only species in the family Scyphoidopsidae. This organism is oval-shaped and covered with rigid plates, forming a shell with seven openings: four for the limbs (which are still mammal-like), two for the ears and one for the tail. They move on the rocks walking on their six underlying nasaria like starfish on tube feet. Adults seem to be hermaphrodites; their overall appearance is similar to a hermit crab, while the swimming larvae are somewhat jellyfish-like.

In 2004, another new discovery is added to the russian edition. A colony of small creatures recognized as Snouters is said to have been found in 1987 attached to a piece of rotten wood. It was composed by five zooids, two of them crushed and unrecognisable, two of them still immature as buds. The only well-developed zooid was 5-6 mm long, and fused through its nasarium to a common root. This specimen has been assigned to the genus Dendronasus, probably close to Epigeonasida such as Columnifax and Dulcicauda.

Dendronasus has large eyes and wide nostrils, probably reduced to an olfactive purpose, as breathing is accomplished by branched gill-like structures, possibly highly modified forelimbs; the hindlimbs are still large (with prehensile feet) and apparently soft, as is the hooked Dulcicauda-like tail; the whole body is covered in fine golden hair. It seems to be capable of asexual breeding: new individuals simply grow by gemmation from the common stalk.

According to a French site, in 1995 a recognisable fossil of Otopteryx was discovered in rocks over 100 million years old, very similar to its modern form; this would suggest that Rhinogrades were already derived and quite widespread in the Mesozoic Era, and thus that some new species of Snouters might still exist somewhere in the world. Following this trail, a 1999 expedition between Slovenia and Croatia managed to find and photograph a living Snouter, assigned to the new genus Acrorrhinos in the section Pedestria, very close to the primitive Archirrhinos.

References and readings

 * The complete text of the book at Sivatherium.
 * Les Rhinogrades, a site dedicated to Snouters' history and study (in French)
 * Two posts about Snouters on Tetrapod Zoology