Jetocetes and Relatives

One of the evolutionary spectacles unique to Snaiad is the
presence of jet-propelled advanced “vertebrates” in its rivers and seas. While
underwater jet propulsion is observed in a lot of small creatures on Earth and
other planets, Snaiad’s Jetocetes are the only known case where this method of
locomotion has evolved in large animals that descended from terrestrial
ancestors.

Needless to say, this adaptation entails a series of drastic
alterations to the traditional “two-headed” Snaiadi bodyplan. Most prominent
among these changes is the splitting of the second-head digestive tract into a
separate canal devoted to propulsion, and the re-routing the section that
handles the food into the first head, where the genital-sheath jaws, uniquely in
Snaiad’s natural history, act as true mouthparts.

While such extreme modifications seem impossible to have
evolved naturally, certain animals that still survive today give us clues about
the transformation of swamp-dwelling swimmers into the jet-propelled masters of
the sea, -and beyond.

Species: Phyllocaudus reticulatus
Common Name: Reticulated
Leaftail.
Size: 90 centimeters or less from snout to tail.
Habitat: Rivers
and tributaries in the Azonic Jungle.

This species, along with the closely related P.
flagellurus, belong to the most basal group of jet-propelled swimmers. The
Reticulated Oartail is found only in the Azonic river system, feeding on
vegetation and small river animals. It swims generally with the help of its
muscular tail and paddle-shaped fins, but when cornered it can rapidly eject
water from its anal sphincter for sudden bursts of speed. Unlike its cousin
groups, Phyllocaudids do not have a differentiated tract of their digestive
systems adapted exclusively for jet propulsion; they merely swallow and expel
water rapidly. Neither is this a preferable way of locomotion for the
Phyllocaudids, since they void all of their stomach contents while jetting and
go hungry as a result. These living fossils are very rare, and research suggests
that their numbers are declining. Captive breeding programs are underway to
protect them from extinction.

Species: Motosuchus phoeniciensis
Common Names: Eyeing
Scooter-Croc, Armadillodile.
Size: Up to 2.5 meters long.
Habitat: The
Scoptic Delta in Lower Vesterna.

Large rivers on almost any continent of Snaiad are patrolled by
Motosuchid jet-crocodiles; swimming in eerie stillness they purr along on their
gastro-intestinal water jets. Ancient and cryptic, these creatures represent an
intermediary branch on the way to truly marine jet-swimmers. The Motosuchid
digestive track has split partly into two; one branch handling food and a blank
tube providing propulsion. Still, they cannot drink saltwater and their jet
engines aren’t efficient enough to provide constant propulsion. For this reason
they are confined to rivers and isolated lakes, but they have adapted to this
limited niche expertly; 40-million year old fossils of the first Motosuchids are
often difficult to tell apart from modern species.

The Eyeing Scooter-Croc, native to the Scoptic Delta, gets its
name from the staring dorsal eye spots that bear a passing resemblance to the
ship decorations of the ancient, distant Earth. Its hooked beak is suitable both
for digging along the bottom sediment, or sharp lunges at unwary prey. Its
distended jet-gut can produce intense five-second power bursts to rocket the
animal towards its terrestrial victims, who usually never get to realize what
hit them.

Species: Helicodectes scylla
Common Name: None.
Size: Up
to 4 meters long.
Habitat: Continental shelves and reef gardens around
Midland

When first caught off the Sea of Midland fifty years ago, this
creature dropped into the world of Snaiadi zoology like a bomb. Nobody could
understand exactly what it was, and how it used its bizarre, ram’s horn jaws
that suspiciously looked like the Helicoprion fossils of the distant
Earth. Investigations in the next few decades have fortunately shed more light
on the lifestyle and the origins of this mystifying creature.

Initially thought to be an aberrant Motosuchid,
Helicodectes was found out to be a specialized Jetocete that had
secondarily lost its torpedo-shaped body shape and tuned down its jet gut to
pursue a specialized lifestyle; feeding on the many species of Sea Serpents
(Ophicarida,) found on Snaiadi reef gardens. Helicodectes has been observed
patrolling slowly along the reefs, using its tail rather than jet gut to propel
itself. Its bizarre jaws make up a perfect tool to snag the ribbon-like bodies
of Sea Serpents.

Even after revealing its mysteries, however,
Helicodectes reminds us that Snaiad is still an alien place, rife with
discoveries, weirdness and wonder.

Species: Jetocetus mediterraneana
Common Names: Jetshark,
Neomed Jetshark, Neo.
Size: 2 meters long.
Habitat: The Neomediterranean,
sometimes seen outside in the Sea of Aar as well.

True Jetocetes bear more derived jet-propulsion systems than
either the Phyllocaudids or the Motosuchids, but not the heart-like pumps of the
Cardiocetes. Part of their digestive system has completely budded off from the
main line, turning into a jet pump that can provide continuous flow. The other
half of the digestive tract has fused into the jaws on the first head. This way,
true Jetocetes (and their descendants, the Cardiocetes,) can actually eat with
their first heads, an unusual condition found in no other lineage on the planet.

Although the terrifying Polycardiac Cardiocetes give them no
quarter on the open ocean, many ordinary Jetocetes still occupy medium-to-large
predator niches in shallow waters and reef gardens. The Mediterranean Jetshark
is a typical example. Possibly a subspecies of the virtually identical Aarite
Jetshark (J. aaritas,) it dwells in the Neomediterranean year-round,
feeding on anything smaller than itself. Although attacks on humans have been
very rare, public beaches on the Neomed regularly post Jetshark alerts to warn
bathers during crowded days, just to be on the safe side.

Species: Pelagoxiphias gladius
Common Name:
Swordpinguin.
Size: 1.5 meters excluding beak.
Habitat: All across the
oceans of the Southern Hemisphere.

Distributed all around Snaiadi oceans, the thirty-plus species
of Thalassoxiphid “Swordfish” are as fast as true Jetocetes can get. These
creatures all have egg-shaped, compact bodies housing well-developed water jets,
but no heart-pumps like the Cardiocetes. Strangely, they have well-developed
rear fins that seem out-of-place on streamlined swimmers, but these limbs
actually serve to vector their water jets in tight angles for increased
maneuverability.

While it would seem that Thalassoxiphid Jetocetes would be at a
disadvantage when competing with the extremely fast Polycardiac Cardiocetes, the
two groups manage to exist side-by-side in most marine ecosystems. The
Cardiocetes prefer more energy-rich prey with their supercharged metabolisms,
leaving a selection of less nutritious prey items to the Thalassoxiphids, who
can live on them since they don’t regularly risk starvation when fueling their
water jets. Thalassoxiphids and their faster descendants thus manage to live in
the same places by exploiting different kinds of prey.

Species: Hadrocetoides balabani
Common Name: None.
Size:
6-7 meters long.
Habitat: All across the Great Northern Ocean, sometimes
found in warmer seas as well.

While the Cardiocetes have some of the largest filter-feeding
species on Snaiad, old-school Balenarhynchid Jetocetes such as Hadrocetoides
actually enjoy larger species diversity and biomass, especially in the cold
climates. These creatures vary in size from just over two meters to thirteen
meters long, and ply the Snaiadi seas for plankton and pelagic swimmers of all
kinds.

Protected from the cold in deep layers of blubber,
Hadrocetoides balabani can be regularly observed around the Great
Northern Ocean. They travel in family pods of up to a hundred individuals, and
in turn are hunted by the two species of vicious Torpedichthyid Polycardiac
Cardiocetes that live across their range.

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