Chapter 3: Aquatic Motion

Created by Sarah Choi (prompt writer using ChatGPT)

Aquatic Motion (Undulation, Jet, Paddle)

Why Aquatic Locomotion Matters for Creature Concept Artists

When a creature enters water, the physics change dramatically. Gravity is partially countered by buoyancy, movement is resisted by dense fluid instead of air, and limbs or tails must push against water in very different ways from pushing against ground or air. If you ignore these differences, your aquatic creatures will feel weightless, stiff, or simply unbelievable.

For creature concept artists, understanding aquatic motion—especially undulation, jet propulsion, and paddle‑based swimming—is as important as understanding walk and gallop cycles on land. This is true whether you’re on the concepting side (cinematic keyframes, exploratory thumbnails) or the production side (turnarounds, motion sheets, animation reference).

In this article, we’ll look at:

  • Core principles of moving through water.
  • Undulation: body and tail waves in fish, serpents, and eels.
  • Jet propulsion: cephalopod‑inspired motion and fantasy jet swimmers.
  • Paddle / limb strokes: aquatic mammals, reptiles, birds, and hybrid designs.
  • How aquatic motion overlaps with footfalls, flight, and climbing in multi‑mode creatures.

The goal is to give you practical, drawing‑friendly tools to design and pose creatures that feel like they truly belong in water.

1. Moving Through Water: Basic Forces and Constraints

1.1 Water vs. Air vs. Ground

Water is hundreds of times denser than air. This has key consequences:

  • Movement faces higher drag—broad surfaces and sudden direction changes are expensive.
  • Bodies tend to be more streamlined, minimizing turbulence.
  • Buoyancy supports weight, so creatures can be heavier yet float, but they must constantly manage orientation.

On land, creatures mostly deal with:

  • Footfalls and impact forces.
  • Friction and gravity.

In air, creatures focus on:

  • Generating lift and thrust while fighting drag.

In water, propulsion comes from:

  • Pushing water backward (tail undulation, paddling limbs, jet streams) so the body moves forward.

For you as an artist, this means aquatic poses should show:

  • Clear surfaces or motions that push water.
  • Fewer hard impacts; motion is smoother, with continuous resistance.

1.2 Three Major Aquatic Strategies

Most aquatic vertebrates and many invertebrates use one (or a combination) of three strategies:

  1. Undulation: Moving the body and/or tail in waves.
  2. Jet propulsion: Expelling water from a cavity to create thrust.
  3. Paddle strokes: Using limbs or fins as oars or wings under water.

Let’s break each down into structure, motion, and design implications.

2. Undulation: Body and Tail Waves

Undulatory motion is common in:

  • Fish and eels.
  • Aquatic snakes and aquatic reptiles.
  • Serpentine fantasy creatures (sea dragons, leviathans, giant eels).

2.1 How Undulation Works

In undulation, the creature sends a wave of bending down its body and/or tail. That wave pushes water backward, generating forward thrust.

Key points:

  • The wave starts near the head or mid‑body and travels toward the tail.
  • The large side‑to‑side motion often increases toward the tail, which acts like a powerful paddle.
  • The head usually moves less than the tail to maintain stability and target focus.

You can think of undulation as a traveling S‑curve along the spine.

2.2 Types of Undulation (for Artists)

You don’t need to memorize scientific names, but different patterns are useful stylistically:

  • Whole‑body undulation (eel‑like):
    • Almost the entire body participates in the wave.
    • Great for long, flexible creatures that can turn sharply.
  • Mid‑body undulation (fish‑like):
    • Front of the body more stable; rear half undulates more.
    • Good for fast swimmers that still need some stability.
  • Tail‑dominant undulation (tuna, shark‑like):
    • Body fairly rigid; motion concentrated in the tail.
    • Ideal for high‑speed, long‑distance swimmers.

When designing a creature, decide how rigid vs flexible its spine is and where the main wave should be.

2.3 Drawing Undulatory Motion

To pose an undulating swimmer:

  1. Start with a smooth S‑curve as the spine line.
  2. Decide where in the cycle the creature is:
    • Head turned one way, tail bending opposite.
    • Wave midpoint somewhere along the torso.
  3. Place the body segments and fins along that curve.

For side views:

  • Emphasize how the curve amplitude increases toward the tail.
  • Keep head relatively stable for predatory or purposeful motion.

For 3/4 or top views:

  • Use foreshortened S‑curves and overlapping segments.
  • Fins and dorsal spines follow the same rhythm as the spine.

2.4 Surface and Structural Design for Undulators

Undulating creatures benefit from:

  • Streamlined cross‑sections (oval or torpedo‑like bodies).
  • Flexible spines and segmented muscles along the sides.
  • Fins that support turning and stability (dorsal, anal, pectoral fins).

Design cues:

  • For eel‑like stealth creatures, drop big fins and go for sleek, sinuous bodies.
  • For fast predators, use stiffer, muscular front bodies and tall, powerful tails.

Production note:

  • Show at least two or three poses along the wave cycle so animators see how the spine and tail are expected to move.

3. Jet Propulsion: Cephalopod‑Style Thrust

Jet propulsion is iconic in cephalopods (squid, octopus, cuttlefish) but is also a great basis for alien or magical designs.

3.1 How Jet Propulsion Works

In jet propulsion:

  • The creature draws water into a cavity (mantle or internal chamber).
  • Muscles constrict the cavity, forcing water out through a narrow opening (siphon/nozzle).
  • The expelled water pushes the creature in the opposite direction.

This creates a burst of thrust, often followed by a glide.

3.2 Visual Characteristics

Jet swimmers often show:

  • Pulse‑like motion: compress → shoot → expand → glide.
  • Bodies that change shape—mantle expands and contracts.
  • Orientation changes: many cephalopods move backwards relative to where their tentacles point, because the jet is behind them.

For fantasy designs, you can exaggerate this:

  • Large mantles or sacs that balloon and shrink dramatically.
  • Glowing or smoky jet streams for magical or sci‑fi creatures.

3.3 Drawing Jet Motion Poses

Think in phases:

  1. Intake/Relaxed:
    • Mantle or sac expanded.
    • Siphon open, drawing water in.
    • Creature moving slowly or hovering.
  2. Compression/Jet:
    • Mantle squeezed smaller.
    • Siphon narrowed, water expelled in a strong jet.
    • Creature body “kicks” in the opposite direction, tentacles trailing.
  3. Glide/Coast:
    • Mantle relaxed, shape elongated.
    • Creature rides momentum; minor adjustments with arms or fins.

When sketching, show the jet stream direction with motion lines or bubbles and keep body distortion visible.

3.4 Structure and Landmarks for Jet Swimmers

Jet propulsion designs often include:

  • A central muscular sac or mantle.
  • A nozzle/siphon that can aim to steer.
  • Stabilizing fins or tentacles for orientation.

Design options for creature artists:

  • Combine jet mantles with vertebrate tails or wings for hybrid locomotion.
  • Use multiple smaller jets (side vents, tail jets) for more complex maneuvering.

Production note:

  • Indicate in callouts where the main jet nozzle(s) are and what range of motion they have—animators will need this.

4. Paddle‑Based Swimming: Limbs as Oars or Wings

Paddle or limb‑based swimming is used by:

  • Aquatic mammals (seals, otters, whales in their fluke region).
  • Reptiles (sea turtles, marine iguanas).
  • Birds (penguins, diving ducks, cormorants).
  • Many fantasy mounts and semi‑aquatic beasts.

4.1 How Paddle Swimming Works

In paddle swimming:

  • Limbs or fins sweep through water in powerful strokes.
  • The power phase pushes water backward; the recovery phase minimizes drag.

This approach is analogous to wing strokes in air, but water’s higher density means strokes are often slower and more forceful.

4.2 Limb Patterns and Roles

Common patterns:

  • Forelimb‑dominant swimmers:
    • Sea turtles, penguins.
    • Big forelimbs act like wings; hindlimbs mainly steer.
  • Hindlimb‑dominant swimmers:
    • Frogs, some reptiles.
    • Hind legs kick symmetrically or alternately for thrust.
  • Full limb swimmers:
    • Dogs, otters.
    • All four limbs paddle in alternating patterns, like an aquatic trot.

Design question:

  • Which limbs are the main engines, and which are rudders or stabilizers?

4.3 Drawing Paddle Strokes

Similar to flight, think in phases:

  1. Power stroke (push):
    • Limb extended and pressing back against water.
    • Joints open; webbing or fins spread.
    • Body slightly lifts or moves forward.
  2. Recovery stroke:
    • Limb flexes, pulling forward with reduced surface to cut water.
    • Webbing may fold; fins angle edge‑on.

Side view tips:

  • Show large arcs for primary limbs.
  • Capture the moment when limbs are fully extended backward—this often reads best.

Top or 3/4 view tips:

  • Use overlapping limbs and foreshortening to show depth.
  • Indicate swirling water or bubble trails behind paddles.

4.4 Morphology for Paddle Swimmers

Paddle swimmers often have:

  • Flattened or broadened limbs with webbing, flukes, or feathers.
  • Streamlined torsos to reduce drag.
  • Shortened or reinforced limb bones for power.

As a creature designer:

  • Emphasize strong shoulders or hips depending on which limbs drive swimming.
  • Consider joint range: underwater strokes may use greater joint motion than walking, but need to remain believable.

Production note:

  • If the creature must both walk and swim, show land gait and water stroke poses so riggers see how limbs adapt.

5. Combining Modes: Walk, Flight, Swim, and Climb

Many creatures in games are multi‑mode movers:

  • Amphibious beasts that walk, swim, and climb.
  • Dragons that fly, swim, and perch.
  • Alien hexapods that skitter on land and jet or paddle in water.

5.1 Translating Footfalls to Aquatic Strokes

Ground gaits involve footfalls; aquatic motion involves strokes. You can map one to the other:

  • A dog‑paddle is essentially a walk cycle with exaggerated limb arcs through water.
  • A frog’s swimming kick is like a powerful hindlimb push in a gallop, repeated symmetrically.

When designing a creature that does both:

  • Decide whether water strokes will resemble its walk, trot, or gallop mechanics.
  • Maintain clear joint behavior across modes—don’t invent new joints underwater unless justified.

5.2 Integrating Flight and Swimming

For winged swimmers (e.g., penguin‑like dragons or manta‑ray flyers):

  • Underwater strokes can look like slower, more powerful wingbeats.
  • Planform changes subtly: wings might be thicker, with stronger bones and edges.

Visually:

  • Above water: wings generate lift in air.
  • Below water: same wings generate thrust and lift in water, with more roll of the body.

5.3 Climbing to Water and Back

Creatures that climb into or out of water (river dragons, cliff‑nesting sea wyrms):

  • Use limbs and claws to grip rocks.
  • Let tails and wings act as counterweights or stabilizers.

When staging:

  • Show water dripping, limbs seeking holds, body angled with gravity.
  • Keep aquatic musculature (tail, limbs) clearly visible so motion direction makes sense.

Production note:

  • If climbing is a key gameplay feature, include transition poses for land ↔ water and water ↔ flight.

6. Concepting vs. Production: Aquatic Motion in Different Contexts

6.1 On the Concepting Side

When concepting, focus on big motion ideas:

  • Is this creature serpentine and eerie, sliding through water with undulation?
  • Is it a jetting ambusher, bursting from shadows, then gliding?
  • Is it a paddle powerhouse, churning water with huge flippers?

Use loose sketches to explore:

  • Spine curves and body waves.
  • Mantle deformations and jet vectors.
  • Limb stroke arcs.

You don’t have to be physically perfect, but you should show a clear logic of how the creature pushes water.

6.2 On the Production Side

In production, aquatic motion becomes technical reference:

  • Provide side‑view swim cycles for undulators and paddlers.
  • For jet creatures, show intake, compression, and glide poses.
  • Clarify how aquatic motion ties into land gaits and flight cycles.

Include in your sheets:

  • Direction arrows for water flow and thrust.
  • Notes on which parts are rigid vs flexible.
  • Range of motion for key joints, tails, mantles, and fins.

The more clearly you communicate motion logic, the easier it is for animators to make your creature feel alive.

7. Practical Exercises for Aquatic Motion

7.1 Spine‑Wave Studies

  • Fill a page with S‑curve spines representing different moments in an undulation cycle.
  • Wrap a simplified fish or serpent body around each.
  • Add tail and fin positions that match the wave.

This trains your eye to see and design traveling body waves.

7.2 Jet Burst Thumbnails

  • Sketch a simple cephalopod‑like silhouette.
  • Draw three thumbnails: intake, jet, glide.
  • For each, exaggerate mantle deformation and the jet stream.

You’ll quickly get a feel for the rhythm of jet propulsion.

7.3 Paddle vs Walk Comparison

For a quadruped creature that can swim:

  • Draw a side‑view walk cycle frame (one leg forward, one back).
  • Below it, draw a paddle stroke frame using the same joints but in water.

Compare limb angles and range: what changes, what stays consistent? Adjust your design to support both.

7.4 Multi‑Mode Sheet: Land, Water, Air

Pick a hybrid creature (e.g., winged sea dragon), and create a sheet with:

  • A land pose (walk or crouch).
  • A swim pose (undulation or paddle).
  • A launch or dive pose.
  • A glide or soar pose above water.

This exercise connects locomotion modes and reveals anatomical or design conflicts early.

8. Bringing It All Together

Aquatic motion—undulation, jet, and paddle—is a rich source of inspiration and a crucial piece of creature believability.

  • Undulation gives you sinuous, stealthy, or high‑speed body‑wave swimmers.
  • Jet propulsion offers explosive bursts and alien, shape‑changing silhouettes.
  • Paddle strokes let land‑capable creatures adapt limbs for powerful swimming.

For both concepting and production work:

  • Think about how your creature pushes water every time it moves.
  • Use clear spine curves, limb arcs, and mantle deformations to show thrust and drag.
  • Connect aquatic motion back to footfalls, flight strokes, and climbing grips in multi‑mode designs.

When an aquatic creature feels “floaty” or unconvincing, ask:

  1. What is its primary propulsion method (undulation, jet, paddle, or hybrid)?
  2. Where is the main engine in the anatomy (tail, mantle, limbs), and am I emphasizing it in the pose?
  3. Are my silhouettes and curves showing water being pushed in a clear direction?

If you can answer those, your underwater beasts, serpents, jetting horrors, and amphibious mounts will feel as grounded in water as your best quadrupeds feel on land—and your concepts will translate smoothly into animation and gameplay.