Whew! This is a really big update. The TL;DR is:

New skin patterns and colors for critters! Temperature system! Scent system! Tweaks, fixes, and more!
Oh, and the Demo has been updated to 1.14, too!

Now then, let's break it down:

NEW LOOKS

• Critters may now develop one of three secondary color patterns, with varying color and intensity.
  • Stripes will make their movement and size less apparent where weeds are present, especially if the stripes are reddish. Stripes of any color will make a critter seem bigger and flashier in open water.
  • A single countershade strip will make their movement and size less apparent in open water, especially if the strip is blueish. A countershade of any color will make a critter seem bigger and flashier among weeds.
  • A mottled pattern of spots will have a modest effect in both environments determined by the color -- so red spots are like "weak" stripes, blue spots are like a "weak" countershade.
  • All of these effects are scaled according to the intensity of the pattern.
  • Standard "plain" critters will still spawn/evolve too.

TEMPERATURE SYSTEM

• A new system tracks the temperature of the water and each Critter's temperature too.
  • In the shallows, where weeds grow, it is warmer -- in the deep, where there are no plants, it is colder.
  • There are new placeable level objects to help you sculpt your environment -- Heaters and Coolers!
  
  • Critters have an "Ideal Temperature" stat that determines where they're most comfortable.
    • An egg or immature Critter grows more quickly the closer its body is to its ideal temperature.
    • When too cold, a critter's movement is slowed and their energy is drained.
    
    • When too hot, a critter's health is damaged.
    
  • To help increase the environmental variation, Fruits behave differently based on temperature too:
    • Cold fruit (slightly bluer) moves more slowly
      
    • Warm fruit provides more energy above the base value

SCENT SYSTEM

• Critters now produce and detect four unique chemical signatures:
  • METHANE (Green) is produced by herbivores.
  • SULFUR (Orange) is produced by carnivores.
  • BLOOD (Red) is produced by dead critters and critters being damaged by attacks.
  • MUSCONE (Purple) can be produced by critters with the activation of a newly repurposed Output Neuron

All this new stuff going on means there's a need for...
NEW UI and ADVANCED OVERLAYS

• TEMPERATURE OVERLAY
  • Does what it says on the tin! Hover over this new UI element to see the temperature of the water. (Big enough critters diving in and out of hot zones will leave neat little trails of warm water!)
• SCENT OVERLAY
  • Just what it sounds like! Hover over the button to see the scents lingering in the water. Really hypnotic.
• REWORKED UI FOR STATISTICS
  • The old "Exceptional Critters" Panel is no more!
  • To see or select the outliers within each stat, hover over or click the arrow buttons next to each stat's hoverable button
  • Big improvement: charting/highlighting is now PINNABLE! Along with the temperature/scent overlays, you can click the button associated with an overlay or highlight to pin that view. You can hover over other views to bring them up, and it will switch back to your pinned view when you remove the mouse. Click your pinned selection (or pin another selection) to un-pin it. Overlays and stat highlights are mix-and-match, too!
  
• MISCELLANEOUS TWEAKS AND FIXES
  • The Main Menu has moved to the upper left of the screen to help it stand out now that the top bar is filling up.
  • All "Basic Critter" spawns have more of their stats randomized instead of starting from a template. Strength, Speed, Diet Compatibility, Breeding Strategy are all randomized.
  • The energy cost of swimming forward or backward now scales exponentially with the Neuron's activation instead of linearly.
  • All movement is (very) slightly more expensive and slow.
  • Instead of Nuts being completely inedible if a Critter lacks the strength to crack it, weak Critters can now bite off smaller bits of the nut (essentially nibbling their way through the shell a bite at a time, wasting some of the nutrition but rewarding their effort a little.)
  • The Size graph's minimum and maximum are now relative to the population instead of fixed. This gives you more detailed information about the distribution.
  • New graph and highlight mode for Ideal Temperature Distribution.
  • New Sensory Neuron in the "Internal State" section tells a Critter how close it is to maturity
  • The Scent system required lots of Sensory Neurons to hook up. I noticed that "meta" inputs like "what's my speed" and "am I biting" were rarely being used. The entire proprioception lobe has been cannibalized into the new olfactory center.
    • Similarly, a new output was needed for musk production -- the Forward/Backward outputs were merged into one trimodal output (negative activation means reverse).
    • The effects of these changes on existing Critters imported into the new version should be minimized by the new Migrations system introduced in the last update. Synapses that were pointed toward the Backward movement output will be remapped.
  • We used to leave some neurons in the grid "empty" until a synapse mapped to them. Now that the NeuroSurgery suite allows you to edit Neurons, it makes more sense to populate these slots and simply leave them "disconnected."
  • New synapse mapping rules: previously, Sensory neurons could only connect directly 1 or 2 layers down, and only in "their half" of the brain horizontally. Now that we have a much larger number of Senses, this rule forces too many unrelated inputs to collide with each other. The new rule allows senses to reach in 3 layers deep, and the horizontal divide is roughly between the internal and external inputs.
  • Fixed a bug in the NeuroSurgery screen that let you try to add Synapses to Output Neurons (or locked you out of adding Synapses to valid neurons)
  • Finally -- the Spacebar can now be used as a quick "Pause/Resume" key