Coral is not a valid tissue, even though it's a valid material, and you also forgot to tell it what FAT and MUSCLE are supposed to be. I would insert;
[USE_MATERIAL_TEMPLATE:FAT:FAT_TEMPLATE]
[USE_TISSUE_TEMPLATE:FAT:FAT_TEMPLATE]
[USE_MATERIAL_TEMPLATE:MUSCLE:MUSCLE_TEMPLATE]
[USE_TISSUE_TEMPLATE:MUSCLE:MUSCLE_TEMPLATE]
[TISSUE:CORAL]
[TISSUE_NAME:coral:coral]
[TISSUE_MATERIAL:CORAL:NO_SUBTYPE]
[STRUCTURAL]
[CONNECTIVE_TISSUE_ANCHOR]
[RELATIVE_THICKNESS:2]
[HEALING_RATE:1000]
[VASCULAR:3]
[PAIN_RECEPTORS:50]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
[SETTABLE]
[SPLINTABLE]
Immediately before the [BODY_DETAIL_PLAN:EXOSKELETON_TISSUE_LAYERS:CORAL:FAT:MUSCLE] line. The game then has enough information to figure out what CORAL, FAT, and MUSCLE should each refer to in this creature
Settings for coral tissue taken from the bone tissue template, because coral and bone arent totally dissimilar.
Checking this creature in arena mode with my changes, there are still errors associated with various organs' tissues and materials, and a couple other spelling/ID errors. So you'll have to add the organ tissues and materials same way I added the muscle tissue and material up there. It's asking for HEART, BRAIN, GUT, LIVER, STOMACH, PANCREAS, SPLEEN, KIDNEY, LUNG and EYE. I would add them right after the coral tissue definition. The other errors are;
PHEANS:Unrecognized Creature Variation: STANDARD_SWIMING_GAITS
PHEANS:Unrecognized Creature Token: NO_PAIN
PHEANS:Unrecognized Creature Token: PERSONLITY
Swiming gaits needs another M in there, NO_PAIN should be just NOPAIN, and PERSONLITY needs an A.
Oh, and with fat the game will want tallow, so you'll need to add that material too (theres no tissue for that)
Oh! Also, for the entity, you're going to want to add after the other values
[VALUE:MERRIMENT:-10]
[VALUE:LEISURE_TIME:-10]
There's a bug with fishing labors where if these social values are too high, they'll spend too much time fishing and their stockpiled fish numbers will climb until they crash the game. I've added this to every entity in my game and it's removed 90% of the random worldgen crashing