Largest size difference between progeny and adult

Which living creature has the largest size difference between the offspring and the adult? I realize theat there are many parameters in this questions. e.g., for a placental mammal, do you compare the fertilized egg to the adult, or the newborn to the adult? Also, how do you define living creature? If you give an answer, you should probably explain your parameters. Here are a couple of definitions to help arrive at an answer.
Animals (Wikipedia: Kingdom Animalia)
Living Creatures (Wikipedia: life)

My guesses would be:
Animal: blue whale, taking difference between fertilized egg and adult.
Living creature: Coastal redwood (example: Lindsey Creek tree) - I remember that coastal redwood “pinecones” are tiny, much smaller than the cone from a regular pine tree; or else, if you count colonies, the Shoestring Rot fungus

I don’t suppose there are any other candidates in the living creatures category, but are there any creatures in the animal kingdom that have a larger difference between offspring and adult? You could measure either total difference (adult mass - offspring mass = biggest number) or proportion (adult mass = X times offspring mass)

If you’re comparing ova in mammals, there probably isn’t that much difference in size. I hope someone addreses that.

For newborns compared to adult, you also have to consider marsupials that deliver very undeveloped young. Adutlt males may be over 200 lbs. If the newborn weighed only 1/2 pound, that would be a 400:1 difference. But I don’t know what a newborn Red weighs. It could be much less.

Adult blue whales may reach 300,000 lbs. (I’ll bet that was an estimated weight). The calves are reported to weight between 5000 and 6000 lbs. Going with 5000 lbs., that’s only 60:1. A 10 lb. human baby could end up weighing over 600 lbs., so Blues don’t seem to be at an advantage here (although I don’t know how many animals aside from humans can develop weight so much in excess of the average for the species).

Polar bear cubs weight about 2 lbs. at birth, and can grow to 1500 lbs. So that’s 750:1, a pretty high ratio.

pandas: birth weight 100-200 grams. Adult male up to 150 kg.

Yes, kangaroo was my first thought.

For animals it would be the giant clam.

The trocophore larva is a true, free living, feeding, independent animal with a size measured in microns. I can’t find any estimates of mass, but if we are exceedingly generous and assume a density of twice seawater and a large trochophore of 50 microns that gives us a mass of 0.0005 grams. The adult clam weighs in excess of 250kg.

So the adult weighs 500, 000, 000 times more than the offspring.

Using more realistic estimates of density and size it would probably be an order of magnitude more than that, but a half-billion times difference means that any vertebrate isn’t even going to get a look in.

Of course pine cones are a composite fruit, not a single seed, so the size of the cone is quite irrelevant. It’s like estimating the size of a pineapple seed by weighing the entire fruit.

Redwoods definitely are not in the running anyway.

Redwood seeds are quite huge by seed standards, and the wood has a fairly low density. In contrast Eucalyptus seeds are tiny and the wood has a very high density, so even a moderately sized eucalypt, say 50 metres of so, will have a much, much higher ratio than a redwood. Some eucalypts are within a hair of being as tall as the tallest redwoods, and are much, much more massive due to the much higher density. When combined with a seed that is less than 1/50th the size, the eucs are going to win out easily as the trees with the highest ration.

However, once again I imagine that the tiny size of the spores of many fungi and algae, measured in the microns, will edge out any of the higher plants. A kelp plant or fungus with a weight of just a few hundred kg would probably have a higher ratio than a euc just because of the tiny size of the spore, but I can’t be bothered to do the maths.

And it has 3 million seeds to the pound. That’s a 36,000,000,000,000:1 ratio.

I think you might have a winner. But then, does anyone know what a fertilized egg of a blue whale would weight? A blue whale is on average 180,000 kg (from Wikipedia) which, divided by 500,000,000 gives .36 grams. Would a blue whale fertilized egg weigh less than that? I can’t find that information.

By the way, one estimate (wikipedia) says that the female eggs have a diameter of 100 μm (micrometres) which would be the double of your size estimate.

Buddy Ryan and Rex Ryan

Eggs, not larvae. Think about it. Is a chicken is smaller or larger than the egg it hatched from?

All organisms must be smaller than the egg they hatch from, of course, otherwise they wouldn’t fit in the egg. In the case of aquatic animals the discrepancy is usually considerable because of the mass of water in the egg.