Without bones weighing them down ... long before bony fish and land animals evolved. Over time, their cartilaginous skeletons have proven to be perfectly suited for survival in their aquatic ...

Animals without a backbone are called invertebrates ... fur and can produce milk to feed their young. They have three ear bones, which allow for better hearing. They also have a special muscle ...

But they’re both invertebrates — animals without bones — which make up more than 95 percent of all species on Earth. Both species are plentiful in Mexico, and both can be admired at ...

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