Back in the day, the Jurassic perioid no less, central Europe was covered by a shallow sea – the so called Tethys Sea. A study in the Zoological Journal of the Linnean Society (September 2019) describes a rich reef teeming with animals – fish, crabs, sea urchins, snails, clams, and oysters. They also include ammonites (squid with external shells) but the focus of the piece is on squat lobsters (which are lobsters that look like crabs, and are much smaller). They all inhabited the Tethys Sea but the squat lobsters became very diverse towards the end of the Juassic (and known fossil beds of the Cretaceous don't seem to show so much diversity). After the K/T boundary event the diversity remained lean. See https://archaeologynewsnetwork.blogspot.com/2019/09/coral-reefs-and-squa…
… One strange comment from one of the authors stuck out like a sore thumb. We know that reefs aren't doing well today because of coral bleaching and other factors (associated with global warming). If these ecosystems continue to deteriorate the reef organisms, including squat lobsters, are going to take a hit. Yet, according to mainstream it was much warmer by far in the Jurassic and Cretaceous period than it is in the modern world. Is he paying lip service to the climate mantra.