Shellfish.

Shellfish are muscle too — the prawn's tail, the mussel's and scallop's adductor, the squid's mantle — and like fish their proteins set at low temperatures. A prawn turns from grey and translucent to pink and opaque as its centre passes about 55–60 °C; by 70 °C it has tightened and is losing juice, and by 90 °C it is rubbery and curled into a tight ring. Small prawns in boiling water take a minute or two. Mussels and clams are cooked in a covered pot with a little liquid and are done as soon as their shells open, a few minutes; scallops want only a hard sear on each face with the centre barely warm.

Live bivalves must be alive before cooking: their shells closed, or closing when tapped. Discard any with broken shells or that stay open. Lobsters and crabs are bought live or freshly cooked; their flesh spoils fast after death. Squid and octopus are the exception to "cook briefly": their muscle has much collagen, so they are either cooked for under two minutes, before it tightens, or braised for 30–60 minutes until the collagen softens (XVIII.9) — anything between is rubber. The workshop boils prawns.

Below: the centre temperature reached by 14 mm prawns dropped into boiling water for the minutes you choose and then into iced water (thermal bench), with the bands for translucent, just done and rubbery.