A luminous creature bottle-fed by Newt Scamander inside his case in 1926 New York (WFT).
While not named in the movie script, the glowing tentacled creature is known as a "Marmite" according to the special effects artists at Deluxe's Method Studios:
On the creatures side, Method handled the shot of Newt bottle-feeding a young marmite – a tentacled cross between a dust mite and squid with a transparent body. Production provided live action plates with the actor, and Method artists added the CG creature to the shot, digitally wrapping 10-foot long tentacles around Newt and creating an underwater feel.
"Marmite" is also the name of a sticky brown paste made from yeast leftover from beer brewing. It is bottled and sold as a snack food in Britain and New Zealand, and is similar in taste to Australia's popular Vegemite.