Pretty sure its not a cucumber the portion your seeing is only 1/4 or less of his length and after lots of Google image scrubbing I am almost 100% its a bristle
I don't think it's a bristle worm. They have hair like spikes on them. The one in you pis has much thicker rounder softer spikes. Man before I got out I new a few good sites for iding critters, but can,t remember them now.