Spotting

Well a very (!) general way to pick out arthropods is any invertebrate (animal without a backbone) that has (hard) segmented (or jointed) legs, at least at some stage, usually when they are mature. There are certainly exceptions but that helps picks up most arthropods we're going to see here. So an octopus has legs but they are not hard and they don't have joints so it is NOT an arthropod. But a soft caterpillar IS an arthropod because when it matures as a butterfly it has hard, segmented legs. Again, this is only a very general way to distinguish most arthropods. "Other" organisms include worms, clams, snails, echinoderms (starfish, sea urchins, sea cucumbers, brittle stars, etc) various micro-organisms, and many "others" ;-)

Thanks Frazier, I'm getting very confused with all these sea creatures.

Hello. The crab partially visible in the first photo is indeed an arthropod but the mussels (and barnacles) in the series belongs to the molluscs, so in the case of Noah spottings, to "other" organisms. Cheers