Growing on my Glass

[Biogeek]

I generally recommend the Hitchhiker FAQ for Reef Aquarists, or Ron Shimek's Odd Critters ID page as good places to look for an ID on unidentified things that show up in your tank.

It is of course very difficult to offer a reliable ID based on the scant description here, but in your case I would guess that the stationary "snowflake-like" animal is a type of hydrozoan jellyfish that have branched tentacles and actually have a small sucker on one branch of the tentacle with which to attach to the wall of the aquarium. They are capable of asexual reproduction under ideal conditions in an aquarium, and can become quite abundant for some time, but usually disappear on their own about as quickly as they appeared in the first place.

I would hazard to guess that the "little sled" animals you're seeing on the glass are flatworms. These animals can range from being essentially non-feeding (living off photosynthetic symbionts - e.g., the "red planaria" pest Convolutriloba retrogemma ) to being carnivorous and preying on other small flatworms or various 'pods in the tank (e.g., here is a nice photo of how these predatory guys actually feed in the aquarium)...

Of course these are just guesses based on my experience with what people are most often seeing in their aquarium, and these may be way off the mark, but without a picture or at least a much more detailed description, that is the best I can offer you.

Rob