What kind of sponge is it? and is it good or bad

[reefdummy]

 

[ISpeakForTheSeas]

Looks like it may be Tethya gracilis - it should be a harmless filter feeder.

 

[reefdummy]

Looks like it may be Tethya gracilis - it should be a harmless filter feeder.

How big do they grow? I couldn’t find any information for it. Not much at least

 

[ISpeakForTheSeas]

How big do they grow? I couldn’t find any information for it. Not much at least

They're not super well known (they were discovered first in a German aquarium), but the study I've found describing them was very informative (linked below).

They grow up to ~1.5cm (though they can contract to be ~80% of their max body size); they can slowly move/"walk" - reportedly, they can move several centimeters a day (especially when smaller), and they do this to remove/shake off sediment that gets on them; and they reproduce by budding (so they'll drop pieces that grow into new sponges).

https://www.researchgate.net/publication/215665065_Three_New_Species_of_Tethya_Porifera_Demospongiae_from_German_Aquaria