ID (For Something I Saw at the Beach) Please

[Great Barrier Reefer]

Hi!
Usually I'm pretty good with my identifications, but this one is a little different.

I live in far north Queensland, Australia, and saw this as I was walking along my local beach. I would like to note that the substrate type is a very fine sand/mud, and these photos were taken inshore of a small fringing reef along the extremes of the reef flat. It should also be mentioned that I saw a number of these little guys, and that the majority of them were at least partially buried in the silt and were exposed to a lot of wave action.

I am thinking something along the lines of a sponge, however I couldn't see any visible pores, and the fact that these guys were almost always covered in mud/silt got me a little puzzled too. If anyone could help out that would be great, and it would be amazing if anyone could give me a common name or scientific name (I'm always keen to learn about my local reefs!). Please also note that I did not aim to harm the specimen in these photos, and that it was returned to it's original position and orientation after photos were taken.

Cheers,
Chris

 

[stylaster]

Maybe Neptune helmet coral

 

[Great Barrier Reefer]

I don't think this is a coral....
In particular, it was very soft and flexible, and had no evidence of a calcerous skeleton. There was also no visible mouth, tentacles or other feeding devices.

 

[Neptunes Cove]

maybe an encrusting sponge that washed in at tide...?