Anyone know what this? Barnacle, scallop, limpet?

[56longroof]

IMO - that's a limpet. Bivalves have two valves (shell halves) and don't stick to rocks except with byssus threads.....

It does appear to have two halves.

 

[ISpeakForTheSeas]

@ISpeakForTheSeas ?

I'm on mobile today and my bivalve ID resources are on my computer, but definitely a bivalve (harmless filter-feeder); when I get time I'll try and pop in here and see if I can get at least a family level ID (hopefully I'll have time this weekend, but no guarantees, unfortunately).

 

[TylerJaid]

@ISpeakForTheSeas ?

I'm on mobile today and my bivalve ID resources are on my computer, but definitely a bivalve (harmless filter-feeder); when I get time I'll try and pop in here and see if I can get at least a family level ID (hopefully I'll have time this weekend, but no guarantees, unfortunately).

That would be awesome I’d like to know what it is, I definitely didn’t add anything like that so it must’ve been in my tank and growing for quite a while to even be the size that it is now

 

[keagan]

That would be awesome I’d like to know what it is, I definitely didn’t add anything like that so it must’ve been in my tank and growing for quite a while to even be the size that it is now

This is a scorched mussel (Brachidontes exustus) the toothed ribs, size, shell shape, and color is what leads me to believe this is the species but that's just an educated guess I'm interested to see what I speak for the seas gets for species. If it's not a member of Brachidontes I'd be surprised. Do you know where your live rock comes from?

 

[TylerJaid]

That would be awesome I’d like to know what it is, I definitely didn’t add anything like that so it must’ve been in my tank and growing for quite a while to even be the size that it is now

This is a scorched mussel (Brachidontes exustus) the toothed ribs, size, shell shape, and color is what leads me to believe this is the species but that's just an educated guess I'm interested to see what I speak for the seas gets for species. If it's not a member of Brachidontes I'd be surprised. Do you know where your live rock comes from?

I think your exactly right that looks identical to it, being able to see it in person I think your spot on, I’m going to have to do some research on it. But that is the weird thing my “live rock” was dry rock when I started so it had to have come off a coral maybe but I only have 6 corals and I haven’t really added anything in the last year. My tank is just over two years old. I was also very careful when adding my corals and don’t believe there would be any hitchhikers. There has never been any other hitchhikers in the tank that I have ever noticed. That’s cool I can’t believe you found it!

 

[TylerJaid]

Now I am wondering where it came from? I definitely didn’t put anything that big in there, so it had to have been a larvae and in some drops of water that got added wen adding snails or something, I’m gonna keep an eye on him and see how he ends up doing, I have never specifically fed it as I just noticed it the other day.

 

[ISpeakForTheSeas]

That would be awesome I’d like to know what it is, I definitely didn’t add anything like that so it must’ve been in my tank and growing for quite a while to even be the size that it is now

Able to get to my computer today (sadly realized one of my two primary resources for bivalve family ID has shut down, so I'll have to see if I can access it another way).

Anyway, looking at the shell shape, it's definitely from the Mytilidae family;* from there, there are a few species in a few of the subfamilies that can resemble this, but I have to agree that between the shape and the radial ribbing, the Brachidontinae subfamily is the most likely by far; so that leaves us with essentially three genera to work with: Brachidontes, Geukensia, and Ischadium (as Mytilaster is usually quite different superficially, typically lacking visible radial ribbing).

The way to officially tell them apart is using the hinge line (the part of the hinge where the external part of the shell turns meets the internal part of the shell; basically the lip on the internal/inward-side separating external and internal) and hinge teeth (see the first pic - not the banner pic - in the second link** below; essentially smooth hinge line + no teeth = Geukensia, smooth hinge line + 3-4 small teeth that don't touch the hinge line = Ischadium, and a typically bumpy hinge line + 1-4 teeth that touch the hinge line = Brachidontes); however, Ischadium recurvum, the one species in the Ischadium genus, generally is darker in color, "squatter"/rounder, and with a much stronger "hook" to its umbone (the "point" of the shell), so I would feel confident in assuming it's not that one.

Between Brachidontes and Geukensia; several Brachidontes species are generally much "squatter" or less elongated, but several can resemble this as well (unfortunately, I am not currently familiar with all of the 28 recognized species of this genus at the moment, so I can't narrow it down effectively yet, particularly without knowing where it's from - I can only eliminate roughly half of the species as strong possibilities and note that a few are superficially strong possibilities); with your specimens and regards to the Geukensia genus, I don't believe I can see any "beading" on the ribbing, the ribbing appears relatively few and large, and the edge of your specimen appears quite flat (not noticeably curved), so I would assume that - if your specimen is a Geukensia species - it's G. demissa, not G. granosissima.***

So, if you can view the hinge line without harming your specimen, that would tell you what genus it's in, and from there you can determine for sure if it's G. demissa or a Brachidontes sp. that would require further investigation to fully ID with confidence.

*Source:

https://hascmarinebiology.weebly.com/uploads/7/6/8/7/7687070/bivalves.pdf

**Source:

Brachidontes exustus | letstalkseashells

olram9.wixsite.com

***Source (differentiating info is partway down, roughly in the middle of the pics):

Geukensia granosissima | letstalkseashells

olram9.wixsite.com

 

[TylerJaid]

Just a update for anyone who cares lol this guy didn’t move for a few days after I plucked him off but I got home after the weekend and he had moved about 3 inches from where I left it, now in the last hour he has moved another three or for inches is this typical for a critter like this I didn’t think they moved very often!
First two pictures are where he was when I got home and last one is a hour later about 4 inches down the rock! Does this change anything on his I’d??

 

[ISpeakForTheSeas]

Just a update for anyone who cares lol this guy didn’t move for a few days after I plucked him off but I got home after the weekend and he had moved about 3 inches from where I left it, now in the last hour he has moved another three or for inches is this typical for a critter like this I didn’t think they moved very often!
First two pictures are where he was when I got home and last one is a hour later about 4 inches down the rock! Does this change anything on his I’d??

Hmm, it's possible that it's being moved by other things in the tank, but assuming it's not, I know several different mytilids from various genera are at least capable of moving around still once they're adults, so while I can't find any info on if these can or can't, I wouldn't be surprised if they could.

 

[TylerJaid]

Just a update for anyone who cares lol this guy didn’t move for a few days after I plucked him off but I got home after the weekend and he had moved about 3 inches from where I left it, now in the last hour he has moved another three or for inches is this typical for a critter like this I didn’t think they moved very often!
First two pictures are where he was when I got home and last one is a hour later about 4 inches down the rock! Does this change anything on his I’d??

Hmm, it's possible that it's being moved by other things in the tank, but assuming it's not, I know several different mytilids from various genera are at least capable of moving around still once they're adults, so while I can't find any info on if these can or can't, I wouldn't be surprised if they could.

I’m pretty sure it is moving on its own it’s hard for me to even pluck him off the rock, I do have a urchin but I don’t even think he could move that thing it has a tight grip. I have never seen it open or do anything like that, maybe I should watch in the dark and see? I don’t know if that makes a difference to them, I really appreciate your help and looking into this!

 

[ISpeakForTheSeas]

I’m pretty sure it is moving on its own it’s hard for me to even pluck him off the rock, I do have a urchin but I don’t even think he could move that thing it has a tight grip. I have never seen it open or do anything like that, maybe I should watch in the dark and see? I don’t know if that makes a difference to them, I really appreciate your help and looking into this!

Setting up a camera to record while you're not in the room may help with catching movement/opening and closing motions.

 

[vetteguy53081]

This looked to be where he was attached to the rock I put it back and it dad attach back onto the rock but I have not seen it move or do anything at all

Bivalve and member of the scallop group and is a filter feeder

 

[TylerJaid]

I’m pretty sure it is moving on its own it’s hard for me to even pluck him off the rock, I do have a urchin but I don’t even think he could move that thing it has a tight grip. I have never seen it open or do anything like that, maybe I should watch in the dark and see? I don’t know if that makes a difference to them, I really appreciate your help and looking into this!

Setting up a camera to record while you're not in the room may help with catching movement/opening and closing motions.

I am going to do this I never thought of that!

 

[TylerJaid]

This looked to be where he was attached to the rock I put it back and it dad attach back onto the rock but I have not seen it move or do anything at all

Bivalve and member of the scallop group and is a filter feeder

He seems to be moving with a foot and from what I read scallops don’t use a foot to move? I could be completely wrong! I’ll read more into them!

 

[vetteguy53081]

He seems to be moving with a foot and from what I read scallops don’t use a foot to move? I could be completely wrong! I’ll read more into them!

What you likely see is their ability to move by quickly forcing water out of their shell and propelling themselves allowing them to move

 

[TylerJaid]

So for anyone still interested in this thread, I was doing some work in the tank today and found another one of these guys but this one is inside of a snail shell, I don’t really know how he ended up in it like that but thought it was cool to see and that I’d share!