Unknown benthic sp. A. Family ?Neomphalidae.

Unknown Benthic sp. AUnknown Benthic sp. A

Size under dissecting microscope: 160-170µm
Size under compound microscope: 150-160µm
Morphology:
This is a small distinctive protoconch. Nearly all the vent protoconchs are planispiral, with a very slight right-hand twist. This one, however, has a distinct left-hand twist, so that if you try to set it on its left side in our standard orientation for photographing the protoconchs, it will roll to show the aperture, as in the SEM above. It has overall regular reticulate sculpture and may be a neomphalid.  The picture at right shows the protoconch as viewed from the top.
Unknown Benthic sp. A
Frequency:
Pump EPR 1999-2000: Common
Pump EPR 2004: Common
Trap EPR 2004-2005: Common

Can be confused with

Unknown 5
Unknown 5 looks very much like this species, though it is about 10µm larger.  It has a distinct flare to the aperture rim, which is wider than that of Unknown A.  The easiest way to distinguish them quickly is to roll them; Unknown A will generally roll to expose the aperture, while Unknown 5 is stable on its side, as shown at left.
Lepetodrilus sp.
Lepetodrilus spp. is about 10µm larger than Unknown A.  It has pitted sculpture rather than reticulate and is also stable on its side.

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