hmmm... looks like my tank...
www.aqua-imports.com
Well they are all characins so your reference is valid. Many consider the hatchets to be 'tetras' as well since the term references the trait they all share, 4 ('tetra') unpaired fins--dorsal, caudal, anal and adipose--which all Carnegiella (hatchets) possess.I haven't seen all 4 lately... but my experience is to lose 25% of the tetras typically... so that wouldn't be unusual ( I know the hatchets aren't really a tetra ) but all the sellers list the hatchets and pencil fish together, with the tetras... so they must be similar, or at least by association