L1 Dytiscus sp. larva, caught while dip-netting through a Potamogeton natans-filled, lentic, beaver pond runoff stream.

Looks to be the same species as my last Dytiscus observation which I believe to be D. harrisii on account of the larvae matching morphological and behavioural descriptions of the larvae described in Leclair et al. (1986) "Prey Choice in Larval Dytiscus harrisii Kirby and D. verticalis Say."
Notably, they have a relatively small head for the genus, shorter mandibles that are thicker basally than other species, a head that bends easily at 90°, and a frontoclypeus that's anterior margin is not rounded as in other Dytiscus sp. larvae and that's lateral apices extend beyond the anterior margin.

Update: has since pupated, with a final instar III length of ~62mm measured from urogomphi to mandibles.

Update: they have emerged as an adult with a final size of ~39mm, spending 19 days as a pupa before emergence.

L1 larva, it looks like the same species as my previous observation and I think it's likely that they came from the same batch of eggs. I saw a couple more L1 larvae but this was the only one that was close enough to photograph.