The comparison scores every group at once. This page is for the moment you already have a pair of names in mind — mayfly or stonefly, scud or sowbug, shad or alewife — and want the structures that keep them apart, in one look. Nothing here is a current hatch.
The differences, and nothing else
Best separating check: Long thin body, eel-likeAt a glance It separates Sand lance (sand eel) from Anchovies cleanly, and every pair of groups still in play differs on it and you can check it at a glance.
What to look at
Sand lance (sand eel)
Anchovies
No pelvic fins underneath at alldecisiveIn hand
Yes
No
Dives into clean sand and vanishesdecisiveWatch it
Yes
No
Dorsal fin layoutdecisiveClose look
One dorsal running most of the back
None of these
Which way the mouth pointsdecisiveClose look
Varies
Snout overhangs the mouth
Long thin body, eel-likedecisiveAt a glance
Yes
Not diagnostic
Body see-through, backbone or gut visibledecisiveAt a glance
Not diagnostic
Yes
Eye wider than the snout is longdecisiveClose look
Not diagnostic
Yes
Sits on the bottom, darts, never hoversWatch it
Not diagnostic
No
Reported size
4–300 mm
20–178 mm
Water it is recorded in
surf, inshore, nearshore, offshore
surf, inshore, nearshore
How it moves
dives head-first into the sand at sixty to seventy-five degrees and disappears; leaves the sand at twenty to sixty degrees, accelerating to about 120 cm per second within the first metre and a half
dense schools; spawning takes place in the evening
Reference seasonality
Winter spawn on sand: Nov, Dec, Jan, Feb, Mar
Warm-season spawn: May, Jun, Jul, Aug, Sep
The same for both: life stages.
Rows come from the reviewed diagnostic weights the comparison scores with. “Decisive” means one answer puts them at least four points apart — the carrier's own rule for a structure that separates a pair.
The two entries, side by side
Ammodytidae
Sand lance (sand eel)
A fish that solves the predator problem by becoming part of the beach.
First check
Look at the underside where the pelvic fins should be. If there is nothing there, on an eel-thin body with one dorsal running most of the back and a forked tail, that is a sand lance.
What it is
Most small silver fish deal with being eaten by schooling tighter and swimming faster. Sand lance took a different route: they dive into the seabed. Head first, at sixty to seventy-five degrees, wriggling until about a quarter buried, then settling to a shallower angle and stopping. A researcher with a stopwatch measured them leaving again at fifty to eighty centimetres a second and accelerating to a hundred and twenty within the first metre and a half off the bottom. That is not a fish hiding. That is a fish with an exit strategy.
Stages
Larva and first year (4–60 mm through the larval period) · Full-grown (76–200 mm typical; the northern species reported over 300 mm)
Water
surf, inshore, nearshore, offshore
Separates from Anchovies
An anchovy's snout stands in front of its jaw. A sand lance leads with the lower jaw, and has no pelvic fins where an anchovy has a pair.
Typical windows
Winter spawn on sand (adult)
Patterns (correspondence)
Surf Candy
Limits
The two Atlantic species are not separable by eye, and one synthesis reports that the standard DNA barcoding gene cannot split them either. This entry does not offer that call.
Can you see light through the body? One dorsal fin, a large mouth and a narrow faint stripe with it, and you are on an anchovy.
What it is
Hold a bay anchovy up against the sky and light comes through it. The body is described as slender, silvery-green and translucent, grey-shaded over the back, with a narrow silver line down the middle of the side and a large mouth.
Stages
First year (No consulted source gives a first-year length; bay anchovy can mature at about 37 mm within a few months of hatching) · Full-grown (51–102 mm typically; the Pacific northern anchovy to about 178 mm)
Water
surf, inshore, nearshore
Separates from Sand lance (sand eel)
A sand lance has no pelvic fins and one very long dorsal. An anchovy has both pelvics and one short dorsal.
Typical windows
Warm-season spawn (adult)
Patterns (correspondence)
None mapped yet.
Limits
The pronounced overhanging snout belongs to the Pacific northern anchovy in the sources, not to the bay anchovy, whose overhang is explicitly described as slight.