mel turner schreef
Good question. But of course the lobes and sticking-out bits
are kept fairly safe inside the shell, even after germination.
[The seedlings are of the hypogeal type in the familiar members
of the walnut family].

One thought that occurs to me is that lobed and dissected food-storage
tissues in seeds may be partly protected from insect damage. There are
teh familiar plates of not-so-edible, fairly hard tissue between the
lobes. An insect attacking the seed might tend to confine its activities
to a single lobe, or at least it would have a harder time making a meal
of the whole seed.

Although the lobed seed structures in the walnut family [Juglandaceae]
are the cotyledons of the seedling, the situation is reminiscent of
something called "ruminate endosperm" that is found in many other
families of flowering plants. In these plants the food-storage tissue
of the seeds is endosperm, which is lobed and dissected by plates and
strands of hard inedible sclerenchyma tissue.

An insect trying to eat such endosperm might have difficulty tunneling
through it, compared to one living in a similar seed without ruminate
[meaning ="chewed"?] endosperm.

+ + +
Who knows? A consideration is that walnuts for their dispersal rely upon
their edibility, like acorns. Also the "hard" bits between the lobes are
surely less so when walnuts are fresh.
PvR

PS walnuts are not nuts.
PS II according to Harris and Harris indeed "ruminate" = "wrinkled, as if
chewed"