Context : Pulsating extremely low-mass pre-white dwarf stars ( pre-ELMV ) , with masses between \sim 0.15 M _ { \sun } and \sim 0.30 M _ { \sun } , constitute a new class of variable stars showing g - and possibly p -mode pulsations with periods between 320 and 6000 s ( frequencies between 14.4 and 270 c/d ) , driven by the \kappa mechanism operating in the second He ionization zone .
On the other hand , main sequence \delta Scuti stars , with masses between 1.2 - 2.5 M _ { \sun } , pulsate in low-order g and p modes with periods in the range [ 700 - 28 800 ] s ( frequencies in the range [ 3-123 ] c/d ) , driven by the \kappa mechanism operating in the He II ionization zone and the turbulent pressure acting in the HI ionization layer .
Interestingly enough , the instability strips of pre-ELM white dwarf and \delta Scuti stars nearly overlap in the T _ { eff } vs . \log g diagram , leading to a degeneracy when spectroscopy is the only tool to classify the stars and pulsation periods only are considered .

Aims : Pre-ELM white dwarf and \delta Scuti stars are in very different stages of evolution and therefore their internal structure is very distinct .
This is mirrored in their pulsational behavior , thus employing asteroseismology should allow us to distinguish between these groups of stars despite their similar atmospheric parameters .

Methods : We have employed adiabatic and non-adiabatic pulsation spectra for models of pre-ELM white dwarfs and \delta Scuti stars , and compare their pulsation periods , period spacings , and rates of period change .

Results : Unsurprisingly , we found substantial differences in the period spacing of \delta Scuti and pre-ELM white dwarf models .
Even when the same period range is observed in both classes of pulsating stars , the modes have distinctive signature in the period spacing and period difference values .
For instance , the mean period difference of p - modes of consecutive radial orders for \delta Scuti model are at least four times longer than the mean period spacing for the pre-ELM white dwarf model in the period range [ 2 000 - 4 600 ] s ( frequency range [ 18.78 - 43.6 ] c/d ) .
In addition , the rate of period change is two orders of magnitudes larger for the pre-ELM white dwarfs compared to \delta Scuti stars .
In addition , we also report the discovery of a new variable star , SDSSJ075738.94 + 144827.50 , located in the region of the T _ { eff } vs . \log g diagram where these two kind of stars coexist .

Conclusions : The characteristic spacing between modes of consecutive radial orders ( p as well as g modes ) and the large differences found in the rates of period change for \delta Scuti and pre-ELM white dwarf stars suggest that asteroseismology can be employed to discriminate between these two groups of variable stars .
Furthermore , we found that SDSSJ075738.94 + 144827.50 exhibits a period difference between p modes characteristic of a \delta Sct star , assuming consecutive radial order for the observed periods .