consider
awk '/'^(a b)^'/' /dev/null

awk: can't open file /b/
source line 1

your case is similar:

T=(a b)
awk '/'^$T^'/' /dev/null

awk: can't open file /b/
source line 1

and finally

awk '/'^$"T^'/' /dev/null

success? note the " before the T in the last one.

> ##script:
> T = 'Eptatretus burgeri'
> echo $T
> awk '/'^$T^'/' all.uniq
> echo '++++++++++++++++'
> T=`{awk 'NR== '23' ' SpeciesList}
> echo $T
> awk '/'^$T^'/' all.uniq
> ## result:
> Eptatretus burgeri
> Eptatretus burgeri (complete) Metazoa; Chordata; Craniata; Hyperotreti; Myxiniformes; Myxinidae; Eptatretinae; Eptatretus. NC_002807 cox1, -S(nga), D, cox2, K, atp8, atp6, cox3, G, nad3, R, nad4L, nad4, H, S(nct), L(nag), nad5, -nad6, -E, cob, T, -P, F, rrnS, V, rrnL, L(yaa), nad1, I, -Q, M, nad2, W, -A, -N, -C, -Y
> ++++++++++++++++
> Eptatretus burgeri
> awk: can't open file /burgeri/
> source line 1
> rc 117587: awk 117593: 2

I think this is a problem with rc treating $T as a list, and you need
a list flattening operator (double quote).

Perhaps what you need is

awk '/'^$"T^'/' all.uniq

[unsure as hasn't had any coffee yet]

-Steve