It depends on how you define "catalogued." There are probably that many
specimens in museums and other scientific collections, though not
individually catalogued. A large block of limestone could easily contain
millions of ostracods or other microinvertebrates. If the museum has the
block of limestone, with presence of ostracods noted, does that count as
"Now, if an invertebrate evolved into a fish, we ought to have billions times
billions of fossils of transition form showing an invertebrate changing into
a fish. As a matter of fact, we have none."
This seems to reflect two errors on Gish's part. First, he seems to think
that all invertebrates should be evolving into fishes. Instead, fishes
evolved just once, so only fossils in that particular lineage are relevant.
Most of the millions, if not billions, of fossil invertebrates and fishes
are totally irrelevant to the transition from invertebrates to fishes.
Secondly, there are invertebrate to fish transitional fossils, as well as
living primitive chordates that are still at grades intermediate between
other invertebrates and fish. Pikaia, from the Burgess Shale, is a fossil
chordate similar to the modern lancelet. Conodont animals are also
chordates, intermediate between invertebrates and true fishes; there may
actually be billions of conodonts (essentially teeth) collected, again as
microfossils, if you count the total number present in rocks rather than
the number actually looked at. Some people might argue that primitive
jawless "fish" that lack a true backbone are not really vertebrates, in
which case there are many more forms that would count as transitional
between fish and invertebrates. Paul Jeffries and some other workers
belive that certain early Paleozoic irregular echinoderms are transitional
betweeen other echinoderms and chordates, but their interpretations are
problematic on various points, and most paleontologists believe that these
forms are simply irregular echinoderms.