See the Nomenclature page
All genes have a corresponding sequence name, which are derived from the cosmid, fosmid or YAC clone on which they reside.
For instance the gene bli-4 has a sequence name of K04F10.4, indicating it was identified when the cosmid K04F10 was sequenced and annotated, and there are at least 3 other genes associated with that cosmid.
Any gene can code for multiple proteins (CDS) as a result of alternative splicing. In the case of bli-4 there are 6 known isoforms, called K04F10.4a, K04F10.4b, ..... K04F10.4f.
The corresponding transcripts for the isoforms are called K04F10.4a.1, K04F10.4b.1, ..... K04F10.4f.1
However if there is alternative splicing in the UTRs, which doesn't change the protein sequence, the alternatively-spliced transcripts are named K04F10.4a.1 and K04F10.4a.2.
... and if there are no isoforms of the coding gene, for example AC3.5, but there is alternative splicing in the UTRs, there will be multiple transcripts named AC3.5.1 and AC3.5.2, etc.
But if there are no alternate UTR transcripts the single coding_transcript is named the same as the CDS and does not have the .1 appended. As in the case of K04F10.4f