Runcinidae and Facelinidae: Two complete mitogenomes of understudied and misleading heterobranch families (Gastropoda, Mollusca)

Here, we present the mitochondrial sequences of two ‘opistobranch’ heterobranchs: Runcina aurata García-Gómez, López, Luque & Cervera, 1986 and Facelina auriculata (O. F. Müller, 1776), the latter type taxon of the genus. The mitochondrial genomes were 14,282 and 14,171bp in length respectively, the two of them with a complete set of 13 CDS, 2 rRNAs, and 22 tRNAs. None of the mitogenomes showed gene reorganization, keeping the standard heterobranch mitogenomic structure. The base composition was completely distant between them, with a 25.7% GC for R. aurata, becoming the mitogenome with more AT content to the date, and 35% for F. auriculata, supposing one case of extremely rich GC content in “opistobranch” mitochondrial genomes.