INTRODUCTION
Although traditional systematics used to rely on morphological features, molecular methods have demonstrated to provide a subjective tool to compare individuals, where only the stochasticity of mutation is taken in consideration, and the overweight of some morphological characters is somehow avoided. In this scenario, these disciplines have merged to give birth to an integrative taxonomy, which has become a key element in modern systematics (Dayrat, 2005). In this regard, integrative taxonomy allows the categorization of species according to both molecular and morphological differences and resemblances. Thus, it is of primal importance to know the taxonomical, but also the molecular nature of species, since the second provides a reliable standard template to compare with and to be compared to other organisms. Here, we aim to fill a knowledge gap in mitogenomes of poorly studied and misleading taxa. On one hand, we have Runcina aurataGarcía-Gómez, López, Luque & Cervera, 1986 (Fig. 1), genus belonging to the order Runcinidae, which englobe close to 100 small sized species (1-4mm) described so far, although it is thought to include much more biodiversity (Araujo et al., 2022). The members of such order feed on macroalgae, contributing to the decomposition of dead matter, being a key element in the balance of the ecosystem (Araujo et al., 2019). However, due to the small size and difficulty to find them in their natural environment, few studies have focused on them so far. On the other hand, Facelina auriculata (O. F. Müller, 1776) (Fig. 1) is the type taxon of the family Facelinidae, which is considered one of the most diverse heterobranch families with more than 200 species (Karmeinski et al., 2021). Its distribution, ranging from the English coasts to the Spanish Atlantic with some introgression in the Mediterranean, overlaps with theR. aurata ’s one. Nevertheless, they do not compete with each other since F. auriculata feeds on cnidarians, from which they “steal” and store the cnidoblasts in specialized organs named ceratas (Goodheart et al., 2018). In view of the needs and scientific circumstances of both taxa, we present here the reference mitogenomes for the two species, which will allow direct comparisons of future genetic information, as well as provide a template for the synthesis of new specific primers.