Descripción histológica del cerebro y órganos sensoriales del milpiés neotropical Pycnotropis sp. (Polydesmida: Aphelidesmidae)

Abstract

Millipedes are key components of terrestrial ecosystems, actively participating in the decomposition of organic matter in soil and distributed across much of tropical and neotropical forests. However, aspects of their biology remain scarce or fragmented, requiring further revision, particularly in their neurobiology. Research on the nervous system (NS) in myriapods especially studies involving sensory organs is significant from both ecological and evolutionary perspectives, as it provides comparative neuroanatomical data and helps identify group-specific characteristics. Therefore, this study focuses on describing the brain and sensory organs of the neotropical millipede species Pycnotropis taenia (Aphelidesmidae), here taxonomically confirmed. We examine in detail the brain structure and its components using hematoxylin and eosin staining. Additionally, we characterize antennal sensilla typologically through scanning electron microscopy. Our observations revealed a small, compact brain with three cerebral neuromeres lacking clear separation, where the protocerebrum is the most prominent. The brain exhibits a characteristic cortex-neuropil organization, along with associated neuropils such as mushroom bodies and olfactory glomeruli. Furthermore, typical globular cell clusters, common in Myriapoda brains, were identified. At the sensillar level, seven types of sensilla (including subtypes) were distinguished on the antennae. Notably, we propose a subdivision of trichoid sensilla into two subtypes and describe species-specific variations, including a serrated termination of the apical cone. This pioneering study establishes a foundation for future research using robust immunostaining techniques and underscores the need to further explore millipedes as understudied neurobiological models.