This study employs X-ray computed microtomography (micro-CT) to investigate the internal structures of microcrinoids, focusing on the roveacrinid Sergipecrinus reticulatus from the Aptian–Albian (112–115 Ma) of the Sergipe Basin, Brazil. For the first time, sub-basal balls were observed in situ and in three dimensions, representing the first 3D documentation of these internal structures in a microcrinoid cup. This constitutes both a methodological advance, the first use of micro-CT applied to this group, and a descriptive and taxonomic advance, as it reveals an unprecedented internal morphology. These structures, previously observed only under SEM and identified in fragments of other genera, might be hollow; however, micro-CT analysis reveals they are dense, containing only small and sub-resolution pores. This discovery suggests that their presence may be more widespread across the Roveacrinidae than previously thought, raising questions about their evolutionary and functional significance. As a cladistics trait, the presence of sub-basal balls contributes to the phylogenetic reconstruction of the family. Moreover, this study underscores the value of micro-CT in revealing detailed, non-destructive insights into microfossil morphology and proposes its broader application to uncover the internal structures of other genera within the Roveacrinidae.

Key words: Echinodermata, Roveacrinida, microfossil, Albian, Sergipe-Alagoas Basin, Brazil.

Bruna Poatskievick-Pierezan [brunapp@unisinos.br; ORCID: https://orcid.org/0009-0001-3250-8939], Bernardo Vázquez-García [bernardovg@unisinos.br; ORCID: https://orcid.org/0000-0001-8108-4215], Marcos Antonio Batista dos Santos Filho [abatistas@unisinos.br; ORCID: https://orcid.org/0000-0001-8409-403X], Simone Baecker-Fauth [sbfauth@unisinos.br; ORCID: https://orcid.org/0000-0001-5201-981X], and Gerson Fauth [gersonf@unisinos.br; ORCID: https://orcid.org/0000-0003-2594-1424], Instituto Tecnológico de Paleoceanografia e Mudanças Climáticas, São Leopoldo, 93022-750, Brazil; Universidade do Vale do Rio dos Sinos, São Leopoldo, 93022-750, Brazil. Andrew Scott Gale [andy.gale@port.ac.uk; ORCID: https://orcid.org/0000-0002-2075-3689], University Portsmouth, Portsmouth, PO13QL, UK; The Natural History Museum, London, SW75BD, UK. Anderson Camargo Moreira [moreiradr78@gmail.com; ORCID: https://orcid.org/0000-0003-1229-3616], Universidade Federal de Santa Catarina, EMC, Florianópolis, 88040-900, Brazil. Lucas Del Mouro [lucas.delmouro@gmail.com; ORCID: https://orcid.org/0000-0001-7829-0683], Universidade Federal de Santa Catarina, EMC, Florianópolis, 88040-900, Brazil; Harvard University, Cambridge, 02138, USA.