Morphological characterization of anterior axial bifurcation in Holothuria (Halodeima) grisea and other puzzling occurrences in Holothuroidea

• Published in: Invertebrate biology 2024-09, Vol.143 (3), p.n/a
• Main Authors: Rupp, Guilherme Sabino, Martins, Luciana, Souto, Camilla, Hamel, Jean‐François, Mercier, Annie
• Format: Article
• Language: English
• Subjects: abnormal morphology; Abnormalities; Apostichopus californicus; axial bifurcation; Bifurcations; Computed tomography; Echinodermata; Holothuria; holothurian; Holothuroidea; Marine invertebrates; micro‐computed tomography; Parastichopus tremulus; Pharynx; sea cucumber; Tentacles; Tomography
• ISSN: 1077-8306; 1744-7410
• DOI: 10.1111/ivb.12434

The present study explores rare but taxonomically and geographically widespread cases of anterior body axial bifurcation in adult sea cucumbers (Echinodermata: Holothuroidea). One individual of Holothuria (Halodeima) grisea, a common intertidal species along the Atlantic coast of Brazil, was studied externally and internally. Individuals of Apostichopus californicus from the northeastern Pacific coast of Washington (USA), H. (Mertensiothuria) leucospilota in the Indian Ocean off La Réunion, H. (Panningothuria) forskali from the Atlantic coast of Spain, and Parastichopus tremulus from the northeastern Atlantic off Norway were also reported to display similar anterior body axial bifurcation. In each of these species, the anterior body presented two mouths with their respective crown of tentacles. In vivo observations of H. (Halodeima) grisea showed that the two tentacle crowns and mouths were independently functional. Micro‐computed tomography (μCT) revealed that the anterior region of the body (up to the pharynx) was duplicated. Internally, two aquapharyngeal bulbs were found, each with their own calcareous ring (one with two plates missing), madreporite, and Polian vesicles. The body presented a normal set of five longitudinal muscle bands, some of which bifurcated orally to support more than one calcareous ring plate. This is the first report of such abnormalities in Holothuroidea and hypotheses that may explain such phenomenon are discussed. Resumo O presente estudo explora casos raros, mas taxonômica e geograficamente amplos, de bifurcação axial da região anterior do corpo em pepinos‐do‐mar adultos (Echinodermata: Holothuroidea). Um indivíduo de Holothuria (Halodeima) grisea, espécie intermareal comum ao longo da costa atlântica do Brasil, foi estudado externa e internamente. Indivíduos de Apostichopus californicus, da costa nordeste do Pacífico (Washington, EUA), H. (Mertensiothuria) leucospilota, das ilhas Reunião no Oceano Índico, H. (Panningothuria) forskali, da costa atlântica da Espanha e Parastichopus tremulus, do Atlântico nordeste da Noruega, também foram relatados como exibindo semelhante bifurcação axial da região anterior do corpo. Em cada uma dessas espécies, a parte anterior do corpo apresentou duas bocas com suas respectivas coroas de tentáculos. Observações in vivo de H. (Halodeima) grisea mostraram que as duas coroas de tentáculos e bocas eram funcionais e com movimentos independentes. A microtomografia computadorizada (μCT) revelou que