Embryonic and early postembryonic development of the freshwater isopod crustacean Asellus aquaticus - staging based on morphology

Bogataj, Urban (author), Mrak, Polona (author), Žnidaršič, Nada (author), Fišer, Žiga (author)

The developmental biology of arthropods has advanced rapidly in recent decades, largely through the application of novel experimental techniques to a limited number of established model organisms. Extending comparative embryology beyond these traditional models is essential for a comprehensive understanding of arthropod evolution. Among crustaceans, the freshwater isopod Asellus aquaticus Linnaeus (1758) represents a promising emerging evo-devo model. This widespread European species inhabits diverse freshwater environments, including groundwater, resulting in pronounced phenotypic variation, most apparent in cave-adapted populations. It is easy to culture in the laboratory, reproduces year-round, and produces numerous accessible embryos with relatively fast development. Here, we present the most comprehensive developmental staging system for A. aquaticus to date. Using light microscopy, fluorescence microscopy with DAPI staining, and transmission electron microscopy, we integrate event-based and age-based landmarks to define nine embryonic stages (S1–S9) and a first postembryonic, premanca stage (S10). We further provide a coarse description of postembryonic development through mancae and juveniles to sexual maturity and provide a practical guide for non-invasive staging of embryos within intact marsupia of live gravid females. This refined staging framework resolves ambiguities in previous descriptions and provides a precise temporal backbone for comparative and functional evodevo studies of arthropods. It enables detailed investigations of developmental divergence between surface and cave populations, facilitates field-based studies of reproductive phenology and environmental effects on development, with potential applications in climate-change biology. Together, these advances establish A. aquaticus as a powerful model for studying the evolution of development across environmental gradients and adaptive transitions.

• Language: English
• Keywords: embryonic development, arthropods, staging system, Asellus aquaticus, Isopoda, Crustacea
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: BF - Biotechnical Faculty
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: Str. 1-20
• Numbering: Vol. 95, article 101574
• PID: 20.500.12556/RUL-190629
• UDC: 595.2/.7
• ISSN on article: 1467-8039
• DOI: 10.1016/j.asd.2026.101574
• COBISS.SI-ID: 303266051
• Publication date in RUL: 30.10.2026

Record is a part of a journal

• Title: Arthropod structure & development
• Shortened title: Arthropod struct. develop.
• Publisher: Elsevier.
• ISSN: 1467-8039
• COBISS.SI-ID: 22931929

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: embrionalni razvoj, členonožci, opis razvojnih stadijev, Asellus aquaticus, Isopoda, Crustacea

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P1-0184-2020
• Name: Integrativna zoologija in speleobiologija

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: I0-0022-0481-0481-07
• Name: IC Mikroskopija bioloških vzorcev
• Acronym: ICMBV