What’s a Spider? Designation of the Neotype for the First Animal Species Ever Described, Araneus angulatus Clerck 1757 (Araneae: Araneidae)

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  What’s a Spider? Designation of the Neotype for the First Animal Species Ever Described, Araneus angulatus Clerck 1757 (Araneae: Araneidae) Abstract We designate a neotype for the Eurasian spider species Araneus angulatus Clerck, 1757, thereby fixing the objective application of the species name, the genus name Araneus Clerck 1757, the family name Araneidae Clerck 1757, and the superfamily name Araneoidea Clerck 1757. By etymology and arachnological tradition, it also unofficially fixes the application of the ordinal name Araneae Clerck 1757 and thus answers the uncontroversial question, “What’s a spider?” A. angulatus also happens to be historically the first animal species ever described because Clerck (1757) has priority over Linnaeus (1758). Neotype designation is justified for three reasons: the syntypes of A. angulatus are lost; “ A. angulatus ” contains significant COI sequence divergence, potentially representing intraspecific variation, misidentifications, or as many...

Micro-CT analysis reveals directional genital asymmetry in a mygalomorph spider with two different sperm-storage organs (Araneae: Mecicobothriidae)

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Micro-CT analysis reveals directional genital asymmetry in a mygalomorph spider with two different sperm-storage organs (Araneae: Mecicobothriidae)

Abstract

Sexual selection is a pervasive evolutionary force shaping the extraordinary diversity of animal genitalia, often driving rapid morphological divergence and complex interactions between male and female reproductive structures. In spiders, sexual selection acts through both pre- and postcopulatory mechanisms, frequently resulting in elaborate male intromittent organs, specialized female sperm-storage structures, and intricate mating behaviours. Despite this diversity, mygalomorph spiders have traditionally been regarded as morphologically conservative, with comparatively simple genitalia and stereotyped reproductive patterns. In this study, we provide the first integrative analysis of genital functional morphology, copulatory mechanics, and mating behaviour in a mygalomorph species, Mecicobothrium thorelli. Our results reveal a surprising degree of anatomical and behavioural complexity. Most notably, we document the first known instance of directional genital asymmetry in a mygalomorph spider. Female genitalia are characterized by two distinct spermathecal types, with one being asymmetric. This asymmetry is matched behaviourally by differential, selective use of the symmetric male copulatory organs. The consistent preference for specific male–female genitalia combinations suggests finely tuned mechanical and functional coordination during copulation. By uncovering these hidden complexities, our study expands current understanding of sexual selection and genital evolution in early-diverging spider lineages.

Panchuk, J., Ferretti, N., Poy, D., Ramírez, M., & Michalik, P. (2026). Micro-CT analysis reveals directional genital asymmetry in a mygalomorph spider with two different sperm-storage organs (Araneae: Mecicobothriidae). Zoological Journal of the Linnean Society, 207(2). https://doi.org/10.1093/zoolinnean/zlag075