Project 4100: M. G. Rix, H. M. Wood, M. S. Harvey, P. Michalik. 2021. Micro-Computed Tomography Reveals a Remarkable Twin Intromittent Organ in Spiders – A Novelty for Arachnids With Direct Sperm Transfer. Frontiers in Ecology and Evolution. 9:null.
Specimen: Austrarchaea tealei Rix & Harvey, 2012 (CASENT 9028385)
View: left palp


The modification of male pedipalps into secondary sexual intromittent organs is one of the hallmark characteristics of spiders, yet understanding the development and evolution of male genitalia across the order remains a challenging prospect. The embolus – the sclerite bearing the efferent spermatic duct or spermophor, and used to deliver sperm directly to the female genitalia during copulation – has always been considered the single unambiguously homologous palpal sclerite shared by all spider species, fundamental to the bauplan of the order and to the evolution and functional morphology of spider reproductive systems. Indeed, after two centuries of comparative research on spider reproduction, the presence of a single spermophor and embolus on each of a male spider’s two pedipalps remains a central tenet of evolutionary arachnology. Our findings challenge this premise, and reveal a remarkable twin intromittent organ sperm transfer system in a lineage of Australian palpimanoid spiders, characterized by a bifurcate spermophor and the presence of two efferent ducts leading to a pair of embolic sclerites on each pedipalp. This is the first time such a remarkable conformation has been observed in any group of arachnids with direct sperm transfer, complicating our understanding of palpal sclerite homologies, and challenging ideas about the evolution of spider genitalia.

Read the article »

Article DOI: 10.3389/fevo.2021.794708

Project DOI: 10.7934/P4100,
This project contains
  • 10 Media
  • 10 Taxa
  • 11 Specimens
Total size of project's media files: 16.12M

Download Project SDD File
Currently Viewing:
MorphoBank Project 4100

    Authors' Institutions

    • National Museum of Natural History, Smithsonian Institution

    • University of Greifswald

    • Queensland Museum

    • Western Australian Museum


    member name taxa specimens media
    Peter Michalik
    Project Administrator
    Michael Rix
    Full membership

    Project has no matrices defined.

    Project views

    type number of views Individual items viewed (where applicable)
    Total project views12020
    Project overview661
    Media views3761Media search (1340 views); M823767 (240 views); M823769 (236 views); M823770 (240 views); M823771 (252 views); M823772 (240 views); M823773 (236 views); M823774 (245 views); M823775 (247 views); M823776 (248 views); M823777 (237 views);
    Views for media list563
    Specimen list4417
    Taxon list2266
    Matrix views4Matrix landing page (4 views);
    Documents list6

    Project downloads

    type number of downloads Individual items downloaded (where applicable)
    Total downloads from project28
    Project downloads27
    Media downloads1M823769 (1 download);