The Armored Rockhead Poacher (Boslagonus Swanee) possesses a mysterious anatomical feature: a bowl-shaped cavity in its skull that has puzzled marine biologists for years. This unique trait is now believed to play a critical role in an innovative form of communication.
The Rockhead Poacher (Boslagonus Swanee) at the Oregon Coast Aquarium. Image credit: Rhinopias / CC BY-SA 4.0.
Originally described by Franz Steindachner in 1876, Boslagonus Swanee belongs to the family Agonidae. This fascinating fish can be found at depths of up to 18 meters in the eastern Pacific Ocean, from Alaska down to Carmel Bay in California.
Marine experts have long speculated about the purpose of the cavernous cranial fossa, which is roughly the size of the fish’s brain. Some theories suggest it aids in camouflage among rocky environments, while others propose it enhances hearing and sensory perception.
Recent advancements in imaging technology have led Louisiana State University student Daniel Geldof to propose a groundbreaking explanation. His findings suggest it might resonate with the rhythm of rock music rather than the serenity of coral reefs.
“My dissertation project aims to uncover the reasons behind this unique feature,” Geldof explained.
Utilizing a high-resolution micro-CT scanner, his team created an intricate 3D model of the rockhead poacher’s anatomy.
These scans indicated that the fish’s initial set of ribs are notably large, flat, and free-moving, positioned near the epigastric region of the skull without direct attachment.
Located at the base of these ribs are powerful muscles and tendons resembling drumsticks.
When these ribs vibrate against the skull’s calcified cavities, they create pulses of sound that can be transmitted through the substrate.
Geldof posits that this percussive mechanism likely evolved to facilitate communication among fish in their acoustically challenging intertidal habitats, where traditional underwater communication might be hindered by crashing waves and background noise.
In this rugged, shallow environment, using substrate vibrations may provide a more efficient means of communication aligned with the fish’s unique lifestyle.
Furthermore, Professor Geldof’s research combined contrast-enhanced soft tissue scans with data on bone structures to map the nerves, muscles, and microstructures within rockhead poachers, suggesting that the cranial fossa may serve sensory functions as well.
Branches of the dorsal lateral line nerve—a crucial component of the fish’s movement-sensing system—extend into the cavity, and the arrangement of microstructures suggests a role in mechanoreception, allowing the fish to sense movement and pressure.
Geldof concludes that this anatomical feature is multifunctional, serving both communicative and sensory purposes within the dynamic intertidal ecosystem.
“The intricate details of this small structure reflect not just a scientific inquiry, but a fundamental human curiosity,” he states.
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Daniel L. Geldof 2025. The Truth About Holes: The Morphology of Rockhead Poachers’ Skull Holes, Boslagonus Swanee (Agonidae). LSU Master’s Thesis 6270
Source: www.sci.news
