The #TetZoo article on turtle penises - first published 2007 and republished 2012 - is now missing ALL of its images due to hosting issues. I need those pics online, so follow this thread and I'll find an excuse to include them... (image (c) http://www.konnamaa.com ). #turtles
The cartoon/fictional idea that #turtles are pathetic creatures with underpowered or small organs is not supported by what we actually know. They're robust animals with remarkable anatomy. I'm talking about everything, not just genitalia.
The turtle penis is not homologous with that of mammals. It contains only one vascular erectile body and develops on the ventral surface of the cloaca, whereas the mammal penis contains two erectile bodies and is derived from non-cloacal tissue. Fig: Kelly (2002). #turtles
In terms of macrostructure, the turtle penis consists of a shaft and a distinct head, or glans, that’s typically dark grey, purple or blackish. Attached schematic representations of turtle penis anatomy from Zug (1966).
A long seminal groove, surrounded on both sides by raised seminal ridges, extends from the urethral opening down at the base of the penis to the glans. The seminal ridges are largest next to the glans; near the glans, they’re surrounded on both sides by fissures, or sinuses.
Anterior and posterior pairs of sinuses are present on the upper surface of the glans. Associated with mobile skin folds, they give the glans an unfamiliar look to we primates. Attached shows glans anatomy in snapping #turtles, river turtles, tortoises & others, from Zug (1966).
In softshell turtles (Trionychidae), the glans is five-lobed. The seminal groove is bifurcated, with each branch leading distolaterally to the tip of a pointed proximolateral structure. But, before reaching the tip of that proximolateral structure, the groove branches again...
... with this more distal branch of the groove extending to the tip of a pointed distolateral structure (Zug 1966). Softshell turtles thus discharge semen from four distinct branches of the seminal groove. Softshell glans image attached from Zug (1966). #turtles
Sea turtle penises are simple compared to this sort of complexity. Is this because they're outside a 'complex penis' clade, or is a secondary feature due to specialisation for marine life? Here's a Cretaceous sea turtle (Archelon) with an extruded penis... #turtles
All turtle penises are proportionally large. In a Green turtle (maximum length c. 1.5 m, carapace length c. 80-110 cm), the penis is typically more than 30 cm long. Here are screengrabs of a leatherback dissection from Inside Nature's Giants, Joy Reidenberg for scale... #turtles
Why is the turtle penis so large? The evolution of the shell probably means that male #turtles were forced to evolve innovative penises in order to make genital contact with their partners. The penis is also used in display or in response to handling (from humans)...
HOW does this relate to female anatomy? As is often the case, this isn't that well understood -- what's been reported so far is not especially remarkable.
And that's the end of that. The #TetZoo article - with longer explanations and more info - is here (now without images, ugh): https://blogs.scientificamerican.com/tetrapod-zoology/terrifying-sex-organs-of-male-turtles/. And, yes, there is TMNT fan-made porn.