Natural History: Greater siren

On a field trip to a local wildlife management area, I was lucky enough to experience a greater siren (Siren lacertina), which had been caught in an aquatic trap set the day before in a heavily vegetated marsh area. After weaving through the vegetation and trying to avoid the possibility of losing my footing in the murky water, I was able to obtain the trap and became very excited after initially observing that it was likely a siren which I had not seen in the wild before. Due to the lack of sexual dimorphism in this species, I was not able to determine the sex with confidence as it would likely require close examination that could not be accomplished in the field. The greater siren was likely around 12 inches long, or 30.48 centimeters, by personal eye measurement and observation. Due to the small size, the siren was only a juvenile and was difficult to identify at first due to the similar size to another species in the family Sirenidae, the Lesser siren (Siren intermedia), which is smaller in size in comparison. The characteristic light stripe along the side of the body for a juvenile greater siren had faded as well and the white spots still remained, likely due to its age and size, served as another difficulty to distinguishing it from Siren intermedia which typically have black or brown spots and no stripe. In order to correctly identify this amphibian, we observed its eel-like body and slimy excretions to narrow the salamander families to Sirenidae and Amphiumidae. It was then observed that it only had a pair of forelegs and no hind limbs, meaning that it was of Sirenidae rather than Amphiumidae, which have hind and forelimbs. The forelimbs that this siren has definitely assist in its movements through the thick vegetation I observed, showing how it had adapted to that certain environment for survival. It also had prominent external gills, which amphiumas lack due to having gill slits for respiration. The external gills allow it to survive in low oxygen waters due to the increase in surface area when respiring through them and show how they have evolved for a purely aquatic lifestyle. The number of toes was then observed on the forelegs, counting at four on each which expelled the Dwarf siren (Pseudobranchus striatus) due to it only having three toes. Because S. intermedia and S. lacertina are very similar in appearance (especially when the greater siren is a juvenile like this particular one), it is often considered difficult to identify them without very close inspection. It did not help that this one was uncooperative when being held! It shows how useful those slimy excretions and smooth skin can help in escaping predators, but also how it provides less water resistance in their aquatic environments. Once it held still for a few moments, it was observed that it had no line or band on its head, which is often seen in the lesser sirens, and light spots rather than darker ones, causing the final identification to be a juvenile S. lacertina. I really enjoyed the privilege to see a greater siren on our last field trip, giving me the opportunity to physically see the differences from amphiumas and gain personal experience in how to identify between the local species of the sirens.