20. Jun, 2021

The mysterious Coelacanth

The Coelacanths are members of the order of Coelacanthiformes that currently includes two species: the West Indian Ocean coelacanth (Latimeria chalumnae) primarily found near the Comoro island of  Africa and the Indonesian coelacanth (Latimeria menadoensis) in the waters of Sulawesi. Coelacanths are deep-sea creatures, living in depths up to 2,300 feet below the surface,  but may sometimes drift to more shallow layers of the  Ocean.  The coelacanths also called ‘’the living fossils’’,   were thought to have become extinct around 66 million years ago, but were rediscovered in 1938 off the coast of South Africa. Little was known of the coelacanth's normal habitat and behavior until observations in 1987 by German biologist Hans Fricke and his research team, using a submersible. Fricke discovered that adult coelacanths cluster in caves during the day and venture into open water at night. Coelacanths can become around 2 meters long and weigh 90 kilo’s. By examining imperceptible annual calcified structures (circuli) on the scales, maritime biologist have recently discovered  (see Current Biology)   that the fish has a slow growth,  can grow very old, around 85 years, and that the species only reach maturity at the age of 55 years, when it also becomes capable of producing offspring.  

Anatomy Instead of a spinal cord, Coelacanths have a stiff, hollow, fluid-filled tube known as the notochord,  functioning as the backbone, which runs from the skull to the tip of the tail and whose outline is clearly visible on the rear portion of the body.  Noticeable features are the two sets of paired lobed fins, pectorals and pelvics, lying to the side and beneath the belly. The muscles steering its pectorals fins consist of a pronator and supinator,  a muscle arrangement equivalent to two human antagonistic pairs of monoarticular muscles. Moreover, the two pairs of fins move in a synchronized pattern, characteristic of four-footed vertebrates. The right pectoral fin or forelimb is coordinated with and moves in the same direction as the left pelvic fin or rear limb.  Likewise, the left pectoral fin moves in the same direction as the right pelvic fin or rear limb (see picture above). This is similar to the gait of a trotting horse. The theory is that the fins behave as primitive ‘legs’, representing the bottom branch on the "family tree"  of evolution that led to legs in higher four-legged vertebrates.