The underwater kingdom brims with miracles and marvels, one such treasure being the comb jellies or ctenophores. These ancient marine creatures have always sparked scientific fascination owing to their exceptional features and unique evolutionary traits. They are differentiated from others in the animal class by their intricate nervous system. They’re also famous for their transparency and other-worldly gelatinous bodies that propel via long ciliary comb plates through the water columns.
Physical Attributes and Habitat of Comb Jellies
The size of these remarkable beings can range from just a few millimetres to an impressive metre in length, with varied shapes and hues adding to their beauty. Furthermore, several comb jelly species even possess the ability to produce bioluminescence – a phenomenon where living organisms emit light.
This group belongs to the Ctenophora phylum, which comprises around 200 species. Their geographical reach is extensive, populating every ocean and dwelling in habitats varying from polar to tropical regions, shallow coastal waters to the profound depths of the sea trenches.
Their diet consists of plankton, small fish and other invertebrates, which they manage to capture using their sticky tentacles or oral lobes. It’s worth noting that invertebrates are animals without backbones or vertebral columns.
The Nerve Net: A Peculiar Nervous System
Comb jellies do not have a brain like most other animals. Instead, they utilize a nerve net – a system of interconnected neurons that extend throughout their body. This nerve net is responsible for controlling numerous functions, such as locomotion, feeding, sensory perception, and bioluminescence.
What sets this system apart is that neurons within it don’t communicate through synaptic junctions, as observed in other animals’ nervous systems. Rather, these neurons fuse and share a continuous membrane to form what scientists term as a syncytium. This means no gaps exist between nerve cells, allowing electrical signals to travel without hindrance across the network.
However, not all neurons in the comb jelly nervous system are fused. Some continue their communication with other nerve cells through synapses. It implies that comb jellies employ two distinct modes of communication among their nerve cells – a synaptic mode and a syncytial mode (without any synapses).
Understanding Syncytia and Synapses
Synapses are junctions where neurons connect and communicate with one another. Each neuron can have anywhere from a few to hundreds of thousands of such synaptic connections. These connections could be with itself, neighbouring neurons, or neurons located in other brain regions.
The discovery of syncytia in comb jellies holds significant implications for comprehending the evolution of nervous systems and neurons. This finding challenges the conventional belief that synapses are indispensable for neural communication, and that they evolved only once in the common ancestor of all animals.
