During major floods, thousands of tiny fish convene at Luvilombo Falls in the upper Congo River Basin to undertake a peculiar vertical migration, described for the first time today in Scientific Reports.
The bodies of the crabs displayed male reproductive structures, while other parts showcased female features, including gonopores, said K.S. Anoop Das.
We think that in this early deuterostome, the median eye contained both ciliary and rhabdomeric cells. As a result, both cellular lineages were incorporated into a single, ancient, cyclopean eye, which later evolved into the vertebrate eyes.
The animals do, however, have neuronsnerve cells that appear interconnected throughout their body. And now a new study shows that how these animals sleep is surprisingly similar to humans, suggesting that sleep may have evolved before even the most primitive brains. The findings, published on Tuesday in Nature Communications, also help answer one of science's prevailing mysteries: Why do animals sleep?
Some deep-sea fish may be able to see light in a different way from most other vertebrates, according to a new study. The fish, found in the Red Sea, have what the scientists behind the new study describe as hybrid photoreceptorslight-sensing cells in the retina that combine elements of two distinct kinds of photoreceptors, cones and rods. In human retinas, cone cells enable us to see in bright environments, detecting color and fine detail,
Which animals came first? For more than a century, most evidence suggested that sponges, immobile filter-feeders that lack muscles, neurons and other specialized tissues, were the first animal lineages to emerge. Then, in 2008, a genomic study pointed to a head-scratching rival: dazzling, translucent predators called comb jellies, or ctenophores, with nerves, muscles and other sophisticated features. That single study ignited a debate that has raged for nearly 20 years, sparking fierce arguments about how complexity evolved in animals.
A simple example of space-tuned cells is HD cells, which persistently fire when animals are facing a particular direction8. Because the head direction of an animal is typically not directly provided to the sensory system, HD cells need to integrate the history of rotational movements that animals make, a process called angular path integration. As a simple, yet biophysically plausible mechanism to implement angular path integration, a class of dynamical models called ring attractors has been proposed9.
