Naked sand darter Naked sand darter The naked sand darter ("Ammocrypta beanii") is a freshwater fish of the family Percidae. It is found in the south-eastern United States. The naked sand darter is a small fish ranging in size from 40 to 50 mm long, the maximum being around 64 mm. Being a long thin darter, it is devoid of scales with the exception of a few rows above and below the lateral line and sometimes the caudal peduncle. Slightly transparent in life with a yellow color and iridescent operculum, the naked sand darter blends in with its habitat. It has darker bands
Caudal cell mass Caudal cell mass In humans and other mammals, the caudal cell mass (sometimes tail bud in humans) is the aggregate of undifferentiated cells at the caudal end on the spine.The caudal end of the spinal cord first begins to form after primary neuralation has taken place, indicating that it develops after the cranial portion of the spinal cord has developed. Following neuralation, the caudal tail begins to form a neurocele as it develops a hollow core. After this, secondary neuralation occurs in which the medullary cord begins to form and is filled with many cavities that ultimatelly form the lumen.