Betaine transporter dependent on Na(+) and Cl(-) ions that functions primarily in the epidermis to clear betaine from the extracellular space. Elicits current in response to betaine but not in response to GABA, L-carnitine, sarcosine, glycine or dimethylglycine. Highly expressed in the head, the excretory canal, tail hypodermal cells, epidermis and vulval epithelial cells. Expressed in the excretory canal-associated neuron and in some non-amphidial sensory neurons in the head (at protein level). Mutant worms are morphologically similar to the wild-type but exhibit mild swimming defects and are lethargic when crawling on a food-free environment with their movement being interrupted by frequent pauses. Worms paralyze in the presence of exogenous betaine. Simultaneous knockdown of snf-3 and egl-8 results in uncoordinated, hypercontracted and paralyzed animals. Belongs to the sodium:neurotransmitter symporter (SNF) family.