An average length for N. californiensis is roughly 115 mm, though this can vary as adult males are noticeably larger than females.  Ghost shrimp morphologically resemble the bodies of lobsters, crayfish, and hermit crabs with qualities such as reduced gills, soft abdomen, and the way in which they carry their fifth legs.  They are soft-bodied.  Like other Decapod crustaceans, N. californiensis has a fused head and thorax called the cephalothorax.  The cephalothorax is quite short compared to Brachyurans, only comprising 1/4 of the total body length.  The carapace is smooth and cylindrical, and the abdomen is long, straight, and symmetrical.  The first abdomen is shortest, and it is slender at the junction with the cephalothorax, which helps the organism with turning inside the burrow.  At the end of the abdomen lies the tail fan.

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Included in the cephalothorax is a pair of compound eyes, 6 pairs of mouthparts (maxilla and maxillapeds), 2 pairs of antennae that end with flagellum, and 5 pairs of legs.  The first pairs of legs are actually chelate, or pincers.  In males, one of these is significantly larger than the other.  There are six segments in the abdomen, the last of which is enlarged to contain uropods.