The Larval Development of the Sand Crab Emerita rathbunae Schmitt 
(Decapoda, Hippidae ) 1 
Margaret D. Knight 
Two species of the sand crab Emerita have been 
found on the western coasts of North and South 
America. Emerita analoga (Stimpson) has been 
recorded from Vancouver Island, British Colum- 
bia (Butler, 1959) to Magdalena Bay, Baja 
California, and from Salavery, Peru to Eden 
Harbor, Territory of Aysen, Chile (Haig, 
1955). Dr. Ian Efford (personal communica- 
tion of unpublished observations) has found 
that the northern limit of the species may be 
Kodiak Island, Alaska, and that the southern 
limit of its range in South America is the Strait 
of Magellan. E. rathbunae Schmitt has been 
found from La Paz, Baja California to Capon, 
Peru (Schmitt, 1935). Specimens of E. rath- 
bunae have also been collected at San Francis- 
quito Bay, on the east coast of Baja California 
above La Paz (Steinbeck and Rickets, 1941). 
The larvae of Emerita analoga were described 
by Johnson and Lewis (1942). The first zoea 
was obtained from eggs hatched in the labora- 
tory and one individual molted to the second 
stage. Later stages were described from pre- 
served plankton samples. Larvae of the species 
have subsequently been cultured from egg to 
megalopa by Dr. Ian Efford (personal com- 
munication). During the present study, larvae 
of the tropical species Emerita rathbunae were 
cultured in the laboratory and compared with 
specimens from the plankton to provide a 
detailed description of the sequence of larval 
development and a means of differentiating the 
larvae from those of the amphi-tropical species 
E. analoga. 
The larvae of three other species of Emerita 
have been investigated. Menon (1933) ob- 
tained five zoeal stages of E. emerita (L.) from 
the plankton, the larvae of E. talpoida (Say) 
have been described both from laboratory cul- 
1 Contribution from Scripps Institution of Ocean- 
ography, University of California, San Diego. Manu- 
script received January 18, 1966. 
tures (Rees, 1959) and from the plankton 
(Smith, 1877), and larvae of E. holthuisi 
Sankolli have been studied in the laboratory 
by Sankolli (1965). 
METHODS 
An ovigerous female of Emerita rathbunae 
was collected from a sandy beach near La Playa, 
Mazatlan, Mexico, on 20 September 1963 dur- 
ing a cruise in the Gulf of California aboard 
R/V "Alexander Agassiz” of the Scripps In- 
stitution of Oceanography. The female was held 
aboard ship in a 3-gallon aquarium. Hatching 
of the eggs began 12 hours after capture. The 
larvae were maintained in groups of 10-25 in 
4-inch glass finger bowls of 1200 cc capacity 
or in plastic containers of 400 cc capacity. They 
were transferred daily to fresh sea water and 
fed newly hatched nauplii of Artemi a salina 
(L.). All larvae molted once during the six 
days’ culture period aboard ship. In addition, 
one second zoea of the species was sorted from 
a plankton tow taken earlier near shore below 
Cape Corrientes, Mexico (19° 22' N, 105° 03' 
W), and was maintained in isolated culture 
aboard ship for 11 days. A surface temperature 
of 29-6° C and salinity of 33-9%o were 
recorded for the water from which the larva 
was taken. The salinity of water used for cul- 
tures was 33.8-33.9%c* As the ship returned 
north from the collecting area, the temperature 
of the water held in the cultures dropped from 
29° to 23° C, subjecting the larvae to consider- 
able cooling during the early zoeal stages. 
At the conclusion of the cruise, the approxi- 
mately 100 larvae hatched aboard ship (then in 
stages II and III), and the single larva taken 
from the plankton were transferred to the lab- 
oratory and isolated either in compartmented 
plastic trays holding 50 cc per compartment, or 
in plastic boxes of 400 cc capacity. They were 
transferred daily to sea water filtered through 
58 
