54 
Fishery Bulletin 108(1 ) 
continental shelf and upper continental slope (Munroe, 
1990) and the largest described larva of S. lactea i=S. 
nigrescens) is 8 mm NL (Kyle, 1913), indicating that 
size at metamorphosis should be bigger than 18 mm. In 
general, all species of Symphurus that inhabit depths 
below 300 m have the conical appendix at the end of 
the abdominal projection and at least two of them have 
exterilium larvae (Fig. 3). Descriptions by S. ginsburgi 
(Kurtz and Matsuura, 1994) and S. nigrescens do not 
mention whether they have exterilium larvae, but the 
shape of the intestine and the conical process would 
indicate so. 
Exterilium larvae are found in several phylogeneti- 
cally unrelated taxa (Ahlstrom et al., 1984). Species 
with exterilium larvae are hypothesized to benefit in 
several ways: 1) an increase in the length and surface 
area of the gut greatly enhances digestion in oligotro- 
phic environments (Moser 1981); 2) the exterilium pro- 
jection protects against predators because pigment pat- 
terns and the physical structure of this feature mimic 
siphonophores or poisonous coelenterates (Fraser and 
Smith, 1974; Moser, 1981; Gordon et al., 1984); and 3) 
the free intestinal loop acts as a specialized structure 
that prolongs pelagic life (Moser, 1981). 
Acknowledgments 
G.A.M. was supported by fellowships from Sistema 
Nacional de Investigadores and G.A.M. and R.S.M. 
by grants from Comision de Operacion y Fomento de 
Actividades Academicas and Estimulo al Desempeno de 
Investigacion. The project was funded with grants from 
Centro Interdisciplinario de Ciencias Marinas-Insti- 
tuto Politecnico Nacional, Secretaria de Investigacion 
y Posgrado (SIP 20080918 and SIP 20090303), Consejo 
Nacional de Ciencia y Tecnologia (FOSEMARNAT 2004- 
01-144 y SAGARPA 2007-117), y Comision Nacional para 
el uso de la Biodiversidad (CONABIO-EC012). We thank 
Carlos Robinson and Instituto de Ciencias del Mar y 
Limnologia at the Universidad Nacional Autonoma de 
Mexico for their facilities to collect the zooplankton 
samples in the Gulf of California, as well as Thomas 
Munroe and all reviewers for their useful comments. 
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