Early Larval Development of Polydora nuchalis Woodwick, 
a Spionid Polychaete 
Keith H. Woodwick 1 
The most recent detailed work treating the 
larval development of Polydora , .that of Han- 
nerz (1956), appeared a little more than one 
century after Oersted (1843) described for the 
first time a larval stage in Polydora ciliata 
(Johnston), Wilson 1928. Related papers pre- 
sented during the interval included those of 
Claparede (1863), Agassiz (1867), Jacobi 
( 1883 ) , Whitelegge ( 1890 ) , Andrews ( 1891 ) , 
Mesnil (1896), Leschke (1903), Soderstrom 
(1920), Wilson (1928), Rioja (1939 and 
1941), Hartman (1941), Thorson (1946 and 
1950), Smidt (1952), and Casanova (1952). 
Each of these added information valuable to the 
understanding of polydorid development, but, 
as yet, in only a few forms is the early develop- 
ment known in detail. 
The purpose of this paper is to make known 
the early developmental stages of a recently de- 
scribed polydorid, Polydora nuchalis Woodwick 
(1953). 
METHOD 
The developmental stages of P. nuchalis were 
cultured either in petri dishes containing sea 
water and sand from the original collecting area 
or in aquaria of circulating aerated sea water 
after the method of Reish (1953). Favorable re- 
sults were obtained with both of these methods. 
Observations were made of encased larvae (in 
egg capsules) as well as free-swimming indi- 
viduals. The study of living material on depres- 
sion slides provided specimens unaltered by 
fixation or cover glass pressure. Drawings of 
living forms were made employing the tech- 
nique of Wilson (1928) and were inked fol- 
lowing a comparative study of several other 
larvae of the same age group. 
The drawings do not constitute a continuous 
developmental series from one individual but 
1 Department of Biology, Fresno State College, 
Fresno, California. Manuscript received October 13, 
1958. 
are a synthesis of a series of observations of in- 
dividuals from a number of egg cases. The ages 
assigned the various stages are not absolute but, 
because they are based on multiple observations, 
are considered to be reasonable. 
composite Polydora life history 
An understanding of the larval development 
of polydorids is expedited by an understanding 
of the relationship of these larval stages to the 
remainder of the life history. A composite life 
history of members of the genus is presented 
below; P. nuchalis follows this scheme in most 
stages but does show individual differences. 
A composite life history as extracted from 
the literature may be summarized in the fol- 
lowing manner. An adult male and female copu- 
late. Fertilization is internal. The female spawns 
the fertilized eggs through the nephridial canal 
and into transparent capsules. The capsules, 
formed in the manner described by Soderstrom 
(1920), are attached to the inner wall of the 
female’s tube or burrow. Cleavage of the fer- 
tilized egg is complete but unequal. Further de- 
velopment of larvae within the egg capsule 
follows one of two types: (1) In Polydora 
ciliata (Wilson, 1928) and certain other species 
each egg in the capsule gives rise to a larva. The 
larvae leave the capsule at the 3 -segment (seti- 
gerous segment) stage as planktotrophic forms 
to begin a long planktonic period (four to six 
weeks) prior to settling and metamorphosis. 
(2) In Polydora hoplura (Wilson, 1928) which 
represents the other type, each egg in the cap- 
sule does not give rise to a larva. The few which 
do develop, feed on the undeveloped eggs 
(nurse eggs). The larvae begin feeding at about 
the 3 -segment stage but do not leave the capsule 
until about the 12 -segment stage. The hatched 
larvae pass through a very short planktonic 
stage, if any, before settling and metamorphosis. 
The latter type of development is found in 
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