Poly dor a nuchalis — Wood wick 
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similar to that described by Hartman (1941) 
for an unknown spionid larva. The melano- 
phores on the third segment have elongated 
laterally and another pair has formed on the de- 
veloping fourth segment. 
This 3 -segment stage has three pairs of eyes. 
Later, the two pairs which are anterolateral fuse 
on each side producing a single anterolateral 
pair. Four eyes, the fused pair and the median 
pair, are retained throughout life. 
The vestibule has enlarged but has not as 
yet opened to the granular intestinal portion of 
the gut. The ciliated posterior invagination of 
the gut nearly reaches the third segment and 
after a few additional hours of development its 
cavity becomes joined to that of the granular 
intestinal portion. This junction, along with 
completion of the vestibular portion, will pro- 
duce a functional digestive tract. In larvae hav- 
ing a long pelagic life, completion of the gut 
development and hatching are concurrent and 
larvae are able to feed upon leaving the egg 
cases; this is usually at the 3 -segment stage. 
Poly dor a nuchalis does not hatch at the 3- 
segment stage but does begin to feed on the 
nurse eggs. The stage at which gut development 
is completed, however, is not so critical in a 
species of Polydora having nurse eggs. 
Five-Segment Larva , One Week. This larva 
is about 0.50 mm. in length. It has five setiger- 
ous segments and at least three more segments 
which are forming. The entire animal is trans- 
parent except for a few yolk granules present 
in the gut. Most larvae of this size have a 
complete digestive tract including a vestibule, 
esophagus, intestine, rectum, and anus. The 
vestibule, esophagus, and rectum are greatly 
ciliated. 
The palpi have elongated but the prototroch, 
telotroch, and pygidium are as described for the 
preceding stage. Two pairs of eyes are present 
in the normal adult position with the lateral 
pair anterior to the median pair. 
The dorsal paired melanophores are elon- 
gated on segment three and smaller pairs are 
• present on segments four and five. There is also 
a single pygidial melanophore. 
Ten-Segment Larva, About Two Weeks. 
(Plate II, Fig. 2.) This larva is 0.65 mm. in 
length and has 10 segments formed with the 
eleventh segment nearly complete in its develop- 
ment. The larva illustrated does not contain 
nurse egg material although it is often found in 
the gut of larvae of this and later stages. The 
large ventral vestibule passes food into the long, 
ciliated esophagus from which it moves to the 
intestine beginning at segment four. The anus 
opens in the central portion of the pygidium 
which has become flattened. The dorsal notch 
characteristic of the adult pygidium is not 
present. 
The eyes are as in the previous stage, but 
the palpi are more elongate. Notopodial lobes 
are present in all the segments. Those of the 
first segment are located more dorsally than the 
others and are, thus, nearer the midline. The 
neuropodial lobes of the first segment are on 
the same lateral plane as the notopodial lobes 
of the other segments. This condition prevails in 
the adult. Branchiae are not present. Melano- 
phores are present on segments three and four 
as paired dorsal elongations and on the succeed- 
ing six segments as paired dots which dim- 
inish in size on the more posterior segments. 
Segments two, seven, and eight have lateral 
pigment spots. The pygidial melanophore is 
present. A single stout spine is situated in the 
notopodium on each side of the modified fifth 
segment. 
Fifteen-Segment Larva, Three Weeks. (Plate 
III.) This form represents the settling stage of 
P. nuchalis. It is similar in appearance to the 
adult, but will be discussed here as the final 
larval stage. It is 0.90 mm. in length and has 15 
fully developed segments and a sixteenth partly 
developed. 
The anterior end is adultlike with the peri- 
stomium and prostomium greatly developed in 
comparison with previously described stages. 
The prostomium is bilobed anteriorly. Two pairs 
of eyes are located on the prostomium. The 
nuchal tentacle, one of the diagnostic characters 
for P. nuchalis, is now present on the posterior 
part of the prostomium. The elongate palpi 
which arise from the peristomium extend as far 
as the modified fifth segment. Each of the palpi 
has a median ciliated groove used in the feeding 
process. The central body portion, like the an- 
terior portion, resembles that of the adult but 
the pygidial portion does not. The pygidium is 
