80 
PACIFIC SCIENCE, Vol. XV. January 1961 
TABLE 1 
Comparative Characteristics 
SPECIES 
PROSTOMIUM 
LENGTH OF 
CARUNCLE 
BRANCHIAE 
FIRST 
SEGMENT 
NOTOSETAE 
POSTERIOR 
SEGMENTS, 
NEUROPODIAL 
SPINES 
HABITAT 
Polydora 
rickettsi 
n. sp. 
rounded 
(lateral 
pigmentation) 
to the 
5th 
segment 
begin 7th, 
large to 
30th 
absent 
absent 
Spirobranchus 
tube 
Polydora 
hoplura 
bifid 
to the 
3rd 
begin 7 th, 
to 10th-20th 
last 
absent 
present 
(boathook) 
shell of Balanus, 
sponges; shore, 
bottom of ship 
Polydora 
giardi 
bifid 
anterior end 
or middle of 
the 4th 
begin 10th, 
to 25th 
present 
absent 
shale 
coralline algae 
Polydora 
anoculata 
bifid 
to the 4th 
or 5 th 
begin 11th 
or 12 th 
present 
absent 
broken shells, 
Amaroucium 
Polydora 
ciiiata 
weakly bifid 
to the 3rd 
or mid-2nd 
begin 7th, 
to 10th last 
absent 
absent 
burrow in 
shells of 
many forms 
The dorsal septal line is broken by the oblique 
muscular bands of the 5 th segment. The mus- 
cles also reach into the 7th segment, but the 
latter is nearly full-sized and holds the 1st gill 
(not fully developed), and also the first rep- 
resentation of the distally bidentate neuropodial 
hooded hooks (Fig. 5). In these neuropodial 
setae the main tooth forms an oblique angle, 
with the shaft following the angle measure- 
ment system of Soderstrom (1920). There are 
seven hooded hooks mixed with capillaries in 
the 7th segment; the capillaries do not persist. 
The branchiae are full-size from the 8th seg- 
ment to the 30th; they decrease in size to the 
66th segment, where they are continued pos- 
teriorly as small papillae. 
There are no posterior notopodial hooks or 
spines. 
The disclike pygidium has a dorsal notch and, 
although not broadly flared, is greater in diam- 
eter than the prepygidial segments (Fig. 7). 
DISCUSSION 
Other polydorids reported from Mexican wa- 
ters are discussed in Rioja ( 1943 ) and include 
Polydora armata, P, ciiiata, P. cirrosa, P. corn- 
mens alts, P. flava, P. giardi, P. heterochaeta, P. 
ligni, P. socialis, and P. tricusp a. Of these species 
P. giardi and P. ciiiata most closely resemble 
P. rickettsi in characteristics and habitat. Some 
of the characteristics of these three forms, and 
of the morphologically similar P. hoplura and 
P. anoculata from other waters, are compared 
in Table 1. In addition to the contrasting char- 
acters shown in the table the five species have 
characteristics in common, including the fol- 
lowing: specialized setae with a main falcate 
tooth and a subterminal accessory tooth in the 
5 th segment, hooded hooks beginning in the 
7th segment, disclike pygidia, and the absence 
of nuchal tentacles. 
TYPE MATERIAL: The holotype and additional 
material have been deposited in the polychaete 
collections of the Allan Hancock Foundation, 
University of Southern California. 
TYPE LOCALITY: P. rickettsi, known only from 
the tube of Spirobranchus incrassatus Morch, 
was collected March 18, 1940, at Cape San 
Lucas, Lower California, Mexico. 
BIOLOGY: The specialized setae of the 5th 
segment, which are like those present in other 
boring polydorid species, and the habitat of 
