50 
PACIFIC SCIENCE, Vol. II, January, 1948 
Chitinopoma may be nearly related to Micro- 
serpula Dons for which the single known spe¬ 
cies, M. inflata Dons, has been recorded from 
Arctic seas (Brattstrom, 1945). In the latter, 
the tube is said to have ovicels distally. 
Chitinopoma occidentalis (Bush) 
new combination 
Fig. 12, a-f. 
Hyalopomatopsis occidentalis Bush, 1904: 229- 
230, pi. 40, fig. 3, 22, pi. 44, fig. 2, 4, 8. 
Collections. Stations 13-40 (several); 21-40 
(3); 20-40 to 22-40 (many); 24-40 (many); 
25-40 (several); 35-40 (several); 47-40 (sev¬ 
eral); 61-40 (several); 70-40 (several); 82- 
40 (few); 84-40 (several); 100^10 (several); 
Mist Harbor (1+). 
White calcareous tubes are attached to shell 
fragments, other serpulid tubes, gastropod shells, 
living rock oysters, branchiopods, carapace of 
crabs, and other hard surfaces. The tubes are 
hard, smooth, and broad; they have a strong, 
median keel with a sharp notch above, at the 
aperture (Fig. 12 /); the aperture is circular 
(Fig. 12 e). Tubes seldom cover one another 
unless crowded; they are sinuous or irregularly 
twisted; they measure 30 to 50 mm. long. 
Larger individuals (fixed in the tube) are 15 to 
20 mm. long. The body consists of a well- 
developed tentacular crown, seven thoracic, and 
50 or fewer abdominal, segments. 
The operculum replaces the dorsal radiole on 
the left side. It has a smooth, straight stalk and 
extends distally beyond the outer ends of the 
radioles. The expanded, distal portion, seen from 
the dorsum is symmetrical, but seen from the 
side (Fig. 12 d) is asymmetrical, the greater 
convexity on the ventral side. It is a soft, pale 
vesicle surmounted by a slightly chitinized, con¬ 
vex cap. The tentacular crown has six radioles 
on the left side, seven on the right one. Ten¬ 
tacular pinnae are longest on the distal third of 
the radiolar length but surpassed in length by 
the long, free distal filament of the rachis. 
The collar is a high, thin membrane; it con¬ 
sists of a pair of long, dorsal lobes that com¬ 
pletely conceal the peristomium; they are sepa¬ 
rated from other parts of the collar by deep, 
dorso-lateral clefts. Laterally and ventrally, the 
collar consists of a still longer piece that extends 
forward to conceal over half of the radiolar 
length. When the collar is pushed back, a pair 
of deep-seated, ocular spots is visible in the 
fleshy base of the peristomium. There is no 
indication of a thoracic membrane. 
Collar setae are arranged in a lengthwise, 
horizontal series, slightly dorsal to the other 
notopodia. They have two kinds of setae; an¬ 
teriorly there are six or seven larger, pointed 
setae with broad, thick expansion (Fig. 12 b)\ 
immediately behind are a comparable number 
of slenderer ones that are also crenulate at the 
outer margin (Fig. 12 c). 
Second to seventh thoracic setigerous seg¬ 
ments resemble one another, but the last one 
has a greatly reduced parapodium. Notopodia 
are each provided with two kinds of setae, in¬ 
cluding six to eight heavier, smooth, slightly 
limbate ones in front, and a comparable num¬ 
ber of slenderer ones farther back. Neuropodia 
have vertical rows of uncinial plates. These 
plates, where best developed in middle thoracic 
segments, number about 50 in a ridge. The 
largest ones are at the ventral end of the series, 
decreasing gradually in size dorsally, so that the 
uppermost one is only about half as long as the 
lowest. The last thoracic neuropodium has only 
about 15 uncinial plates. 
The structure of the uncinial plates is such 
that their three-dimensional arrangement is dif¬ 
ficult to ascertain in any one view. As typical 
of other serpulids, they lie in a closely appressed 
row. It is difficult to dissect them out in¬ 
dividually, since there is a strong tendency for 
all of them to hold together and to spring back 
after depression. The reason for this is only 
partly that they are bound together by fleshy 
fibrils and muscles. Actually, each plate (Fig. 
12 a) is provided with a locking mechanism 
which interlaces with the plates on either side; 
