Robb
Diet of Cyanoplax
page 2
INTRODUCTION
Although chitons are abundant along California shores,
studies of their food and feeding have been limited largely
to species of Mopalia (e.g. Barnawell, 1960; Boolootian, 1964).
Placiphorella (see McLean, 1962), and Cryptochiton (Macginitie
and MacGinitie, 1968). The purpose of this study was to
examine the diet of the chiton Cyanoplax hartwegii (Carpenter,
1855) in different habitats. I also include a few notes on
the slit formula of the plates of C. hartwegii.
Intertidal Habitats of Cyanoplax hartwegii.
Cyanoplax hartwegii on the Monterey Peninsula, California,
is found in the mid and upper intertidal zones. Three
general habitats where large numbers of C. hartwegii were
present were studied.
First, at approximately the +2.0 ft. tide level, C.
hartwegii was most common underneath the brown alga Pelvetia
fastigiata (J. G. Agardh) DeToni on otherwise nearly bare
rock in an area of low wave action. Here Pelvetia covered
approximately 70% of the rock area, providing a shady and
moist environment even during daylight hours and at low tide.
Because of shading by algae and by other rocks, only about 5%
of the rock was exposed to sunlight at low tide. Pelvetia
was by far the dominant alga; small amounts of Hildenbrandia
occidentalis Setchell, Petrocelis franciscana Setchell and
Gardner, Gigartina papillata (C.A. Agardh) J. G. Agardh,
Fucus distichus Linnaeus, and crustose corallines were also
RoBb
Diet of Cyanoplax
page 4
using Smith (1944) and were verified by Dr. I. A. Abbott.
The digestive diverticulum was not extensively examined since
several dissections yielded only blue green algae and yeast
cells.
Specimens of Cyanoplax hartwegii were identified as
such on the basis of size, color, shape, insertion plate
slit formula, and comparison with museum specimens of C.
hartwegii and Cyanoplax dentiens (Gould, 1846) identified by
Allyn G. Smith and kindly provided by the California Academy
of Sciences. Average insertion plate slit formulas (11-1-11
for C. hartwegii, 11-1-10 for C. dentiens) proved unreliable
for identification. In specimens conforming to C. hartwegii
in all other respects, numbers of slits ranged 9-12 in the
head valve and 8-11 in the tail valve (Fig. 1). The formula
11-1-10 occurred most often, which is the slit formula
given for C. dentiens.
SSULTS
The results of the gut content analyses of 65 Cyanoplax
hartwegii from the various habitats are shown in Figures 2
and 3.
Since Pelvetia made up 70% of the plant cover of the
Pelvetia habitat, it is not surprising that the 18 Cyanoplax
hartwegii taken here ate large amounts of this alga. Pelvetia
occurred in 89% of the digestive tracts and comprised the bulk
Robb
Diet of Cyanoplax
page 5
of the material in each individual. Hildenbrandia occidentalis,
and Petrocelis franciscana were found in much smaller
quantities in many individuals.
In the crevice habitat where Pelvetia was absent,
Cyanoplax hartwegii ate moderate amounts of Hildenbrandia,
Petrocelis, Endocladia, and Cladophora spp. The relative
quantities of these algae in the digestive system varied in
the 17 individuals examined, but for the population as a whole
they occurred in roughly equal amounts in the total gut content.
In the tidepool habitat the 30 Cyanoplax hartwegii
examined displayed a more varied diet. Gigartina leptorhynchos
appeared in many Cyanoplax here, but many other algae were
present in small quantities, including crustose corallines.
Even when Gigartina and crustose corallines were present in
the Pelvetia habitat and crevice habitat, they were not eaten.
Thus, it would appear that there is a preference for Pelvetia,
Hildenbrandia, Petrocelis, Endocladia, and Cladophora spp.
when these are present.
In the gut of C. hartwegii, larger algal species (e.g.
Pelvetia) and encrusting algae (e.g..Hildenbrandia) appear
in very small pieces indicating feeding by rasping. However,
algae with slender branches or highly dissected blades (e.g.
Endocladia muricata, Gigartina leftorhynchos) appear in the
gut much larger pieces, reminiscent of algal fragments found
in the guts of Nuttallina californica (Reeve, 1847) by
Robb
Diet of Cyanoplax
page 6
Nishi (1974), and suggestive of feeding by biting or tearing
algal branches.
SUMMARY
1. Stomach contents were examined in 65 specimens of Cyanoplax
hartwegii taken from three different intertidal microhabitats
near Monterey, California.
2. In the Pelvetia bed habitat, Pelvetia made up 80% of the
total diet, while in the higher crevice habitat, the algae
Hildenbrandia, Endocladia, Petrocelis, and Cladophora spp.
comprised 90% of the diet and were eaten in relatively
equal amounts.
3. In the high tidepool habitat, C. hartwegii ate a much
wider variety of algae.
Gigartina and Hildenbradia together
made up 40% of the diet. Crustose corallines and Gigartina
occurred in all habitats examined, but were eaten by Cyanoplax
only in the tidepools.
ACKNOWLEDGMENTS
I would like to express my thanks to Dr. Isabella A.
Abbott for technical help in all aspects of the gut content
analysis and identification of algae. My appreciation cannot
be measured. Her guidance in all areas of the study, and her
insight and beauty as a sincere, warm human being made my time
at Hopkins Marine Station an experience I will never forget.
Robb
Diet of Cyanoplax
LITERATURE CITED
Barnawell, Earl B.
1960. The carnivorous habit among the Polyplacophora.
Veliger 2(4): 85-88, pl. 19.
(1 Apr 1960)
Boolootian, Richard A.
1964. On the growth, feeding, and reproduction in the
chiton Mopalia muscosa of Santa Monica Bay.
Helgolander wiss. Meersunters. 11: 186-199; 3 figs.
(Dec 1964)
McLean, James H.
1962. Feeding behavior of the chiton Placiphorella.
Proc. Malacol. Soc. 35(1): 23-26, figs. 1 & 2.
(Apr 1962)
MacGinitie, G. E., and Nettie MacGinitie.
1968. Notes on Cryptochiton stelleri (Middendorf, 1846).
Veliger 11(1): 59-61, pl. 6.
Nishi,
Rae.
1974. The diet and feeding habits of Nuttallina
californica (Reeve, 1847) from two contrasting
habitats in central California with notes on their
natural histories.
Veliger.
page 7
Mark Robb
page 2
Diet of Cyanoplax
Figure Captions
Figure 1. Number of Cyanoplax hartwegii with a specific slit formula.
Figure 2. Ihe percentage of the total number of guts where a specific alga
chitons from
was found inthree
habitats.
Figure 3. The percent occurrence of the dominant algae in the total gut
of chitons from
three
content
habitats.
SNenter op Cjono pos vitk sgerttie sit formila
no S heao valve
23
o0
Figure 1
Mark Rebb
Jo Occorrance of
Léggool kabrtt
10 20 2040 90 601000 00 k
——
20 o
12070 ildenbvaudt
0% toeels
0% Endocladu
10% Gronta
10% Chach merghe
5% Crustosz cotalline
5% Palfse
10% oher
Dmmant Akge in Qudt
Crevice habites
Pleha kabtt
30 40 9 10 70 80 40 100
20 2040 9 40 7 20 70 10
—
209 Reto
30% Hildenbande
10% Hildenbrandia
—20% Rtoocelis
16% Rlocelis
—20% Endoelade
20% Clado pheca
16% other
10% ater
tigyre 3
Alga Hound
o guts wilk Specifi
o-age
70 8010 00
20 40 S60 70 80 40 100
O 2O304056
10 20

— — | — — | — | — —  —
—



—.- --—
Cladophora 29.



e
—-
—




Choetomohe
elis fronciscara



— —
+-
—

tteromopha sp.

Goia nnicate

—


nela
Ehtoclodig eiaens

ndionalis
Setchell and Gardner
enberg ard Abboff
— —
Gomontia polyrhiza


dium 50
(Logerheim) Bornet and Hahaut

g 3

idiaia minima

(kgeli) Kglin

UWe 2p.
—
bse cotallines
— —
Beudoubella consoeiato
Setchell ard Gardrer
kaaaaa-
ina 7.
—
—
Pelveha fastgase
pysalis
eneghie:) Drouct and Delg
——
— —



Lalssia 39.
labria sp.
—
Leahese 2p.


waria 59
—


este
-18
cide Coickie):
Rhena habitar

os0ad 5.
7
Crevice habitat


oms
—



ge Sicules

Tdz pool Fobtt
1-
tote Ne
Figure 2