Vol.2, No.4, 192-201 (2012) Open Journal of Ecology
http://dx.doi.org/10.4236/oje.2012.24023
Polyplacophora species richness, composition and
distribution of its community associated with the
intertidal rocky substrate in the marine priority
region No. 32 in Guerrero, Mexico
Rafael Flores-Garza1*, Lizeth Galeana-Rebolledo1, Adriana Reyes-Gómez1,
Sergio García Ibáñez1, Carmina Torreblanca-Ramírez2,
Pedro Flores-Rodríguez y Arcadio Valdés González1
1Unidad Académica de Ecología Marina, Laboratorio de Ecología Costera y Sustentabilidad, Fraccionamiento Las Playas, Acapulco,
Mexico; *Corresponding Author: [e-mail]
2Doctorado en Ciencias Ambientales, Unidad de Ciencias de Desarrollo Regional, Universidad Autónoma de Guerrero. Calle Pino
s/n Colonia El Roble Acapulco, Acapulco, Mexico.
Received 31 August 2012; revised 7 October 2012; accepted 14 October 2012
ABSTRACT
The coast of Acapulco is located within the Ma-
rine Priority Region No. 32 (MPR No. 32) at the
State of Guerrero, Mexico. The National Com-
mission for the Knowledge and Use of Biodiver-
sity has stated the lack of information on marine
species that live there, among which are the
Class Polyplacophora. This study aimed to: 1)
determine species richness, 2) the community
structure based on the representative families, 3)
estimate the density, 4) locate species distribu-
tion, 5) determine their degree of occurrence
(hierarchical position) within the community, 6)
analyze the structure of length and width across
the populations and 7) estimate the diversity in-
dex. The intertidal rocky substrate at seven
beaches was sampled from 2009 to 2012. The
sampling unit 1 m2, while the area sampled was
10 m2. It was analyzed 2.548 specimens of Poly-
placophora, with 20 species identified. Tonicel-
lidae and Ischnochitonidae were the Families
better represented inspecies richness and Chi-
tonidae in abundance. Lepidochitona flectens is
a new record for the Mexican Tropical Pacific
and Stenoplax mariposa for MPR. No. 32. The
density was 25.48 specimens/m2. Eight domi-
nant species were determined. Chiton al-
bolineatus had the highest density. Ischnochiton
muscarius, Chaetopleura unilineata, Chiton al-
bolineatus and Chiton articulatus presented wide
distribution. Chiton articulatus showed the larg-
est size in length and width. H’ = 2.01 bits/indi-
vidual. Numerous dominant species were pre-
sent with broad and regular distribution, proba-
bly due to Polyplacophora body design, which
allows for better adaptation to the rigorous en-
vironmental conditions of the rocky intertidal.
Keywords: Polyplacophora; Species Richness;
Distribution; Sizes
1. INTRODUCTION
The National Commission for Knowledge and Use of
Biodiversity in spanish: Comisión Nacional para el Con-
ocimiento y Uso de la Biodiversidad (CONABIO) stated
the existence of 70 marine priority regions for the con-
servation of Mexico’s biodiversity on coastal and ocean
regions. On the coast of Guerrero, there are located four
Marine Priority Regions (MPR) which denoted the lack
of information about marine species that inhabit these
regions. Marine Priority Region No. 32 (MPR No. 32) is
one of the regions that are located on the coast of Guer-
rero and according to CONABIO, one of the major is-
sues is the lack of knowledge in the conservation and
diversity of the zone [1].
An important part of the marine fauna on the MPR No.
32 are the Polyplacophora or chitons, mollusks whose
shell is composed of eight valves hinged to each other,
most of these are herbivores, that inhabit rocky substrates,
including the intertidal zone, but also known from deep-
water [2].
Despite their diversity and abundance, chitons are
usually underestimated in mollusks faunal studies con-
ducted in Mexico, except for Chiton (Chiton) articulatus
(Sowerby, 1832) due to its commercial importance has
been the species that is largely studied [3-7], there is

R. Flores-Garza et al. / Open Journal of Ecology 2 (2012) 192-201 193
widespread ignorance about the species component of
this Class. This lack of knowledge is not only present at
marine priority regions of the State of Guerrero, but covers
most of the Mexican Pacific. This may be due to several
factors, such as the absence of commercially important
species, the cryptic habits of most species and mainly,
the difficulties of collecting in the harsh waves pounding
areas on the surf zone at rocky shores, where chitons are
abundant [8]. There are reports in the literature of Poly-
placophora with taxonomic scope and geographical dis-
tribution made in the Mexican Pacific, such as [9-12] and
those made in the Mexican coast by [6,8,13-20]. With
respect to marine priority regions on the coast of Guer-
rero, the information is based on reports mostly made in
communities where Polyplacophora mollusks are part of
all the classes analyzed [21-26].
The objectives were to improve the information on ma-
rine fauna from the MPR No. 32 and specifically on: 1)
know species richness, 2) The community structure of Poly-
placophora based on the representative families, with two
criteria: a) species richness and b) abundance, 3) density, 4)
species distribution, 5) occurrence of species by hierarchical
position within the community, 6) size by length and width
across the populations that constitute the community and 7)
estimate their diversity by Shannon-Wiener (H’) and the
index of uniformity or equity of Pielou (J’).
2. FIELD METHODOLOGY
2.1. Study Area
The MPR No. 32 (Coyuca-Tres Palos area) is located
at latitude 16˚35'24'' to 17˚28'12'' and longitude 99˚25'12''
to 100˚33' (Figure 1).
The climate is warm sub-humid, presents an average
annual temperature over 26˚C, tropical storms and hurri-
canes occur from May to November. Belongs to the
North American plate, is constituted by metamorphic
rocks and a narrow platform. It is bathed by Costa Rica
Coastal and North Equatorial Currents, receives fresh-
water input from rivers, some areas are hit by harsh high
surf waves, el Niño, red tide and other processes of tur-
bulence occurs. It is an area with a rich and abundant
biodiversity: mollusks, polychaetes, echinoderms, crus-
taceans, turtles, fish, birds, marine mammals, endemic
fish and mangrove, and is an important bird feeding area.
There are also regulatory issues; ignorance of current
regulations for the use of resources and illegal fishing is
frequent. This region has particular importance since
represents an area for several zoological groups with
respect to conservation, especially birds and their diver-
sified habitat, and the potential impact by tourism and
the lack of information on this issue [1]. Acapulco is
located in the RMP No. 32, has a coastline of 62 km. and
almost the entire intertidal zone is constituted of bedrock.
2.2. Fieldwork
Sampling was conducted from 2009 to 2012 at seven
sites: Parque de la Reina, Tlacopanocha, Majahua, Muelle,
Manzanillo, La Angosta and Pie de la Cuesta. Geo-
graphical coordinates was registered for each site and
described according to the following criteria: approxi-
mate length of the sampling area, the substrate structure
and stability, rock type, and wave exposure of the sub-
strate. Descriptions of the collection sites were based on
[27], geological maps of the National Institute of Statis-
tics, Geography and Informatics “Instituto Nacional de
Estadística, Geografía e Informática” INEGI (Acapulco
maps E14-11, 1:50,000), and complemented with field
observations (Table 1).
The sites may change with the type of substrate, its
stability and exposure to wave impact; and were classi-
fied as Type of substrate: a) Rock masses: fixed struc-
tures such as walls, cliffs, terraces, and alike. b) Large
boulders: unattached rocks larger than 50 cm, immovable
or difficult to move by the wave’ simpact. c) Rolled
boulders: loose rock smaller than 50 and greater than 8
cm. that can easily be moved by the impact of the waves.
d) Gravel: loose rocks o pebbles no larger than 8 cm. The
substrate stability was classified as: a) high: when the
substrate remains practically unchanged by the impact of
waves, b) middle: when basically does not change the
configuration of the substrate by the waves impact but
there is some rock displacement, c) low: when the site
configuration changes by the impact of waves, most of
rocks are moved. Wave exposure was classified as: a)
High: when waves hits the substrate directly, unprotected,
b) Middle: when the wave impact on the substrate is sof-
tened or hampered by barriers and c) Low: when the wave
does not hit directly, since the sites are protected by dif-
ferent types of barriers.
Sampling was conducted on new moon, in the months
of low rainfall and drought, where the tide is shallow and
allows collecting on the intertidal zone. For the quantifi-
cation of the organisms, a sampling area of 10 m2 was
established. The sampling unit was 1 m2 1/2 inch vinyl
polychloro frame, randomly selected the starting point
where the frame was placed parallel to the coast, by set-
ting the place with a rope of 30 mts length, to provide
continuity and representation of the area. All specimens
of Polyplacophora found alive within the sampling unit
were collected. Completed the collection of the first
sampling unit, a two meters transect down the rope was
allowed, and then again the vinyl polychloro frame was
placed. This system was repeated until the 10 m2 total
was sampled on each time. The specimens collected were
preserved with 96% ethyl alcohol and labeled. The jars
with specimens were transferred to the laboratory to be
identified and quantified for further work.

R. Flores-Garza et al. / Open Journal of Ecology 2 (2012) 192-201
194
Figure 1. Illustration of the Marine Priority Regions, including No. 32, at the State of Guerrero, Mexico, which includes the
study area.
Table1. Sampling sites considered in the study, indicating the location and relevant characteristics of the habitat.
Coordinates
Site
Latitud N Longitud W
Length
of the Site
Type of
Substrate
Type of
Rock
Substrate
Stability
Wave
Exposure
1 Parque de
la Reina 16˚50'58.27" 99˚54'01.85" 66.74 metrosRolled boulders and gravel
Artificial substrate
(construction rubble)and
igneous rocks
Low Middle
2 Tlacopanocha 16˚50'41.53" 99˚54'25.02" 200 metrosLarge boulders and
gravel
Artificial substrate
(construction rubble)and
igneous rocks
Media Middle
3 Majahua 16˚50'58.27" 99˚54'01.85" 600 metros
Large boulders and
rolled
boulders
Metamorphic High Low
4 Muelle 16˚50'56.86" 99˚54'02.39" 60 metros
Large boulders and
rolled boulders
Metamorphic rocks and
artificial substrate
(construction rubble)
Media Middle
5 Manzanillo 16˚50'27.90" 99˚54'38.14" 22.87 metrosRolled boulders and
gravel
Metamorphic and
artificial substrate
(construction rubble)
Low Low
6 La Angosta 16˚60'29.86" 99˚54'55.70" 48.14 metrosRock masses and
rolled boulders Metamorphic rocks High High
7 Pie de la
Cuesta 16˚52'25.64" 99˚56'34.64" 66 metros Rock masses and rolled boulders Metamorphic rocks High High

R. Flores-Garza et al. / Open Journal of Ecology 2 (2012) 192-201 195
2.3. Laboratory Work and Analysis
Species identification was based on [10-12] and for
systematic classification on [28]. The specimens col-
lected were counted, identified, length and width meas-
ured (mm) and subsequently registered at the Mollusk
Collection on the Academic Unit of Marine Ecology at
the Autonomous University of Guerrero (“Colección de
Moluscos de la Unidad Académica de Ecología Marina
de la Universidad Autónoma de Guerrero”) and also
deposited in the National Collection of Mollusks in the
Malacology Laboratory, National Institute of Biology, of
the National Autonomous University of Mexico (“Colec-
ción Nacional de Moluscos en el Laboratorio de Mala-
cología del Instituto Nacional de Biología, Universidad
Nacional Autónoma de México”).
Richness was measured based on the number of
species found per sample. The community structure was
analyzed using the representation of families, which was
evaluated based on species richness (amount of species
per family) and abundance of organisms per family and
expressed in percentage. The density is measured by esti-
mating the average amount of specimens per m2. Species
distribution of Polyplacophora, was interpreted as cri-
terion on the percentage of sites at which a species was
present (frequency of occurrence) and graded as follows:
a) Wide distribution when the species is present at least
in six sites, b) Regular distribution when the species was
collected in four or five sites, c) Limited distribution when
the species is found in two or three places and d) Ir-
regular distribution when the species was only found in
one place. Occurrence of the species (hierarchical posi-
tion) within the community, was determined using the
method of Olmstead-Tukey correlation, represented by
the quadrant graphs [29], which was based on two esti-
mators, one was the average of relative abundance of all
species expressed in the logarithm of abundance +1, and
two, the average frequency of occurrence (expressed in
percentage) of all the species represented in the sample.
The percentage of frequency graphically analyzed the
occurrence of each species (x axis) against the averaged
percentage of relative abundance of each species, ex-
pressed in log abundance +1 (y axis). The dominant spe-
cies were those whose values of abundance and fre-
quency of occurrence exceeded the average of both esti-
mates. Constant species were those whose abundance
value, did not exceed the average value of the total abun-
dance, but exceeded the average estimate for the frequen-
cy of occurrence. Numerous little frequent species were
characterized by having their abundance value higher
than the estimated average value for the abundance and
frequency of occurrence value did not exceed the esti-
mated average value for this variable. The occasional
species were those that their value of abundance and
frequency of occurrence did not exceed the arithmetic
mean of estimated frequency of occurrence and abun-
dance. The analysis of sizes and structure of the popu-
lations of chitons, was performed by measuring the length
and width expressed in millimeters and obtaining the
values of descriptive statistics such as maximum, mini-
mum, mean and standard deviation. To measure the length
of the chitons was performed from girdle from the ante-
rior cephalic plate, to the posterior region in the anal
plate, the width is measured from side to side of the
girdle between the fourth and fifth plate [19]. For these
purpose a digital caliper Vernier type (precision 0.01 mm)
was used. The diversity was assessed by the Shannon-
Wiener index (H’) and the index of uniformity or equity
of Pielou (J’).
3. RESULTS
2548 Polyplacophora specimens were sampled in the
MPR No. 32. Twenty species from 10 genera and six
families were identified. The best represented families in
terms of species richness were Tonicellidae with one
genus and six species, followed by Ischnochitonidae with
three genera and five species. The best represented fam-
ily on richness was Chitonidae with 70.95% of the col-
lected specimens, and the least abundant was Acantho-
chitonidae with 0.11% (Table 2). On the inventoried
analysis, two species were identified as new record for
the MPR No. 32: The first of them, Lepidochitona (Den-
trochiton) flectens (Carpenter, 1864) which inhabits at
the rock masses and boulders, with metamorphic type of
rock, and high wave exposure. The material analyzed is
of one specimen, which measured 8.95 mm long and 5.5
mm wide. The second species as a new record, was
Stenoplax (Stenoplax) mariposa (Bartsch MS, Dall, 1919);
the habitat for this was pebbles and gravel, the substrate
of artificial type represented by construction rubble and
debris characterized by concrete remains of floors and
columns, mixed with igneous rock, and with middle wave
exposure. The specimen measured 7.65 mm and 5.55
mm wide. For the whole region it was estimated a den-
sity of 25.48 specimens per m2. Parque la Reina was the
site with highest density, 66.9 specimens per m2, and the
lowest one happened at Manzanillo with 4.5 specimens
per m2. The species that showed the highest density was
Chiton (Chiton) albolineatus Broderip & Sowerby, 1829,
followed by Ischnochiton (Ischnochiton) muscarius (Reeve,
1847) (Table 2).
With respect to geographical distribution in the MPR
No. 32, species of wide distribution were I. muscarius,
Chaetopleura (Chaetopleura) unilineata Leloup, 1954, C.
articulatus and C. albolineatus found in six of the seven
sites sampled, five species were found with regular dis-
tribution, eight species were of limited distribution and
three species with irregular distribution (Table 3, Figure
2).

R. Flores-Garza et al. / Open Journal of Ecology 2 (2012) 192-201
196
Table 2. Species richness, relative abundance per family, density by species and descriptive statistics across Polyplacophora in the
Marine Priority Region No. 32, at Guerrero, Mexico.
Length (mm) Width (mm)
Families/Species A/F Den
Mín Máx MedS.D. Mín Máx MedS.D.
Ischnochitonidae
Ischnochiton (I.) muscarius (Reeve, 1847) 2.78 3.57 27.71 14.425.18 2.60 15.86 8.993.13
Stenoplax (S.) limaciformis (Sowerby, 1832) 0.56 4.25 2.54 14.916.69 2.04 10.26 5.111.85
Stenoplax (S.) rugulata (Sowerby, 1832) 0.04 5.33 6.13 5.730.56 2.76 3.63 3.190.61
Stenoplax (S.) mariposa (Bartsch MS, Dall, 1919)* 0.01 7.65 7.65 5.55 5.55
Lepidozona (L.) serrata (Carpenter, 1864)
14.36%
0.27 4.96 10.17 6.431.78 2.96 3.99 3.660.47
Callistoplacidae
Callistochiton elenensis(Sowerby, 1832) 0.2 4.39 11.66 7.501.76 2.44 5.70 4.141.10
Callistoplax retusa (Sowerby in
Broderip & Sowerby, 1832)
3.53%
0.7 4.55 24.07 13.624.98 2.37 9.00 5.641.40
Chaetopleuridae
Chaetopleura (C.) hanselmani (Ferreira 1982) 0.04 3.17 31.84 19.309.96 2.31 2.95 2.630.45
Chaetopleura (C.) unilineata Leloup, 1954 0.51 5.60 23.59 11.445.19 3.81 14.44 8.314.05
Chaetopleura (C.) lurida (Sowerby in
Broderip & Sowerby, 1832)
9.85%
1.96 5.11 30.97 18.434.66 4.37 17.98 11.132.87
Chitonidae
Chiton (C.) articulatus Sowerby, 1832 1.89 6.09 50.74 22.839.39 3.69 28.70 13.765.58
Chiton (C.) albolineatus Broderip & Sowerby, 1829 16.01 3.18 33.61 17.567.00 2.09 14.46 12.566.15
Tonicia forbesii forbesii Carpenter, 1857
70.95%
0.18 6.32 39.58 19.356.02 8.56 19.79 13.993.61
Tonicellidae
Lepidochitona (L.) salvadorensis (García-Ríos, 2006) 0.12 6.01 13.77 9.392.65 3.96 6.43 5.080.97
Lepidochitona (L.) beanii Carpenter, 1857 0.05 6.12 6.28 6.200.11 3.01 3.77 3.390.53
Lepidochitona (L.) hartwegii (Carpenter, 1855) 0.01 4.50 4.50 2.77 2.77
Lepidochitona (L.) flectens(Carpenter, 1864)* 0.01 8.95 8.95 5.05 5.05
Lepidochitona sp. 1 0.07 6.50 24.07 14.164.51 2.79 5.53 4.060.99
Lepidochitona sp. 2
1.17%
0.04 3.43 8.46 5.272.21 2.22 4.25 3.810.89
Acanthochitonidae
Acanthochitona arragonites (Carpenter, 1857) 0.11%0.03 6.12 8.37 6.951.02 3.78 6.12 4.951.65
*New report; A/F Abundance per family; Den = Density (Specimens/m2); mm = millimeters; Min = Minimum; Max = Maximum; Med = Media; S.D. = Standard
Deviation.

R. Flores-Garza et al. / Open Journal of Ecology 2 (2012) 192-201 197
Table 3. Distribution type by frequency of occurrence of species of Polyplacophora in the Marine Priority Region No. 32 Guerrero,
Mexico.
Collecting Sites
Species A B C D E F G
Type of
Distribution
Degree of
Appearance
I. muscarius X X X X X X Wide Dominant
S. limaciformis X X X X X Regular Dominant
S. rugulata X X X Limited Occasional
S. mariposa X Irregular Occasional
L. serrata X X X Limited Constant
C. elenensis X X X X Regular Dominant
C. retusa X X X X X Regular Dominant
C. hanselmani X X Limited Occasional
C. unilineata X X X X X X Wide Dominant
C. lurida X X X X X Regular Dominant
C. articulatus X X X X X X Wide Dominant
C. albolineatus X X X X X X Wide Dominant
T. forbesii forbesii X X X X Regular NPF
L. salvadorensis X X
Limited Occasional
L. beanii X X X Limited Occasional
L hartwegii X Irregular Occasional
L. flectens X Irregular Occasional
Lepidochitona sp. 1 X X Limited Occasional
Lepidochitona sp. 2 X X X Limited Occasional
A. arragonites X X X Limited Occasional
Density of specimens/m2 21.2 66.9 9.5 19.9 4.5 27.97.9
A: Tlacopanocha; B: Parque de la Reina; C: Majahua; D: Manzanillo; E: Parque de la Reina Muelle; F: La Angosta; G: Pie de la Cuesta; X = Presenceat the site.
Figure 2. Distribution type by frequency of occurrence of spe-
cies of Polyplacophora in the Marine Priority Region No. 32
Guerrero, Mexico.
The degree of occurrence of the species (hierarchical
position) in the community, found that eight were domi-
nant, one was constant, one was numerous little frecuent
and 10 were casual (Table 3, Figure 3).
Figure 3. Polyplacophora degree of occurrence by hierarchical
position in the Marine Priority Region No. 32 of Guerrero,
Mexico.
The largest species was C. articulatus with 50.74 mm
(minimum = 6.9, mean = 22.83 and standard deviation =
9.39 mm) and the smallest one was Chaetopleura
(Chaetopleura) hanselmani (Ferreira, 1982) measured

R. Flores-Garza et al. / Open Journal of Ecology 2 (2012) 192-201
198
3.17 mm and (maximum = 31.84 mm, mean = 19.30 mm
and standard deviation = 9.96). The species with largest
width was C. articulatus, with 28.77 mm (minimum =
3.69 mm, mean = 13.76 mm and standard deviation =
5.58) and Stenoplax (St e noplax) limaciformis (Sowerby,
1832) showed the lowest height which was of 2.04 mm
(maximum = 10.26 mm, mean = 5.11 mm and standard
deviation = 1.85) (Table 2).
The diversity index value of Shannon-Wiener (H’)
calculated for the MPR No. 32 was H’ = 2.01 bits/indi-
vidual, while the value of uniformity or equity index of
Pielou (J’) was J’ = 0.45
4. DISCUSSION
4.1. Species Richness
We found agreement with the reports made to the
Mexican Pacific shores where have analyzed the Class
Polyplacophora [6,13-22,24,30], have found in the MPR
32 to the following species: I. muscarius; S. limaciformis;
S. mariposa; Stenoplax (St e nop l a x) rugulata (Sowerby,
1832); Lepidozona (Lepidozona) serrata (Carpenter,
1864); Callistochiton elenensis (Sowerby, 1832); Callis-
toplax retusa (Sowerby in Broderip & Sowerby, 1832);
Chaetopleura (Chaetopleura) lurida (Sowerby in Brode-
rip & Sowerby, 1832), C. hanselmani, T. forbesii forbesii
Carpenter, 1857; C. albolineatus, C. articulatus; Lepi-
dochitona (Lepidochitona) salvadorensis (García-Ríos,
2006); Lepidochitona sp.; Lepidochitona (Lepidochitona)
beanii Carpenter, 1857 and Acanthochitona arragonites
(Carpenter, 1857). And species reported by them and not
found in the MPR No. 32 were: Ischnochiton sp. Ischno-
chiton (Ischnochiton) tridentatus Pilsbry, 1893; Steno-
plax (Stenoplax) corruguta (Carpenter in Pilsbry, 1892);
Lepidozona (Lepidozona) clathrata (Reeve, 1847); Lepi-
dozona (Lepidozona) clarionensis Ferreira, 1983; Lepi-
dozona (Lepidozona) rothi Ferreira, 1983; Callistochiton
infortunatus Pilsbry, 1893; Callistochiton sp. Chiton (Chi-
ton) virgulatus Sowerby, 1840; Chiton (Chiton) stokesii
Sowerby, 1832; Chaetopleura mixta Dall, 1919; Chae-
topleura scabricula (Sowerby, 1832); Nuttallina crossata
(Berry, 1956); Acanthochitona avicula Carpenter, 1864;
Acanthochitona exquisite Pilsbry, 1893 and Lepidochi-
tona (Lepidochitona) keepiana Berry, 1948 .
Previous reports on the MPR No. 32, which discusses
the Class Polyplacophora were those of [21,23,25,26,32,
33] and were in agreement with the following species: I.
muscarius, S. limaciformis; S. rugulata, L. serrata, C.
elenensis, C. retusa; Chaetopleura (Chaetopleura) uni-
lineata Leloup, 1954; C. hanselmani, C. lurida, C. ar-
ticulatus, C. albolineatus, T. forbesii forbesii; Lepido-
chitona sp. 1; Lepidochitona sp. 2; L. salvadorensis, L.
beanii, L. hartwegii and A. aragonites; and their reported
species not found in our work were Radsiella triden-
tata Pilsbry, 1893 and Stenoplax conspicua sonorana
Berry, 1956.
Species richness of Polyplacophora found for the MPR
No. 32 on this research was higher than that reported for
other sites in the state of Guerrero and the Mexican
Tropical Pacific, and corresponds to that expected in a
tropical zone characterized by slight variations in tem-
perature, complex bedrock that varies greatly from
gravel to large blocks, creating different habitat spaces
where many organisms can live in.
In the samples analyzed L. flectens was identified,
which is a new to the coast of Guerrero and first time
record for the Mexican Tropical Pacific; Its known dis-
tribution is along the west coast of North America, be-
tween latitudes 53˚N (Hot Springs Island, off Queen
Chalotte Island, British Columbia and 30˚N (San
Geronimo Island of the Baja California, Mexico); its
distributional depth goes from the intertidal zone to 38m
deep [10]. The new location where found was in Pie de la
Cuesta (16˚52'25.64" N latitude and 99˚56'34.64" W lon-
gitude). Also recorded for the first time in the MPR No.
32 was S. mariposa, its distribution reported was at the
low intertidal zone. Previously reported from subtidal
and shallow shores, as in many locations along the Pa-
cific coast of Baja California, as at Punto Malarritmo,
Sebastian Vizcaino Bay to San Felipe in the Gulf of
California and southward to along the coast of Mexico,
recorded on Cholla Bay, Sonora, Cabo Corrientes, Jali-
sco, Revillagigedo Islands, Colima and coral reefs of
Oaxaca [8,9,11,20,34,35]. The new location was at Par-
que La Reina (16˚50'58.27"N latitude and 99˚54'01.85"W
longitude).
One reason to have a thorough knowledge of the dis-
tribution of species is that it allows the precise determi-
nation of suitable habitat for each of them. It is important
getting to know the habitat requirements and availability
for species in a region, since makes it possible to assess
the population status of the species in the spatial and
temporal context. Also a precise knowledge of the dis-
tribution of species facilitates the identification of prior-
ity areas for conservation. Moreover, the inventory may
provide more arguments to justify the conservation of
important areas for conservation or reserves [36].
4.2. Community Composition Based on the
Representation of Families
In previous reports such as [21-24] mentioned that the
Chitonidae family as the one with best represented in
number of species and abundance. Regarding species
richness [25] listed Ischnochitonidae; and Tonicellidae
was mentioned by [26] as best represented. This study
also found Chitonidae as best represented family in
abundance; and agreed with [26] in which the family
Tonicellidae proved to be best represented in terms of

R. Flores-Garza et al. / Open Journal of Ecology 2 (2012) 192-201 199
species richness. Chitonidae and Tonicellidae therefore
are considered the representative families of the bedrock
at MPR No. 32.
4.3. Density
[25] Reported a density of 30.91 specimens/m2 of
Polyplacophora in three beaches of Acapulco, which is
very similar to this study.
[21-24] reported as the most abundant species C. ar-
ticulatus. [25,26,37] reported I. muscarius, C. retusa, C.
lurida, C. albolineatus and C. articulatus as those with
high density. This research coincides with the above men-
tioned authors that the species I. muscarius, C. articu-
latus, C. albolineatus and C. lurida as those with high
population density and therefore are considered to be as
the representative species of Polyplacophora at the inter-
tidal rocky substrate of the MPR No. 32.
The difference with other reports made to various sites
in the state of Guerrero in terms of species richness and
density representation of families is due to the substrate
structural nature of the seven sites sampled, which to-
gether represent the different types of environments and
a wide variety of habitats. Another element to consider is
the method of collection used, since the area at the sam-
pling unit was carefully checked, which was possible due
to the size of the area sampled and the characteristics of
easy accessibility of staff to the sites, further that most of
the sites have middle or low wave intensity.
4.4. Geographic Distribution
[8] study on the distribution of chitons made in field-
work and visits to formal collections and literature review,
reported 23 species of Polyplacophora distributed in the
Mexican Tropical Pacific coast, from which in this study
11 species in MPR No. 32 were found, which are: I.
muscarius , S. limaciformis, C. elenensis, C. retusa, C.
lurida, C. unilineata, C. hanselmani, C. articulatus, C.
albolineatus, T. forbesii forbesii and L. beanii. The
species reported by these authors and were not found in
the region are: Leptochiton (Leptochiton) alveolus (Lovén
1846, ex M. Sars); Leptochiton belknapi Dall, 1878; Lep-
tochiton incorgruuns Dall, 1908; Stenoplax (St e n opla x )
boogii (Haddon, 1886), L. clathrata; Lepidozona (Lepi-
dozona) formosa Ferreira, 1974; L. rothi; Lepidozona
(Lepidozona) skoglundi (Ferreira, 1986); Callistochiton
expressus (Carpenter, 1865); Callistochiton colimensis
(Smith, 1961), C. angelica and Acanthochitona stokesii
Dall, 1919; the latter was reported by [35] as widely
distributed species in the Mexican Pacific.
Species that found by [26] in the MPR No. 32 were S.
rugulata, L. serrata, L. hartwegii, L. salvadorensis, Lepi-
dochitona sp. 1, Lepidochitona sp. 2 and A. arragonites.
This study reports for the first time L. flectens for the
Mexican Tropical Pacific and S. mariposa for MPR No.
32.
[24] reported C. articulatus as widely dispersed on the
coasts of Guerrero because it was found in nine beaches
in the three coastal regions where his study was
conducted. This study further the chitons C. articulatus
was found to be widespread in the MPR No. 32, and
three species more: I. muscarius, C. unilineata and C.
albolineatus.
4.5. Hierarchical Status
With respect to the degree of species occurrence (hier-
archical position), [26] reported that Polyplacophora
represented 47.05% of the dominant species. Our find-
ings are in agreement with it on the percentage of domi-
nant species. It also agrees that I. muscarius, C. retusa, C.
lurida, C. articulatus, C. albolineatus and T. forbesii
forbesii, were the dominant species. In this investigation,
S. limaciformis, C. elenensis, C. elenensis and C. uni-
lineata also classified as dominant.
The set of dominant species were considered as repre-
sentative of the community of rocky intertidal Polypla-
cophora MPR No. 32.
By the number of Polyplacophora species considered
as representative, we believe that these organisms are
well adapted to environmental conditions of the rocky
intertidal, which is reflected in their design of its body
(flat, oval, articulated sections, belt, and large muscular
foot) is quite efficient to move and withstand the extreme
conditions of this environment.
4.6. Size Structures
Information on the size structure of C. articulatus as
commercially important species was mentioned by [3,4,
38,39]. Regarding to size structure for other chiton spe-
cies, [38] reports that, no biometric information was found
for other than C. articulatus. On size structure on the
community, reports by [26,37] mentioned C. articulatus
and T. forbesii forbesii with greater size. The present
study is consistent with the reports above mentioned.
These relationships enable biometric estimates such as
condition factor and growth rate for any individual, and
enable the estimations of different coefficients, which
can then be compared to others obtained in the future.
4.7. Diversity Index
[25,37] reported high diversity indices similar to those
estimated in this study. The diversity and equity index
here reported indicate, the MPR No. 32 has a highly di-
versified community.

R. Flores-Garza et al. / Open Journal of Ecology 2 (2012) 192-201
200
5. ACKNOWLEDGEMENTS
This work was partly funded by CONACYT (Consejo Nacional de
Ciencia y Tegnología-National Council of Science and Technology)
and the state government of Guerrero through the research project No.
91624 Ecological study of the Acapulco Bay FOMIX 2008-C01 and the
research project No. 91724 Diversity and abundance of marine cock-
roach off the coast of Guerrero state Fomix 2008-C01.
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