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Population size structure and abnormalities in the number

of rays of the Sea Star Pentaceraster cumingi (Valvatida: Oreasteridae)

in Bahía Chamela, Mexican Pacific

Cristian Moisés Galván-Villa

* & Francisco Alonso Solís-Marín

1. Laboratorio de Ecosistemas Marinos y Acuicultura, Departamento de Ecología Aplicada, Centro Universitario

de Ciencias Biológicas y Agropecuarias, Universidad de Guadalajara, Camino Ramón Padilla Sánchez No. 2100,

Nextipac, Zapopan, Jalisco, México. C.P. 45200; cristian.galvan@academicos.udg.mx

2. Colección Nacional de Equinodermos “Dra Ma. Elena Caso Muñoz”, Laboratorio de Sistemática y Ecología de

Equinodermos, Instituto de Ciencias del Mar y Limnología (ICML), Universidad Nacional Autónoma de México, Av.

Ciudad Universitaria 3000, Coyoacán, Ciudad de México, México. C.P. 04510; fasolis@cmarl.unam.mx

* Correspondence

Received 28-VII-2020. Corrected 20-XI-2020. Accepted 27-XI-2020.

ABSTRACT. Introduction: The Panamic Cushion Star Pentaceraster cumingi is widely distributed along the

Tropical Eastern Pacific. This species strictly produces only five arms, but sometimes, this number varies or

show another kind of abnormality. Objective: We aimed to evaluate the population size structure and abnormali-

ties occurrence in the radial pattern of P. cumingi in Bahía Chamela, Jalisco, Mexico. Methods: The population

was monitored along four years (2016-2019), in two seasonal periods (warm and cold). During fieldwork, a

random sample of individuals was collected. Every starfish was measured, weighted, and evaluated to identify

any abnormality on its radial pattern. Results: The highest density of P. cumingi was found in October 2019

(2.03 ± 0.05 ind/m

-2

), the lower in March 2017 (0.66 ± 0.13 ind/m

-2

). A total of 849 individuals were collected.

For 5-armed starfishes, the average length was 123.8 ± 15.2 mm and the average weight of 326.0 ± 62.4 g. The

most frequent length classes ranged from 110 to 120 mm. Of the total of individuals sampled 0.82 % had four

arms, 1.06 % six, and 1.41 % had one bifurcated arm. Conclusions: There were differences in the population

density and size structure of P. cumingi between seasons. The main causes of abnormalities in the starfish could

be due to the changes that occur during larval metamorphosis or by an abnormal regeneration of the arms after

a predation attempt.

Key words: Sea star; abnormality; density; echinoderm; structure size; Tropical Eastern Pacific.

Galván-Villa, C.M., & Solís-Marín, F.A. (2021). Population size structure and abnormalities

in the number of rays of the Sea Star Pentaceraster cumingi (Valvatida: Oreasteridae)

in Bahía Chamela, Mexican Pacific. Revista de Biología Tropical, 69(1), 262-273.

DOI 10.15517/rbt.v69i1.43239

ISSN Printed: 0034-7744 ISSN digital: 2215-2075

Echinoderms are an ancient lineage of

invertebrates that exhibit primitive characters

like autotomy, regeneration, radial symmetry,

and asexual reproduction (James, 1999). The

asteroids (sea stars or starfishes) are present

in many different marine environments, from

deep abyssal depths to the intertidal zone, from

the tropics to the poles (Mah & Blake, 2012;

O’Hara & Byrne, 2017; Diupotex-Chong,

Solís-Marín, & Laguarda-Figueras, 2017).

Although asteroids are not typically abundant

in marine ecosystems, they influence biodi-

versity, population dynamics, and can exert

control on community structure as predators in

intertidal and subtidal ecosystems (Lawrence,

2013; Menge & Sanford, 2013).

Starfish exhibit usually a pentameral sym-

metry, although numerous-armed starfish have

DOI 10.15517/rbt.v69i1.43239

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between six to 40 rays (Hotchkiss, 2000a), e.g.,

Heliaster helianthus (Lamarck, 1816), Pyc-

nopodia helianthoides (Brandt, 1835), Acan-

thaster planci (Linnaeus, 1758). Starfish rays

exhibit a great variety of functions like loco-

motion (Migita, Mizukamib, & Gunji, 2005;

Lawrence, 2013), to force open the shells of

mollusks (Lavoie, 1956), parental care (Chia,

1966; Hamel & Mercier, 1995), food detec-

tion (Lawrence, 1987; Moore & Lepper, 1997;

Dale, 1999), to right themselves (Migita et al.,

2005), respiration (Lawrence, 2013), to adhere

to the seabed when buffeted by waves (Thomas

& Hermans, 1985; Santos, Gorb, Jamar, &

Flammang, 2005), and to flee under emergency

conditions (Emson & Wilkie, 1980).

Regeneration is a common phenomenon

in all actual echinoderm classes (Yousra et al.,

2018; Byrne, 2020). It has been particularly

well-studied in asteroids, where three main

aspects have been identified: 1) regeneration

of body parts (arms) following self-induced or

traumatic amputation; 2) regeneration of inter-

nal organs (pyloric caeca and cardiac stomach)

following self-induced or traumatic mutilation,

and 3) fission processes (Candia-Carnevali,

2006). Regeneration of body parts and envi-

ronmental perturbations on the metamorphosis

of larvae can result in an abnormality in the

number of starfish arms (Hotchkiss, 1979).

Worldwide the largest record of occur-

rences of abnormal starfishes have been

reported in India, where at least 13 species

have been listed: Anthenea pentagonula

(Lamarck, 1816) (Maheswaran, Narendran,

Yosuva & Gunalan, 2015), Asterina lorioli

Koehler, 1910 (James, 1999), Astropecten indi-

cus Döderlein, 1888 (James, 1999; Prabhu

& Bragadeeswaran, 2012; Chamundeeswari,

Saranya, Shanker, Varadharajan, & Rajagopal,

2013), A. karankawai Lawrence, Cobb, Her-

rera, Durán-González & Solís-Marín, 2018

(ICMYL Unpublished data), Echinaster pur-

pureus (Gray, 1840) (James, 1999), Goniodis-

caster vallei (Koehler, 1910) (Maheswaran et

al., 2015), Linckia laevigata (Linnaeus, 1758)

(James, 1999), L. multifora (Lamarck, 1816)

(James, 1999; Maheswaran et al., 2015), L.

columbiae Gray, 1840 (Fisher, 1945), Nardoa

galatheae (Lütken, 1864) (James, 1999), Pen-

taceraster regulus (Müller & Troschel, 1842)

(James, 1999; Shanker & Vijayanand, 2014),

Pisaster ochraceus (Brandt, 1835) (Fisher,

1945), and Protoreaster linckii (Blainville,

1830) (James, 1999; Chelladurai, Balakrish-

nan, Jayanthi, Ajeesh-Kumar, & Mohanraj,

2015; Chelladurai & Doss, 2016). Other spe-

cies where abnormal ray numbers have been

recorded include Protoreaster nodosus (Lin-

naeus, 1758), a starfish widely distributed in

the Indo-Pacific region (Chim & Tan, 2012)

and Archaster angulatus Müller & Troschel,

1842 from the Indian Ocean and western

Pacific (Keesing, 2017).

The Panamic Cushion Star Pentaceraster

cumingi (Gray, 1840) (Asteroidea: Oreasteri-

dae) is one of the most common starfish in

the Tropical Eastern Pacific (TEP) (Solís-

Marín et al., 2014; Reyes-Bonilla, Vázquez-

Arce, González-Cuéllar, Herrero-Pérezrul, &

Weaver, 2016). It has a highly variable color-

ation, from red-orange or red-green to a gray

background color with an overlying bright

red network (Kerstitch & Bertsch, 2007). P.

cumingi, like most starfish, has pentameric

symmetry, is relatively large (up to 17.4 cm

of diameter), with an inflated body wall, and

immobile spines stud in the upper surface. It is

distributed from the Gulf of California, Mexico

to Northern Perú, inhabits rocky reefs, patch

reefs, and sandy areas, from low intertidal zone

up to 183 m deep (Hickman, 1998; Solís-Marín

et al., 2014).

The Mexica buried echinoderms in their

ritual deposits for at least a half-century. Six

species of starfish have been found so far in the

offerings, and the presence of P. cumingi was

common (10 000 elements have been found

in 13 offerings) (Martín-Cao-Romero et al.,

2017). While it is true that many animals (or

artifacts made from them) were buried as gifts

to the supernatural, in most cases they were

manipulated as symbols of specific divini-

ties, of particular regions of the universe, or

of important cosmic processes (López-Luján,

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Chávez-Valderas, Zúñiga-Arellano, Aguirre-

Molina, & Valentín-Maldonado, 2012).

It is well known that this starfish forms

large aggregations, which may correspond to

feeding (Reyes-Bonilla, González-Azcárraga,

& Rojas-Sierra, 2005) or a reproductive strat-

egy (Reyes-Bonilla et al., 2016). The Panamic

Cushion Starfish plays an important ecologi-

cal role, maintaining the benthic communities

in the TEP by feeding on microorganisms

and other echinoderms, such as sea urchins,

controlling populations of those species (Dee,

Witman, & Brandt, 2012; Reyes-Bonilla et al.,

2016). The present study focuses on the popu-

lation density, size structure, and occurrence of

abnormalities in the radial pattern of an estab-

lished population of P. cumingi from the central

Mexican Pacific.

MATERIALS AND METHODS

The study was carried out in front of El

Novillo islet in Bahía Chamela, Jalisco, in

the Central Mexican Pacific (19º33’15” N

& 105º07’25” W). The Bahía Chamela was

declared a Natural Protected Area in 2002, with

the Sanctuary category. Includes seven main

islands (Pajarera, Cocinas, La Colorada, San

Agustín, San Pedro, San Andrés, and La Negra)

and some islets. El Novillo islet (also called

Islote Novillos) is rocky with a maximum

elevation of 13 m, its surface of 0.73 ha, and

its located 1 400 m from mainland. Around the

islet, the habitat consists of a sandy plain and

mixed rubble substrate, with maximum depths

of ~7-10 m (Ríos-Jara et al., 2013). Organisms

were sampled from June 2016 to October 2019

(cold and warm seasons). One sampling event

was conducted at each season for every year.

To determine the density of starfishes in the

area, three belt transects of 20x1 m were made,

per sampling campaign, by SCUBA diving.

Transects were placed parallel to each other

and separated two meters between them. A total

of 849 starfishes were collected randomly. The

measurements that were took were arm length

(A, B, C, D, and E) from the mouth center to

the tip of arm, minor radius length (r) from

mouth center to the end of interradius (C-D),

arm breadth (br) at the base of the A-arm (in

the case no A-arm, it was replaced with the

B-arm), the number of arms, and weight (using

a portable electronic balance, 1 g accuracy). All

specimens were drained on a plastic tray before

recording the weight, to eliminated variability

on weighing. Arms position was determined

following the Carpenter system, which rec-

ognized the C- and D-arm where the madre-

porite exists in-between, and the opposite arm

to madreporite as A-arm (Hotchkiss, 2000a).

Starfishes with an abnormal number of arms

were photographed in oral and aboral views,

to determine the presence and direction of the

ambulacral grooves. After being measured and

photographed, all individuals were returned

to the sea. Water temperature and maximum

depth were recorded with a diving computer

(Dive Rite Nitek duo). To calculate radius

length-weight relationships, pentameric speci-

mens were selected. Abnormal starfishes were

examined independently. All data was analyzed

using the Minitab 17 software.

RESULTS

Population size structure: For analysis

of population size structure, only five armed

starfishes were considered. The density of

P. cumingi in El Novillo islet exhibited lit-

tle variation throughout the sampling period

(Kruskal-Wallis test H = 9.14, P = 0.243). The

highest mean density was found in October

2019 (2.03±0.05 ind/m

-2

) and the lowest in

March 2017 (0.66±0.13 ind/m

-2

). Mean den-

sity for the other months ranged from 1.34 to

1.91 ind/m

-2

(Fig. 1). In general, the highest

densities were found during the warm season,

although no relationship was observed between

abundance and temperature. Cold season tem-

perature values ranged from 20.6 to 27.9 °C

and warm season ranged from 29.0 to 30.5 °C.

Average major radius (R), minor radius (r), and

arm breadth (br) were similar between the sam-

pling months, except for br in October 2016

which was the lowest of all (Table 1).

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The maximum size (R) of collected starfish

was 160 mm. The average length for normal

starfish was 123.8±15.2 mm and the average

weight was 326.0±62.4 g (Table 2). The most

frequent length classes ranged from 110 to 120

mm (Fig. 2). Larger individuals (> 150 mm)

were found in October 2019 and small indi-

viduals (< 50 mm) were found in October 2016,

2017 and February 2018. The length classes

were widely separated in October 2016 than

the other months. Differences in the arm length

(t = -3.95; P < 0.05) and body weight (t = 2.82;

P = 0.005) were found between cold and warm

seasons (Fig. 3).

Occurrence of abnormal starfish. A total

of 849 individuals of P. cumingi were collected

and measured, 28 of them (3.29 %) had an

abnormal arm number (i.e. individuals with

four arms, six arms, and with a bifurcated arm,

Table 1). From all samples, 0.82 % had four

arms, 1.06 % had six arms, and 1.41 % had one

Fig. 1. Density of individuals (bars) and water temperature (dotted line) records by sampling date.

TABLE 1

Abundance and growth rates of Pentaceraster cumingi by sampling date

Sampling date

Number of

starfish in

sample

Number of

abnormal

starfish*

Mean R

(mm)

Mean r (mm) Mean br (mm) Depth (m) Temp (°C)

Jun. 2016 94 0 112.1±11.2 56.0±5.6 - 9.3 27.0

Oct. 2016 148 10 112.8±13.7 52.4±6.3 38.6±14.7 7.2 30.5

Mar. 2017 81 2 114.8±8.7 50.2±5.6 52.4±8.6 7.2 21.9

Oct. 2017 119 2 113.6±12.4 46.9±6.1 59.2±9.7 7.6 29.0

Feb. 2018 115 7 114.0±14.1 46.8±6.1 55.2±10.9 6.5 27.9

Oct. 2018 90 0 114.9±10.8 45.9±5.2 53.9±7.2 7.7 29.0

Mar. 2019 80 1 113.5±11.1 47.4±5.6 58.8±13.2 7.2 20.6

Oct. 2019 122 6 123.0±13.0 50.0±7.0 58.0±9.0 7.3 30.4

Total 849 28

Arm breadth for June 2016 were not measured. *excluded from the mean values.

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bifurcated arm. The largest number of abnor-

mal starfish was found in October 2016 when

the individual size was the lowest, followed by

February 2017 and October 2019.

Abnormalities in P. cumingi radial pat-

tern are caused at least by three processes: 1)

by mutilation of one arm, which gives rise to

a four-armed starfish (Fig. 4b). In this case,

an external mechanism, such as predation,

causes the abnormality, and because a remnant

of the lost arm is present there is a possibil-

ity for regeneration; 2) malformations during

Fig. 2. Size-frequency distributions of Pentaceraster cumingi from Bahía Chamela, Mexico.

Fig. 3. Length-weight relationships of Pentaceraster cumingi in cold (black circles) and warm (white circles) seasons.

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development, can give rise to four or six armed

starfish (Fig. 4c, Fig. 4e), one individual pre-

sented a fusion of two ambulacral grooves

(Fig. 4d); and 3) by regeneration, can give rise

to a bifurcated arm (Fig. 4f). Bifurcated arms

were found only in five-armed starfish and no

more than one bifurcated arm was found in the

same individual.

DISCUSSION

The species richness of Asteroidea in

Bahía Chamela is low. Only three species have

been recorded in the bay: Phataria unifas-

cialis (Gray, 1840), Pharia pyramidata (Gray,

1840), and P. cumingi (Ríos-Jara et al., 2013).

The low species richness maybe related to a

poor sampling effort on starfishes itself. Tak-

ing into consideration that some starfish have

specific habits, like being nocturnal, roost

under rocks, inside cavities, or are buried in

soft bottoms, therefore their record can be

hard or less detectable with common methods.

However, these three species are dominant

because they can colonize easy different types

of habitats (Luna-Salguero & Reyes-Bonilla,

2010). The occurrence of P. cumingi at Bahía

Chamela is continuous throughout the year,

with densities that are constant in both seasons

(cold and warm). The species reaches popula-

tion densities from 0.8 ind/50 m

in the Gulf of

California, Mexico (Reyes-Bonilla et al., 2005)

to 0.02 ind/m

in the Gulf of Chiriqui, Panama

(Alvarado, Guzmán, & Breedy, 2012). Star-

fish densities in Bahía Chamela ranged from

0.66 to 2.03 ind/m

, above of those reported

for other sites. Population density is similar

to those found in aggregation events (prob-

ably for a reproduction event) in the Southern

Gulf of California, where densities of up to

3 ind/m

were reported (Reyes-Bonilla et al.,

2016). However, these aggregations have been

observed only for a few days, unlike the popu-

lation at Bahía Chamela, which is constant all

year. Physical and environmental conditions in

the bay such as shallow water, weak currents

that provide protection of islands and islets,

warmer temperatures, and extensive sandy

TABLE 2

Mean and standard deviation of normal and abnormal starfish Pentaceraster cumingi

Number of arms N Weight (g)

R (mm)

r (mm) br (mm)

A B C D E X

Normal 5 arms 821 326.0±62.4 123.8±15.2 122.8±16.2 120.9±14.2 120.3±13.5 119.1±12.7 - 50.5±7.3 57.5±16.4

Abnormal 5 arms (two ends) 12 308.2±70.2 104.9±23.0 112.1±20.8 111.0±18.5 113.7±20.9 106.3±18.1 - 47.1±6.0 51.8±12.2

Abnormal 4 arms (*A) 3 263.0±45.9 - 130.0±64.0 125.0±18.5 125.0±8.1 125.0±5.0 - 50.0 65.0±7.0

Abnormal 4 arms (*B) 2 284.5±54.4 131.0±18.3 - 125.5±27.5 133.5±19.0 133.0±18.3 - 43.5±9.1 58.0±1.4

Abnormal 4 arms (*C) 1 248 120 120 - 110 120 - 40 80

Abnormal 4 arms (*D) 1 258 115 114 115 - 116 - 50 50

Abnormal 6 arms 9 368.2±41.9 124.2±18.3 108.0±25.6 124.8±20.0 117.0±18.5 109.8±14.3 125.2±19.3 53.8±4.2 38.6±11.5

*A = No arm A; *B = No arm B; *C = No arm C; *D = No arm D.

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bottoms can provide sufficient resources (space

and food) to maintain a persistent aggregation

of P. cumingi (Sloan & Aldridge, 1981; Guil-

lou, 1996; Reyes-Bonilla et al., 2005).

Due to the lack of studies of P. cumingi

populations in other localities, it is not possible

to compare the mean population sizes present

in Bahía Chamela. The P. cumingi population

exhibited a seasonal growth pattern, with dif-

ferences between cold and warm seasons. A

possible explanation for this difference is that

the length-weight relationship between seasons

varied according to factors such a food avail-

ability, feeding rate, gonad development, and

spawning period (Sebens, 1987). The growth

rate for P. cumingi seems to be related to

seawater temperature as higher growth rates

were recorded in the months when seawater

temperature was also higher. Seasonal variation

in growth had been described for other starfish

Fig. 4. Position and sequence of ambulacral grooves abnormalities in Pentaceraster cumingi in oral view. A. Five rays. B-D.

Four rays. E. Six rays. F. Five rays with one bifurcation. * Represents madreporite position.

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species, which usually showed a decrease in

growth rate associated with gonad maturation

(Freeman, Richardson, & Seed, 2001).

Recruitment events are thought to have

occurred between June and August (summer),

however, recruits of P. cumingi occur in cryptic

habits and their observation is hard. One recruit

(< 10 mm) was found attached under a rock in

a rocky reef habitat, away from the area where

adults were found (Galván-Villa pers. obser.).

Possibly, juveniles (> 30 mm) may migrate

from rocky reefs to rubble areas, where adults

feed to continue its growth. Spatial patterns in

the recruitment of starfishes have been asso-

ciated with different habitat characteristics

such as depth, substrate type, temperature, and

hydrodynamics (Metaxas, 2013). This selection

of habitat has been associated with increased

survival, which in turn is affected by the avail-

ability of food and predation pressure (John-

son, Sutton, Olson, & Giddins, 1991; Manzur,

Barahona, & Navarrete, 2010).

Pentaceraster cumingi belongs to the fam-

ily Oreasteridae, which is one of the twenty

living families of starfishes that are exclusive-

ly five-rayed (Hotchkiss, 2000a). Arm num-

ber abnormalities are relatively common in

the family Oreasteridae. Other studies have

reported similar conditions for the congener P.

regulus, a common starfish from the Western

Central Pacific (James, 1999; Shanker & Vijay-

anand, 2014), P. linckii, widely distributed in

the Indian Ocean (James, 1999; Chelladurai et

al., 2015; Chelladurai & Doss, 2016), and P.

nodosus, from the Indo-Pacific region (Chim

& Tan, 2012). Abnormal arm number have

been attributed to several causes like injury,

regeneration errors, malnutrition, congenital

issues, or damages in the metamorphosis pro-

cess (Moore, 1974; Hotchkiss, 1979; Watts,

Scheibling, Marsh, & McClintock, 1983). The

most common cause seems to be by regen-

eration process (Hotchkiss, 1979). Incidence

of mutilation in some starfish has been sug-

gested by fishing gears (Ramsay et al., 2001;

Byrne, 2020). It is not considered in this study

because the population studied was located

inside a protected area where fishing activities

are not allowed.

Some lab experiments have shown that

changes in environmental factors like salinity

can influence ray formation during early devel-

opment in asteroids (Watts, Scheibling, Marsh,

& McClintock, 1982; Marsh, Watts, Chen,

& McClintock, 1986; Clark, 1988). Watts et

al. (1983) reported a rise of metamorphosed

individuals with ray number abnormalities by

increasing salinity to 39 %. The incidence of

arm abnormalities in P. cumingi from Bahía

Chamela was higher in comparison with anoth-

er species studied. For the starfish Archaster

angulatus Müller & Troschel, 1842, Lawrence,

Keesing and Irvine (2010), found an incidence

of 0.4 % of both four and six arm abnormali-

ties, and Keesing (2017) found an incidence of

1.5 % of four arms and 1.3 % of six arms in the

same species. It is not possible to determine the

causes of this high level of arm abnormality

in P. cumingi, due to the lack of more envi-

ronmental data. Other factors, such as sample

method, size distribution area, and habitat type

should be considered for estimation of the inci-

dence of abnormalities.

Four arm condition is not common in

starfishes. Some specimens with four evident

arms, but with five ambulacral grooves, were

found in Bahía Chamela. In these cases, injury

or arm mutilation for depredation is the cause

of the apparent abnormality, but the arm can

be regenerated, as it was observed in other

specimens. On the other hand, specimens with

four arms and four ambulacral grooves support

the synchronic hypothesis, in which abnor-

malities arise during the metamorphosis, when

the pathway to form the rudiments of the five

primary rays operates for only a short time,

switches off and does not re-occur (Hotch-

kiss, 2000a). As mentioned above, changes in

environmental parameters may be the cause

of this abnormality.

Only one specimen with a double ambula-

cral groove was found. This abnormality is very

rare, and it has been reported in a few other sea

stars as Asterias forbesi (Desor, 1848), A. prob-

lema Lutken, 1872, A. rubens Linnaeus, 1758,

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Eremicaster vicinus Ludwing, 1907, Pisaster

ochraceous segnis Fisher, 1926, and Stephan-

asterias albula (Stimpson, 1853) (Hotchkiss,

2000b) and it is considered a result of injury

or a regeneration process. Hotchkiss (2000b)

deduced that this abnormality is a rare result of

regeneration, in which the two terminal plates

remain coalesced along their inner margin, the

ambulacral grooves are kept parallel, and there

is just one tip to the double ray. However, in

the specimen found in Bahía Chamela, the two

ambulacral grooves were fused at the base, and

most of this abnormality likely arose during

metamorphosis, and not by a regeneration pro-

cess. A detailed examination of terminal plates,

adambulacral, inferomarginal and superomar-

ginal plates is necessary to establish the origin

of the abnormality. Other conditions there will

develop two tips to the ray but no individuals

with this characteristic were found.

Due to the basic skeletal structure of aster-

oids with flexible arms, they have both species

and genera with pentameral and other symme-

tries (Stephenson, 1967). The supernumerary

rays of multiradiate species as Acanthaster,

Pycnopodia, Solaster, Crossaster, etc., was

explained by the ‘Five-Plus’ hypothesis, that

proposes that supernumerary rays develop by

independent pathways that operate after the

five primary rays have initially formed (Hotch-

kiss, 2000a). For pentamerous species, the

apparition of an extra ray is an unusual event

that has not been well studied. The six-armed

abnormality was the most common (1.06 %)

in P. cumingi. Examination of the ventral view

of specimens allowed to confirm the presence

of six ambulacral grooves and to separate from

specimens with a bifurcation caused by an inju-

ry. The presence of well-defined six ambulacral

grooves could demonstrate that the abnormal-

ity is the result of the metamorphosis process,

altered maybe for environmental changes (e.g.

Marsh et al., 1986).

The presence of morphological abnormali-

ties is less favorable to survival of individuals,

and the incidence of abnormalities can be an

indicator of environmental degradation (Jan-

goux, 1987). Wu, Ji, Wang, and Lv (2012) used

mathematical and physical methods to evaluate

the superiority of starfish with five arms in

comparison with those with a different number

of arms, concerning detection, turning over,

autotomy, and adherence. They conclude that

the optimal number of arms varies under dif-

ferent environmental conditions. In the case of

multiradiate taxa some advantages have been

identified. Supernumerary rays increase the

number of tube feet, then multiradiate asteroids

could be more mobile, more resistant to being

detached from the seabed, and more success-

ful feeders (Herringshaw, Smith, & Thomas,

2007). Although four-armed starfish exhibited

such disadvantages that it is hard for them to

survive, the relatively smaller disadvantages of

six-armed starfish might allow a few species

to exist but the advantages of five arms will

permit it to evolve into the dominant pattern of

species. As other authors suggest, further stud-

ies are needed to understand the causes for the

abnormality in pentameral starfishes and the

mechanisms that cause it.

Ethical statement: authors declare that

they all agree with this publication and made

significant contributions; that there is no con-

flict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are

fully and clearly stated in the acknowledge-

ments section. A signed document has been

filed in the journal archives.

ACKNOWLEDGMENTS

Thanks to all students of the “Recur-

sos Marinos” course who contributed with

the fieldwork. To Manuel Ayón and Cande

Hernández for field support in Chamela for

many years. To Kevin Cummings for the

English writing and grammar revision. Spe-

cial thanks to the Biology Station of Chamela

(IBUNAM) for all facilities during field sam-

pling. This research was supported partially by

P3E program from the University of Guadala-

jara. Field collection of specimens was done

with the official permission of SEMARNAT

271

Rev. Biol. Trop. (Int. J. Trop. Biol.) • Vol. 69(1): 262-273, March 2021

(SGPA/DGVS/05775/12). The authors would

like to thank anonymous reviewers for sub-

stantial comments that contribute to the final

version of this manuscript.

RESUMEN

Estructura de tallas poblacional y anormalidades

en el número de radios de la estrella de mar Penta-

ceraster cumingi (Valvatida: Oreasteridae) en Bahía

Chamela, Pacífico mexicano. Introducción: La Estrella

Cojín Pentaceraster cumingi está ampliamente distribuida

a lo largo del Pacífico Oriental Tropical. Esta especie pro-

duce estrictamente cinco brazos, pero en algunas ocasiones

el número puede ser menor o mayor de cinco, o mostrar

otro tipo de anormalidad. Objetivo: Evaluar la estructura

de tallas poblacional y la presencia de anormalidades en el

patrón radial de P. cumingi en la Bahía Chamela, Jalisco,

México. Métodos: La población fue monitoreada a lo largo

de cuatro años (2016-2019), durante dos periodos estacio-

nales (cálido y templado). Durante el trabajo de campo se

recolectó una muestra aleatoria de individuos. Cada estrella

de mar fue medida, pesada y revisada para identificar algu-

na anormalidad en el patrón radial. Resultados: La mayor

densidad de individuos se encontró en octubre de 2019

(2.03 ± 0.05 ind/m

-2

), la menor en marzo de 2017 (0.66 ±

0.13 ind/m

-2

). Un total de 849 individuos fueron recolec-

tados. Para las estrellas de mar con 5 brazos, la longitud

promedio fue de 123.8 ± 15.2 mm y el peso promedio de

326.0 ± 62.4 g. La clase de talla más frecuente varió entre

110 y 120 mm. Del total de individuos muestreados el 0.82

% tuvieron cuatro brazos, el 1.06 % con seis, y el 1.41 %

tuvieron un brazo bifurcado. Conclusiones: Se encontra-

ron diferencias en la densidad poblacional y en la estructura

de tallas de P. cumingi entre estaciones. Las principales

causas de anormalidades en la estrella de mar pueden ser

debidas a los cambios que ocurren durante la metamorfosis

de las larvas o por una regeneración anormal de los brazos

a causa de la depredación.

Palabras clave: estrella de mar; anormalidad; densi-

dad; equinodermo; estructura de tallas; Pacífico

Oriental Tropical.

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