222 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 70: 222-234, January-December 2022 (Published Apr. 18, 2022)

Internal ultrastructure of the planktonic larva

of the coral Porites panamensis (Anthozoa: Scleractinia)

Jeimy D. Santiago-Valentín1,2; https://orcid.org/0000-0003-2152-7875

Alma P. Rodríguez-Troncoso3*; https://orcid.org/0000-0001-6243-7679

Eric Bautista-Guerrero3; https://orcid.org/0000-0002-4975-1767

Andrés López-Pérez2; https://orcid.org/0000-0003-1246-7401

Amílcar L. Cupul-Magaña3; https://orcid.org/0000-0002-6455-1253

1. Departamento de Estudios para el Desarrollo Sustentable de Zonas Costeras, Centro Universitario de La Costa Sur,

Universidad de Guadalajara, Gómez Farías 82, San Patricio-Melaque, Jalisco 48980, México;

jeimysantiagov@gmail.com

2. Departamento de Hidrobiología, Universidad Autónoma Metropolitana, San Rafael Atlixco 186, 09340 Distrito

Federal, México; alopez@xanum.uam.mx

3. Laboratorio de Ecología Marina, Centro Universitario de la Costa, Universidad de Guadalajara, Av. Universidad No.

203. Puerto Vallarta, 48280 Jalisco, México; pao.rodriguezt@gmail.com (Correspondence*),

ericbguerrero@gmail.com, amilcar.cupul@gmail.com

Received 13-X-2021. Corrected 22-II-2022. Accepted 01-IV-2022.

ABSTRACT.

Introduction: The scleractinian coral life cycle includes planktonic larvae that settle on the benthos, allowing

the primary polyp to clone and build a sexually reproducing adult colony. The larval physiology and ecology of

Eastern Tropical Pacific scleractinians needs the exploration of basic aspects such as the internal morphology

of planulae.

Objective: To describe histological and cytological characteristics of Porites panamensis larvae.

Methods: During August-July 2019, at Islas Marias Biosphere Reserve, Central Mexican Pacific, we made 14

collections of coral larvae and identified the species with cytochrome oxidase subunit 1 gene. We used a scan-

ning electron microscope and other techniques.

Results: The ectoderm was composed by heterogeneous, mono-ciliated, columnar epithelial cells. Nematocysts

were clustered at the oral pole of the ectoderm, and cells were evident in the aboral pole of the ectoderm gland.

The endoderm had secretory cells, lipids and symbionts.

Conclusions: The abundance of secretory cells and nematocysts in the aboral pole suggests their importance in

substrate exploration and larval settlement. Our results support previous descriptions of larval ultrastructure in

other coral species.

Key words: ultrastructure; histology; planulae; larvae biology; larvae settlement; Eastern Pacific.

https://doi.org/10.15517/rev.biol.trop..v70i1.48648

INVERTEBRATE BIOLOGY

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Revista de Biología Tropical, ISSN: 2215-2075, Vol. 70: 222-234, January-December 2022 (Published Apr. 18, 2022)

Scleractinian coral sexual reproduction

involves the fertilization of eggs that develop

into swimming larvae. Upon settlement, these

larvae undergo a metamorphosis with polar-

ity reversal to develop a sessile polyp, which

reproduces asexually by budding to grow into

a colony with the ability to mature gametes

(Fadlallah, 1983; Harrison & Wallace, 1990;

Richmond, 1990; Sammarco, 1994). The lar-

vae possess lipid vacuoles, and these serve as

energy repositories that contribute to their posi-

tive buoyancy (Vandermeulen, 1974); which

contributes to the maintenance of the larvae in

the plankton (up to 100 days) and allow a more

strict selection of the substrate (Richmond,

1987; Wilson & Harrison, 1998) and disperse

to new habitats and promotes gene flow (Ayre

et al., 1997).

Overall, early development involves cell

division that forms a blastula and a subsequent

upper and lower ectoderm excision resulting

in a second tissue layer, which develops as the

endoderm (Babcock & Heyward, 1986; Ball

et al., 2002; Hirose & Hidaka, 2006; Okubo et

al., 2013). Cilia allow planulae to swim with

an oral orientation (Ball et al., 2002; Gleason

& Hofmann, 2011). The aboral pole acts as a

sensor for recognizing suitable settling sites

(Chia et al., 1984; Vandermeulen, 1974). Lar-

val settlement is regulated synergistically by

multiple tactile and chemical cues (Gleason &

Hofmann, 2011; Ritson-Williams et al., 2009),

allowing an adequate selection of substrate

and survival advantage of these organisms

(Kitamura et al., 2007; Müller & Leitz, 2002).

Even though larvae have chemoreceptors, the

chemotaxis from a distance and in highly

dynamic environments is not strong enough

to detect an appropriate substrate, but specific

factors are likely to be present directly on its

surface (Müller & Leitz, 2002). Therefore, spe-

cialized cells should be a key in the detection

of both chemical and mechanical forces such

as compression or tension (Katta et al., 2015),

and cellular structures present in the ectoderm

of the aboral zone have been associated with

larval settlement (Chia & Koss, 1979; Martin,

1983; Vandermeulen, 1974).

The mode and reproduction patterns of

scleractinian corals are both species-specific

and spatiotemporally variable (Chávez-Romo

et al., 2013; Santiago-Valentín et al., 2018). At

the regional level, the Eastern Tropical Pacific

(ETP) environmental conditions are consid-

ered limiting for the development of coral

communities (Dana, 1975; Glynn et al., 1996;

Richmond, 1990). Conditions such as the wide

ranges of annual temperature fluctuations (18

to 32 °C), low pH (7.72 to 8.03) (Cupul-Cortés

et al., 2018), high sedimentation rates (Glynn

et al., 2017), seasonal upwellings (Portela et

al., 2016) and internal waves that results in

abnormal daily sea temperature fluctuations

(Plata & Filonov, 2007), promotes non-optimal

conditions that affect physiological processes

with high energy demand, such as reproduc-

tion (Glynn, 2000; Glynn & D’ Croz, 1990;

Santiago-Valentín et al., 2018; Spalding et

al., 2001). However, gamete development has

recently been documented in all reef-building

scleractinian corals examined in the region

(Carpizo-Ituarte et al., 2011; Chávez-Romo

& Reyes-Bonilla, 2007; Glynn et al., 1991;

Glynn et al., 1994; Glynn et al., 1996; Glynn

et al., 2017; López-Pérez et al., 2007; Medina-

Rosas et al., 2005; Rodríguez-Troncoso et

al., 2011; Santiago-Valentín et al., 2015), and

even the developmental stages and morphol-

ogy of the larvae within adult colonies have

been described (Glynn et al., 2017; Santiago-

Valentín et al., 2019).

The hermatypic coral Porites panamensis

Verrill, 1866 is endemic to the ETP and, as

such, displays a high tolerance to a wide range

of sea surface temperature and turbidity daily

and seasonal fluctuations (Halfar et al., 2005;

Reyes-Bonilla et al., 2007). This species is

a gonochoric brooder (Carpizo-Ituarte et al.,

2011; Glynn et al., 1994; Rodríguez-Troncoso

et al., 2011) and is the only one for which

larvae have been found in the water column

in the ETP (Santiago-Valentín et al., 2019).

Considering that the survival of coral reefs

given anthropogenic disturbances, including

the consequences of climate change, hinges

on successful recruitment, and in turn, this

224 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 70: 222-234, January-December 2022 (Published Apr. 18, 2022)

depends on phenotypic diversity and plasticity

of larvae (Roth & Deheyn, 2013). In addition,

a comprehensive understanding of coral larval

morphological structures suitable for settle-

ment provides the basis for the conservation

of coral populations (Aranda et al., 2011).

Hence the high relevance to characterizing P.

panamensis larvae through the description of

histological and cytological features of the lar-

vae during their planktonic phase. In addition,

we generate data that in the future can be com-

pared with other cnidarian larvae; this would

aid in learning about specific adaptations of

settlement in corals.

MATERIALS AND METHODS

Coral larvae were collected in Islas

Marias Biosphere Reserve (21°17’24.0” N -

106°14’24.0” W). Sampling was performed

in July and August 2017, recorded period of

gamete maturation for P. panamensis in the

region (Carpizo-Ituarte et al., 2011; Santiago-

Valentín et al., 2019). The collection of larvae

was performed at noon, slowly dragging a net

(30 cm diameter with a mesh size of 150 µm)

in the vicinity of live coral colonies for ≈20

min covering an approximate area of 250 m2. A

total of six samples per month were obtained.

Samples were transported to the laboratory

and separated using a dissecting microscope

(Carl-Zeiss®).

Morphological and molecular identifica-

tion were carried over as previously described

in Santiago-Valentín et al. (2019), using the

molecular marker (Cytochrome oxidase sub-

unit I gene: COXI), amplified with PCR,

using the primers: LCOI490 (5´-GGGT-

CAACAAATCATAAAGAYATYGG -3´) and

HCOI21908 (3´- TAAACTTCAGGGTGAC-

CAAARAAYCA -5´) (Folmer et al., 1994).

Forward and reverse sequences were manually

edited in order to obtain a consensus sequence

using Geneious® V.4.8.5 software (Biomatters,

2010). The consensus sequences were ana-

lyzed using Basic Local Alignment Search Tool

(BLAST) of National Center for Biotechnology

Information (NCBI). In order to determine the

relationship among samples collected in other

regions of Mexican Pacific and recognize the

taxonomic identity of the larvae, a maximum

likelihood (ML) tree with Hasegawa Kishimo

Yano distances and gamma distributions was

created (Kumar et al., 2016) using MEGA7®.

The tree was build using, sequences from the

genBank (MN005653, MN005652, MF969052,

NC024182.1, KU956960.1, MN005655) and

Gorgonia flabellum (GQ342418.1) was includ-

ed as outgroup. The consensus sequence was

deposited in the NCBI with accession number:

MZ350963.

To describe the ultrastructure of the larva,

each larva was individually fixed in 2.5 %

glutaraldehyde in 0.2 M Millonig’s phosphate

buffer (pH 7.4) and 0.14 M NaCl for 7 days,

and then rinsed with phosphate buffer for 40

min; it is important to highlight that the fixa-

tion process can cause a slight shrinkage of the

larvae. Post-fixation was performed in 1 %

osmium tetroxide in 0.1 M sodium cacodylate

buffer, with overnight washing using the same

buffer. Larvae were dehydrated using an etha-

nol gradation series (50, 70, 80, 95, and 100

%), with infiltration in a diluted epoxy resin for

24 h (Hayat, 1986).

Thin sections (0.5 µm) were cut on an

ultra-microtome (MT-x, RMC®), mounting

onto glass slides, contrasted with uranyl acetate

and lead citrate, and stained with toluidine blue

1 % in 0.1 M sodium borate solution at alkaline

pH. Slides were first observed under Carl Zeiss

AxioScope® optical microscope to assess the

regionalization of structures. Electron micro-

graphs were taken with a transmission JEOL®

electron microscope (model JEM-1010) oper-

ated 60-80 kV with to resolution of 0.25 nm,

and cellular structures were identified accord-

ing to previous studies (Muscatine, 1974; Van-

dermeulen, 1974; Vandermeulen, 1975).

The total length of all planulae was deter-

mined, as well as the oral and aboral pole

diameter (using photographs of larvae before

the fixation process) and the length of cilia of

both poles (using electron micrographs). The

measures were done with the image analysis

software AxioVision® (Carl Zeiss Microscopy,

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2005). Data recorded are expressed as the mean

± S.D. Statistical differences in cilia length

between oral and aboral poles were tested

throughout t-test employing Sigma-plot V.11.

RESULTS

Fourteen P. panamensis larvae were col-

lected during two different sampling periods:

three in July and 11 in August. The maximum

likelihood tree analysis revealed that the col-

lected larvae were clustered with P. panamensis

recruits and adults of Islas Marias, Islas Mari-

etas, and the Gulf of California (Fig. 1). The

BLAST analysis showed that sequence com-

parisons of larvae revealed a 100 % nucleotide

similarity with the species P. panamensis,

which also coincides with taxonomic charac-

teristics, concluding that the identity of the

collected larvae is P. panamensis.

Larvae were fusiform in shape, and the

analysis of planulae revealed typical two-lay-

ered anatomy (Fig. 2); a full ciliated translucent

light brown ectoderm, and dark brown endo-

derm (Fig. 2A), separated by a thin acellular

mesoglea (Fig. 2B). Specimens were 595.80 ±

113.57 µm in length and has an anterior pole

(aboral pole; 253.84 ± 46.63 µm in diameter)

that tapers to the posterior pole (oral pole;

114.97 ± 25.78 µm).

The ectoderm was densely covered by

cilia and clusters of microvilli (Fig. 3A); the

cilia showed a 9 + 2 axoneme arrangement

Fig. 1. Maximum Likelihood Tree of DNA secuences of partial fragment of the cytodhrome oxidase subunit I gene (COXI).

Number bootstrap values 1 000 replicates. GC: Golf of California.

Fig. 2. Free-swimming P. panamensis larva. A. External morphology, B. longitudinal (median) section. ap: aboral pole; ec:

ectoderm; en: endoderm; m: mesoglea; op: oral pole.

226 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 70: 222-234, January-December 2022 (Published Apr. 18, 2022)

Fig. 3. Longitudinal section of the ectoderm of P. panamensis larva. A. Oral pole region stained with toluidine blue stained,

B. Aboral pole region, C. Transmission electron microscopy (TEM) image of ectoderm cells of the oral pole, D. TEM

image showing epithelial cells with cilia, the square is a magnification of the cross-cut of cilia. c: cilia; cm: cell membrane;

col: coelenteron; l: lipids; m: mesoglea; mi: mitochondria; mu: mucus- secreting cell; mv: microvilli; ne: nematocyst; nu:

nucleus; rc: root of cilia; s: symbiont dinoflagellate; sc: secretory cell.

associated to the apical-central region of the

ectodermal cell and each possessed a vertically

oriented rootlet (Fig. 3D). The cilia did not

present differences in length (Student-t = 1.26,

N = 10, P = 0.242) between oral (1.48 ± 0.11

µm) and aboral pole (1.48 ± 0.083 µm). The

ectoderm was composed by heterogeneous,

mono-ciliated, columnar epithelial cells. Nuclei

were present as peripheral islands of hetero-

chromatin situated at different “levels,” causing

a pseudo-stratification of the epithelium (Fig.

3A, Fig. 3C). Mitochondria were observed as

spherical and ovoid structures (Fig. 3C). The

apical section of the ectoderm also showed

semi-oval structures (Fig. 4A) with projections

and other structures identified as viruses (Fig.

4B) (Vega-Thurber et al., 2017).

Cnidocytes encapsulating nematocysts

(Fig. 5) were most commonly associated with

the ectoderm of the oral pole (Fig. 3B) and two

types (shapes) of nematocysts were evidenced

b-mastigophores (Fig. 5A, Fig. 5B) and isorhi-

zas (Fig. 5C, Fig. 5D).

The highest concentrations of mucus-

secreting cells (mucus polysaccharides) were

observed associated with the aboral pole area

(Fig. 6). The secretory cells were visualized

along the ectoderm and endoderm (Fig. 6A,

Fig. 6B), which differed in electron-density,

shape, and size (Fig. 6D). In this study, they

were classified as type I and type II, follow-

ing the descriptions of Martin & Thomas

(1980) and Vandermeulen (1974) (Fig. 6B).

Symbionts were evident in the endoderm, and

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Fig. 5. TEM image showing epithelial ectoderm of the aboral pole of P. panamensis with the presence of cnidocytes. A. -

B. nematocysts b-mastigophores. C. - D. nematocysts isorhizas. cn: cnida; mu: mucus- secreting cell; ne: nematocyst; sh:

shaft; tb: tubule.

Fig. 4. Transmission electron microscopy of the ectoderm of P. panamensis larva of the semi oval structures with

projections. A. Longitudinal sections of the epithelial layer with cells containing viruses. B. Close-up of some viruses

(denoted by arrows).

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few cells in the ectoderm (Fig. 6A, Fig. 6B);

micro-algae cells were surrounded by complex

periplasts and lipid vacuoles. Each contained

nuclei bounded by a double membrane and

chromosomes attached to a prominent nucleo-

lus. In addition, these micro-algae contained

single, peripheral, multi-lobed chloroplasts, as

well as pyrenoids attached to the chloroplast by

one to three stalks (Fig. 6C).

DISCUSSION

The external anatomy of P. panamensis

larvae share similarities with larvae of other

scleractinian corals (e.g. Pocillopora damicor-

nis in central Pacific) (Vandermeulen, 1974),

Leptastrea purpurea in North Pacific (Nietzer

et al., 2018), and Porites astreoides (Edmunds

et al., 2001). However, differences of internal

structures (e.g., the presence of symbionts, the

location and development of cnidocytes, the

presence of lipid vacuoles) were observed, and

all are involved in their physiological perfor-

mance, in response to both regional and local

conditions, such as energy storage, length, and

competence (pre-metamorphosis) stage. This

contributes to explaining the reproductive suc-

cess of P. panamensis in the region, unlike the

Fig. 6. Lipid and secretory structures of P. panamensis larvae. A. Median section of the endoderm and ectoderm on the

lateral part of the larva. B. Aboral pole of the larva. C. TEM image of a cross-section of a symbiont dinoflagellate located

in the middle region of the gastrodermis. D. TEM of a different type of secretory cell of the aboral ectoderm. ca: calcium

oxalate crystal; ch: chromosome; cl: chloroplast; ec: ectoderm; en: endoderm; m: mesoglea; mi: mitochondria; mu: mucus-

secreting cell; nc: nucleoli; p: cell wall; py: pyrenoid; s: symbiont dinoflagellate cell; sc: secretory cell; v: vacuole.

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other species present at the site (Glynn et al.,

2017; López-Pérez et al., 2007; Medina-Rosas

et al., 2005).

Cilia fully covered the P. panamensis lar-

val ectoderm, with no differentiation in orga-

nization or morphology along the oral-aboral

axis, the basal anatomy of the cilia is equal

or similar to the majority of the cilia present

in metazoan (Pitelka, 1974). The distribution

of cilia in the larva allows that planulae can

control over the depth, swimming actively up

in a spiraling motion concerning increasing

pressure even in areas with strong tidal cur-

rents (Mileikovsky, 1973; Stake & Sammarco,

2003). However, the dispersion horizontal is

mostly associated with marine currents’ effect

(Sammarco, 1994). Cilia provide locomotion

and funciont as transductors of chemical cues

(Nielsen, 1987; Nielsen 2012; Vandermeulen,

1974), influencing the dispersal and substrate

selection processes, both important for larval

settlement and maintenance of the population.

Two types of nematocysts were observed

in the aboral pole of the planula, isorhizas, and

b-mastigophores. The composition of nema-

tocysts may vary depending on developmen-

tal stages or physiological conditions (Fautin,

1988; Fautin, 2009). The isorhizas are present

in planulae but absent in adult colonies of the

coral Pocillopora damicornis (Paruntu et al.,

2000). Nematocysts specific (e.g isorhizas) to

larvae might have functions including attach-

ment to the substrate. When larvae detect an

adequate substrate for settlement, spirocysts

and isorhizas are work as a pre-attachment

tool (Strömberg et al., 2019; Vandermeulen,

1974; Vandermeulen, 1975), as planulae use

them as an anchoring system that latches on

the substrate (Chia & Bickell, 1978). We only

observed isorhizas in the collected larvae;

however, the presence of spirocysts cannot be

ruled out, and possibly, they develop in a more

advanced stage of larva maturity or during the

metamorphosis phase. The b- mastigophores

has been considered as a nematocist (Mariscal,

1974), and as P. panamensis planulae is lecito-

trophic and not feed during its planktonic stage,

larval cnids b- mastigophores must not be used

for capture prey. Thus, the b-mastigophores

in planulae are expected to work as a defense

system against predators, as observed in other

cnidarians (Buss, 1990; Lange et al., 1992).

Also, three types of secretory cells were

observed throughout the epidermis and gastro-

dermis. The cell mucus (mixture of polymeric

glycoproteins) in the aboral epidermis they

play an essential role for rapid adhesion of the

coral larvae (Chia & Crawford, 1977; Vander-

meulen, 1975) and, is different from the mucus

in pole oral, which is characterized by its high

carbohydrate content (around 80 %) (Bansil &

Turner, 2006) and can also act as a stored ener-

getic budget used during metamorphosis (Davy

& Patten, 2007; Futch et al., 2010). Other

secretory cells (type I, II) represent differences

in the chemistry of their secretions or, are suc-

cessive developmental stages of other cell

types and classified as zymogen cells, which

are responsible for secreting proteins (Rose &

Burnett, 1968), and are located in the central

region of the gastrodermis and considered as

precursor cells of the specialized cells respon-

sible for digestion in adult organisms (Haynes

& Davis, 1969).

Viruses were observed in the apical zone

of the epidermal cells in the larvae. Coral lar-

vae can obtain bacteria and viruses from their

progenitor, but also from the water column

in early larvae and recruit stages, in fact they

generally possess a far more diverse bacterial

microbiomes and virus than later life stages

(Van Oppen & Blackall, 2019). The viruses

observed in the epidermis of the larvae appar-

ently belong to different families including

mega-virus and mini-virus (Claverie et al.,

2009; Vega-Thurber et al., 2017). However,

metagenomics studies are required to charac-

terize the virus type and its possible role in

early coral larvae and recruit stages.

In the gastrodermis, the presence of lipid

vacuoles and symbionts was clearly evidenced.

Porites panamensis larvae are non-feeding

planulae lacking a mouth opening and tentacles,

contrary to the planktotrophic larvae devel-

oped by spawning coral species. Contrastingly,

planktonic larvae from gonochoric brooders

230 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 70: 222-234, January-December 2022 (Published Apr. 18, 2022)

rely on nutrients stored in their tissues, and the

organic carbon traslocated through symbiosis

(Muscatine & Cernichiari, 1969), and by the

absorption of organics from the water column

(Ben-David-Zaslow & Benayahu, 2000; Van-

dermeulen, 1974; Vandermeulen, 1975). The

energy reserves of planulae are thus critical to

their longevity and dispersal potential (Gleason

& Hofmann, 2011; Harrison, 2011). Esters and

triacylglycerol are the most common storage

lipids in corals (Yamashiro et al., 1999); in

addition, the released planulae have mater-

nally derived endogenous lipids (up to 70 % by

weight) which does not only acts as an ener-

getic source but also contribute to the buoyancy

and favors a vertical posture and displacement

along the water column (Vandermeulen, 1974;

Vandermeulen, 1975).

The acquisition of symbionts for P. pana-

mensis larvae is horizontal, as they “inherit”

symbiotic cells during the maturation of the

oocyte (Carpizo-Ituarte et al., 2011; Rodríguez-

Troncoso et al., 2011). All planktonic larvae

samples evidence symbiotic cells mostly in the

endoderm and, few cells in the ectoderm, later

disappear from the ectoderm as the planulae

matured (see Hirose et al., 2000; Hirose &

Hidaka et al., 2006), as the larvae are essen-

tially lecithotrophic upon emission and the

energy translocated from the symbionts is

minimal in the planulae compared with adult

coral (Kopp et al., 2016).

The successful survival of larvae and the

subsequent recruitment is important for the

healthy maintenance of the whole community,

as it contributes to population replenishment

and connectivity among broadly dispersed

populations. Also, the development of sensory

structures is a specific key process, such as

the adequate selection of substrate and its sub-

sequent settlement, which will determine the

survival of the future colony. The present study

supports previous descriptions of the ultrastruc-

ture of larvae of other coral species. Structures

such as secretory cells and nematocysts are

abundant in the aboral pole, which suggests

their importance in the substrate exploration

larval settlement.

Ethical statement: the authors declare

that they all agree with this publication and

made significant contributions; that there is no

conflict 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

Jeimy Denisse Santiago-Valentín received

a postdoctoral fellowship from Mexico’s

Teacher Professional Development Program

(PRODEP-NO.920007). We thank the authori-

ties of the Islas Marias Biosphere Reserve

(CONANP) and Protección y Restauración de

Islas y Zonas Naturales for the logistical sup-

port and Lourdes Palma Tirado (INB-UNAM)

for the processing of the TEM images. Finally,

the authors thank Anderson Mayfield for pro-

viding comments on the article, as well as

proofreading it.

RESUMEN

Ultraestructura interna de la larva planctónica del

coral Porites panamensis (Anthozoa: Scleractinia)

Introducción: El ciclo de vida del coral escleractinio

incluye larvas planctónicas que se asientan en el bentos, lo

que permite que el pólipo primario se clone y construya una

colonia de adultos con reproducción sexual. La fisiología y

ecología larvaria de los escleractinios del Pacífico Tropical

Oriental necesita la exploración de aspectos básicos como

la morfología interna de las plánulas.

Objetivo: Describir las características histológicas y cito-

lógicas de las larvas de Porites panamensis.

Métodos: Durante agosto-julio 2019, en la Reserva de

la Biosfera Islas Marías, Pacífico Central Mexicano, rea-

lizamos 14 recolectas de larvas de coral e identificamos

las especies con el gen citocromo oxidasa subunidad 1.

Utilizamos un microscopio electrónico de barrido y otras

técnicas.

Resultados: El ectodermo está compuesto por células

epiteliales columnares heterogéneas, monociliadas. Los

nematocistos se agrupan en el polo oral del ectodermo,

mientras que en el polo aboral son visibles células glan-

dulares. El endodermo presentó células secretoras, lípidos

y simbiontes.

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Conclusiones: La abundancia de células secretoras y

nematocistos en el polo aboral sugiere su importancia en la

exploración del sustrato y asentamiento larvario. Nuestros

resultados respaldan las descripciones previas de la ultraes-

tructura de las larvas en otras especies de coral.

Palabras clave: ultraestructura; histología; plánula; biolo-

gía larval; asentamiento larval; Pacífico Oriental.

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