ORIGINAL ARTICLE /ARTÍCULO ORIGINAL

ACANTHOSTOMUM GNERII SZIDAT, 1954 (DIGENEA: CRYPTOGONIMIDAE) FROM

SILVER CATFISH RHAMDIA QUELEN (QUOY & GAIMARD, 1824)

ACANTHOSTOMUM GNERII SZIDAT, 1954 (DIGENEA: CRYPTOGONIMIDAE) DE

RHAMDIA QUELEN (QUOY & GAIMARD, 1824)

1* 1 2 3 4

Maurício L. Martins ; Karen R. Tancredo ; Natália C. Marchiori ; Joaber Pereira Jr. ; Luis A.S de Castro ;

1 5

Patrícia Garcia & Juan Esquivel

AQUOS Laboratório de Sanidade de Organismos Aquáticos, Departmento de Aquicultura, Universidade Federal de Santa

Catarina, Rod. Admar Gonzaga 1346, 88040-900, Florianópolis, SC, Brasil.

2 Empresa de Pesquisa Agropecuária e Extensão Rural de Santa Catarina, Campo Experimental de Piscicultura de Camboriú,

Rua Joaquim Garcia, s/nº, Centro, CEP 88340-000, Camboriú, SC, Brasil.

3 Laboratório Biologia de Parasitos de Organismos Aquáticos, Caixa postal 474, Cassino, Rio Grande, RS, Brasil.

4 Laboratório de Imunologia, EMBRAPA Clima Temperado, BR 392, km 78

Monte Bonito, Pelotas, RS, Brasil.

5 Piscicultura Panamá Ltda., Est. Geral Bom Retiro, km 8, 88490-000, Paulo Lopes, SC, Brasil.

*Correspondence to author: mauricio.martins@ufsc.br

Neotropical Helminthology, 2016, 10(2), jul-dic: 189-203.

ABSTRACT

Keywords: Acanthostominae – Cryptogonimidae – Digenea – histology – parasite – silver catfish

Acanthostomum gnerii is a digenean frequently reported from intestine of Siluriformes and it is

well distributed over Central and South America. The aim of this study is to provide additional

information on morphological features of A. gnerii by histological sections and scanning

electron microscopy, as well as to provide comparative measurements of Acanthostomum spp. In

contrast to previous reports of this helminth in Rhamdia sp., specimens in the present study

showed two arms in the anterior portion of the body, just after the pharynx. They join and

terminate in one lateral pore on the left side of the body similar to that reported in A.

proctophorum and A. minimum. Such morphology was not described as a valid characteristic for

Acanthostomidae. This morphological variation could be associated with different populations

of the same species. New studies using molecular techniques are recommended to determine if

this character corresponds to a diversity of A. gnerii found in other fish species.

189

ISSN Versión impresa 2218-6425 ISSN Versión Electrónica 1995-1043

190

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016

INTRODUCTION

T h e s i l v e r c a t f i s h Rhamd i a quele n

(Pimelodidae), commonly known as “jundia”

is one of the most cultivated freshwater fish in

Southern Brazil due to its wide distribution,

easy management, hardness and good feed

conversion. This catfish is found from the

South to North of Mexico and Central to South

of Argentina (Silvergip, 1996; Fracalossi et al.,

2004).

It lives in lagoons and rivers bottomless pits,

preferring lentic environment with sandy

bottom and mud, near border vegetation

(Baldisserotto et al., 2010). It has also a

benthic behaviour (Bizerril & Lima, 2000)

which facilitates the Digenea recruitment

(Eiras et al., 1999).

Acanthostomum gnerii is a digenetic fluke

commonly found in the digestory tract of

f r e s h wa te r S i l ur i f o r m e s ( i n c lu di ng

Heptapteridae and Pimelodidae). It is well

distributed along Central and South America (;

Lamothe-Argumedo & Ponciano-Rodriguez,

1985; Watson, 1976; Kohn & Fróes, 1986;

Ostrowski de Nuñes & Gil de Pertierra, 1991).

In South and Southeast Brazil, it has been

reported from Rhamdia quelen (=R. sapo)

(Brandão, 1977; Kohn & Fróes, 1986; Fortes

& Hoffman, 1995) and Pseudoplatystoma

corruscans (Corrêa & Brasil-Sato, 2008).

The aim of this study is to provide additional

information on morphological features of the

A. gnerii by histological sections and scanning

electron microscope, as well as provides

c o m p a r a t i v e m e a s u r e m e n t s o f

Acanthostomum spp.

Silver catfish total length 23.70 ± 5.01 cm and

weight 131.6 ± 94.71 g were obtained from

o o

Madre river (27 57' 38'' S, 48 45' 27'' W),

Santa Catarina State, Brazil between May

2010 and April 2012. Fish 45 were donated

from a local fisherman and the digestory tract

was removed, placed in Petri dishes with tap

water and then examined for parasites with the

aid of a stereomicroscope. Specimens of A.

gnerii were fixed in AFA (alcohol, formaline

MATERIAL AND METHODS

RESUMEN

Palabras clave: Acanthostominae – bagre – Cryptogonimidae – Digenea – histología – parásito

Acanthostomum gnerii és un digenea frecuentemente reportado en el intestino de Siluriformes y

bien distribuida en el centro y suramérica. El objetivo de este estudio es proporcionar

información adicional sobre las características morfológicas de la A. gnerii por secciones

histológicas y microscopio electrónico de barrido, así como para proporcionar mediciones

comparativas de Acanthostomum spp.. Diferente de registros anteriores de este helminto en

Rhamdia sp., los espécimes de presente estudio presentearon dos brazos en la porción anterior del

cuerpo luego después de la faringe. Ellos se juntan en un poro lateral en el lado esquierdo del

cuerpo semelhante al observado en A. proctophorum y A. minimum. Esta morfología no hay sido

descripta como característica válida para Acanthostomidae. La variación morfológica podria

estar asociada a diferentes poblaciones de la misma especie. Nuevos estudios usando tecnicas

moleculares son recomendados para certificar se esta característica coresponde a la diversidad de

A. gnerii encuentrada en otras especies de peces.

Martins et al.

laticeps in Lunaschi (1986); Ostrowski de

N u ñ e z & G i l d e P e r t i e r r a ( 1 9 9 1 ) ;

Pseudoplatystoma corruscans in Corrêa &

Brasil-Sato (2008); Hypostomus commersoni;

Loricariichthys anus and Pimelodus

maculatus in Fortes & Hoffmann (1995).

Site of infection: stomach, intestine.

Locality: Argentine (Type locality, Szidat,

1954; Lunaschi, 1986; Ostrowski de Nuñez &

Gil de Pertierra, 1991; Gil de Pertierra &

Ostrowski de Nuñez, 1995); Costa Rica

(Caballero & Brenes, 1958, Brenes, 1961);

Brazil (Brandão, 1977; Kohn & Fróes, 1986;

Fortes & Hoffmann, 1995; Corrêa & Brasil-

Sato, 2008; present study); Nicaragua

(Watson, 1976) and Mexico (Lamothe-

Argumedo & Ponciano-Rodriguez, 1985).

Prevalence, mean intensity of infection, mean

abundance: P 40%; MI 1.88 ± 1.27; MA 0.75 ±

1.22

Material examined: 34 specimens (21 stained

with acetic alum carmine; 8 stained with H&E;

5 analyzed with a scanning electron

microscope)

Voucher specimens deposited: CHIOC (2

vouchers).

Description of the studied specimens:

Elongate body 1.437 ± 0.443 (0.984-2.840)

length by 0.393 ± 0.061 (0.304-0.560) greatest

width. Tegumental spines small, rounded and

dense in forebody, becoming smaller and less

dense until absent towards posterior end of

body. Multiple agglomerations of glandular

cells intermediating the proteinaceous spines.

Two tegumental pits or infoldings close to the

ventral sucker, one anterior and the other

posterior to ventral sucker. Unicellular glands

abundant around the pharynx (seen in

histological sections (Fig. 2F); such glands are

also present in the body tegument, becoming

less dense towards posterior end of body.

Retractile oral sucker larger than ventral

191

and acetic acid), stained in acetic alum

carmine, dehydrated in ethyl alcohol, cleared

in beechwood creosote and mounted in Canada

balsam. For histological sections, previous

fixed specimens were dehydrated in ascending

grades of alcohol, cleared in xylene and

embedded in paraffin. Cuts of th ree

micrometers sections were made on a

microtome. The sections were stained with

standard Harris' haematoxylin and eosin (H &

E) stain. For scanning electron microscopy,

specimens were fixed in 2.5% gluteraldehyde

in 0.1 M sodium cacodylate buffer and 2%

osmium tetroxide, dehydrated in a graded

series of alcohol, critical-point dried using

liquid CO and examined using a scanning

electron microscope (Zeiss DSM-940A) at

EMBRAPA - Clima Temperado, Pelotas, RS,

Brazil. All measurements are expressed in

millimeters and are presented as follows: mean

± standard deviation (if n > 30) (minimum and

maximum values). The ecological terms

“prevalence” (P), “mean intensity” (MI) and

“mean abundance” (MA) follow Bush et al.

(1997). Vouchers were deposited in the

“Helminthological Collection of the Oswaldo

Cruz Institute (CHIOC)”.

Taxonomic summary

Hosts: Rhamdia quelen (= Rhamdia sapo) in

Szidat (1954); Travassos et al. (1969);

Brandão (1977); Lunaschi (1986); Ostrowski

de Nuñez & Gil de Pertierra (1991); Fortes &

Hoffmann (1995); Gil de Pertierra &

Ostrowski de Nuñez (1995); present study);

Rhamdia rogersi in Caballero & Brenes

(1958); Brenes-Madrigal (1961); Rhamdia

nicaraguenses and Rhamdia managuensis in

Watson (1976); Rhamdia guatemalensis in

Lamothe-Argumedo & Ponciano-Rodriguez

(1985); Rhamdia sp. in Kohn & Fróes (1986);

Cyphocharax gilbert (=Pseudocurimata

gilbert) in Lunaschi (1986); Pimelodella

RESULTS

Acanthostomum gnerii from Rhamdia quelen

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016

esophagus short. Ventral sucker pre-equatorial

0.138 ± 0.022 (0.088-0.176) long by 0.139 ±

0.030 (0.088-0.232) wide submerged in

tegument or elevated above tegument surface

(it depends on the state of the worm at

fixation). Genital pore immediately pre-

acetabular. One sinistral epitheliated intestinal

caecum 0.122 ± 0.040 (0.092-0.198) with two

arms terminating blindly disposed anterior up

to the level of pharynx. Posteriorly, it ends into

192

sucker, terminal, funnel-shaped 0.256 ± 0.054

(0.168-0.320) long by 0.204 ± 0.046 (0.096-

0.264) wide. Its opening is surrounded by a

single ininterrupted row of 23-24 large

retractile spine-like structures of 0.036 ± 0.008

(0.024-0.056) by 0.016 ± 0.004 (0.008-0.024).

Pre-pharynx long 0.069 ± 0.049 (0.004-0.178),

but appears shorter when contracted. Pharynx

muscular, 0.135 ± 0.017 (0.112-0.176) long by

0.078 ± 0.024 (0.004-0.112) wide. Epitheliated

Table 1. Comparative measurements of Acanthostomum gnerii Szidat, 1954. The averages ± standard deviation are

followed by minimum and maximum values and the number of structures or specimens measured in parenthesis.

L w

Length, Width.

Present study

Szidat

(1954)

Brandão

(1977)

Kohn & Fróes

(1986)

Hosts Rhamdia

quelen

Rhamdia quelen

Rhamdia sapo

(=R. quelen)

Rhamdia sp.

Site of

infection

Stomach,

intestine

Intestine

BodyL

1.437 ± 0.443

(0.984-2.840)

1.64-2.00

1.64-2.0

2.8 (1.9-3.48)

BodyW

0.393 ± 0.061

(0.304-0.560)

0.50-0.64

0.65 (0.49-0.80)

Oral suckerL

0.256 ± 0.054

(0.168-0.320)

0.245-0.250

0.28 (0.24-0.32)

Oral suckerW

0.204 ± 0.046

(0.096-0.264)

0.200

0.24 (0.21-0.30)

Number of

peribuccal

spines

23-24

21-23

20-24

SpineL

0.036 ± 0.008

(0.024-0.056)

0.069

0.041-0.060

SpineW

0.016 ± 0.004

(0.008-0.024)

0.012

0.012-0.020

Ventral

suckerL

0.138 ± 0.022

(0.088-0.176)

0.10

Ventral

suckerW

0.139 ± 0.030

(0.088-0.232)

0.15

0.18 (0.15-0.21)

PrepharynxL

0.069 ± 0.049

(0.004-0.178)

PharynxL

0.135 ± 0.017

(0.112-0.176)

0.12

0.14 (0.11-0.15)

PharynxW

0.078 ± 0.024

(0.004-0.112)

0.10

OesophagusL- - - -

TestisL0.15-0.18 -0.28 (0.21-0.35)

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016 Martins et al.

193

Present study

Szidat (1954)

Brandão

(1977)

Kohn & Fróes

(1986)

Hosts Rhamdia

quelen

Rhamdia quelen

Rhamdia sapo

(=R. quelen)

Rhamdia sp.

Site of

infection

Stomach,

intestine

Intestine

0.116 ± 0.037

(0.064-0.232)

Posterior

0.139 ± 0.044

(0.096-0.288)

TestisW

0.25-028

0.30 (0.21 -0.38)

0.171 ± 0.034

(0.112-0.256)

Posterior

0.177 ± 0.037

(0.112-0.288)

OvaryL

0.113 ± 0.032

(0.064-0.192)

0.12-0.13

0.18 (0.14-0.21)

OvaryW

0.125 ± 0.035

(0.064-0.176)

0.19 (0.15-0.24)

Seminal

receptacleL

0.104 ± 0.032

(0.072-0.176)

Seminal

receptacleW

0.104 ± 0.028

(0.056-0.152)

EggL0.028 ± 0.003

(0.023-0.032)

0.029-0.037 0.029-0.37 0.030 (0.027-0.032)

EggW0.011 ± 0.002

(0.007-0.013)

0.014-0.016 0.014-0.016 0.014 (0.012-0.015)

Table 1. Continued. Comparative measurements of Acanthostomum gnerii Szidat, 1954. The averages ± standard

deviation are followed by minimum and maximum values and the number of structures or specimens measured in

L w

parenthesis. Length, Width.

tube, strongly coiled in its proximal region and

less coiled and more sac-like in its distal

region. Vitellaria consisting of compact

follicles arranged in two irregular or more or

less regular lateral rows, generally 7 on the left

side and 6 on the right side extending between

the posterior extremity of the uterus to post-

ovarian. Uterine loops entirely preovarian,

occupying the space from the ventral sucker to

the ovary. Operculate eggs 0.028 ± 0.003

(0.023-0.032) by 0.011 ± 0.002 (0.007-0.013).

Excretory vesicle Y-shaped very long,

bifurcating immediately posterior to ventral

sucker and extending close to the level of

pharynx (Fig. 2D). Excretory pore terminal.

a dorsal-lateral anal pore in posterior extremity

of body. Ovary compact, entire and spherical

0.113 ± 0.032 (0.064-0.192) long by 0.125 ±

0.035 (0.064-0.176) wide, dextral in most

specimens, slightly anterior to testes. Saclike

seminal receptacle of variable size 0.104 ±

0.032 (0.072-0.176) by 0.104 ± 0.028 (0.056-

0.152) situated between ovary and anterior

testis. In fully relaxed specimens, ovary

separated from anterior testes by seminal

receptacle. Two dextral testes tandem, ovoid,

wider than long; anterior testis 0.116 ± 0.037

(0.064-0.232) by 0.171 ± 0.034 (0.112-0.256)

somewhat smaller than posterior testis 0.139 ±

0.044 (0.096-0.288) by 0.177 ± 0.037 (0.112-

0.288). Seminal vesicle composed of a long

Acanthostomum gnerii from Rhamdia quelen

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016

194

Figure 1. Scanning electron micrographs of the external morphology of Acanthostomum gnerii,. A. Everted oral sucker

surrounded by circum-oral spines. Note the presence of spines in the tegument surface on anterior-dorsal region of the body. B.

Region of the elevated ventral sucker (white arrow).

A B

E F

Figure 2. Light micrographs of histological sections of adult Acanthostomum gnerii stained with haematoxylin & eosin. A, B.

Longitudinal section of the body. C. Region of the ventral sucker showing preacetabular and postacetabular pits (arrows). D.

Longitudinal section showing the excretory vesicle. E. Section of the anterior end. F. Longitudinal section of the anterior sucker

revealing the proteinaceous spines (S) with an agglomerated of glandular cells between two of them (GC). Bar: A: 0.15; B: 0.25;

C: 0.10; D: 0.15; E: 0.20 F: 0.035 mm.

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016 Martins et al.

195

gnerii

Szidat (1954) in

Lunaschi (1986)

gnerii

Szidat (1954) in

Ostrowski de Nuñes

& Gil de Pertierra

(1991)

astorquii

Watson (1976)

Hosts

Rhamdia quelen

(=R.

sapo),

Cyphocharax

gilbert

(=Pseudocurimata

gilberti) and

Pimelodella

laticeps

sapo

R. nicaraguensis

Site of infection

Stomach and

intestine

Intestine

BodyL

0.434-0.990

1.538 ± 0.372 (0.900-

2.484)

0.825 (0.750-

0.875)

BodyW

0.171-0.389

0.356 ± 0.091 (0.18-

0.576)

0.300 (0.255-

0.390)

Oral suckerL0.094-0.187

0.212

± 0.033 (0.130-

0.284)

0.169 (0.147-

0.180)

Oral suckerW

0.092-0.214

0.169 ± 0.0317

(0.087-0.232)

0.130 (0.119-

0.135)

Number of

peribuccal

spines

20 (19-23)

20 (19-21)

SpineL

0.0509 ± 0.010

(0.029-0.066)

0.033 (0.032-

0.036)

SpineW

0.012 ± 0.001 (0.008-

0.014)

0.011 (0.009-

0.013)

Ventral

suckerL

0.051-0.124

0.128 ± 0.022 (0.088-

0.188)

0.099 (0.086-

0.107)

Ventral

suckerW

0.064-0.131

0.129 ± 0.022 (0.087-

0.182)

0.103 (0.090-

0.114)

PrepharynxL0.053-0.059 0.046

PharynxL0.071-0.148 0.139 ± 0.023 (0.087-

0.185)

0.104 (0.100-

0.107)

PharynxW0.055-0.080 0.100 ± 0.024 (0.055-

0.150)

0.088 (0.057-

0.118)

OesophagusL--

Table 2. Comparative measurements of Acanthostomum spp. The averages ± standard deviation are followed by

minimum and maximum values and the number of structures or specimens measured in parenthesis. Length,

wWidth.

Acanthostomum gnerii from Rhamdia quelen

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016

196

Table 2. Continued. Comparative measurements of Acanthostomum spp. The averages ± standard deviation are

followed by minimum and maximum values and the number of structures or specimens measured in parenthesis.

L w

Length, Width.

A. gnerii

Szidat (1954) in

Lunaschi (1986)

gnerii

Szidat (1954) in

Ostrowski de Nuñes

& Gil de Pertierra

(1991)

astorquii

Watson (1976)

Hosts

Rhamdia quelen

(=R. sapo),

Cyphocharax

gilbert

(=Pseudocurimata

gilberti) and

Pimelodella

laticeps

R. sapo

R. nicaraguensis

Site of infection

Stomach and

intestine

Intestine

TestisL

0.064-0.092

0.141 ± 0.032 (0.084-

0.24)

0.105 (0.096-

0.121)

Posterior

0.057-0.104

0.165 ± 0.038 (0.096-

0.300)

0.114 (0.107-

0.121)

TestisW

0.099-0.198

0.192 ± 0.050 (0.096-

0.324)

0.122 (0.116-

0.132)

Posterior

0.085-0.193

0.194 ± 0.052 (0.108-

0.336)

0.125 (0.107-

0.144)

OvaryL

0.053-0.110

0.120 ± 0.030 (0.072-

0.252)

0.086 (0.082-

0.093)

OvaryW

0.044-0.113

0.1159 ± 0.027

(0.060-0.216)

0.079 (0.052-

0.100)

Seminal

receptacleL

0.050

Seminal

receptacleW-0.063 (0.054-

0.071)

EggL0.025-0.034 0.030 ± 0.002 (0.026-

0.037)

0.030 (0.029-

0.032)

EggW0.016-0.022 0.014 ± 0.002 (0.011-

0.020)

0.019 (0.018-

0.020)

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016 Martins et al.

197

Table 3. Comparative measurements of Acanthostomum spp. The averages ± standard deviation are followed by

minimum and maximum values and the number of structures or specimens measured in parenthesis. Length,

wWidth.

minimum

Stunkard

(1938)

minimum

Stunkard (1938)

(=Stunkardiella

minima)

Lamothe-

Argumedo &

Ponciano-Rodriguez

(1985)

A. proctophorum

(Dwivedi, 1966)

Yamaguti, 1971 in

Dwivedi (1966)

Hosts

Rhamdia

guatemalensis

Rhamdia

guatemalensis

Tropidonotus

piscator

Site of infection

BodyL

0.63-1.18

1.271-2.270

1.98-2.85

BodyW

0.39-0.42

0.241-0.418

0.18-0.21

Oral suckerL

0.17

0.165-0.285

0.135-0.150

Oral suckerW

0.18

0.191-0.234

0.105-0.130

Number of

peribuccal spines

18-20

19-20

20-22

SpineL

0.04

0.037-0.52

0.052-0.054

SpineW

0.015-0.018

0.013-0.014

Ventral suckerL

0.12

0.101-0.146

0.075-0.090

Ventral suckerW

0.13

0.093-0.150

0.060-0.075

PrepharynxL

0.157-0.255

0.075-0.150

PharynxL

0.10-0.11

0.086-0.135

0.060-0.090

PharynxW

0.068-0.085

0.067-0.136

0.060-0.075

OesophagusL0.037-0.048 0.018-0.021

TestisL0.14-0.22

Anterior 0.138-0.176 0.090-0.135

Acanthostomum gnerii from Rhamdia quelen

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016

A. minimum

Stunkard

(1938)

A. minimum

Stunkard (1938)

(=Stunkardiella

minima)

Lamothe-

Argumedo &

Ponciano-Rodriguez

(1985)

A. proctophorum

(Dwivedi, 1966)

Yamaguti (1971) in

Dwivedi (1966)

Hosts

Rhamdia

guatemalensis

Rhamdia

guatemalensis

Tropidonotus

piscator

Site of infection

Posterior

0.097-0.243

0.112-0.165

TestisW

0.07-0.15

0.146-0.217

0.090-0.105

Posterior

0.112-0.281

0.090-0.105

OvaryL

0.07-0.15 in

diameter

0.090-0.120

0.080-0.100

OvaryW

0.037-0.131

0.064-0.080

Seminal

receptacleL

0.08-0.13 in

diameter

0.071-0.136

0.076-0.084

Seminal

receptacleW0.112-0.138 0.076-0.080

EggL0.028-0.030 0.026-0.033 0.032

EggW0.016-0.018 0.011-0.015 0.012

Table 3. Continued. Comparative measurements of Acanthostomum spp. The averages ± standard deviation are

followed by minimum and maximum values and the number of structures or specimens measured in parenthesis.

L w

Length, Width.

198

DISCUSSION

Acanthostomum gnerii was first described by

Szidat (1954) parasitizing R. quelen from

Argentina. In his original description, Szidat

(1954) described A. gnerii with 21 to 23

circumoral spines and two intestinal ceca, each

with an anal pore at distal end. Later, Lunaschi

(1986) re-observed the three existed

specimens and stated that one caecum was

completely atrophied, promoting therefore a

redescription of the species. Surprisingly, most

reports of A. gnerii made before the

redescription promoted by Lunaschi (1986)

characterized the species with 2 caeca,

following the findings of the original author. In

this way, Caballero & Brenes (1958) identified

A. gnerii from R. rogersi in Panama with 19-20

circumoral spines and two intestinal ceca

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016 Martins et al.

199

astorquii as valid species, the authors did not

present morphological distinction between the

two, both defined as “having testes oblique;

vitelline follicles sparse and one caecum

atrophied”.

Despite the similarities shared by these

species, the present authors prefer to maintain

them as separate species until further studies

prove otherwise. In the present study, it was

possible to analyse specimens of A. gnerii in

various states of contraction and yet, all of

them presented the same disposal of testes

(tandem) unlike A. astorquii, which is oblique

and the same extent of vitellaria, never

extending anteriorly to posterior margin of

seminal vesicle (as in A. minimum and A.

proctophorum).

Miller & Cribb (2008) stated once the

importance of the relative length and

termination of caeca as usefull taxonomic

characters in the classification of the group.

The absence of one caecum in some

acanthostomines led Simha (1958) to create

Haplocaecum, later considered valid by

Dwivedi (1966). For Khalil (1963) and Carter

& Etges (1972), Haplocaecum was considered

a subgen us of Acanthostomum; as a

synonymous of the subgenus Atrophecaecum

according to Yamaguti (1971) and finally as a

synonymous of Atrophecaecum by Brooks

(1980). It is known a great diversity on the

patterns of organization of the gut, especially

within the acanthostomines (sensu Brooks,

1980). Usually, they end blindly, but there may

be separate ani, a uroproct, a cyclocoel, one

caecum ending blindly and one opening at an

anus, one atrophied caecum, or only a single

caecum that ends blindly or at an anus.

However, through histological sections made

in the present study, it was possible to

comprehend a new pattern of organization for

A. gnerii, not registered so far. The intestine of

the present studied specimens is composed of a

single cecum which bifurcates and originates

(however, only one caecum was drawn).

Brandão (1977) recognized A. gnerii from

South Brazil and described it with two

intestinal ceca, each with an anal pore at distal

end. Kohn & Fróes (1986) defined A. gnerii

from Rhamdia sp. in Rio de Janeiro, Brazil,

with 20 to 24 circumoral spines and

represented the species in their schematic

illustration with two intestinal ceca. From

Nicaragua, Watson (1976) reported A. gnerii

from R. nicaraguensis and R. managuensis and

also described a new species, A. astorquii from

R. nicaraguensis with 20 circumoral spines

and one atrophied caeca: the left one five to six

times as broad as the right one, each cecum

with anus at posterior end of body.

From the 20 species comprising this genus

(Brooks, 1980; Catto & Amato, 1993; Brooks,

2004), Acanthostomum proctophorum and A.

minimum closely resembles A. gnerii in

inumerous characters. However, they mainly

differ in the extent of the vitelline follicles (on

both species they are distributed laterally in the

body from the lower margin of the seminal

vesicle up to the posterior level of the ovary,

while in A. gnerii they are restricted to the

posterior portion of the uterus to post-ovarian).

According to Ostrowski de Nunes & Gil de

Pertierra (1991), although Stunkard (1938)

reported “the digestive ceca arise just behind

the pharynx and open to the surface of the body

on either side near the posterior end” for A.

minimum, the author illustrated only one

caecum in its representative drawing for the

species. The same author also compared A.

gnerii with A. minimum and realized that the

latter also had only one caecum present.

Additionally, Brooks (1980) analysed

holotypes of both A. minimum and A. astorquii

and concluded that the two appeared

indistinguishable. However, the author alerted

for the need of further examination on larger

series of specimens to better elucidate their

status. Indeed, although Brooks & Holcmann

(1993) recognized A. minimum and A.

Acanthostomum gnerii from Rhamdia quelen

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016

200

A, B and D), leaving no doubt that those

branches refer to the intestinal tract.

Although the great diversity on the patterns of

organization of the gut of A. gnerii, all other

biometric characters of the present studied

specimens remained constant with previous

reports for the species (Tables 1 and 2).

However, the occurrence of intestinal arms

disposed anteriorly has, so far, never been

associated to this digenetic family and should

therefore be included as a valid feature for the

Acanthostomidae.

An interesting feature that seems to be

associated with all acanthostomes is their

ability to retract the entire oral sucker and

circum-oral spines into the anterior part of the

body. Tkach & Snyder (2003) identified such

ability in Proctocaecum macroclemidis

(Tkach & Snyder, 2003) (=Acanthostomum

macroclemidis) and concluded that the spines

associated with muscles and the tegumental

surface form what the authors called a collar

like structure that can be retracted almost

entirely. Ibraheem (2006) also found this

capacity in A. spiniceps (Looss, 1896) and A.

absconditum (Looss, 1901) and correlated this

capacity either to anchorage of spines for

attachment into host's gut wall or to making a

firm attachment during forward movement of

the worm. The same author also showed

numerous secretory granules on the outer

openings of definite pores on the tegumental

crown of early juveniles of A. absconditum.

These granules were also reported in the

present study in the form of multiple

a g g l o m e r a t i o n s o f g l a n d u l a r c e l l s

intermediating the proteinaceous spines

(Figure 2, E, F).

This study provides additional information on

morphological features of the A. gnerii,

however it is needed to make new studies using

molecular tools to determine whether

characters found have correspondence with the

diversity of species mentioned in the literature.

two arms terminating blindly oriented

anteriorly (Figs. 2 A, B); these branches are

joined together to form only one intestinal

cecum, which ends into only one lateral anal

pore. Ibraheem (2006) studied the morphology

of Acanthostomum spiniceps (Looss, 1896)

through histological sections and showed that

the short oesophagus clearly bifurcates into

two lateral intestinal caeca for this species. It

shows, however, two very discrete extensions

of the intestine oriented anteriorly arising just

after the oesophagus (maybe these branches

are atrophied for this species).

Ostrowski de Nuñes & Gil de Pertierra (1991)

studied the life cycle of A. gnerii collected in

Argentina and defined the metacercariae stage

as possessing one intestinal caecum in one side

well developed, opening into an anal pore at

the end of the body and another one in the other

side of the body in variable degrees of atrophy.

However, in metacercariae older than 45 days

post-infection the atrophied caecum was not

observed anymore by the authors. With respect

to the adult stage, all analysed specimens

presented one caecum completely atrophied.

Furthermore, these authors, concluded that

64.3% of the specimens had their functional

caecum on the left side of the body, while

35.7% had it on the right size.

As they stated once, “because of the great

similarity of Argentine, Central American and

Mexican species it is doubtful that they are

really diferent species”. In the same way with

specimens collected from Brazil, the present

authors believe that it may be a matter of

morp hologi cal vari ation o f diff erent

populations of the same species. The presence

of two anterior arms associated with the

digestory tract initialy intrigued the present

authors: this character was only seen through

histological sections and a doubt had arisen if

they did not correspond to the excretory

vesicle, as suggested by Lunaschi (1986).

However, its internal composition differs

greatly from the vesicle composition (Figure 2,

Neotropical Helminthology. Vol. 10, Nº2, jul-dic 2016 Martins et al.

201

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