316
26
Lecanicephalidea Hyman, 1951 (Order)
Luis García-Prieto, Berenice Adán-Torres, Omar Lagunas-Calvo, and
Brenda Atziri García-García
Phylum Platyhelminthes
Class Cestoda
Subclass Eucestoda
Order Lecanicephalidea
doi:10.32873/unl.dc.ciap026
2024. In S. L. Gardner and S. A. Gardner, eds. Concepts in Animal Parasitology. Zea Books, Lincoln, Nebraska, United States.
Open access CC BY-NC-SA
317
Chapter 26
Lecanicephalidea Hyman,
1951 (Order)
Luis García-Prieto
Laboratorio de Helmintología, Instituto de Biología,
Mexico City, Mexico
Berenice Adán-Torres
Departamento de Zoología, Instituto de Biología,
Mexico City, Mexico
Omar Lagunas-Calvo
Departamento de Zoología, Instituto de Biología,
Mexico City, Mexico
Brenda Atziri García-García
Laboratorio de Vertebrados, Departamento de Biología
Introduction
Lecanicephalidea (the name derived from Greek, lekane
= dish or pot and kephalē = head) is an order of cestodes
remarkably diverse in its morphology. They are mainly
parasites of the spiral intestine of batoid elasmobranchs dis-
tributed around the world (Jensen et al., 2016). The main
diagnostic trait of this group is the presence of an apical struc-
ture on the scolex, called a myzorhynchus or, more recently,
termed the apical organ, which is found in a wide variety of
forms. Other important characteristics of this group include:
The presence of 4 suckers (also termed bothridia), proglottids
with the vagina opening posterior from the cirrus sac into
the genital atrium (Jensen et al., 2017), and a sizeable vas
deferens often expanded into a sacciform external seminal
vesicle that extends from the level of the ovarian isthmus to
the cirrus sac (Jensen et al., 2016).
described for this order was Polypocephalus radiatus Braun,
1897; however, the ordinal status of Lecanicephalidea has
been questioned (their elevation to this level was even invali-
dated by Butler (1987)) and its species were often included
in the order Tetraphyllidea (Jensen et al., 2017). Currently,
based on molecular data analyses, Lecanicephalidea is con
-
sidered the earliest diverging lineage among the acetabluate
cestode orders (Jensen et al., 2017).
According to Jensen and colleagues (2017), Lecani-
cephalidea contains 8 families with 29 genera and 90 de-
scribed species, as well as 7 incertae sedis species and 66
species inquirendae. Polypocephalus is the genus with the
Adelobothrium, Cephalobothrium, Collicocephalus, Rexapex,
Anthemobothrium, Corrugatocephalum, and Quadcuspiboth-
rium are monotypic.
Main Morphological Characteristics
The strobila of this group of polyzoic cestodes is rela
-
tively small since the smallest worm measures less than 500
mm (Jensen, 2005) and only a few species have strobila
measuring up to 6 cm, according to Butler (1987). Lecani-
cephalideans are generally euapolytic, but some species can
be anapolytic, apolytic, and hyperapolytic. The proglottids
Polypocephalus moretonensis
Butler, 1987, holotype specimen from the Queensland Museum,
South Brisbane, Queensland, Australia. See https://www.gbif.org/
occurrence/1066763010 for more information about this specimen.
Source: Queensland Museum, 2023. License: CC BY.
CONCEPTS IN ANIMAL PARASITOLOGY
318
tend to be craspedote (or may rarely be acraspedote) and
may be laciniated (fringed in the posterior end) or not (Jen-
sen et al., 2016).
With the exception of Aberrapex and Paraberrapex, which
lack an apical structure in the scolex, the remaining leca-
nicephalideans are distinguished from most other orders of
cestode parasites of elasmobranchs by having this structure
(Jensen, 2005). The apical organ can be external or entirely
internal; its morphology varies from a foldable sheet to an
oval muscular pad or may present as an inverted cone with
papilliform projections. In families such as Cephaloboth-
riidae, there can be a glandular sphere. In others, such as
Polypocephalidae, the apical organ is divided into tentacles.
The tentacles can be retractable (or not) and some are invag-
inable. The scolex is also characterized by having 4 unilocu-
late acetabula or bothridia (and are biloculate only in Zanoba-
tocestidae and diamond-shaped only in Quadcuspibothrium).
Immature proglottids may be laterally expanded or not, and
may form a trough (although only in Eniochobothriidae) (Jen-
sen et al., 2016).
Reproductive Structures
Lecanicephalideans are hermaphroditic.
The female reproductive system is markedly heteroge-
neous; it consists of the following structures. It contains an
ovary that is variable in form (it may be H-shaped, bi-lobed,
tetra-lobed in cross section, digitiform, irregularly lobed with
each lobe divided in 3 sub-lobes, etc.). It includes a vagina,
which may be positioned medially, laterally, or sub-laterally
(or may even be absent), opening into a genital atrium pos-
terior to the cirrus sac. It includes a follicular vitellarium,
generally arranged in 2 lateral bands. The vitellarium may
reach the posterior end of the proglottids or only the anterior
border of the ovary, and they do not exceed the anterior limit
2 lateral bands before the cirrus sac) or may present in 2 lat-
eral bands from the middle of the cirrus sac to the level of the
ovarian isthmus. It includes a uterus that is medial, saccate, or
bisaccate (and constricted to the level of the genital atrium),
and is variable in extent, from the anterior of the ovary to
the genital pore, or almost occupying the entire length of the
proglottid (Jensen, 2005; Jensen et al., 2016).
In contrast, the morphology of the male reproductive sys-
tem is more homogeneous: The number of testes varies from
4 (in Seusapex karybares) to more than 40 (in Tetragono-
cephalus kazemii) that are distributed commonly in 1 to 2
columns, located anteriorly to the genital pore, ovary, or cir-
rus sac (Russell and Jensen, 2014; Jensen et al., 2016; Roohi
and Malek, 2017). Internal and external seminal vesicles may
be present or absent. The cirrus sac is pyriform (or elliptical
in some Polycephalidae). The cirrus is unarmed (although it
is armed in Tetragonocephalidae and Eniochobothriidae and
rarely in Polycephalidae and Lecanicephalidae). The genital
pore is lateral (or sub-lateral in Polycephalidae), alternating
irregularly (Jensen, 2005; Jensen et al., 2016).
Description and Summary of a Representative Species
Note: This work is not intended for the purposes of zoo-
logical nomenclature.
Aberrapex senticosum Jensen, 2001
These are small, euapolytic worms, 1.48–6.33 mm-long,
with a maximum width of 31–38 mm at the ends of the stro-
bila. The scolex consists of 4 bothridiated acetabula. There is
absent. The acetabula and scolex proper are partially covered
microtriches. A cephalic peduncle is absent. The strobila has
-
rior margins of the proglottids. The proglottids are craspedote
and laciniate. There are 29–36 immature proglottids with 1 or
from the anterior margin of the proglottid to the anterior limit
of the ovarian isthmus. The external seminal vesicle is wide
and saccate, while an internal seminal vesicle is absent. The
cirrus sac is pyriform and the cirrus is unarmed. The ovary
is H-shaped in the dorsoventral view and tetra-lobed in cross
section. It is also lobulated and symmetrical. The vagina runs
laterally from the ootype zone to the genital pore; it is open
posterior to the cirrus sac into the genital atrium. The genital
pore is lateral, pre-equatorial, and alternates irregularly. The
uterus is saccate, extending along the midline of the proglot-
tid, almost reaching the anterior margin of the proglottid. A
uterine pore is absent. The vitellaria are follicular, medullar,
and lateral. The follicles are distributed along the entire length
of the proglottid, only interrupted by the ovary (Jensen, 2001).
Taxonomic summary.
Type host: Bat eagle ray Myliobatis californica Gill, 1865
(Rajiformes, Myliobatidae).
W), Baja California, Mexico.
Site of infection: Spiral intestine.
Type specimens are listed here and additional details can
be found in the original paper where this species was de-
scribed: Holotype (CNHE 4188) and 2 paratypes (CNHE
4189); 3 paratypes (USNPC 91208); 2 paratypes (HWML
16374); 7 paratypes (LRP 2152–2158).
319
CHAPTER 26. LECANICEPHALIDEA HYMAN, 1951 (ORDER)
Lecanicephalidea Hyman, 1951 Taxonomy
In addition to Aberrapex senticosum, 6 more species of
the genus parasitizing myliobatiform batoids from tropical
and temperate waters have been described to date: A. arrhyn-
chum (Brooks, Mayes, and Thorson, 1981) Jensen, 2001; A.
ludmilae Menoret, Mutti & Ivanov, 2017; A. manjajiae Jen-
sen, 2006; A. sanmartini Menoret, Mutti & Ivanov, 2017; A.
vitalemuttiorum Menoret, Mutti & Ivanov, 2017; and A. wei-
paensis Koch, Jensen & Caira, 2012 (Menoret et al., 2017).
Aberrapex senticosus can be distinguished from the other spe-
cies included in the genus since it has the highest number of
testes (20–40 versus 18–25, 24–31, 10–19, 11–16, 15–21, and
10–17, respectively). In addition, A. ludmilae and A. arrhyn-
chum lack an external seminal vesicle (while it is present in
A. senticosum). In the remaining species, hastate spinitriches
are entirely absent in the acetabular surface (A. weipaensis),
restricted to the central region of the acetabula (A. manjiajae)
or cover only two-thirds of the distal acetabular surface (A.
sanmartini and A. vitalemuttiorum) while in A. senticosus
hastate spinitriches cover the entire distal acetabular surface
(Jensen, 2001; 2006; Koch et al., 2012; Menoret et al., 2017).
based on morphological data (Caira et al., 1999; 2001; Jen-
sen, 2005). In such studies, this group of cestodes was gen-
erally nested as a clade by the presence of an apical struc-
ture in the adult stage. When authors such as Jensen (2005)
included some species lacking apical structure, they were
-
tive to its relationship with other orders of cestodes, Caira
cyclophyllideans.
Almost simultaneously, several works based on molecular
evidence established Lecanicephalidea as the earliest lineage
among the acetabulate cestode orders (Olson and Caira 1999;
Olson et al., 2001; Caira et al., 2005; Waeschenbach et al.,
2007).
The most recent and comprehensive analyses on the re-
lationship among lecanicephalidean cestodes was conducted
the monophyletic nature of the order and recognized 8 ma-
jor groups as independent families: 4 previously existing
(Lecanicephalidae, Polypocephalidae, Tetragonocephalidae,
and Cephalobothriidae) and 4 new families (Aberrapecidae,
Eniochobothriidae, Paraberrapecidae, and Zanobatocestidae).
Life Cycles
Life cycles of cestodes of the order Lecanicephalidea are
poorly known; however, according to Caira and Reyda (2005)
larvae of these cestodes have been registered in some groups
of invertebrates, mainly bivalves (molluscs) and crustaceans,
as well as in few actinopterygians. Based on the scarce avail-
able information on the developmental stages of lecanice-
phalideans, Caira and Reyda (2005) suggested that they lack
a coracidium (that is, a hexacanth embryo is inside the egg);
plerocerci have been found in bivalves and gastropod mol-
luscs and plerocercus, their terminal larval stage, in actinop-
terygians such as Scomberoides commersonnianus from the
Arabian Gulf (Bannai et al., 2014).
Lecanicephalideans have circumglobal distribution; cur-
rently, members of this cestode order have been described
from 8 of the 12 marine biogeographic realms, with the great-
est concentration of species (69%) recorded in the central
Additional Notes about the Morphology
As noted above, Lecanicephalidea is an order of cestodes
lecanicephalideans possess additional features of proglot-
tid anatomy that are unusual for other cestodes hosted by
Hexacanalis was erected by Perrenoud (1931) based on the
presence of 6 excretory vessels, while the most common con-
dition in the cestodes is the presence of 2 dorsal and 2 ventral
excretory vessels. Jensen and colleagues (2016) pointed out
or more) is so particular, that it can be considered a diagnos-
tic trait of the family Lecanicephalidae. In the same way, 1
species included in this genus (Hexacanalis folifer) is unique
among lecanicephalideans by having a U-shaped ovary in
cross section and proglottids with prominent posterior dor-
soventral processes in the form of large lappets (Cielocha
and Jensen, 2011).
On the other hand, despite the scarce knowledge about the
gravid proglottids of the members of this order, it has been
determined that the morphology of the eggs shows drastic
variations, even among the congeneric species: In Anteropora
comica, the eggs are covered with numerous small, regularly-
in A. klosmamorphis, the eggs have a corrugated surface and
-
curs with the cocoons, since in some species (for example,
Zanobatocestus major), cocoons contain only 2 eggs while
in others (such as Z. minor), these are arranged in cocoons
with hundreds of eggs (Jensen et al., 2014).
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Supplemental Reading
Caira, J. N., K. Jensen, and C. J. Healy. 2001. Interrelationships
among tetraphyllidean and lecanicephalidean cestodes. In
D. T. J. Littlewood and R. A. Bray, eds. Interrelationships
Kingdom, p. 135–158.
Olson, P. D., and J. N. Caira. 1999. Evolution of the major
lineages of tapeworms (Platyhelminthes: Cestoidea) inferred
of Parasitology 85: 1,134–1,159. doi: 10.2307/3285679
