1

Comparative Topography and Ultrastructure of the Tegument in a

polyopisthocotylean parasite (Metamicrocotyla cephalus) and a

monopisthocotylean parasite (Dactylogyrus extensus)

Ola A. Abu Samak and Ashraf E. Said

Zoology Department, Faculty of Sciences, Damietta Branch, Mansoura University

Key words: Tegument – Metamicrocotyla cephalus – Polyopisthocotylea -

Dactylogyrus extensus – Monopisthocotylea.

Abstract

In the present study, comparative topography and ultrastructure have been

made of the tegument architecture between a polyopisthocotylean parasite

(Metamicrocotyla cephalus) and a monopisthocotylean parasite (Dactylogyrus

extensus) for the first time. This comparison revealed that the tegument of

Metamicrocotyla cephalus is characterized by many foldings producing closely

packed annular corrugations superimposed with a complex configuration of

many robust papillae bearing microvillus-like projections, thin terminal web just

underneath the apical plasma membrane, membranous projections from the

basal plasma membrane inside the syncytium, one type of tegumental cell

producing two tegumental secretory bodies inside the syncytium (electron-lucent

bodies "ts1" and electron-dense bodies "ts2") and the syncytium is thick (1.3-

3µm). In contrast, the tegument of Dactylogyrus extensus was characterized by

weak annulations and many minute folds like microvilli, some invaginations in

the apical plasma membrane form small vacuoles, eruption of some secretory

bodies through the apical plasma membrane, three kinds of secretory bodies

inside the syncytium from two different tegumental cells (small electron-dense

granules "td1" and large fusiform moderately electron-dense bodies containing

fibrous threads "td2" from one cell type and thin dumbbell-shaped electron-

dense bodies "td3" from other cell type) and the syncytium is thin (1.4-1.5 µm).

The possible functions of the distinctive features of the tegument whether

presence or absence have been discussed, especially the proposed role played

during the life of the parasite and the possibility of making them as

characteristic features of the polyopisthocotyleans than monopisthocotyleans.

Introduction

Monogeneans are the most common and abundant ectoparasites of fish.

They have been divided into two main taxonomic groups, the

monopisthocotyleans which are distinguished by a single undivided posterior

attachment organ and are probably "nearer" to ancestral type of monogenean

than the other group, polyopisthocotyleans which have a subdivided posterior

attachment organ.

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There are some solitary works concerning the function of the

characteristic tegumental structures that are specific for each monogenean

species. However, there were no comprehensive structural studies discus these

different compartments and also, to show weather these structures are differ in

their appearance or function or if there is another feature like the "terminal

web", could used as a taxonomical characteristic feature distinguishing

polyopisthocotyleans from monopisthocotyleans. The main purpose of the

previous literatures that deal with the study of topography and ultrastructural

studies of the monogenean tegument is to investigate the tegument of individual

species inside these two main groups or to elucidate the phylogenetic isolation

of class Monogenea from the other parasitic classes of Platyhelminths (see

Smyth and Halton, 1983; Tyler and Tyler, 1997; Cohen et al., 2001; Xylander,

2001; Tyler and Hooge, 2004). However, few literatures have been deal with a

comparison between of two monopisthocotyleans (see Lyons, 1970) or of two

polyopisthocotyleans (see Rohde, 1980; Ramasamy and Hana, 1989).

The present unique revise of representative work aims to use one model

of polyopisthocotylean (Metamicrocotyla cephalus) and another representative

of monopisthocotylean (Dactylogyrus extensus) in study the tegumental

structures to explore the similarity and dissimilarity between these two

monogenean groups and to use as specific taxonomical features for each group.

Moreover it will be try to prove if the similarity or dissimilarity in the taxonomic

group of the parasite or in the host or host environment must be followed by

similarity or dissimilarity in the ultrastructural compartment or in its suggested

function. Also, it will be look weather the tegument which is the first organ that

directly contact with the host tissue or host environment of the different

parasites belonging to different taxonomic groups, may play different role

during the parasite life and this idea may more valid or pronounced.

Materials and Methods

Parasites

Gills of Mugil cephalus (the mugilid fish) infested with Metamicrocotyla

cephalus (Polyopisthocotylea) were obtained from Ras El-Bar on the

Mediterranean Sea, Damietta, Egypt. Gills of Cyprinus carpio (the common

carp) infested with Dactylogyrus extensus (Monopisthocotylea) were obtained

from lake El-Manzala near Damietta City, Egypt.

Electron microscopy studies

The monogenean parasites were washed in several changes of cold

distilled water to free them of gill mucus.

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i-Scanning electron microscopy (SEM)

The parasites were fixed in 1% osmium tetroxide solution (OsO4) in

sucrose-containing sodium cacodylate buffer pH (7.2 – 7.4) for 1h at 4°C then

were post-fixed for 2-3h at 4°C in a 2.5% glutaraldehyde buffered solution. The

specimens were washed gently with the cold buffer and dehydrated specimens

were critical point dried using liquid CO2, mounted on aluminium stubs using

double adhesive tape and finally coated with gold in a Jeol-JEC-1100 ion –

sputtering device. Examination was done with a 5300 Jeol SEM operating at

20kV.

i-Transmission electron microscopy (TEM)

The parasites were fixed in 2.5% buffered glutaraldehyde solution for 2-

3h at 4°C and post-fixed in 1% buffered OsO4 for 1h at 4°C. The specimens

were washed in several changes through the cold buffer then were dehydrated in

graded ethanol to propylene oxide and embedded in Epon-Araldite resin.

Ultrathin sections were collected on 200 mesh grids, contrasted with uranyl

acetate and lead citrate, and examined under a JEOL 100CX TEM operating at

80kM.

Results

Surface Topography of tegument

i- Metamicrocotyla cephalus

There are major foldings of the body surface, producing closely packed

annular corrugations. Superimposed on these major folds is a complex

configuration of many robust papillae, bearing short microvillius-like

projections (Figs.1&2). This structure is nearly reduced from the regions in

between the foldings (Fig. 2). Uniciliated dome-shaped ornamented papillae,

presumed sensory structures occur on dorsal and ventral body surfaces (Fig. 1).

ii-Dactylogyrus extensus

Numerous minute folds like microvilli appear covering the tegument of

the body surfaces (Fig. 3). There are weak annular corrugations of the tegument

surfaces. These structures are completely disappeared on the head lobes while

the uniciliated structures project from pit-like depressions are pronounced (Fig.

4).

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Ultrastructure of the tegument

i- Metamicrocotyla cephalus

The body tegument is composed of an external syncytial layer and an

inner layer containing musculature and tegumental cells. The external syncytial

layer is 1.3 -3µm and delimited by apical and basal plasma membranes (Fig. 5).

The apical plasma membrane has irregular pattern of intervals forming folds and

bears irregular evaginations similar to microvilli (Figs. 6). A thin fibrous

"terminal web" appears to be present directly under the apical plasma membrane

(Fig. 5). The basal plasma membrane presents thin membranous projections

which extend into the syncytial layer, continuous with the basal lamina which is

just beneath (Figs. 5&6). The basal plasma membrane and basal lamina undulate

forming zigzag-like pattern. The syncytial layer contains two kinds of secretory

bodies and small mitochondria. The mitochondria are present in the proximal

region of the syncytium in between the projections and beneath the apical

plasma membrane (Fig. 5).

Discontinuous layers of outer circular, inner longitudinal and deeply

inner diagonal myofibers lie in the interstitial layer of connective tissue beneath

the external syncytial layer (Fig. 6). The circular muscle layer is composed of

separate bundles, one lying beneath each elevation of the basal plasma

membrane/basal lamina complex (Fig. 5) and supports the external tegument.

The longitudinal muscle layer is also composed of separate bundles, deeply

lying in between the tegumental cell reservoirs-like ducts (Fig. 6), which support

the tegumental cell ducts or reservoirs while the bundles of diagonal muscle

layer lie deeply in the region of the tegumental cell bodies (Fig. 7).

Single type of tegumental cell bodies lies at the distance 7.6µm far from

the external syncytial layer. Each cell produces a cytoplasmic connection like

reservoir or duct joining itself to the external syncytium. The cytoplasm of these

connections is denser than that of the area around the nucleus. These

connections are rich with ribosome and two kinds of secretory bodies similar to

those in the syncytium. However, the area around the nucleus contains large

number of spherical to oval mitochondria with several short cristae, granular

endoplasmic reticulum (GER), free ribosomes and few number of secretory

bodies (Fig. 7). The nucleus is large, oval in shape, irregular in outline and

contains central and peripheral patches of chromatin bodies (Fig. 7) and lateral

nucleolus.

The secretory bodies that fill the tegumental reservoirs and characteristic

of the external syncytial layer are roughly spherical, membrane-bound, electron-

lucent bodies (ts1) and spherical to oval electron-dense bodies (ts2). These

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secretory granules are varied in their abundance throughout the syncytium. The

electron-lucent bodies (ts1) are more abundant to consist most of the syncytial

content, than the dense electron bodies (ts2) which are concentrated at the apical

region of the syncytium just beneath the apical plasma membrane and also fill

the tips of the processes like microvilli (Figs. 5&6).

ii-Dactylogyrus extensus

The basic structure of the tegument is of a similar appearance to that of

the above parasite, in being the nucleated secretory regions of tegument lie in

the parenchyma beneath the tegumental muscle fibers and are connected to a

superficial syncytial covering layer. The latter is not microvillus but is

irregularly folded (Figs. 8). Cytoplasm of the syncytium is electron-dense and

can be recognized three kinds of secretory bodies; small spherical electron-dense

bodies (td1), fusiform, membrane-bound bodies containing parallel fibrous

threads embedded in a moderately electron-dense ground substance (td2) and

thin dumbbell-shaped, electron dense-bodies embedding in an electron-lucent

matrix (td3) (Fig. 8). Also, numerous small mitochondria were detected (Fig. 8)

but neither Golgi bodies nor GER were observed in the syncytium. The

syncytium measures 1.4-1.5µm in depth and is bounded by apical and basal

plasma membranes. Sometimes, the apical plasma membrane is invaginated

forming vacuoles or some secretory bodies that are apparently eventually erupt

through the membrane as dilute vacuoles (Figs. 9). The basal plasma membrane

is thrown into irregular folds. This membrane is in intimate contact with the

basal lamina. These membranes are composed of fairly constant thickness (0.2

µm) of moderately electron-dense fibrous material (Fig. 8). It merges proximally

to invest the tegumental muscles where the circular muscle fibers lie beneath its

elevations and follows by the inner continuous layer of longitudinal muscle

fibers (Fig. 8). The tegumental nucleated cells lie in the parenchyma underneath

the muscles. There are two kinds of these cells. It can be differentiated between

these two cell kinds, not only by the presence of secretory bodies but also by the

electron density of the cytoplasm. The td1 and td2 bodies are produced from the

cell having pale cytoplasm while the td3 bodies are produced from the cell

having highly electron-dense cytoplasm (Figs. 10&11). The cell body producing

td1 and td2 bodies is larger than the cell producing the td3 and its cytoplasm

extends to house the body of the other cell kind. The cytoplasm of the two

tegumental cell kinds shows regional differentiation. The region around the

nucleus is more highly electron-dense and is filled with granular endoplasmic

reticulum. The later is with dilated cisternae in the first cell kind. The region far

away the nucleus in both cell kinds is filled with the secretory bodies and with

much paler cytoplasm (Figs. 10&11). The first cell kind contains ovoid nucleus

with prominent and lateral nucleolus (Fig. 11). Also, thin chromatin patches lie

on the nuclear envelope. The nucleus of the second cell kind is irregular in shape

with large nucleolus and thin peripheral chromatin bodies (Fig. 10). Free

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ribosomes are common between the reticular membranes and in the general

cytoplasm of both cell kinds. Also, fairly mitochondria and Golgi bodies are

present (Figs. 10&11). Each cell body may produce many cytoplasmic

connections carrying the secretory inclusions and joining itself to the outer

syncytial layer.

Discussion

The present ultrastructural comparative study of the tegument of one

model of polyopisthocotyleans (Metamicrocotyla cephalus) and another model

of monopisthocotyleans (Dactylogyrus extensus) has revealed that these two

models possess the same basic tegumental structure like other previously studied

monogeneans, in being a syncytial cytoplasmic layer connected to tegumental

cells (cytons) lying beneath the tegumental muscle layers. In spit of this great

similarity, there are some unique structures that are dissimilar and serve as

different taxonomical criteria.

The first unique structure is the presence of "terminal web" just beneath

the apical plasma membrane in the present polyopisthocotylean (M. cephalus)

and in all previously studied members of this group, while it did not

observed in the present monopisthocotylean, D. extensus and in the other

previously studied members of this group. Careful revision by the authors has

found that the thickness of this web is directly proportion with the thickness of

syncytium. It is thin in the species having thin syncytial layer as in M. cephalus

(0.07 µm / 1.3 – 3 µm) and increase as syncytium increases as in Rajonchocotyle

emarginata (0.4 µm / 5-6 µm) (Lyons, 1972). Besides, its basic structure of

fibrous material, this criterion may have a role in the performance of parasite

through its life. This role may be protective from the foreign forces that fall

down on its tegument. These forces may exert from the movement of gill

filament that accommodate such parasite during host normal respiration.

Consequently, this characteristic tegument resists the successive shocks creating

during the host normal breathing. Furthermore, this suggestion may gain support

from our finding that the longer polyopisthocotyleans (2mm to 14mm) have this

unique structure (terminal web) rather than shorter monopisthocotyleans (less

than 0.5mm up to 2mm) which did not have such structure. In addition to this,

the longer polyopisthocotyleans have haptor attached to secondary gill lamellae

with their projecting body between primary gill lamellae whereas, the shorter

monopisthocotyleans have haptor accommodated between two successive

secondary gill lamellae and their body still shielded in this place. This

accommodation makes the longer polyopisthocotyleans more receive to

ventilation forces and consequent shocks of primary gill lamellae however,

shorter monopisthocotyleans gain more shielding effect from its place. In

general, the absence of this specific specialization of the tegument indeed leads

to the fag of its function which should be compensated either by another similar

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specialization or by the loss of this function. Previously, Lyons (1972), Rhode

(1975), Ramasamy et al. (1987) suggested other functions of this terminal web

as supportive, skeletal or transmitted structure. Its only finding in the

polyopisthocotyleans let' s workers to suggested that it could has a specific

criterion of polyopisthocotyleans as reported by Lyons (1973) and has a

phylogenetic value as stated by Justine (1992).

The second unique structure is in the form of thin membranous

projections cross the syncytial layer arising from the basal plasma membrane in

M. cephalus (a polyopisthocotylean) rather than D. extensus (a

monopisthocotylean). This structure may be rudiments of the embryonic

extracellular spaces. This may be used as osmoregulation of intra and extra body

fluids as well as the movement of endogenous or exogenous molecules through

the syncytial layer of the tegument. The later function may improve the

physiological impact work of the tegument. Also, we can go deep to say that this

may be a strong evidence of the sharing propriety of tegument specially haptoral

tegument in feeding or survival of the whole parasite. This may be by allowing

the host blood fluids to inter the body of the parasite in away rather than mouth.

Moreover, this membranous structure may have a supporting mechanism. This

supporting mechanism may help the parasite to tolerate the repeating movement

of adjacent primary gill lamellae in the case of polyopisthocotyleans having long

body length. This characteristic structure is mostly prominent in

polyopisthocotyleans and has not been previously observed in

monopisthocotyleans with some exceptions. The authors have noticed that this

unique structure in previously mentioned in the work by Lyons (1970) without

referring to it in its paper text. Also, in some other polyopisthocotyleans;

Vallisia indica (Ramasamy et al., 1987) and Allodiscocotyla diacanthi

(Ramasamy et al., 1995), we didn't have noticed this structure, however, it is

found in the other polyopisthocotyleans. This makes the generalization of this

taxonomical character in distinguishing between these two groups difficult.

Consequently, it is generally recommended that the tegument of those species

should be reviewed carefully to enable us or not to use this character as general

taxonomical feature.

The third unique finding is the variation in surface topography of

tegument from the simplicity in a monopisthocotylean parasite to complexity in

a polyopisthocotylean parasite. The tegument of D. extensus in the present study

is characterized by weak annulations and many minute folds like microvilli,

however M. cephalus is characterized by many foldings producing closely

packed annular corrugations superimposed with a complex configuration of

many robust papillae bearing microvillus-like projections. The simplicity in

other monopisthocotyleans is constricted in the presence of microvilli,

transverse annulations, folds and /or finger-like invaginations (Shaw, 1980; El-

Naggar et al., 1991; Khidr, 1996; Ramasamy and Brennan, 2000; El-Naggar and

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Cable, 2007). In contrast, the complexity in other polyopisthocotyleans is varied

widely between annular corrugations, tegumental ridges, microvilli, tegumental

protrusions forming reticulum, bosses, folds, lamellate-like reticulum, honey

comb-like array, deep invaginations, serration and shallow invaginations

(Ramasamy and Hanna, 1986a, b; Williams and Mckenzie, 1995). Considering

the difference in length of parasitic monopisthocotyleans in compare to the

polyopisthocotyleans, this length difference give a very obvious distinguish in

the presence and shape of tegumental structures. These structures in

polyopisthocotyleans may provide protection and supporting mechanism

(forces) and firm attachment to antagonize respiratory current and movement of

primary gill lamellae. On the other hand, the tegumental topography of

monopisthocotyleans is devoid of the richness and variation of specific

structures that appear clearly in polyopisthocotyleans. At is also noteworthy

mentioning that, this complex structure may help the parasite as mechanical

barrier against the hits of antibodies and immunological cells of the host blood

since polyopisthocotylean parasite is facing by host blood due to its feeding

habit rather than mucus feeding monopisthocotylean parasite. In general, the

authors are wondering if this variation in surface topography from this

simplicity to complexity may be used as a taxonomical key to differentiate

between monopisthocotyleans from polyopisthocotyleans.

In the present study, there are two kinds of secretion in the syncytium of

the polyopisthocotylean parasite namely M. cephalus, one is electron-lucent

which constitute the most cytoplasmic components of the syncytium, however,

the other is electron-dense constituting only few of the cytoplasmic components.

These two secretory bodies are produced from one kind of tegumental cell. In

contrast, the syncytium of D. extensus was characterized by the presence of

three kinds of electron-dense secretory bodies produced from two kinds of

cytotic cells. One of these cells produce two kinds of secretory bodies (small

electron-dense bodies "td1" and large fusiform moderately electron-dense bodies

containing fibrous threads "td2") and the other cell kind produce only one

secretory kind (thin dumbbell-shaped electron-dense bodies "td3"). These

secretions were randomly distributed within the cytoplasm (as in Fig. 8).

Concerning monopisthocotyleans, it is most common that each secretion is

produced only from a specific kind of secretory cell, but it was rarely that one

secretory cell can produce two kinds of secretion and electron-lucent secretion is

common than other kinds. However in polyopisthocotyleans, it is most common

that one kind of secretory cell can produce two kind of secretions and electron-

lucent secretion also is common than the other kind, i.e., the secretions produce

by monopisthocotyleans are more specific and have a wide variety of secretory

cells while that of polyopisthocotyleans are not. These findings are similar to the

polyopisthocotylean of the present work, M. cephalus and with some difference

with the monopisthocotylean of the present study, D. extensus.

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The present study shows clearly that the tegument of the

monopisthocotylean, D. extensus, exhibit exo/endocytotic movement of

secretory bodies while this feature couldn't be confirmly observed for the

polyopisthocotylean, M. cephalus. However, the previous studies (Rohde, 1975;

Kritsky and Kruidenier, 1976; Ramasamy et al., 1987; 1995; El-Naggar et al.,

1991; El-Naggar and Cable, 2007) have shown that for general sense the

tegument of monogenean parasites could exhibit exo/endocytotic movement of

tegumental secretory bodies freely with uncertainty for the kind of these

secretory bodies or their functional roles. It is greatly suggested that further deep

biological studies were needed to elucidate the chemical, physical and

immunological nature of these secretions.

Finally it can said that all the previous literatures concerning the

tegumental studies in Monogenea either singular or in a comparative subject, did

not clearly listed an exactly differential criteria that could used for distinguished

between the monopisthocotyleans and polyopisthocotyleans. Consequently, we

could advice that the recent studies should take in concentration a certain major

criteria in studying ultrastructure of the tegument. This will unable us to

differentiate between the two major monogenean groups taxonomically or this

will establish some basic features and re-arrange for a review article to enclose

all characteristic features and fill the gaps about the essay of tegument.

Legend of Figures

Figure 1. Scanning electron micrograph of tegument of Metamicrocotyla

cephalus, showing many foldings producing closely packed annular

corrugations superimposed with a complex configuration of many robust

papillae bearing microvillus-like projections and few uniciliated dome-

shaped ornamented papillae (arrows), presumed sensory structures.

Figure 2. Scanning electron micrograph of tegument of M. cephalus, showing

some foldings (stars) superimposed with a complex configuration of many

robust papillae (rp) bearing microvillus-like projections (mp).

Figure 3. Scanning electron micrograph of tegument of Dactylogyrus extensus,

showing weak annulations and many minute folds like microvilli (mf).

Figure 4. Scanning electron micrograph of D. extensus tegument covering the

head lobes, showing uniciliated structures (head arrows) projected from pit-

like depressions.

Figure 5. Transmission electron micrograph of the body tegument of M.

cephalus, showing the deep infoldings of both apical and basal membranes

that bounded the outer syncytium and thin membranous structures (arrows).

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cmf, circular muscle fibers; m, mitochondrion; ts1, electron-lucent bodies;

ts2, electron-dense bodies and tw, terminal web.

Figure 6. Transmission electron micrograph of the body tegument of M.

cephalus, showing thin membranous structure (arrows). cmf, circular muscle

fibers; f, folds; lmf, longitudinal muscle fibers; mp, microvilli-like

projections; rp, robust papilla and tr, tegumental reservoir.

Figure 7. Transmission electron micrograph of the body tegument of M.

cephalus, showing the tegumental cell bodies. ch, chromatin body; dmf,

diagonal muscle fibers; GER, granular endoplasmic reticulum; m,

mitochondria; n, nucleus; nu, nucleolus; td, tegumental duct and ts2,

electron-dense bodies.

Figure 8. Transmission electron micrograph of the body tegument of D.

extensus, showing the irregularly weak folded syncytium containing small

electron-dense bodies (td1), fusiform, membrane-bound bodies containing

parallel longitudinal fibrous threads (td2) and thin dumbbell-shaped, electron

dense-bodies embedding in electron-lucent bodies (td3). bl, basal plasma

membrane/basal lamina complex; cmf, circular muscle fibers and lmf,

longitudinal muscle fibers.

Figure 9. Transmission electron micrograph of the body tegument of D.

extensus, showing the exocytotic (stars) and endocytotic (head arrows)

movements throughout the apical plasma membrane.

Figure 10. Transmission electron micrograph of the body tegument of D.

extensus, showing the tegumental cell bodies producing thin dumbbell-

shaped, electron dense-bodies (td3). GER, granular endoplasmic reticulum;

n, nucleus and nu, nucleolus.

Figure 11. Transmission electron micrograph of the body tegument of D.

extensus, showing the tegumental cell bodies producing small electron-dense

bodies (td1) and fusiform, membrane-bound bodies containing parallel

longitudinal fibrous threads (td2). GER, granular endoplasmic reticulum; n,

nucleus and nu, nucleolus.

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مقارنة السمات السطحية والتركيب الدقيق إليهاب طفيلى بولىبيثوكوتيلين

( اكستنسس داكتيلوجيرس)وطفيلى مونوبيثوكوتيلين (سيفالس ميتاميكروكوتيل)

عال عبد الحليم أبو سمك و أشرف المتولى سعيد مصر - جامعة المنصورة – فرع دمياط – كلية العلوم –قسم علم الحيوان

تم فى الدراسة الحالية ألول مرة مقارنة السمات السطحية و التركيب الدقيق إليهاب

وطفيلى من المونوبيثوكوتيليدات (سيفالس ميتاميكروكوتيل)طفيلى من البولىبيثوكوتيليدات

ميتاميكروكوتيلوقد كشفت هذه المقارنة عن تميز إيهاب الطفيلى . (اكستنسس داكتيلوجيرس)

بالعديد من الطيات التى شكلت تموجات حلقية متقاربة على نحو وثيق تحمل تشكيل سيفالس

معقد من الحلمات الغليظة التى تنتهى بنتوءات تشبه الخمالت الدقيقة، ووجود غشاء طرفى

رقيق يقع مباشرة تحت الغشاء البالزمى القمى ، ووجود امتدادات من الغشاء البالزمى

القاعدى داخل المدمج، إضافة لوجود نوع واحد من الخاليا الجلدية التى تنتج نوعان من

وتراوح (أجسام المعة الكترونيا و أجسام أخرى داكنة الكترونيا)اإلفرازات داخل المدمج وهما

داكتيلوجيرسوفى المقابل تميز إيهاب الطفيلى .ميكرون3الى 1.3سمك المدمج بين

بحلقات ضعيفة وطيات تشبه الخمالت الدقيقة، ووجود بعض االنغمادات فى الغشاء اكستنسس

لبعض ءالبالزمى القمى مكونة فجوات صغيرة وأيضا ظهور تفجر افرازى من خالل هذا الغشا

ينتج النوع األول أجسام : األجسام اإلفرازية، وتميز أيضا بوجود نوعان من الخاليا الجلدية

صغيرة داكنة الكترونيا و أجسام أخرى مغزلية كبيرة ذات كثافة متوسطة الكترونيا بينما النوع

1.5-1.4)الثانى أجسام إفرازية داكنة الكترونيا تشبه الدمبل وقد كان المدمج أكثر رقة

وقد تم مناقشة الوظائف المحتملة للسمات المميزة لغطاء جسم الطفيليان سواء . (ميكرون

بالوجود أو بالغياب وخصوصا الدور المقترح الذى تضطلع به أثناء حياة الطفيليات ومدى

إمكانية جعلها صفات مميزة لمجموعة البولىبيثوكوتيليدات عن مجموعة

. المونوبيثوكوتيليدات