Table Of ContentPROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
116(1):215-22L 2003.
Description of subadult Pallisentis (Pallisentis) rexus
(Acanthocephala: Quadrigyridae) from the vertebrate intermediate
host in Thailand with an examination of the species identity
Omar M. Amin and Horst Taraschewski
(OMA) Institute of Parasitic Diseases, P.O. Box 28372, Tempe, Arizona 85285, USA;
(HT) Zoologische Inst. Abt., Okologie, Univ. Karlsruhe,
Kaiserstrasse 12, 76128 Karlsruhe, Germany
—
Abstract. Subadults (considerably developed immatures) ofthe quadrigyrid
acanthocephalan Pallisentis rexus Wongkham & Whitfield, 1999 are described
from the swamp eel, Monopterus albus (Zieuw, 1793) in Thailand. The species
is placed in the subgenus Pallisentis. Our specimens are compared with adults
of the same species collected from the freshwater snakehead Ophicephalus
striata Bloch also from Thailand. Discrepancies from the original description
are noted, certain structures, e.g., proboscis hook roots and brain (cepahalic
ganglion), are re-interpreted, and additional information provided.
The genus Pallisentis Van Cleave, 1928 hind gut. The encapsulated worms were
was revised, three subgenera were erected, mostly alive when liberated from their cysts
and a key to the valid species, and other in fish physiological solution. Forty-two
taxonomic information were provided by worms (16 males, 26 females) were refrig-
Amin et al. (2000). About the same time, erated in tap water overnight then fixed and
Wongkham & Whitfield (1999) described shipped in 5% formalin. They were subse-
Pallisentis rexus from the freshwater snake- quently transferred to 70% ethanol, stained
head, Ophicephalus striata Bloch, from the in Mayer's acid carmine overnight then
Chiang Mai Basin in Thailand. More re- briefly destained, dehydrated in ascending
cently, we have collected subadults of P. concentrations of ethanol, cleared in grad-
rexus from the swamp eel, Monopterus al- uated concentrations of terpineol in 100%
bus (Zieuw, 1793) from Bangkok, Thai- ethanol, and whole mounted in Canada bal-
land. Our specimens and type material ex- sam.
amined by us shed considerably more light Measurements are in jjim unless other-
on the morphology and status of P. rexus wise stated. The range is followed by mean
which the present study reports in a com- values (in parentheses). Width measure-
parative context. ments refer to maximum width. Trunk
length does not include proboscis, neck, or
Materials and Methods male bursa. The term subadults is used to
describe the highly developed immature
Ten 40-80 cm long swamp eels, M. al- forms. They are practically identical to
bus, were examined for parasites on 20 adults; all males and females were distend-
March 2001. The fish, obtained from a fish ed with sperm and ovarian balls, respec-
market in Bangkok, Thailand, had been col- tively. Specimens were deposited in the
lected from local streams. The 10 fish were United States National Parasite Collection
infected with a total of 257 (range 5-74 per (USNPC) no. 91753. Beltsville, Maryland,
fish) ovoid whitish nodules in the body cav- U.S.A. Seven adult paratypes (3 males, 4
ity especially at the external surface of the females) from the British Museum of Nat-
216 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
(BMNH)
ural History (no. 1997.6.3.2-13) attachment organs to ensure establishment
were also studied. of new recruits in the gut of the definitive
host (see Amin 1986, 1987 for other ex-
Results and Discussion amples).
Omissions in the original description in-
It is important to note that all character- clude accounts of the giant nuclei of the
istics of our P. (P.) rexus subadults listed hypodermis, lemnisci, and proboscis/neck,
in Table 1 and illustrated in Figures 1-3 as well as some details of the male repro-
match those observed in the adult paratypes ductive system and hook and spine inser-
borrowed from BMNH. The anatomy of the tion. We noted that one dorsal and one ven-
subadults is generally similar to that of the tral elongate giant hypodermal nuclei were
adults as described by Wongkham & Whit- normally present. They were rarely absent
field (1999). However, misinterpretations on either side. Two similarly elongate giant
and omissions exist in the original descrip- nuclei were also noted within the proboscis
tion which otherwise was adequate. The retractor muscles in the proboscis/neck
quality of staining of paratypes produced area. These nuclei are rarely reported in the
faded and often indistinguishable structures, genus Pallisentis but have been recently ob-
e.g., proboscis hook roots and cephalic gan- served in Pallisentis (Brevitritospinus) viet-
glia, which readily explains Wongkham & namensis Amin, Heckmann, Ha, Luc &
Whitfield's (1999) version of worm anato- Doanh, 2000. Each lemniscus had one large
We
my. shall report these discrepancies in oval giant nucleus located at the level of the
the following section in an attempt to pro- posterior half of the proboscis receptacle.
vide an accurate and complete description Wongkham & Whitfield (1999) made no
of the species. reference to the two large nuclei in the wall
Pallisentis rexus is placed in the subge- of Saefftigen's pouch which was properly
nus Pallisentis according to Amin et al. described posterior to the cement reservoir
(2000) because the proboscis hooks gradu- (Fig. IB) but not "at the posterior margin
ally decline in size posteriorly and the ce- of cement gland" as stated in the Abstract
ment glands are long and with many giant (Wongkham & Whitfield 1999). No refer-
nuclei. ence was made to the prominent sperm duct
Qualitative and quantitive traits of P. (P. which ran parallel to the cement gland or
)
rexus subadults are provided and compared the large common sperm duct which ran
with those of adults, when available (Table parallel to and overlapped Saefftigen's
1). Measurements of subadults largely fell pouch and the posterior half of the cement
within the range of those reported for adults reservoir. Proboscis hooks had variably el-
by Wongkham & Whitfield (1999). On the evated cuticular rims that were often prom-
average, subadults, especially females, were inent and body spines consistently had dis-
relatively smaller than adults in only one tinct cone-shaped cuticular sleeves that left
character, trunk length. However, mean size only spine tips naked.
of proboscis, proboscis hooks, proboscis re- Misinterpretation in the original descrip-
ceptacle, and lemnisci were somewhat tion includes accounts of the proboscis
greater in subadults than in adults. This ob- hook roots, brain (cephalic ganglion), collar
servation is attributed to two factors: the and trunk spines, and position of the female
apparent precocious state of development of gonopore. Each of these characteristics has
subadult P. (P.) rexus (with sperm and important taxonomic significance that can
ovarian balls) in their vertebrate interme- not be overlooked. Three aspects of pro-
diate host M. albus; this phenomenon has boscis hook roots need to be addressed. All
been observed in other acanthocephalans hook roots extend laterally for a short dis-
(Amin 1982); and the early development of tance then loop back posteriorly in a direc-
VOLUME NUMBER
116, 1 217
Figs. 1-3. Diagnostic features of Pallisentis (P.) rexus. 1. One row ofproboscis hooks and roots of female.
2. Posterior part of female proboscis receptacle showing triangular brain (cephalic ganglion) and ventro-lateral
nerve cord passage through indented part of proboscis receptacle. 3. Posterior end of female showing slightly
subterminal position (near terminal on ventral site) of gonopore. Scale bars =100 [xm.
tion paralleling that of the blade thus form- an unrepresentative ratio of 1:2, 1:2, 1:2,
ing an inverted U-shaped structure (Fig. 1). and 1:3 from anterior (Fig. 2A). In the same
In the original description, the angle be- figure, Wongkham & Whitfield (1999)
tween hook and root was shown to be about show the roots to be simple and with round-
120-140° inaccurately creating an inverted ed corners. Actually, the roots do not have
open V-shaped blade-root complex (Fig. rounded corners and are not all simple.
2A). Roots were only slightly shorter than Hook roots in the second circle have con-
blades in all circles with a ratio of 1 : 1 .0- spicuously long anteriorly directed manu-
1.2, 1:1.4-1.5, 1:1.3-1.4, and 1:1.1-1.2 bria and those in the third circle have prom-
from anterior (Fig. 1). In the original de- inent but shorter anteriorly directed manu-
scription, roots were shown to be consid- bria (Fig. 1 ).
erably shorter than blades in all circles with The brain was not mentioned in the orig-
'
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
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220 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
inal description but was drawn as an oval field (1999) in a completely ventral position
structure at the center of posterior part of some distance anterior to the posterior tip
the proboscis receptacle (Fig. lA). Clearly of the trunk. In our subadults, it was slight-
this is a misinterpretation of the lemniscal ly subterminal (Fig. 3). In paratypes, it was
giant nucleus which usually overlaps the in the same position as observed in our
proboscis receptacle in the same location. specimens and not as illustrated in Fig. IC
The brain is actually triangular in shape and of Wongkham & Whitfield (1999).
is situated near the posterior part of the pro-
boscis receptacle on the ventral side where Conclusions
the passage of the ventro-lateral nerve cre-
The taxonomic implications of inadequa-
ates an indentation in its wall. No corre-
cies in the original description of P. (P.)
sponding dorso-lateral nerve was observed.
rexus are noted. The description of that spe-
Only two other major nerves are evident,
the anterior median and posterior median cies as revised in the present report is con-
sidered accurate and complete. It increases
nerves (Fig. 2).
the number of species of the genus to 30.
Collar and trunk spines were longest in
Twenty-six valid species were reviewed and
the middle of the trunk then decreased in
keyed by Amin et al. (2000). The remaining
size towards both extremities. In males, an-
three species are Pallisentis chongqingensis
terior collar spines were 20-28 (23) long & &
Liu Zhang, 1993, P. fotedari Gupta
increasing to 20-28 (26) long in posterior
Sinha, 1991, and P. jagani Koul, Raina,
most circle and anterior trunk spines were &
20-30 (26) long decreasing to 20-25 (23) Bambroo Koul, 1991. The first of these
three species belongs in the subgenus Pal-
long in posteriormost circles. Correspond-
lisentis Van Cleave, 1928 and the latter two
ing measurements in females are 20-29
in the subgenus Brevitritospinus Amin,
(22), 25-30 (28), 25-31 (28), and 18-27 &
Heckmann, Ha, Luc Doanh, 2000 ac-
(21), in the same order. All collar and trunk
cording to Amin et al. (2000).
spines have cuticular cone-shaped sleeves
While Wongkham & Whitfield (1999)
encircling the whole spines except for their
were correct in stating that the "invariable
distal tip. The morphology of spines is re-
12 proboscis hooks per circle ... is the pri-
vised as follows. Collar spines triangular,
mary basis for considering the acantho-
broadest at base, split longitudinally, fused
cephalan under study as a new species," we
at tips but separated into 2 or 3 branches
add two other unique characteristics that
anteriorly. Trunk spines are also triangular
distinguish P. (P.) rexus from all other spe-
in shape but are split only posteriorly.
Some measurements in the original de- cies of the genus. These are the unique
shape and location of the brain and the split
scriptions (Table 1) relating to some organs
are questioned: maximum length of probos- nature of collar and trunk spines. The anat-
cis receptacle in males; minimum length of omy of proboscis hook roots is also unusual
long and short lemnisci in males; minimum for the genus Pallisentis and represents an
length of collar spines in males; minimum important distinguishing characteristic.
trunk width in females (at widest point);
minimum proboscis width in both males Literature Cited
and females; See Table 1 for details. One Amin, O. M. 1982. Description of larval Acanthoce-
of these proboscis measurements is in error phalus parksidei Amin, 1975 (Acanthocephala:
since the proboscis is consistently markedly Echin—orhynchidae) from its isopod intermediate
wider than long. host. Proceedings ofthe Helminthological So-
ciety of Washington 49:235-245.
The position of the female gonopore was
. 1986. Acanthocephala from lake fishes in
described as "slightly subterminal" but il- Wisconsin: Morphometric growth of Neoechi-
lustrated in Fig. IC of Wongkham & Whit- norhynchus cyclindtratus (Neoechinorhynchi-
— —
VOLUME NUMBER
116, 1 221
—
dae) and taxonomic implications. Transactions Koul, R L., M. K. Raina, R Bambroo, «& U. Koul.
of the American Microscopical Society 105: 1991. Pallisentis ja—gani sp. nov. from Channa
375-380. channa in Jammu. Indian Journal of Helmin-
-. 1987. Acanthocephala from lake fishes in thology 43:124-128.
Wisconsin: Morphometric growth of Pomphor- Liu, D., & Z. K. Zhang. 1993. A new species of the
hynchus bulbocolli (Pomphoorhynchidae). genus Pallisentis Van Cleave (Neoechinorhyn-
—
Journal of Parasitology 73:806-810. chidea: Quadrigyridae). Acta Zootaxonomica
-. R. A. Heckman, N. V. Ha, R V. Luc, & R N. Sinica 18:5-9.
Doanh. 2000. Revision of the genus Pallisentis Van Cleave, H. J. 1928. Acanthocephala from China.
t(iAocnanotfhotchreepehanlea:w Qsuuabdgreingeyrrai,dathee) dweistchritphteioenreoc-f I. New—species and new genera from Chinese
fishes. Parasitology 20:1-9.
Pallisentis (Brevitritospinus) vietnamensis sub- Wongkham, W., & R J. Whitfield. 1999. Pallisentis
gen, et sp. n., a key to species of Pallisentis,
and the description ofa new Quadrigyrid genus, rexus n. sp. (Eocanthocephala: Quadrigyridae)
Pararaosentis gen. n.—Comparative Parasitol- from snakehead fish, Channa st—riata Bloch,
ogy 67:40-50. from Chiang Mai Basin, Thailand. Thai Jour-
Gupta, v., & G. Sinha. 1991. On a new acanthocepalan nal of Agricultural Sciences 32:241-261.
parasite Pallisentis fotedari sp. nov. from the Zieuw, B. 1793. Biga Muraenarum, novae species.
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