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Eodiaptomus indawgyi n. sp., a pelagic calanoid copepod presumed endemic to
ancient Lake Indawgyi, Myanmar
Henri J. Dumont
1,
*& Jim Green
2
1
Animal Ecology, Ghent University, Ledeganckstraat, 35, B-9000 Gent, Belgium
2
17, King Edwards Grove, Teddington Middx. TW119LY, UK
(*Author for correspondence: Tel.:+32-53681633, Fax: +32-53684708, E-mail: henri.dumont@UGent.ac.be)
Received 12 May 2004; in revised form 25 May 2004; accepted 27 May 2004
Key words: ancient lakes, calanoid copepods, endemics, South-East Asia, Myanmar, biogeography, taxonomy
Abstract
The little-known prepleistocene Lake Indawgyi (Myanmar) is shown to harbour an endemic pelagic
Eodiaptomus species, described herein. The area around the lake is inhabited by another species in the same
genus. Related species occur throughout South-East Asia, and a presumed close relative is endemic to a
chain of pre-pleistocene lakes in Celebes.
Introduction
Lake Indawgyi (2502¢N, 9618¢E) is the largest
lake in Myanmar, with an area of ca. 120 km
2
, and
a maximum depth of about 22 m. It is elongated
north to south, with a length of 23.8 km and a
maximum width of 9 km. The lake lies at an alti-
tude of 175 m asl, and is separated from the
Ayeyarwaddy (Irrawaddy) by two ranges of hills,
rising to over 1000 m. To the west it is separated
from the Chindwin valley by a similar range. The
outflow from the lake travels northwards for about
50 km before joining the Mogaung Chaung, which
flows southeastwards for 100 km, eventually join-
ing the Ayeyarwaddy. The age of the lake is not
accurately known. This part of Myanmar is on a
plate which is thought to have detached from
Gondwanaland in the late Jurassic, drifting
northeastwards to reach its present position be-
tween India and Indochina by the late Eocene (cf.
Audley-Charles, 1987). The lake may be, in part at
least, of tectonic origin. There is a local oral tra-
dition that an earthquake caused a village to dis-
appear in the lake. The lake is almost certainly
younger than the Ayeyarwaddy valley, which is
thought to have tertiary origins.
In January 2003, numerous plankton samples
were taken from Lake Indawgyi. Diaptomid co-
pepods formed about 50% of the total Crustacea
in the plankton taken with a coarse net (250 lm
mesh). Two species were present: Heliodiaptomus
elegans Kiefer, and an Eodiaptomus which differed
from the known forms reviewed by Ranga Reddy
& Dumont (1998).
Eodiaptomus indawgyi n. sp.
Material examined: an abundant collection of
males and females from Lake Indawgyi, Myan-
mar, 21 Jan. 2003, leg. J. Green.
Holotype: a partially dissected male in glycerol,
mounted on a set of three slides, deposited at the
BM (accession number BMNH 2004. 2123).
Paratypes: A series of males and females, half
of which are deposited at the BM (accession
numbers BMNH 2004. 2124 and BMNH 2004.
2125) and half at the KBIN (Royal Institute of
natural Sciences Brussels), accession number
30252.
Hydrobiologia (2005) 533: 41–44 Springer 2005
Diagnosis: a small Eodiaptomus (<1 mm) of the
lumholtzi-group, with a single seta on the inner
side of segment 3 of the endopodite of P2–P4.
Basipodite of right P5 of male apically widened,
with a membrane obliquely extending from the
foot of the exopodite. Endopodite curved inwards,
apically tapered. Apical claw of female P5 with
external row of spinules longer than internal row.
Description
Male (Fig. 1)
Size 0.8–1.1 mm (n¼7). A small species (Fig. 1)
with fourth and fifth pedigerous body segments
fused; lateral wings somewhat asymmetrical,
rounded (Fig. 1). Both wings provided with two
spines each. Right wing with longest spine. Uro-
some of five segments. Genital segment with short
spine on left side and long spine on right side
(Fig. 1). Second to fourth urosomites with pos-
terior row of spinules. Fourth urosomite with
posterior border asymmetrical, wavy. Caudal rami
with hairy inner margins, naked outer margins.
Right antennule (Fig. 1) geniculated at segment
19. Spines present at segments 8, 10, 11, 12, 13, 14
and 15. Spine on segment 13 massive, typical for
genus. Spines on segments 8 and 12 smallest, of
equal size. Spine on segment 14 about half as long
as that on segment 15. Spinous process on segment
20 finger shaped, about as long as segment 21. Left
antennule and swimming legs (P1–P4) as in female.
Right P5 (Fig. 1)
Coxa with external spine implanted on a small
lobe. Basis widened at insertion of endopodite,
with membrane extending obliquely from base of
endopodite. No inner membrane. A short sensory
seta at inner distal corner. First exopodite segment
squarish, with spine shaped process at distal outer
corner and swelling at distal inner corner (Fig. 1).
Second expodite segment elongate, curved in-
wards. Lateral spine straight and naked, distinctly
shorter than segment, freely articulating with seg-
ment (Fig. 1), implanted close to base of apical
claw. End claw robust. long, curved, its inner
margin lined with a hyaline membrane set with
smallest marginal denticles. Endopodite charac-
Figures 1–7.Eodiaptomus indawgyi n. sp., male. 1: Habitus in
dorsal view. 2: Prehensile antennule. 3: terminal zone of meta-
some and urosome in dorsal view. 4: P5. 5: Apex of second
segment of exopodite of right P5. 6: First segment of exopodite
of right P5. 7: Left P5.
Figures 8–11. Eodiaptomus indawgyi n. sp., female. 8: Habitus
in dorsal view. 9: Dorsal view of terminal zone of metasome and
urosome. 10: P1. 11: P5.
42
teristically curved inwards and at an angle (often
close to 90) with the exopodite, tapering towards
apex, its outer margin convex and inner margin
concave (Fig. 1). A distal and subdistal serration
and apical row of spinules.
Left P5 (Fig. 1)
Coxa with short spine at distal inner corner. Basis
about as long as wide, with seta at distal outer
corner. First exopodite segment elongate, curved
inwards, with field of setules along distal half of
inner surface. Second exopodite segment with ba-
sal half of inner margin fringed with hair-setules.
Apical process triangular, tapered towards apex,
with transverse row of spinules some distance from
tip, and inner margin set with rather strong spin-
ules. Seta long, slender, naked, almost at right
angle with body of segment. Endopodite bi-seg-
mented, apically tapered, with subapical and api-
cal rows of spinules.
Female (Fig. 2)
Slightly bigger than male (0.95–1.12 mm, n¼8)
and generally more symmetrical (Fig. 2). Fourth
and fifth pedigers fused, their demarcation indicated
by groups of spinules (Fig. 2); some spinules also on
dorsum of fourth pediger. Fifth pediger with a
couple of spines on either side of median axis. Lat-
eral wings of fifth pediger well developed. Right
wing somewhat shorter and more rounded than left
wing (Fig. 2). Both wings provided with a couple of
similar-sized spines. Urosome of three somites.
Genital segment about 60% of length of entire
urosome, somewhat asymmetrical, proximally di-
lated and with a spine on either side. Right spine
shorter than left spine. Second urosomite short.
Anal somite slightly larger than furcal rami. Furcal
rami with rows of inner and outer hair-setae. Prin-
cipal furcal setae without widened basis. Antennule
25 segmented, as for genus. Antennae and mouth-
parts as for genus. Swimming legs (P1–P4) typical
for subfamily Diaptominae. P1 with three seg-
mented exopodite and two segmented endopodite
(Fig. 2). Third endopodite segment of P2–P4 with
single-internal seta. P2 without Schmeil’s organ.
P5 (Fig. 2) Symmetrical
Coxal spine robust, blunt-ended, constricted su-
bapically, with few spinules at constriction site.
Seta at base of P5 much shorter than first exopo-
dite segment. Terminal claw with external and
internal row of spinules. External row (c. 20
spines) distinctly longer than internal one (C 12
spinules). Endopodite about 3/4 the length of first
expopodite segment, tapering apically, with ob-
lique row of spinules.
Derivatio nominis
The species is named after the lake where it was
discovered.
Discussion
E. indawgyi is an obvious member of the lumholtzi-
species group, composed of closely related species
and distributed from Australia to South-East Asia
(Ranga Reddy, 1994; Ranga Reddy & Dumont,
1998). Of these, the majority is geographically
limited to a rather restricted range, with the
nominal species itself inhabiting northern Austra-
lia and New Guinea, but at least one species
complex (E. wolterecki Brehm, 1933) restricted to a
chain of prepleistocene lakes in Celebes. Unfor-
tunately, this is a poorly described species. Bre-
hm’s (1933) rudimentary figures suggest a much
longer second segment of the right male P5, as well
as differences in the male right antennule (spines
on segments 10 and 15 shorter than in indawgyi),
but a redescription of the species is highly desir-
able. From all other members of the lumholtzi-
group, E. indawgyi differs by the position and size
of the membrane on the basipodite of the male
right P5. In all species of the group, this membrane
is shifted basad, and runs along the inner margin
of the basipodite, thus standing in a vertical po-
sition. This character takes its extreme form in
E. phuphanensis Sanoamuang from Thailand,
where the membrane occupies the entire inner
margin of the segment (Sanoamuang, 2001a). In
E. indawgyi, the membrane is relatively short and
only covers the widened inner apex of the ba-
sipodite (Fig. 1), standing in a horizontal or
slightly oblique position relative to the axis of the
segment. An additional difference with E. sano-
amuangae Ranga reddy & Dumont, 1998 and with
E. phuphanensis Sanoamuang, 2001, is that in both
these species the apical segment of the endopodite
43
of P2–P4 carries a supplementary seta. Whether
the female is distinctive is uncertain, but published
evidence suggests that the external row of spinules
on the end-claw of the female P5 is shorter than
the internal one in all species where this character
has been studied, as opposed to E. indawgyi, where
the reverse is true. The pattern of hair-setae and
spinules on the dorsum of pedigers 4 and 5 in fe-
males might be diagnostic as well. Brehm (1952)
shows a similar arrangement in E. draconisigniv-
omi, but this species shows a marked asymmetry,
with a much larger spinule on the right of the
central field of hair-setae. This character has been
confirmed in specimens from Myanmar and is also
illustrated in a recent redescription from Thailand
by Sanoamuang (2001b). Other species of Eodia-
ptomus do not have this character. Further, the
male of E. draconisignivomi has a very different P5,
with two or three deep serrations on the inner
margin of the right endopod. It so happens that E.
draconisignivomi, widespread in Thailand, is the
only other Eodiaptomus so far found in Myanmar.
It has been found in five localities, four of which
are oxbow lakes in the floodplain of the Ayeyar-
waddy between Bhamo and Myitkyina (ca. 24–
25N). The fifth locality is much further south, in
the extensive shallow lake of the Moyingyi Wildlife
Sanctuary, near Bago (1730¢N). All these habi-
tats are very different from the deeper open waters
of Lake Indawgyi.
The presence of an endemic Eodiaptomus in
Lake Indawgyi, of presumed prepleistocene age,
supports the idea that in all such old lakes a cal-
anoid copepod dominates the pelagial and evolves
to endemic status (Dumont, 1994). However, the
lake also harbours a Heliodiaptomus, which is non-
endemic, as well as six species of planktonic
Cladocera. Perhaps it is prepleistocene, but simply
not yet old enough to have reached the status
where its pelagic space is fully dominated by a
single herbivore with endemic status. Another
alternative might be that the lake has been reju-
venated at some time by tectonic activity.
Acknowledgments
The material for this paper was collected during a
survey of wetlands in Myanmar. Jim Green is
particularly grateful to Simba Chan, and the Wild
Bird Society of Japan for the opportunity to visit
Lake Indawgyi. Jon Davies played a crucial role in
the survey, and the collection of samples. Our path
in Myanmar was smoothed by U Khin Maung
Zaw and his officers in the Nature and Wildlife
Division of the Forestry Department, Yangon.
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44
