Hypsirhina polylepis
Fischer, 1886 Abhandlungen und Gebiet der Naturwissenschaften in Hamburg, 9:14.
Type locality: Fly River, Papua New Guinea. Collector: Unknown. Holotype:
Dresden Museum MTKD D437 (probably destroyed in WWII, fide Obst, 1977).
Pseudoferania macleayi
Ogilby, 1891 Proceedings of the Linnaean Society of New South Wales, ser. 2,
5:51. Type locality: Herbert River, Queensland, Australia. Holotype: Australian
Museum R460. Cogger (1983:212) placed this in the synonymy of polylepis.
Hypsirhina macleayi
- Boulenger, 1896 Catalogue Snakes in the British Museum 3:9.
Enhydris polylepis
- Kinghorn, 1929 Snakes of Australia, p. 86.
Enhydris enhydris
– Parker, 1982 Snakes of the Western Province, no pagination.
Pseudoferania
polylepis – Wells and Wellington, 1983 Australian Journal of Herpetology,
1:108.
Pseudoferania
harritosi Wells and Wellington, 1985 Australian Journal of Herpetology, 1:
Supplement, p. 43. Collector: Harold Cogger. Type locality: “…Daly River
(upstream from ‘Police Station Crossing’), Northern Territory…” holotype: AM
R72982.
Note: Some Australian herpetologists consider polylepis and macleayi distinct species. They may be correct in the sense that
this may well be a complex of two or more species. But, the details need to be
worked out using both molecular and morphological evidence.
Etymology: Presumably polylepis is derived from the Greek
poly meaning “many,” and lepido meaning, “scale.” Common Names: Macleay's Water
Snake (Griffiths, 1981); Macleay's Smooth Water Snake (O'Shea, 1986).
Distribution: The coastal plains of northern Australia
(Queensland, Northern Territory and southern New Guinea, it is also known from
the island Groote Eylandt (a continental island). There is a record of a
specimen (CAS 135490) from Yongtau, New Guinea that was found at 1800 ft (548
m) above sea level. It seems likely that this species will eventually be found
in Western Australia, but records are absent.
Diagnosis: In Australia it is the only freshwater
homalopsid. It has 21 - 25 rows of smooth scales at mid-body, 137 - 162 ventral
scales, and upper labials five or 5 - 6 under the orbit. Myron, an Australian
homalopsid has 19 - 23 rows of keeled scales at mid-body and the nasals
separated by the internasal, a character state not found in Enhydris. The
presence of upper labials five, or 5-6, under the orbit and the contact between
upper labials 2 - 3 or 2 - 4 with the loreal should separate it from all other
Enhydris. The pattern and coloration of some polylepis is most similar to E.
enhydris, which has upper labial number 4 under the orbit, and upper
labials 1 - 3 in contact with the loreal scale, and it usually has more than
153 ventral scales. It can be distinguished from Enhydris punctata, which has
23 - 27 scale rows at mid-body, on the number of upper labials, punctata has
more than 10, and polylepis has eight. Also, it should be noted that this is
the only Enhydris to have keeled
dorsal scales, these scale ornaments are found only on the posterior dorsal
rows.
Size: The largest snake measured was a female with a total
length of 807 mm, and a 107 mm tail. The largest male was 803 mm with a 114 mm
tail. Tail lengths of males were 16.5 -
19.6% of the SVL, while tail lengths of females were 16.5 - 21.5% of the SVL.
Table 14 suggests tail/SVL ratios are sexually dimorphic when examined by
population.
External Morphology: The head is depressed and elongated;
the body is cylindrical; the eyes are dorsolateral. On the head the rostral
scale is pentagonal and 2 - 3 times wider than tall, and it is barely visible
from above. The nasals are in contact, they are equal to or larger than, the
prefrontals and they are very irregular in shape; the nasal cleft touches the
first or second labial; and they are slightly penetrated by the internasals.
The internasal may be single or double, and it may or may not make contact with
the loreal. The prefrontal scales are larger than the internasals and may
extend between the loreal and the preocular to contact the upper labials in
some specimens. The frontal is triangular and may show signs of fragmentation.
The parietals are longer than the frontal. The loreal is single and makes
contact with upper labials 2 - 3 or 2 - 4. The ocular ring is composed of a
quadrangular supraocular; a preocular that is usually single, rarely double; two
postocular scales; and no subocular scales, instead upper labials 4 - 5 or 5 -
6 enter the orbit (rarely is only number four in the orbit, and one specimen
had 6 - 7 in the orbit on one side). The temporal formula is 1 + 2. Upper labials
usually number eight, but one specimen had seven on one side, another had nine
on one sided (of 52 sides). The largest
upper labial is number five. On the chin lower labials number usually number
11, but they can number 10 or 12. The largest lower labial is usually number
six, occasionally it is number seven.
The first three lower labials contact the anterior pair of chin shields.
There are two pairs of slightly enlarged chin shields; the pairs are about equal
in size; and a pair of smaller scales separates the second pair. The chin
shields are often tuberculate. Gular scales number 8 - 9. On the body the
dorsal scale rows on the neck are usually 23 (AMNH 82443 has 29, and MCZ 134898
has 26). Dorsal rows at mid-body usually number 21 in the Queensland
population, 23 in the Northern Territory population, and range from 20 - 25 in
the Papua New Guinea population. Table 14 summarizes dorsal scale row counts
and ventral counts from various parts of the range and includes data O’Shea
(1996) has reported on scale differences between the upper Fly River and
Trans-Fly populations (New Guinea) of this species. Scales on the body tend to
be ovate in the first row and become more lanceolate toward the midline. Dorsal
rows in the posterior third of the body are keeled and striated. Scales on the
dorsum of the tail are similar to those on the body, keeled, striated, and
sometimes tuberculate. The ventral scale count range is 137 - 162; my data
suggests that ventral scale counts are not sexually dimorphic in this species,that
may change as individual populations become better known. At anterior body the
ventrals are 3 - 4 times wider than the height of a nearby dorsal; at midbody
they are three times as wide as a nearby dorsal, and at posterior body they are
about 2.5 times as wide as a nearby dorsal. Based on the sample examined no
geographic variation or sexual dimorphism in the ventral count of this species
has been found. The anal plate is divided. On the tail the divided subcaudal
scales number 37 - 46. There appears to be no sexual dimorphism or geographic
variation in the subcaudal counts when all populations are lumped together, but
Table 14 suggests that the Queensland and Papua New Guinea populations have
sexually dimorphic subcaudal counts and tail/SVL ratios. However, I have not
seen any males from the Northern Territory. At the base of the tail the width
is 82% of the height based on the average of five specimens. Color and pattern.
The pattern of this species is highly variable. Often there is a dark stripe on
scale rows 1 - 2 and the dorsum is a uniform brown, and the ventral surface is
cream (Plate 26, Figure F). The underside of the tail has a dark stripe or may
be mottled. The dorsum may have dark spots or indistinct bands. The ventral
surface is mottled in some specimens. The chin is mottled and some specimens
have an eye stripe that extends into a postocular stripe that borders the light
stripe on scale rows 1 - 2. O’Shea (1986) described a juvenile from Papua New
Guinea’s Western Province as having dorsolateral orange stripes extending the
entire length of the body. The stripes are edged with dark pigment, as are the
two ventrolateral cream stripes.
Habitat: This is a freshwater species that uses backwaters,
billabongs, lagoons, swamps, marshes, creeks, rivers, stream impoundments, and
other wetland habitats. Like many other homalopsids it rarely leaves the water
to travel overland. Museum material (USNM 213440) notes states, “On floating
vegetation and mud at night, burrows into mud when disturbed.” Thompson (1935)
wrote, “Hypsirhina polylepis was numerous in freshwater lagoons in the vicinity
of the estuary of the Archer River, and a single specimen was secured in the
swiftly-running water of the Coen River, a tributary of the Archer, at Coen.
The snake was also abundant in the swamps close to the Edward and Coleman
Rivers in the Gulf of Carpentaria….” Cogger (1981) reported it from floodplain
and paperbark swamps. Gow (1989) wrote, “A nocturnal aquatic species, only
found in freshwater habitats such as swamps, billabongs, creeks and rivers. It
prefers areas of overhanging banks, especially those with dense pandanus root
systems. In still waters it often shelters among the matted roots of floating
water plants.” Griffiths (1981) observed them “lying on the bottom of large
still pools with the front portion of their body covered in leaf litter and
just the tip of the snout protruding.” Parker (1982) reported one from a well,
and also found it in swamps parallel to beaches. Worrell (1963) found that in
the wet season this snake appears in low-lying parts of the streets of Cairns.
Diet and Feeding Behavior: This species has been reported to
eat crustaceans, fish, frogs, and their larvae. There is also a report of it
scavenging chicken bones (Cameron and Cogger, 1992). Shine (1991a) found one to
contain the shrimp Macrobrachium sp.
(Family Palaemonidae) and the oxeye herring Megalops
cyprinoids (Family Eleotridae). Shine describes the oxeye herring (16 cm,
51 g) being captured by the snake (79 cm, 320 g). The snake seized the fish in
50 cm deep water that was flowing fast. The fish leaped out of the water and
partially lifted the snake out of the water, but it retained its hold on the
fish, and the prey died in less than two minutes. The prey-predator mass ratio
was 0.16. Thompson (1935) wrote, “The usual food of this snake, on Cape York
Peninsula, consists of small frogs. Specimens in captivity readily capture and
swallow frogs when in the water.” It may use both ambush and active searching
to locate prey. Griffiths (1981) suggests that this is an ambush predator; he
observed one along a stream in mid-morning with its body on a root out of the
water and its head in the water, apparently waiting for fish. However, Kinghorn
(1929) reported one, “…observed by R. Mackay apparently stalking a small fish
in a pond off the Peach River, Cape York.”
Shine et
al. (2004) studied the foraging behavior of this snake in the field and found
it takes sleeping fish in shallow water. The fish were located visually
detecting movement and strikes are elicited by tactile cues created by
splashing water. The snakes were observed during a seasonal aggregation in
shallow water due to wet-season flooding. The snakes were feeding mostly on 3 -
8 cm purple spotted gudgeons; Mogurnda
mogurnda (Family Eleotridae) but they also took rainbow fish, tarpons, and
eels.
Reproduction: litter
sizes reported in the literature are encompassed by Parker’s range of 4 - 27.
The specimen containing 27 embryos was 755 mm TL (119 mm tail). Shine (1991a)
reported a mean of 11.6 young (r = 7 - 18) for 10 litters. A specimen I
examined (MAGNT R12650) is a 700 mm SVL female that contained 13 eggs. Birth
and neonates Thompson (1935), wrote that parturition occurs in the water. The
litter of 10 was apparently born on 22 January. He also describes the litter as
staying together for about three months; it is unclear if this was because of
captive conditions or normal social behavior for this snake. Parker (1982) gave
neonate and late term embryo total lengths as 205 - 242 mm, with tails that
were about 36 mm. Gow (1989) reported neonates at 180 mm.
Predators: Shine (1991b) contains a photograph of a
long-necked turtle, Chelodina rugosa, regurgitating an Enhydris polylepis.
Thompson (1935; 1949) found that the aboriginal people living near the Coen
River prize this species as food. Parker (1982) wrote about the people in Papua
New Guinea’s Western province collecting this snake, “Villagers catch them by
wading barefoot into the swamps, feeling for the snakes with their
feet…Villagers of Sigabaduru eat this snake.”
Population and Abundance: Griffiths (1981) believed this
snake to be common. Shine et al. (2004) did a mark and recapture study at Fogg
Dam in the Northern Territory and suggested that there were several thousand
animals in the population.
Venom: Thompson
(1935) wrote about the bite and envenomation of prey, “…I was bitten on the
finger, and an aboriginal was also bitten on the leg; no symptoms followed in
either case. On account of the situation of the fangs on the posterior end of
the maxilla…Frogs that were bitten, usually on the hind legs, by snakes of this
species, succumbed quickly, exhibiting severe discoloration and oedema at the
site of the bite.” Guinea et al. (1992) found the venom had protease activity,
and had at least four major proteins and seven minor ones that were mostly
acidic. They obtained 15 μl from a single specimen.