Myron richardsonii
Gray, 1849 Catalog of specimens of snakes in the collection of the British Museum,
p. 70. Type locality: North West Australia. Holotype: BMNH 1946.1.2.43.
Collector: Sir J. Richardson. [type specimen is a female and has had the skull
removed.]
Neospades kentii
de Vis, 1889 Proceedings of the Royal Society of Queensland, 4:238, pl. 14.
Type locality: Cambridge Gulf, Western Australia. Holotype: QM J681. Collector W. H. Saville-Kent.
Myron richardsoni
– de Rooij, 1917 Reptiles Indo-Australian Archipelago, 2:192. Figures 73 and 74.
Etymology. The name richardsonii
is in honor of Sir J. Richardson, the collector of the holotype.
Common names: Richardson’s
fresh-water snake (Glauert, 1950); The Australian Myron, The three striped Myron
(Gray, 1849); Gray’s water snake (Kinghorn, 1929); Richardson’s grey mangrove
snake (O’Shea, 1996);Grey mangrove snake (Parker, 1982); Richardson’s mangrove
snake (Worrell, 1963).
Distribution: Coastal northern Australia, from the Gulf of
Carpentaria this range is most likely disjunct and its presence is most likely
dependent upon the presence of mangroves. It also occurs along New Guinea’s
south coast.
Diagnosis: A small, mottled gray-brown-black homalopsid;
with a white belly and cream color on the first two scale rows. The internasal
separates the nasal scales. There are 19
- 21 scale rows at mid-body, with rows above number six containing keeled
scales.
Size: Eighteen specimens were measured for this study; the
largest was a male with a total length of 436 mm and a tail that was 64 mm. Two
females measured both had a total length of 415, one had a 57 mm tail, and the
other had a 59 mm tail. The smallest measured was a male with a total length of
223 and a 32 mm tail. Literature on the size of this species tend to confirm that
this is a small homalopsid: Glauert (1950) “grows to 20 inches;” Gow (1989)
wrote, “…maximum length is about 500 millimeters.” Parker (1982) stated,
“…growing to about 0.4 m...a female from Daru, was 368 mm long, the tail 52
mm...smallest juvenile was 130 mm long, tail 20 mm.” And, O’Shea (1986)
reported one specimen at 405 mm. Shine (1991a) reported male body sizes as 207
- 294 mm, and females as 255 - 370 mm. The sample data suggests that tails of
males are 17 - 19% of the SVL, while female tails are 16 - 17% of the SVL. At
the base of the tail the width is 72% of the height based upon the average of
five specimens.
External morphology: The head is distinct from neck,
moderate in length and not depressed. The eyes are dorsolateral and their
diameter is less than the eye-mouth distance. On the head the rostral scale is about as tall as broad, and
the dorsal margin is rounded. The nasals are completely separated by the
internasal; and they may be divided or semi-divided with the nasal cleft
touching the first labials and or the internasal. The internasal is triangular
and equal to or slightly larger than a nasal scale. The prefrontals contact the
loreals and each has about the same area as a nasal; they also contact the
supraocular and or pre-ocular scales. The frontal length is slightly less than
the interorbital distance and it is pentagonal. The parietals are about 1.25
times the length of the frontal. The single supraocular is elongate and
quadrangular; preoculars may number one or two; postoculars are usually two.
The bottom postocular scale may go under the orbit and keep the labials from
entering. The temporal formula is 1 + 2. Upper labials number 8 - 10 (usually
nine). The largest is usually the sixth, but may be five, seven, or eight. The
fourth through sixth enter, or occur below the orbit, and upper labials 2 - 4
or 2 - 4 contact the loreal scale. The upper labials are slight flared outward
and there is a groove formed just above them. On the chin the lower labials number 9 - 12 (usually 10).
The first three contact the anterior chin shields. The fifth or the sixth is
the largest. There are three pairs of chin shields, the first or second may be
the largest; the third pair is separated by small scales. Gulars number 3 - 4. On the body the dorsal scales rows on the neck and at mid-body
number 19 - 21, and near the vent dorsal rows number 17 - 19 (usually 19).
Scale rows 1 - 5 are not keeled; all the other rows have keeled scales. Gyi
(1970) reported that males have strongly keeled scales on the dorsal rows
anterior to the vent. Dorsal scale rows 1 - 6 are extremely ovate, other rows
become lanceolate toward midline. Ventral scales number 131 - 138 (131 - 138 in
males, 131 - 135 in females). They are wide, about 3.5 times the length of a nearby
dorsal scale. The anal plate is divided, and is about twice the length of the
preceding ventral. On the tail the divided subcaudal scales number 31 - 39, (33
- 39 in males and 31 - 34 in females). Dorsal scales on the tail are similar to
those anterior to the vent.
Color and pattern. Most specimens are a purple gray with 35
- 48 dark dorsal spots that are 5 - 6 scale rows wide on the midline. Scale
rows 1 - 2 have white pigment. Each ventral has a dark anterior margin.
Posterior upper labials are light while the anterior ones are dark. The chin is
cream. There are several color morphs of this snake and some specimens may be
almost black, while other specimens are orange. Color polymorphism is also seen
in other homalopsids of the Sahul Shelf.
Habitat: Myron
richardsonii uses mangroves, nearby mud flats, tidal rivers, and other
associated habitats. Like Fordonia and Cerberus it uses the intertidal burrow
system and does not hesitate to burrow into liquid mud (Glauert, 1950; Gow,
1989; O’Shea, 1986; Worrell, 1963). Gow (1989) considered this a nocturnal
snake that lives in small colonies. Parker (1982) observed this snake in New
Guinea and wrote it is, "...found along with Fordonia
leucobalia, but is far less common. Only 33 were recorded from daru island,
and a few from Abam, Emeti and Buji on the south coast. None were caught on Bobo
island, which appears unusual. Most were found swimming in shallow water among
mangroves with larger numbers of Fordonia.
At Emeti they were in fine soft mud at low tide – they would swim and dive into
the mud as if it were water, and they always dived into the mud to escape. A
few were off the Daru wharf at high tide, and one was caught at night at sea in
a net, 2 km off Buji.
Diet and Feeding Behavior: Fish of the family Goboidae are
the only prey i have found in their stomachs. Although both Worrell (1963) and
Gow (1989) have suggested it feeds on crustaceans. Nobbs and Blamires (2004)
reported finding a nudibranch (Mollusca: Gastropoda) in the mouth of a
specimen. Gow (1989) suggested it feeds in and around pools of water. Shine and
Schwaner (1985) reported it uses constriction on small fish. Gyi (1970) noted
this species has long anterior mandibular teeth, and these may be useful in
snagging and holding slippery gobies or slime covered gastropods. Greer (1997)
suggested that the one caught at night suggests this species may forage in deep
water.
Reproduction: Litter sizes of 6 - 8 have been reported (Gow,
1989; Shine, 1991a). And, Gow suggested neonates are about 120 mm.
Predators: Taylor (1979) took one from the stomach of a Crocodylus porosus.