2000

Asiatic Herpetological ResearchVol. 9, pp. 130-138

Buccopharyngeal Morphology and Feeding Ecology of Microhyla ornata
TadpolesMuhammad S. Khan
7740

NW 47thSt.,

Lauderhill, FL 33351 USA

Abstract.- The oropharyngeal morphology of Microhyla ornata tadpoles is described. Anatomical peculiarities

are correlated to feeding ecology. Microhylid anatomical features are discussed andcompared with ranoid

tadpoles.

Key words.- Amphibia, Salientia, Microhylidae, Microhyla ornata, larval oropharyngeal morphology, feeding
ecology.

(Khan, 1974) and Azad Kashmir (Khan, 1979), wereused as comparative material.

Introduction
The common southeast Asian narrow-mouth
Microhyla ornata

frog

widely distributed throughout
N.W.F.P.
and Azad Kashmir (Khan,
Sindh.
Punjab,1974; 1979; 1988; Khan andTasnin, 1987). Normally,small size makes it inconspicuous and difficult to

its

detect in the field.

However, after a summer heavy

downpour, the characteristic rasping call of Microhyla
ornata is easily distinguishable from rest of the local

amphibians (Khan and Malik, 1987b). Microhyla
ornata readily takes refuge under vegetation, leaf litter,

Collection, preservation and storage methodology

islogs, stones, in holes and fissures in the ground,and often is mistaken as a juvenile of some larger species.

followed Khan (1982b), while surgical procedures

and descriptive terminology are from Khan and Malik(1987a) and Khan and Mufti (1994b, 1995), exceptthat for M. ornata tadpole, the lateral cuts throughbuccopharyngeal walls, must pass through mid-eye,unlike ranoid tadpoles where cuts pass below the eye.
Fine particulate mucilage-trapped material accumulating in the filter cavities is cleared by a jet of waterfrom an ordinary eyedropper. Drawings of the buccopharyngeal surfaces were made with the help ofcamera lucida.
Tadpoles at Stage 35 were selected, since at thishave already attained maximum size andAt mid-monsoon, M. ornata invades large water
bodies, which, by this time, are filled with water andhave developed thick planktonic growth. Solitary
males perch well away from water among marginal
vegetation to call. Eggs are laid in patches of jelly,
which float at water surface as "egg-rafts" (Khan,stage, they

their characteristic

functional.

organs are fully developed and

The tadpole at this stage is voraciously

feeding and its digestive system is functioning at its
fullcapacity. Shortly after this stage,

metamorphic

1982b).

changes start occurring.

The present study describes oropharyngeal morphol-

For identification of Stage 35, tadpoles were compared with Khan's (1965) table of normal develop-

ogy of Microhyla ornata tadpole, at Stage 35 and correlate it to the tadpole's feeding ecology. Moreover, it
iscompared with already known morphologies of

sympatxic tadpoles belonging to the genera Bufo andRana (Khan and Malik, 1987a; Khan and Mufti,

ment. Data for present study are recorded from 10

specimens.

Description

1994b, 1995).

External morphology

The tadpole's body is perfectly streamlined; the head

Material and Methods

dorsoventrally depressed while its belly is laterallycompressed and oval in dorsal profile. The snout isis

Tadpoles for the present study were collected during
the summers of 1986-88 from different localities
along the northwestern border of Rabwah City (Khancountersunk, displacing mouth anterodorsally. The
tail is more than twice the length of the head andand Malik, 1987b). They were netted at midstream
with a hand net. Microhyla ornata tadpoles frombody. Broad caudal fins narrow abruptly in the poste-

Ghakkhar,

District

Gujranwala,

Punjab,PakistanAsiatic Herpetological Research

2000

Vol. 9, p. 131

nfralabial papillae

tongue analage
buccal floor arena(BFA)
buccal pocket
lottis

BFA papillae

preglottal
papillalaryngeal discbuccal pocket
canalventralvellumtracheafilter cavity

esophagus
Figure 1. Morphology of surgically exposed buccopharyngeal floor of Microhyla omata\adpo\e at Stage 35 (scale
1mm).

nor half of the tail, passing into a delicate long flagel-

cle)

lum.

space 0.5-1.95;

The body is widest at the level of laterally disposed small eyes. The nostrils are imperforate; theirposition is marked by heavily pigmented anterolateralpits lying just anterior to eyes. The mid- ventral spira-3.2-3.4;

tail finheightinterorbital
tailspace 2.3-2.4;

internarialmuscle height (at base)(at midtail)1.7-2.0;

4-4.4; length of tail flagel-lum 2.0-2.3.
Internal Morphology

The horizontal mouth has a median U-shaped cleft in

Buccal region. Khan and Mufti (1994b; 1995) distinguished a tadpole's buccal cavity in two functional
units: anterior food gleaning part and posterior foodthe middle of the lower lip

retrieving part. The dorsoventrally depressed head and

cle

is

close to posterior ventral end of the abdomen,with a distinct prespiracular valve (Khan 1982b).

which remains perma-

abdominal wall, give it apeculiar position of the mouth in M. ornata tadpoles
have affected the form and shape of the tadpole's buc-characteristic silvery shine, which is lost within two to

cal cavity; reducing the food gleaning part and widen-

A median dorsal band of

melanophores covers the brain and extends onto theing the food retrieval part which occupies most of the
buccal region.

base of eyes and the nasal pits.

Ventral buccal (Fig.l). The floor of the food glean-nently open (Khan and Mufti, 1994a, Fig. 2).

ence of iridiocytes

in thethree weeks, on preservation.

Measurements (in mm). Body

length5.2-5.8;

Pres-

tail

length (including flagellum) 12.6-13.7; total length
17.8-18.9; greatest breadth of body (at the level ofeyes) 2.7-2.9; greatest depth of body (at level of spira-ing part consists of vertical U-shaped prelingual
chamber which opens out through mouth at snout top

and

is

lined by a series of three simple infralabial

papillae. Posteriorly, it opens in food retrieval part of2000

Asiatic Herpetological ResearchVol. 9, p. 132

prenarial papillapostnarial ridgenans
narial papillabuccal roof arena(BRA)

BRA papillaposterolateral

BRA ridge

buccalroof
glandularareapressurecushions—I

dorsalvellum1esophagus

mm

Figure 2. Morphology of surgically exposed buccopharyngeal floor o\Microhyla oma/a\adpo\e at Stage 35 (scale1

mm).

the buccal.

A non-papillated tongue analage, a conicalthickening which is broader anteriorly pointed poste-

guarded by a long preglottal papilla which is tipped
left.

riorly, guards the opening of the food gleaning partThe broad ventral velum has a strong spicular sup-into the food retrieval part. The spacious food retrieval

port. It covers about l/2-l/4th of the underlying bran-

part

forms the main buccal cavity. The buccal floor

arena (BFA)

rectangular, laterally raised with aismedian shallow passage.
tipped,large, flatanterior end of trachea.
liepapillaeA group of 12-14 fine

BFA papillae lie on lateral sides of

A pair of smaller midpocket

the level of mid-pockets.

at

A buccalpocket is a long, narrow, club shaped longitudinal slit
running anteroposteriorly on each lateral side of the

BFA with a posterior narrow canal connecting it withthe pressure cushions. Anterior, wider, parts of buccal

pockets have 3-6 pre- and 5-8 post pockets, small,conical papillae.

The trachea is a long cylindrical pipe that extends
medially to the base of the BFA, carrying the glottis
far anterior to the ventral
lateralhalves.

exposed,

lies

The

thin

velum and dividing it intolippedglottison a bulbous laryngeal

is

disc,

100%
and

is

chial baskets

and consists of three distinct long anddeep filter cavities. The free margin of the velum issmooth, with a single broad projection above third filter plate and is covered by a narrow strip of minutesecretory pits. Rows of melanophores run along thelateral sides of the buccal arena and are aggregated on
the sides of the tongue analage; a row runs along lateral sides of trachea.

Dorsal buccal (Fig. 2). The food gleaning part of the
buccal is roofed by a broad prenarial arena, which has
a median V-shaped depression with an anterior prenarial papilla and several pustules. The position of theimperforate naris is marked by a shallow depression
from which a flat ribbon like twisted narial papillahangs down in the buccal cavity. A thin delicate, narrow, papillated, postnarial ridge dorsally delimits narial region and the food gleaning part of the buccal.

2000

Asiatic Herpetological ResearchVol. 9, p. 133

laryngeal discglottistracheasecretory ridg

Figure 3. Underside of ventral velum showing details of filter cavities (diagramatic).

The food retrieval part is roofed by a spacious,
broader than long, buccal roof arena (BRA), which isfeaturedmainly by a distinct posterolateral

BRA

margin of which is cut into flat finetipped BRA papillae, increasing in length from out
smallest, to inside longest, with blunts on their innerridge, the freesides, while smaller are without blunts. The

BRA sur-face is pustular.

The broad glandular area of the buccal roof isdivided into lateral rectangular halves and is covered
with dense minute secretorypits.

The dorsal velum

narrows gradually mesoid, at mid-BRA it staggers to(Fig. 3) that run in line with toric ridges,

which areedged with fine secretory pores.

A tight filter ruffle cover the surface of filter
plates. The

number of filter rows on filter plates varyfrom minimum 9 on the 4th ceratobranchial to 23 on
second (Table 1 ). The filter ruffle is 3° dense with tertiary foldings.

Successive filter rows abut across fully

canopied deep filter canals. The filter ruffle covers
both sides of second and third filter plates (Fig. 3: cb2,
cb3).

Three pressure cushions are distinct on posterolateral sides of the dorsal pharynx (Fig. 4). The first andcontinue with that of other side.

second are four times longer than broad. The first, andBranchial region. Branchial baskets are more thanouter-most,iscontinuous anteriorly with the buccal

twice the length of the buccal. Three filter cavities arepocket ofitsside through a buccal pocket canal.

distinct in each branchial basket. The first filter cavity
largest while the third is smallest. The filter cavities

Meanwhile, the third, innermost, is broadest and has amedian hook-like appendage. Deep ciliary groove

are always packed with fllocular matter. The third isruns along posterior border of the pressure cushions

tilted outwards, partially blanketing the second. About

towards esophageal orifice along posterior sides of thehalf to one third of the filter cavities are covered withpressure cushions.

isvelum. A distinctly ridged oval torus (Fig. 3:1, II, III) is
present in each filter cavity. The subvelar surfaceisprofusely ridged with fine transverse secretory ridges

The lungs at Stage 35 are well developed, eachrunning along the dorsolateral sides of the abdominal
cavity, extending to the posterior end of the abdomen.
Anterior half of the lungisbroad, with well-devel-

Table 1. Branchial elements of Microhyla ornata tadpoles at Stage 35 (Ant=anterior aspect; B=breadth; cb=ceratobranchial; L=length; Post=posterior aspect). Data from 10 specimens, all measurements in mm.

Ceratobranchial

Filter plate

cb. 1

3.5

cb.2

3.7

cb.3
cb.4

Filter rows/side

1.8

Vol. 9, p. 134

Asiatic Herpetological Research

2000

Table 2. Comparison of microhylid and ranoid tadpole.

Character

Microhylid

RanoidHeaddepressed

depressed

Bellycompressed

depressedColortransparent

Drab + pattern

Tail length

2-3 times body

2-2.5 times

Tail muscle

narrow

broad

Tail fins

broad

moderate

Tail tip

produced in a flagellum

round/pointed

Spiracle

median ventral

dextralBelly wall

silver-shinytransparent or drab

Mouthantero-dorsal

anterior/antero-ventral

Oral discabsentpresent

Nostrils

imperforate

perforate

Narial flap/papillae

flap

papillae

Infralabial papillae

simplepalmate

Lingual papillae

absentpresent

Postnarial papillae

small on a membrane

long solitary

Lateral ridge papillaabsentpresent

Median ridge

absentpresent

Buccal musculaturepoor

well developed

Branchial basket

longer than broad

broader than long

Pharyngeal/buccal ratio

75%

45-50 %

Prenarial ridge

absentpustules or ridge

BRA/BFA papillae

flat fine tippedshort forked blunted

BRA/BFA papillae

form membranes

distinct no membranes

Glottis

100% exposed

not or partiall exposed

Glottal discbulbousconcealed

Glottal position

anterior to vellum

posterior to vellum

Glottal papillapresent

absentTrachealongabsentSecretory tissue

single celled

multicellular

Subvelar secretory tissue

ridgedridged/pitted

Filter cavities

3

2/3

Maximum filter rows

15-23

10-14

Position of tori

all filter cavities

absent or first cavity

Filter cavity depth

as long as deep

longer than deep

Asiatic Herpetological Research

2000

tail

Vol. 9, p. 135

flagellum and the jet of water from median ventral

spiracle

supports

themicrohylidtadpoleatmid-stream, while its buoyancy is maintained by dorsally

buccal pocket canal

placed air filled lungs. A long broad finned tail helps
the tadpole to react quickly to any stimulus including

enemies and foodpressure cushions

inthe water

column above andbelow.

pressure cushion

Microphagous tadpoles are characterized by an

hook

exaggerated oropharyngeal region (Wassersug, 1980).
All
modifications
distinguishingoropharyngeal
ciliary

groovemicrohylid tadpoles from bufonids and ranids are
adaptations to microphagy: reduction of infralabial
cartilage, corresponding reduction in prelingualandprenarial arenas: displacement of mouth to snout top;

simple infralabial papillae; absence of lingual papillae;

membranous

postnarial

and

BRA

papillaryridges; divided fine pitted buccal glandular zone; fineridged subvelar and toric glandular surfaces; broad
medially divided spicularly supported ventral velum;compact thick filter ruffle on broad and deep filter
plates; deep filter cavities with distinct tori. Thesemicrohylid structures are part of obligate micropha-

Figure 4. Morphologyofposterolateralpartofdorsal buc-copharyngeal region, showing details.

oped air sacs, it gradually narrows down caudally andits terminal part is a dark pigmented cord.

gus filter feeding technology. Similarly long tubular
trachea, bulbous laryngeal cartilage, distinct anteriorly displaced glottis with a preglottal papilla,anddorsal, long, air filled lungs are not only efficient partsof an efficient pulmonary aeration system, but at thesame time, serve to maintain hydrostatic balance ofthe tadpole at mid-stream position. The complex mor-

Ecological Correlates

phology of pressure cushions and their connection
with buccal pockets are a part of a system which

The adult Microhyla ornata is sharply contrasted frommaintains a sustained drainage of excessive buccal
water in pressure cushions, providing necessary tur-its

sympatric ranoids in its choice of breeding site andmode of egg deposition. Usually its breeding sites are

gidity during each stroke of bucco-pharyngeal pump-deep ponds, which develop rich planktonic bloom
during summer. Such sites are quite restricted and rareing. Turgid cushions act as pharyngeal valves in theprocess and play key role in sustained pumping offood-laden water current in buccopharyngeal passage.

temperate Punjab, unlike sympatric ranoids who
breed in temporal sites that dry in the summer. Intermittent unpredictable rains or irrigation seepage saves
in

such

populationsof tadpoles(Khan and Malik,

1987b).

Table1

and 2 summarize peculiar features of M.

Morphologically, the Microhyla ornata tadpole isa perfect model suited for sustained midstream swim-

ming. It has all the necessary oropharyngeal technology to filter and feed on the planktonic bloom indeeper ponds in temperate Punjab.

ornata tadpole necessary to suit its lentic habits: per-body and long broadwith independently vibratile terminal fla-

fectly streamlined transparent

finnedtailgellum, lateral eyes, median ventral spiracle, abdominal silver-shine, are adaptations to nektic habits of theM. ornata tadpole. A school of tadpoles swimming at

Microhylid Tadpole Characters
The microhylid tadpole is ranked as Type 2 in Orton's
It markedly differs in morphofrom
ranoidType 4 macrophagus tadpole
logically(1953) classification.

(Table 2). Microhylid is the only tadpole, in Punjab

midstream is almost invisible from above the watertransparent bodies. Meanwhile
abdominal coloration makes them invisible in water

due

to

tadpole'ssince the water surface viewed from inside appears

shiny due to reflection of light from water. A vibrating

riparian

ecosystem,

occupyinguniquemidstream

feeding niche, while rest of the sympatric ranoid tadpoles are bottom grazers and in no way compete withmicrohylidtadpole.

Distinguishingmorphologicalcharacteristics of Microhyla ornata tadpoles are:

Microhylids are phylogenatically connected with

External morphology
1. Transparent

body and tail, silver-shine on abdomen.

2. Head dorso-ventrally depressed, body and tail later-

ally compressed.
3. Antero-dorsal

gies like Psedohemisus granulosa (Wassersug, 1984)

androbusta

Otophryne(Wassersug

andPyburn,mouth, without keratinized oral disc

Discussion

4. Eyes prominent, laterally disposed on head.

broad finned, its tip produced into a terminal

vibratile flagellum.
6. Spiracle

ranoids through tadpoles with intermediate morpholo-1987).

and other associated organs.

5. Tail

2000

Asiatic Herpetological ResearchVol. 9, p. 136

median-ventral, mid-abdominal, squarish

Independent vibratile distal caudal flagella are characof mid-stream swimming microphagus tad-teristicpoles (Wassersug, 1980, 1989; Wassersug and Sperry,
1977; Nishikawa and Wassersug, 1988, 1989; Hoff

Maintenance of midstream

opening, with a prespiracular flap.

and Wassersug,

7. Anal tube straight, median-ventral anal opening.

position is made possible by independent movementsof the caudal flagellum and ventrally directed continu-

Schools of tadpoles swim at midstream schools,
never rest at bottom. Capable of making spontaneous
movements from midstream to darker parts of the8.

pond to avoid intruders,same midstream site.

shortly reappearing at the1986).

ous water from the spiracle giving a sustained upward(Khan, 1982a, 1991). Apart from morphologi-

thrustcal differences in structure of notochord and arrange-

ment of caudal nerves, microhylids and ranoids differ
the site of generation of propulsive locomotory
waves. In ranoids, waves are generated at the tail; theinInternal morphology

tip acts as a steer. In microhylids,

9. Opercular chamber extending to vent.
10.

Smooth broad ventral vellum, divided into rightand left halves.
1 1.

waves are generated

at the end of the caudal flagellum.

Long pipe like trachea carries, bulbous glottal car-

The limited tail musculature and bulky form of theamphibian tadpole restricts its movements so that it
cannot evade its potential enemies, fishes, niads, etc.,

tilage,(Khan and Mufti, 1994b; 1995). Amphibian tadpoles

for forward in buccal cavity. Glottis thin lipped, 100%

rely

exposed.

blends well against natural aquatic background with moderate to thick vegetation (Caldwell,pattern

12. Preglottal papillae guarding glottis.

13.

No lingual papillae.

14.

No lateral ridge papilla and median ridge.

15.

Pharyngeal region exaggerated, about 75

et al.,% offllocular matter in dissected tadpoles.

maximum number of filter rows

13-23 on either sides of the ceratobranchials.
17. Branchial food traps with microscopic openings ofsecretory glandular tissue borne on fine parallel ridges
forming distinct crescentric torus in each branchialcavity.
18. Imperforate nares

with a foliaceous broad narial

palp, descending into the buccal cavity.
19.

1981; Gatten et1984; Kehr and Basso,al.,1990; Khan and Mufti, 1994 b. 1995). The microhylid
thistadpole, which is exposed at midstream, solves

oropharyngeal region, branchial baskets large with
distinct, deep filter cavi ties, which are usually full of

16. Tight filter mesh,on a reduced conspicuousness. Its drab spotted

Ceratohyal with a ventrally directed lateral arm,

problem differently. Transparency of its body reduces
its shadow at pond bottom and its abdominal shine
blends well against water surface reflecting sun rays,

making it invisible from inside pond as well from out
side, to its predators.

Microhyla omata has a larger buccal volume thanranoids. It constantly pumps large amounts of water toget food (Seale and Wassersug,

1979; Wassersug,1980). Due to its specialized feeding habits, several

elements universally present
missingridge,

inits

lateralinranoid tadpoles are

oropharyngeal morphology: medianridgepapillaeand lingual

papillae.

Moreover, papillae in the food retrieval part are a partof particulate food guiding membrane rather particu-

and an an tero-posterior median arm.

late

20. Broad based BRA and BFA papillae, which usu-

have fine-ridged oral and branchial glandular system

ally coalesced to form fine membranes.

with fine pits, a specialization to entrap finest particu-

21. Narrow lateral buccal pockets with distinct connection with pressure cushions, forming an elaborate

system to control function of pressure cushions.

food retrieving sieves. Moreover, microhylids

late food.

tight filter

Deep filter cavities, long filter plates andmesh are more a part of food retrieval sys-

tem rather respiratoryinfunction (Wassersug andMurphy, 1987). Particulate food filtering capacity of2000

Asiatic Herpetological Researchfiltering system is enhanced by development of a fine-Vol. 9, p. 137

Kehr, I, K„ and N. G. Basso. 1990. Description of theridged torus in each filter cavity. A well-developed
pulmonary system with long tubular trachea, a totally

tadpole of Lysapsus limellus (Anura: Pseudidae) and

exposed guarded glottism, and inflated dorsal functional lungs are adaptations to the midstream sustained swimming and are efficient respiratory organs

575.

(Khan, 1991).

Tadpoles of the microhylid genera Otophryne andPsdudohemisus show both ranoid as well as microhylid characteristics. Frogs of Family Microhylidae
and Ranidae have distinctive adult morphology, how-ever definition of microhylid larva stands only on
imperforate naris, since the ranoids have always per-some consideration on its biology. Copeia 1990:573Khan, M. S. 1965. A normal table of Bufo stomaticus(Bufo melanostictus). Biologia (Lahore), 11:1 -39.

Khan, M. S. 1974. Discovery of Microhyla ornata
Dumeril and Bibron from Punjab, Pakistan. Biologia(Lahore) 20: 179- 180.

Khan. M. S. 1979. On a collection of amphibians
from northern Punjab and Azad Kashmir, with ecological notes. Biologia (Lahore) 25:37-50.

Khan, M. S. 1980 Affinities and Zoogeography of her-

forated naris (Wassersug, 1989).

Tadpoles of M. ornata from Pakistan differ in morphological details from those collected from Thailand

petics of Pakistan. Biologia (Lahore), 26: 1 1 3- 1 7

Khan, M.

S.

1982a.

Key

1

for the identification.

ofby Inger (1985) in having longer infralabial papillae,

amphibian tadpoles from the plains of Pakistan. Paki-

more filter rows, presence of postnarial membranousstan Journal of Zoology 14:133-145.

ridge, BRA and BFA membranous papillae, mesiallydivided dorsal buccal glandular zone, and a single
preglottal papilla. Moreover, no silver shine istification

reported on the belly of tadpoles from Thailand, as isreported from India (Rao, 1917; Azad Kashmir(Khan,

1979) and District Jhang, Punjab Pakistan(Khan 1982a). Flower (1899) reported morphologicaldifferences among adults and larvae of this species
from Malay peninsula and Siam, while Liu (1950) has
reported dextral anal tube in tadpoles from China,
which is straight in Pakistani tadpoles. These morphological differences

may refer to geographical races

within this widely distributed southeast Asian
speciesof narrow-mouth frogs.

J.

P.,

of amphibian eggs from the plains of Paki-

stan. Pakistan Journal of Zoology

14:241-243.

Khan, M. S. 1991. Morphoanatomical specializationsof the buccopharyngeal region of the anuran larvae
and its bearing on the mode of larval feeding. Ph.D.
thesis.

Department

Zoology,

Punjab

University,

Lahore. 93 pp.

Khan, M. S., and S. A. Malik. 1987a. Buccopharyngeal morpology of tadpole larva of Rana hazarensis

Dubois and Khan 1979, and its torrenticole adaptations. Biologia (Lahore), 33:45-60.

Khan, M. S., and S. A. Malik. 1987b. Reproductive
strategies in a subtropical anuran population in arid
Punjab, Pakistan. Biologia (Lahore) 33:279-303.

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