A NEW SYNBRANCHID FISH, MONOPTERUS DIGRESS US FROM KERALA, PENINSULAR INDIA

Of the four genera, the Old world genus M onopterus comprises of altogether eight species (Bailey & Gans, 1998). Excluding Monopterus boueti (Pellegrin) from Africa and Monopterus desilvai Bailey and Carl Gans from Sri Lanka, the species reported from India include Monopterus albus (Zuiew), Monopterus eapeni Talwar, Monopterus cuchia (Hamilton), Monopterus fossorius (Nair), MOllopterus indicus (Silas and Dawson) and Monopterus roseni Bailey and Carl Gans. Of these, the three from Kerala, viz., M. eapeni, M roseni (both from Kottayam Dist.), M. fossorius (from Thiuvananthapuram Dist.) and the one from Mahabaleswar, Maharashtra, viz., M. indicus are endemic to Peninsular India. M. eapeni and M. roseni are blind cavernicoles living in subterranean waters. A new species, and the third cavernicole of the genus, is described here as Monopterus digressus from Calicut Dist., Kerala, Peninsular India. The new species is the fourth species known from Kerala, the fifth from Peninsular India and the seventh from India. The type specimens are deposited in the faunal collections of the Western Ghats Field Research Station, Zoological Survey of India, Calicut.

A new species, and the third cavernicole of the genus, is described here as Monopterus digressus from Calicut Dist., Kerala, Peninsular India.The new species is the fourth species known from Kerala, the fifth from Peninsular India and the seventh from India Diagnosis: A small, blind species of Monopterus.Body slim, naked, subcylindrically elongate and cord-like.Head slightly to moderately conspicuous, with muscular occiput.Upper jaw with j~wl-like lip, slightly overhanging the lower jaw.Gill aperture ventral, wide, subtriangular or lunate without lateral folds.Branchiostegal membrane internally fused with isthmus, its skin ventrally drawn into shallow longitudinal folds.Paired suprapharyngeal pouches present.Lateralis system distinct with prominent cephalic pores.Trunk and tail nearly identical in shape (depth and width) except at the tail extremity.Tail extremity compressed and tapering with rudimentary dorsal and anal fin folds (dermal ridges) confluencing at the caudal tip.Branchiostegal rays 6. Vertebrae: Precaudal 86-88, caudal 80-82, total 166-170.
Description: Body: (Figs. 1 & 7) : Slim, naked, subcylindrically elongate and cord or thread-like.Dorsal and ventral profiles, excluding head and tail extremity, nearly parallel.Snout to vent (SV) length 62.7% of TL.Tail long, nearly identical in shape to that of trunk except at posterior extremity, about 37.3% ofTL, 59.6% of SV length.Tail extremity well compressed and tapering with rudimentary dorsal and anal fin folds (dermal ridges) confluencing at the caudal tip.Body depth (maximum) about 1.8%, at vent 1.75% of TL, 40.4% of head length (HL).
Jaws slightly unequal in forward extension, anteriorly truncated or squarely rounded; upper jaw surrounded with a jowl-like tissue (lip) slightly overhanging the lower jaw.Gape length 31.7% of HL.Teeth on palate, and laterally on jaws uniserial, but anteriorly in two, sometimes three, rows.
Anterior nostrils small, at the tip of snout; posterior nostrils large, subrectangular.Distance from snout tip to posterior nostril 0.8% of TL, 18.1 % of HL.Cephalic lateralis system distinct with a number of pores (figs.2,3 & 4) : dorsally a pair of internasal pores between anterior and posterior nares, a median coronal pore just behind the level of posterior nares and a pair of post nasal pores; ventrally 3 pairs of mandibular pores; a fourth pair, one each, behind the gape angles and a fifth pair, one each on either side, in the mid-lateral position.Files of minute sensory papillae also present, becoming indistinct in mucous coating after the preservation of specimen.
Branchial region: (Figs.4,6 & 9) : The gill aperture ventral, wide, subtriangular or lunate, its width 22.4% of HL, 64% of head width, internally divided into a pair of pore-like lateral apertures by a midventral fusion between branchiostegal membrane and isthmus; skin of branchiostegal membrane ventrally drawn into shallow longitudinal folds, skinfolds not extending laterally to angles of gill aperture.Buccopharyngeal cavity ventrally opening to each of the paired branchial chambers through 4 gill slits.The first and the anterior-most one, the hyo-branchial slit (between hyoid and first branchial arches), the largest, followed by the fourth slit (between fourth and fifth arches).The second and third branchial slits (between one and two, and two and three branchial arches respectively) are comparatively smalter.The third and fourth arches lie closely without a slit in between.Gills are greatly reduced, with only thin flanges of tissues on branchial arches one to three, each one with a single affero-efferent vessel.The vessel on the fourth arch is thick and continuous, merging dorsomedially with its counterpart to form an unpaired dorsal aorta.A pair of accessory suprapharyngeal pouches, each one on either side of head, present; pouches posteriorly extending to slightly beyond neck-line, above angles of gill aperture, anteriorly opening to pharynx by a pair of apertures at the roof of pharynx, opposite to the hyo-branchial slits on the floor of pharynx.
Colouration : Body colour in life blood-red, caudal extremity transparent, making visible the vertebral column and blood vessels; in alcohol, tawny white or pale flesh in colour.
Morphometric data: Given in thousandths of total length (TL) in Table I; certain morphometric ratios (in percentages) are also presented in Table II.
Etynl0logy : The specific epithet digressus is derived from Latin 'digressus', meaning deviation, a reference to this species being different from other closely resembling species of Monopterus.Relationship : M. digressus closely resembles M. eapeni and M. roseni, but differs from both by its characteristic body shape, differences in vertebral count, presence of suprapharyngeal respiratory pouches, prominent cephalic lateralis system etc.The body of M. digressus is cord-like (uniformly subcylindrical and elongate), rather than whip-like as in M. eapeni or M. roseni.
The count of vertebrae from 3 dissected specimens (TLs : 208 mm., 196 mm., and 180 mm.) of M. digressus showed a range of 86-88 precaudal and 80-82 caudaL total 166-170 in contrast to 135 precaudal and 24 caudal, total 159 in M. eapeni (Eapen, 1963, Talwar andlingran, 1991), and 76 precaudal and 71 caudal, total 147 in M. roseni (Bailey and Gans, 1998).Accessory suprapharyngeal respiratory pouches are distinctly present in M. digressus, whereas they are presumed to be absent in M. eapeni and M. roseni (Talwar and linghran, 1991;Bailey and Gans, 1998).The lateralis system of the new species is seen with more number of pores on head compared to a lesser number of pores in M. eapeni or M. roseni.M. digressus is further distinguishable from M. eapeni by its vestigial dorsal and anal fin folds (ridges) restricted to caudal extremity (vs.dorsal fin fold commencing from opposite to vent and anal fin fold far posterior to vent in M. eapeni), and from M. roseni by its slightly overhanging upper jaw (vs.both jaws equal in forward extension in M. roseni).
M. digressus can be easily separated from the large and robust bodied species such as M. albus, M. cuchia, M. fossorius, M. indicus etc. by its smaller size, slim body, absence of eyes and the ratio of precaudal to caudal lengths, besides differences in vertebral count.(Bailey and Gans, 1998).
(Measurements in mm and thousandths of total lengths)
But, according to Rosen and Greenwood (1976), the development of suprapharyngeal pouches is a derived shared character (synapomorphy) found in the species of cuchia, indicus andfossorius.
Considering more synapomorphies of head anatomy, especially of branchial arch elements, branchial vascular system etc., they have indicated in their proposed phylogenies that the species of Monopteruso form a monophyletic group and that the African species M. boueti having neither suprapharyngeal pouch nor body scales, is more closely related to M. fossorius, M. cuchia and M. indicus than to M. albus and M. eapeni.Bailey and Gans (1998) regard Amphipnous a group name of convenience rather than a subgenus.
M. digressus is having paired suprapharyngeal popches for aerial respiration, but is devoid of scales on body.This combination of characters is, therefore, not in conformity with the grouping of species of Monopterus as proposed by Talwar and Jingran (1991).Nelson (1994) mentioned that most of the synbranchid species are, probably, capable of aerial breathing.Therefore, till its relationship to other species, especially to the closely resembling ones, of the genus Monopterus is further revealed, the new species is, presently, not placed under any subgenus or subgroup of Monopterus.

Table I .
Morphometric data of MOllopterus d;gressus sp.nov.(the holotype and 7 paratypes) and the holotype of MOIlOpterus rosen;