Larvae of Neenchelys Bamber are rather short and deep bodied,
reaching about 75 mm before metamorphosis. They have a relatively short gut
which is pigmented and slightly swollen at intervals along its length, as in larvae
of other myrophine ophichthids. Neenchelys leptocephali also have a conspicuous
midlateral patch of pigment about midway between the anus and
caudal tip, and develop ova before metamorphosis

Castle, PHJ

Pacific Science

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Pacific Science (1980), vol. 34, no. 2© 1981 by The University Press of Hawaii. All rights reservedLarvae of the Ophichthid Eel Genus Neenchelys in the Indo-Pacific1P. H. J. CASTLE2ABSTRACT: Larvae of Neenchelys Bamber are rather short and deep bodied,reaching about 75 mm before metamorphosis. They have a relatively short gutwhich is pigmented and slightly swollen at intervals along its length, as in larvaeof other myrophine ophichthids. Neenchelys leptocephali also have a con-spicuous midlateral patch of pigment about midway between the anus andcaudal tip, and develop ova before metamorphosis.THE DANISH "Dana" Oceanographical Ex-pedition Round the World (1928-30) col-lected huge numbers and many differentspecies of eel larvae (leptocephali) in theIndo-Pacific. Included among these was onelarval type of quite distinctive pigmentation,consisting principally of an obvious patchof deep and surface melanophores on thelateral musculature about halfway along thebody (Figure lA, lD). This pigment patchis so conspicuous and so specific in shapeand position that these leptocephali cannotbe confused with any other eel larvae.There were some 150 specimens of thislarval type in the "Dana" collection, mainlyfrom the central West Pacific, but also fromas far west as the southern tip of Africa.Other collections yielded further specimens.The size range was 26-85 mm with mostabout 50 mm total length (TL). Some weremetamorphic, but as the distinctive pigmentpatch disappears before metamorphosis iscomplete, an immediate identification wasnot possible without reference to othercharacters.IDENTIFICATIONIn overall body form the larvae are moder-ately deep bodied, with a rather acutelyI Manuscript accepted 3 July 1979. This work wassupported in part by a grant from the Internal ResearchCommittee, Victoria University of Wellington.2 Victoria University of Wellington, Department ofZoology, Private Bag, Wellington, New Zealand.pointed head which is flexed downward inmost specimens, although this may possiblybe an artifact of preservation. The gut isrelatively short, occupying the anterior thirdof the body, and is pigmented more or lessregularly with groups of melanophores alongits length. There are about four slight swell-ings along the length of the gut. In thesecharacters, the larvae more closely resemblethose of Myrophis (Ophichthidae, Myrophi-nae) as illustrated by Castle (1965) and Blache(1977) than any other leptocephali.However, the characters of greatest signifi-cance in the identification of these larvae arethe presence and location of accessory bran-chiostegal rays (jugostegalia of Parr 1930),which can be seen through the body wall ofthe branchial region in metamorphic andother specimens (Figure lB, IF), and thepossession ofa well-developed caudal fin evenin the metamorphics. The accessory rays over-lap and cross over in the ventral midline andare quite separate from the anterior bran-chiostegals which are attached to the hyoidarch. Among the ophichthid eels, this con-dition together with the complete, unab-breviated caudal distinguishes members ofthe Myrophinae from the Ophichthinae(McCosker 1977).The most advanced metamorphic specimen("Albatross" station D5456, Philippines, Fig-ure IF) has a rounded snout, simple, lateral,posterior nostril, and a moderately developedpectoral fin, which is relatively as large asthat of premetamorphic specimens. Whileventral movement and restriction of the pos-terior nostril to the upper lip (a position165166 PACIFIC SCIENCE, Volume 34, April 1980..~,,,:.,,:-,..;-Ip© :'!./!! {!! J.I!III, if ii fiji/iii/! ! / / / / /! / ! ! I~I;'/~irifr!dm. / / ;' j / / ..,...f~~~~~~~~~sm\ ' \ ' \\ \ \ ',' \ \. \ ''i' ~. ... \\'./.".'-----::; mm ,o opFIGURE I. A-E, Neenchelys microtretus, leptocephalus, "Alpha Helix" station 25, 75 mm TL; D, detail of lateralpigmentation; E, detail of posterior part of intestine to show ova and pigmentation; F, "Albatross" station D5456,67.5 mm TL; metamorphic. ab, accessory branchiostegal rays; 01, anterior lobe of liver; an, anterior nostril; dm,deep melanophore;fm, melanophores on base of fin; Ip, lateral pigment patch; 0, ova; op, opisthonephros; pi,posterior lobe of liver; pn, posterior nostril; sm, superficial melanophore..$ ·ii In ;;; AM .... g!-Larvae of Neenchelys in the Indo-Pacific-CAsTLE 16725170155 160MVOMERES1501455•holotype of!:i. microtretus20 0 syntype of!i bUitendij!ij~ larvae> 15uzw::I0-Wa:::k.. 10FIGURE 2. Number ofmyomeres in Neenchelys larvae and the type specimens of N. microtretus and N. buitendijki.characteristic of many ophichthids) andpossible regression of the pectoral fin cannotentirely be discounted, my knowledge ofophichthid larvae and my assessment of thepresent material suggest that neither of thesechanges would be likely to occur duringsubsequent growth.The identification is thus restricted to thegenera Benthenchelys Fowler, 1934, Neen-chelys Bamber, 1915, and PseudomyrophisWade, 1946. Benthenchelys may be immedi-ately excluded because it has a dorsal originover the anus, i.e., around the middle of thebody length (Castle 1972). In these larvae itis much further forward, at about myomere28 of a preanal number of about 50. Neen-chelys and Pseudomyrophis are closely similar(McCosker 1977), possibly even congeners(Nelson 1966; Bohlke, pers. comm.). Pseudo-myrophis contains the elongate species P.micropinna Wade, 1946 from the easternPacific (holotype with 174 vertebrae: Mc-Cosker 1977) and P. atlanticus Blache, 1976from the eastern Atlantic (with 168-181vertebrae: B1ache 1976). P. nimius Bohlke,1960 from the Caribbean (with 212-216vertebrae: McCosker 1977), also markedlyelongate, is considered by Dean (1972) torepresent a further, but monotypic, genuswithin this group. Neenchelys contains twospecies, neither of which is greatly elongate:N. microtretus Bamber, 1915 from the RedSea (holotype with 151 vertebrae: Bohlke,pers. comm.) and N. buitendijki Weber andde Beaufort, 1916 from the Indian Ocean(with 145-148 vertebrae: Mohamed 1958;142: Kotthaus 1968; syntype with 144:Bohlke, pers. comm.).The frequency distribution of myomeres inthe larvae is expressed in Figure 2. All speci-mens fall within the range 143-170. The ver-tebral number in the adults for all but a fewof these larvae would therefore be well out-side the range for any of the Pseudomyrophis168species. Further disagreements are that atleast in P. nimius the dorsal origin is muchfurther back, at about vertebra 49 (Bohlke1960), and the pectoral is absent or virtuallyabsent externally.The larvae are therefore identified withNeenchelys. The 2 specimens with 143 and144 myomeres are referred to N. buitendijkiand those with 149-163 to N. microtretus.Two other specimens with 166, another with167, and another with 170 myomeres appearto represent a third undescribed species ofNeenchelys. Adults are not well enoughknown to provide detailed information onvertebral numbers. As far as I can determine,N. buitendijki is known from only 3 speci-mens, together with at least 15 described byMohamed (1958), while N. microtretus isknown only from the holotype.Neenchelys larvae occur so frequently incollections of leptocephali and the biologyof the species is so poorly known that adescription of the material is warranted. Ingeneral, body form and pigmentation of thelarvae of the 3 species are more or less identi-cal and therefore a detailed description isgiven only for the most abundant, N. micro-tretus. There are differences in total myomerenumber and correlated differences in numberof dorsal and anal fin-rays.Neenchelys microtretus BamberFigures 1-3Neenchelys microtretus Bamber, 1915, p. 479Material ExaminedOne hundred fifty-four (20.5-80.5 mm)leptocephali from 40 collections. ZMUC:RRjS "Dana" station numbers 3676 (haulsIII, IV, VIII), 3681 (IV), 3687 (III), 3689(IX, X), 3712 (IV), 3714 (II, IV, V), 3715(III), 3734 (IV), 3735 (IV), 3736 (VIII), 3753(III), 3757 (1), 3759 (I, XIII), 3766 (XXI),3768 (XV), 3774 (II), 3775 (II), 3778 (1, III,IV), 3796 (V), 3800 (III), 3809 (II), 3814 (II,III, IV, V, VI, VII), 3817 (VII), 3824 (VIII),3826 (III, VI), 3830 (I, III, VIII), 3838 (1,11$PACIFIC SCIENCE, Volume 34, April 1980III), 3840 (V), 3841 (II), 3842 (I), 3844 (III),3874 (I), 3898 (1), 3971 (V); RRjS "Galathea"station number 298; RjS "Albatross" stationnumbers D5456, D5531; ORSTOM: HMAS"Diamantina" station number Dm 2-63-63;Cruise "Diaphus 10" station number 262."Alpha Helix" Bioluminescence Cruise sta-tion numbers 22, 25. Locations of these sta-tions are shown in Figure 3A.DescriptionTotal myomeres 149-163 (n = 139, x =156.57, s = 2.96), preanal 44-54, dorsal rays293-326 (8 specimens), anal rays 240-247(8 specimens), anterior margin of gall bladderat myomere 18-22 (100 specimens), dorsalorigin at myomere 26-33 (l00 specimens),last vertical blood vessel at myomere 48-55(89 specimens).The leptocephalus is relatively short bodiedand deep, attaining about 75 mm at fullgrowth, occasionally larger. The body tapersabruptly to a pointed head and rounded tail;the snout is acute; there is a well-developedpectoral and a forward dorsal origin. The gutis relatively short, so that the anus is placedwell in front of the midlength, and is swollenslightly at 4 more or less equidistant pointsalong its length. There are about 28 freebranchiostegal rays supporting the throat.Pigmentation is in the form of melanophoresdistributed as follows: a row on the roof ofthe mouth, 1 or 2 on the tip of the lower jaw,several scattered deep on the brain and onthe branchial region; groups ofmelanophoreson the swellings of the gut, between whichthere are intermediate groups; widely spacedgroups on the bases of the dorsal and analfins behind the level of the anus; a prominentmidlateral patch of somatic melanophoresbetween the anus and the caudal tip, thepigment cells of which merging deeply witha group underneath the vertebral column,1 of 4 such groups; a few melanophores onthe base of the caudal fin.Several of the larger specimens have dis-tinct ova which form irregular chains of cellsabove the intestine in front of the opis-thonephros.- ,Larvae of Neenchelys in the Indo-Pacific-CASTLE 169FIGURE 3. Distribution of Neenchelys. A, N. microlrelus adult (holotype, large circle) and larvae (small circles);S, N. builendijki adult (large filled circles: syntype-Weber and de Beaufort 1916; Hardenberg 1931; Mohamed 1958;Kotthaus J968) and larvae (small filled circles); Neenchelys sp. larvae (small open circles).RemarksThe midlateral, postanal group of mel-anophores which is typically divided intothree subgroups (as illustrated in Figure ID)is a most characteristic feature of Neenchelyslarvae. While the larvae resemble the lep-tocephali of Myrophis in the pointed headand simple gut with more or less regularlyspaced groups of melanophores, Myrophishas no midlateral series, or if present, it isrestricted to a midlateral row (Castle 1965;170Blache 1977). A feature of this larva is that thedorsal origin is always placed well forward,at about myomere 28, even in small speci-mens. The presence of ova in some specimensis a further example of their occurrence atthe larval stage in some leptocephali, notedfor other eels (Castle 1978) and possibly morecommon than hitherto suspected. Mohamed(1958) noted that his specimens of N. bui-tendijki of above 160 mm TL were maturingor mature.Neenchelys buitendijki Weberand de BeaufortFigures 2, 3BNeenchelys buitendijki Weber and de Beau-fort, 1916, p. 268Material ExaminedTwo (39 and 61 mm) leptocephali from 2collections. ZMUC: RRjS "Dana" stationnumbers 3676 (haul VIII), 3830 (III). Loca-tions of these stations are shown in Figure 3B.DescriptionTotal myomeres 143 and 144, preanal 50and 53, dorsal rays 329, anal rays 229, anteriormargin of gall bladder at myomere 20, dorsalorigin at myomere 26, last vertical bloodvessel at myomere 51.RemarksThese larvae differ from those of N.microtretus in having fewer tota'l myomeres,although the difference is expressed speci-fically in the postanal number. Mohamed(1958) records 335-346 dorsal and 225-228anal rays in N. buitendijki with which thepresent 2 larvae more or less conform.Neenchelys sp.Figures 2, 3BMaterial ExaminedFour (70-85 mm) leptocephali from 4 col-lections. ZMUC: RRjS "Dana" station num-PACIFIC SCIENCE, Volume 34, April 1980bers 3753 (haul III), 3767 (I), 3780 (III);ORSTOM: HMAS "Diamantina" stationnumber 04-150-62. Locations of these sta-tions are shown in Figure 3B.DescriptionTotal myomeres 166-170, preanal 53-56,dorsal rays 386-413 (3 specimens), anal rays307-333 (3 specimens), anterior margin ofgall bladder at myomere 18-19, dorsal originat myomere 26-28, last vertical blood vesselat myomere 56-58.DISCUSSIONNeenchelys is known from adults or post-metamorphic specimens from widely sepa-rated parts of the Indo-Pacific (Red Sea,India, Indonesia), but not as yet from theAtlantic. These are records from few speci-mens although Mohamed (1958) states thatthey may be locally abundant seasonally. Asthese eels almost certainly live in shallowwater in fine sediments, it is possible thatthis distribution may merely reflect inade-quate collecting.Except for the single specimen collectedoff southern Africa, larvae of N. microtretusshow a relatively restricted distribution inthe central West Pacific (Figure 3A). In con-trast, the only known adult is from Suez.The compact larval distribution is probablya fair representation, since many more haulswere made by the "Dana" elsewhere acrossthe whole of the Indo-Pacific than the posi-tive ones shown in Figure 3A. Of more than7000 leptocephali collected in 600 hauls byORSTOM (Noumea) in the central Pacificduring 1967-72 there was only a single speci-men of Neenchelys microtretus. These ob-servations suggest that the larval life ofNeenchelys species is relatively short, so thatextensive dispersal of the larvae does notnormally occur.No Neenchelys larvae have been taken inthe Atlantic, where there has been even moreextensive coIlecting for leptocephali than inthe Indo-Pacific.• 5. it €::a:J1 i e .:#.#'_### ! #tk Mn $$ u"a: sz &£&£Larvae of Neenchelys in the Indo-Pacific-CASTLEACKNOWLEDGMENTSSpecimens studied are in t~e c0.uection ofthe Zoological Museum, Umverslty of Co-penhagen (ZMUC) and at ORSTOM, Centrede Noumea (ORSTOM). I thank the au-thorities of these institutions for the oppor-tunity of studying the mater!al. I es~eciallythank James E. Bohlke for mformatlOn onadult specimens.LITERATURE CITEDBAMBER, R. C. 1915. Reports on the marinebiology of the Sudanese Red Sea, fromcollections made by Cyril Crossland. XXII.The Fishes. J. Linn. Soc. London 31 :477-485.BLACHE, J. 1977. Leptocephales des poissonsanguilliformes dans la zone sud du Golfede Guinee. Faune Tropicale 20: 1-381.BOHLKE, J. E. 1960. A new ophichthid eel ofthe genus Pseudomyrophis from the Gulfof Mexico. Notulae Naturae 329: 1-8.CASTLE, P. H. J. 1965. Ophichthid lep-tocephali in Australasian waters. Trans.Roy. Soc. New Zealand Zool. 7:97-123.---. 1972. The eel genus Benthenchelys(Fam. Ophichthidae) in the Indo-Pacific.Dana Rep. 82: 1-32. .---. 1978. Ovigerous leptocephalI of thenettastomatid eel genus Facciolella. Copeia1978: 29-33.171DEAN, D. M. 1972. Osteology and system-atics of the echeline worm eels of the At-lantic Ocean (Pisces, Anguilliformes).Ph.D. Thesis. University of Miami.HARDENBERG, J. D. F. 1931. The fish faunaof the Rokan mouth. Treubia 13: 119.KOTTHAUS, A. 1968. Fische des IndischenOzeans. Ergebnisse der ichthyologischenUntersuchungen wiihrend der Expeditiondes Forschungsschiffes "Meteor" in denIndischen Ozeans, Oktober 1964 bis Mai1965. A. Systematischer Teil, III. Os-tariophysi und Apodes. "Meter" Forsch.-Ergebn. D: 14-56.MCCOSKER, J. E. 1977. The osteology, classi-fication and relationships of the eel familyOphichthidae. Proc. Calif. Acad. Sci. Ser.4,41: 1-123.MOHAMED, K. H. 1958. On the occurrenceof the eel Neenchelys buitendijki Weber &de Beaufort in Indian waters. J. BombayNat. Hist. Soc. 55:511-517.NELSON, G. J. 1966. Osteology and relation-ships of the eel Neenchelys buitendijki.Copeia 1966:321-324.PARR, A. E. 1930. Jugostegalia, an accessoryskeleton in the gill cover of the eels of thegenus Myrophis. Copeia 1930:71-73.WEBER, M., and L. F. DE BEAUFORT. 1916. Thefishes of the Indo-Australian archipelago.3 Ostariophysi: II Cyprinoidea, Apodes,Synbranchi. Leiden: Brill.

Larvae of the Ophichthid Eel Genus Neenchelys in the Indo-Pacific

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Larvae of the Ophichthid Eel Genus Neenchelys in the Indo-Pacific

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