A Comparison of the Ammocoete and Macrophthalmia Stages of Mordacia Mordax and Geotria Australis (Petromyzonidae)

A Comparison of the Ammocoete and Macrophthalmia Stages of Mordacia mordax and Geotria australis (Petromyzonidae) R. STRAHAN 1 VERY LITTLE IS KNOWN of the biology of dacia are the late developmental stages of the lampreys of the Southern Hemisphere. On Geotria, but this is unlikely since the dentition the available evidence (Strahan, 1959 ), there of M ordacia is very characteristic, it being the appears to be only one species of Geotria, C. only lamprey with two supraoral laminae on the australis Gray 1851, extending from Western buccal funnel. Certainly the situation cannot be Australia eastwards to the Falkland Islands. Al clarified until more is known of the development most nothing is known of its distribution while of Mordacia. in the marine stage of its life history. The Maskell (1932) stated that the ammocoete northern limits of its distribution in estuaries of Mordacia has one intestinal (exocrine pan and rivers appear to be 32 0 S. on the west coast creatic ) diverticulum on the left side of the of Australia and 3r S. on the east coast of Aus oesophagus, and can thereby be distinguished tralia and the North Island of New Zealand; from the ammocoete of Geotria, which has both 40 0 S. on the west coast of South America and right and left diverticula, and from the ammo 35 0 S. on the east coast. It extends southwards to coete of Petromyzon, which has no diverticula. Tasmania, the South Island of New Zealand, and However, the question arises: How did Maskell Tierra del Fuego. know that the ammocoetes with only one diver .Three species of Mordacia have been de ticulum were referable to Mordacia? The only scribed. M . mordax (Richards) 1846 has a author to comment upon the external ap north-south distribution similar to that of Ceo pearance of Mordacia amrnocoeres was Ogilby tria australis but is restricted to the Pacific ( 1896), who stated that the dorsal and caudal coasts of Australia (where it extends northwards fins are continuous in the ammocoete but sepa to about 34 0 S.) and of South America. The rate in the adult. This is also characteristic of other two species, M ordacia lapicida (Gray) Geotria. Some of Maskell's Mordacia ammo 1851 and M•. fI ,utiden s (Philippi ) 1863, are coetes were obtained from the Australian apparently restricted to the Pacific coast of South Museum, Sydney, N .S.W. Since they were dem America (Plate, 1902; Lahille, 1915; Holly, onstrably not Geotria, they could have belonged 1933; Mann, 1954 ). only to M. mordax or, rather improbably, to In the course of the past century, Geotria some undescribed Australian lamprey. Others australis was divided into as many as seven were obtained from the British Museum (Nat genera and nine species. This seems to have ural History) , London, and their place of col been due partly to enthusiastic "splitting," but lection is not recorded . It is probably fortuitous more to ignorance of the life history of the that these were correctly identified . Conclusive species, which is now known to comprise well proof of identity depends upon establishing a marked ammocoete, "rnacrophrhalmia," "vela series of intermediate stages between the am sia," and adult stages (Maskell, 1929; Strahan, mocoete and identifiable ' posrmerarnorphic in 1959 ). In the almost complete absence of in dividuals. formati on on the life history of any species of Mordacia, the possibility arises that a similar DESCRIPTION OF MACROPHTHALMIA OF confusion exists here. Mann ( 1954 ) has sug M . mordax gested that the Chilean forms described as Mor- The author had the good fortune recently, while revising the British Museum collection of I Department of Zoology, University of Hong Kong, Hong Kong. Manuscript received April 16, 1959. lampreys from the Southern Hemisphere, to find 416 Mordacia-STRAHAN 417 A .....~ <. <. c ~ 10cm FIG. 1. A, Macrophthalmia stage; B, Arnmocoere of Mordacia mordax. a jar of ammocoetes labelled, "Geotria, 1925, When opened to its full extent, its diameter is from Sydney, N.S.W." For want of better knowl less than the diameter of the body. The mouth edge, this diagnosis might have been accepted, is surrounded, except posteriorly, by small, had the jar not also contained a macrophthalmia bluntly conical cirri lying just outside the rim (a large-eyed, recently-metamorphosed stage) of the buccal funnel. Just within the rim is a which was markedly different from the macroph complete series of small, flat, fringed processes thalmia of G. australis. It possessed two tri lying closely side by side. Two large supraoral cuspid supraoral laminae which showed it to be tooth plates lie just anterior to the centre of the a Mordacia, and three conical teeth anterior to buccal funnel, separated from each other by a the supraoral lamina and separating the rows of distance equal to the width of a tooth plate. Each lateral tooth plates, which identified it as M. tooth plate bears three sharp-pointed cusps mordax. This stage in the life history of the which are directed posteriorly. From the shape species has not previously been recorded or of the tooth plates, it appears that each tricuspid described. plate may have arisen by the fusion of three The specimen, which is preserved in alcohol, unicuspid elements . Anterior to the supraoral is of a uniformly pale yellowish-brown colour, tooth plates and in the mid -line are three small as are the ammocoetes with it. The body is unicuspid teeth arranged in a triangle with the laterally compressed, much more so than in an apex pointing anteriorly. On the right and on ammocoete of the same length. It is 122 mm. the left side of the buccal cavity is a series of long, being about 2 em. shorter than the largest five small bicuspid lateral tooth plates arranged ammocoete in the sample. The eye is large and radially. Posteriorly, external to the infraoral prominent and the iris has a silvery sheen. Meas lamina, is a series of eight bicuspid tooth plates, uring from the anterior tip of the head, the also having a radial orientation. The infraoral nasal aperture lies at 6 mm. and the centre of lamina bears nine low, pointed cusps, the penul the eye at 7 mm. Eight lateral line pits form timate of these at each end being slightly higher an infraorbital series and no other lateral line than the others. The ant erior lingual tooth plate organs are discernible. The branchial region ex has a finely serrated edge. The two posterior tends from 12 mm . to 22 mm. Th e first dorsal fin lingual tooth plates cannot be seen very well in the specimen. arises at 70 mm . and extends to 76.5 mm.; the second dorsal fin extends from 88 mm . to 108.5 mm. and is contiguous with the caudal fin. All COMPARISON OF MACROPHTHALMIA STAGES the fins have distinct fin rays and are rather OF G. australis AND M. mordax triangular in profile, differing from the fins of The macrophthalmia of G. australis has been the ammocoete, which take the form of a low described by Maskell ( 1929) and it is unneces quadrilateral. The anterior border of the cloacal sary to repeat the description here. Table 1 aperture lies 102 mm. from the anterior end summarizes the differences between the ma of the body (Fig. 1A) . crophthalmia stages of the two species. The mouth aperture is oval in shape, being Apart from the dentition, which alone is suf longer longitudinally than transversely ( Fig. 2 ). ficient to separate the macrophthalmia stages of 418 PACIFIC SCIENCE, Vol. XIV, October 1%0 sample of Geotria ammocoetes, but examination of these showed that in the position of the cloaca they closely resembled the Mordacia specime n and differed from known ammocoetes of Geotria (Table 2).Dissection of several of the ammo coetes revealed that each possessed only one intestinal diverticulum, thus confirming Mas kell's origina l observation. Figure IE shows the body proportions of an ammocoete 123 mm. long. DISCUSSION It is unfortunate that the sample of Mordacia ammocoetes contained no smaller specimens which could be compared with small specime ns of Geotria. However, the great uniformity in proportions over the length range, 100-160 mm ., suggests that smaller ammocoetes of M. mordax 5mm would also be distinguishable by the position of the cloaca. In adult specimens of M ordacia the FIG. 2. Ventral view of head of macrophthalmia of cloaca is found at 83-84 per cent of the length M ordacia mordax. of the body, there being no difference in this respect between M. m ordax, M. lapicida, or M. the two species, another striking difference be acutidens specimens in the British Museum. In tween them is the more posterior position of the velasia stage of G. australis the cloaca the cloacal aperture in M. mordax, This is ex occupies almost the same position as in the pressible in relation to the total length of the macrop hthalmia and the ammocoete. Eleven body, in relation to the anterior border of the unpouched specimens had the cloaca at 77 ± second dorsal fin, or in the number of precloacal 1 per cent of the total length. However, the myomeres. resorption of the tail tissues, consequent upon the cessation of feeding in the adults, causes a COMPARISON OF AMMOCOETES OF relative backward shift in the position of the G. australis AND M. mordax cloaca and the first dorsal fin. In 11 pouched It was possible that the Mordacia macroph adults, these occurred at 79 -+- 3 per cent of the thalmia had been accidentally included in a total length . TABLE 1 COMPARISON OF MACROPHTHALMIA STAG ES OF Mordacia mordax AND Geotria australis, BASED ON ONE SPECIMEN OF M.

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