Leeches of several genera of Piscicolidae have the same general facies as the present specimen, but in spite of our knowledge of the family it is necessary to rely heavily on internal morphology in generic analyses. Johansson (1896) and subsequently other workers have drawn attention to the value of the absence, or presence in varying form, of the posterior pair of gastric caeca (“postcaeca”) in grouping the various genera, and I have here utilised this criterion for all genera for which data are available. Such caeca are absent from Phyllobdella, Pterobdella, Pterobdellina, Trulliobdella, and Bdellamaris. They are present as independent, paired, simple elongate caeca, in Oceanobdella (= Abranchus), Ganymebdella, Ottoniobdella and Ozobranchus. In a third group there is a single elongate caecum extending posteriorly ventral to the intestine. This group contains Pontobdella, Trachelobdella, Illinobdella, Myzobdella, Notostomobdella, Piscicolaria, and Ingram's “Ichthyobdella” platycephali. Finally, there is a group in which there is a long caecum ventral to the intestine but showing evidence of a paired nature in the presence of median dorsoventral perforations and/or a somewhat bifid termination.

This latter group, to which the present leech belongs, includes Platybdella, Hemibdella, Piscicola, Cystobranchus, Calliobdella, Austrobdella, Branchellion, Crangonobdella, Cryobdella, Cryobdellina, Oxytonostoma, Johanssonia, and Moore's recently (1952) described Marsipobdella. Unfortunately as yet I have no data to enable the placing of Janusion, Notobdella, Carcinobdella, Cyrillobdella, and Stibarobdella in their appropriate groups as above; but these can be set aside from consideration in the present case as follows: Stibarobdella is a trimeric tuberculate leech resembling Pontobdella in general facies; Cyrillobdella has only 8 pairs of pulsatile vesicles and 5 annuli in the fully-formed somite; Janusion is bimeric; Notobdella is decorated with longitudinal stripes like Crangonobdella, but is, so far as is known, trimeric; Carcinobdella lacks pulsatile vesicles, has 14 annuli in a complete somite and 4 pairs of eyes on the anterior sucker.

The genera known as having the posterior caeca fused but still showing evidence of a double origin by perforations, bifid termination, etc., are a relatively compact group, being plain, excepting Branchellion, which stands apart in its possession of lateral gills and Oxytonostoma which is ornamented with tubercles. The presence or absence of vesicles external to the muscular envelope may not be always a reliable point for the separation of the other genera, since such vesicles, as in the present leech, may be inconspicuous; but the absence of such structures is well-established for at least Platybdella, Hemibdella, Crangonobdella, and Austrobdella, which have 5 pairs of testes. In Austrobdella, these vesicles are replaced by a continuous contractile lacuna external to the muscular envelope on either side. Such vesicles are lacking also from Cryobdella and Cryobdellina, which are distinct from other genera in the group in having only 4 pairs of testes Three genera have, in common, 11 pairs of external vesicles and 6 pairs of testes. These are Piscicola, Cystobranchus, and Calliobdella. Piscicola has no seminal vesicles, but such structures are present in Cystobranchus and Calliobdella. Cystobranchus has 7 annuli to the fully formed segment. If any relationship is evidenced in the above analysis, it appears that the Makara leech may stand close to Calliobdella but in that genus there are (following Leigh-Sharpe, 1915) 6 pairs of testes, medianly placed ovaries, and other features distinct from the present specimen.

There is little relationship to Marsipobdella, which Moore (1952) establishes as having 5 pairs of testes, a bluntly terminating posterior caecum perforated at five places, an intersegmental arrangement of gastric pouches, no external vesicles, and 12 annuli in a fully formed somite. Johanssonia is a genus containing species which have 14 annuli to a somite, 6 pairs of testes, 11 pairs of vesicles, 5 perforations in the posterior caecum, etc. in two species but only 5 pairs of testes and two perforations in a third species.

In the above comparative account of genera, in general I follow Dr. E. Cabellero's (1956) revised list of ichthyobdellid genera excepting that I retain the genera Hemibdella, Cryobdella and Janusion as distinct from Platybdella. Likewise in view of the difference in the posterior caecum, Calliobdella is retained as separate from Trachelobdella. I still lack adequate generic definitions for Ichthyobdella Blainville 1827, Adenobdella Leidy 1885, Mysidobdella Selensky 1927, Ophibdella van Beneden and Hesse 1863, Ostreobdella Oka 1927, Podobdella Diesing 1850, or Phyllobranchus Gerard 1851.

The ovaries in the present specimen are lateral in position, in line with the testes, so that at first sight there appear to be 6 pairs of testes. This is not common. So far as I can find in the literature this position for the ovary is described for Hemibdella soleae by Selensky (1931), who mentioned at that time that it was the only genus where the condition was known. Since then it has been recorded by Dr. Meyer for Illinobdella alba, where the ovaries are larger than the testes, in Piscicola rectangulata, by Oka in Ichthyobdella uobir, and by Ingram (1957) in her Trachelobdella leptocephali and “Ichthyobdella” platycephali. I have been able to check young, that is, small specimens of Branchellion, Piscicola and Bdellamaris. In these I find that the ovaries have the same relative position as in the adult, nor apparently have other workers found the ovaries in a lateral position in the young of species they have examined. At least it is not reported as such. Thus the situation of the ovaries in the line of the testes and their relative size is probably at least of specific significance.

The recognised stability of the nervous system in leeches has been of great morphological and systematic value. In surveying the genera of Piscicolidae, it has been of interest to note that there are a few cases showing variation from the usual pattern in the posterior abdominal ganglia. In the leech described below, ganglia XXV and XXVI are contiguous and not separated by a length of the ventral nerve cord. Ganglion XXVII is independent, displaced anteriorly to XXVI/XXVII and separated from the posterior ganglionic mass formed by the fusion of XXVIII-XXXIV. In Branchellion parkeri Richardson, 1949, ganglion XXVI is recognisable as an independent ganglion, but XXVII is incorporated into the posterior ganglionic mass. In Abranchus blennii (Knight-Jones, 1940), this process of condensation is more fully developed, since the posterior ganglionic mass contains ganglia XXV to XXXIV. The three species referred to are in no obvious way closely related, and in the case of Branchellion parkeri the inclusion of ganglion XXVII in the posterior ganglionic mass is not paralleled in such other species where these structures are described in the literature, nor in other species I have so far examined. Accordingly such a feature does not appear to have generic value, and can only be regarded as specific in nature.

I wish to express my great appreciation of the assistance extended to me by Dr. Marvin C. Meyer, who has made available literature otherwise unobtainable; by Professor J. Percy Moore for advice; and Mr. J. A. F. Garrick for assistance with Fig. 7.

It is clear that the leech from Makara must be regarded as belonging to a new genus, which I name and define as follows:

Makarabdella n.g.

Cylindrical, the neck and abdomen not obviously delimited, integument thin, lacking papillae and tubercles; suckers thin, both distinct from the body, lacking ornamentation; gastric caeca segmentally arranged, smoothly rounded, not laterally subdivided; posteriorly directed gastric caecum entire excepting for three perforations and distally bifid, nowhere digitate laterally; 5 pairs of testes, seminal vesicles present; atrial cornua open widely into bursa and without a muscular eversible organ; 6 annuli on fully divided abdominal segments; external vesicles present, small; genital pores widely separated.

Genotype: Makarabdella manteri n.sp. as below.

Makarabdella manteri n.sp. (Figs. 1–6; Fig. 7.)

An elongate subcylindrical leech with relatively thin but large suckers narrowly attached, the clitellum not well-developed and the body-regions continuous, not strongly set-off from one another, but, as Badham (1916) has shown for Austrobdella, the latter may indicate a young specimen, and a clitellum and shoulders may be present in larger individuals. The integument is naked, lacking such ornamentation as tubercles or ocelli, and sufficiently translucent that the outlines of major organs such as gonads, posteriorly directed gastric caecum, and intestine are visible in the preserved specimen. Generally colourless excepting for segmentally placed transverse bands of a brown colour which is due to deeply situated “cells”, neither clitellar gland cells nor chromatophores. These occur as a dorsal cluster on the anterior sucker and 18 more or less complete transverse bands of which 4 are prechtellar, 2 clitellar, and 12 are abdominal, the last incomplete and situated on XXIV. Posterior to this, and the caudal sucker, plain.

The anterior sucker thin, shallow ventrally and widely open, shorter than wide and the width (0.6 mm) equal to that of the abdomen; lacking eyes, papillae or tubercles, showing no indications of annuli; narrowly attached posterior to its centre; margin, entire. The mouth (proboscis pore), in the posterior third of the sucker, circular in outline but not concealed by the infolded ventral margin. The neck, cylindrical, widening to 0.4 mm and continuing at about this width to the slightly wider clitellum which is nearly the width (0.6 mm) of the abdomen throughout the testicular region behind which the abdomen tapers to a moderately broad almost central attachment to the subcircular sucker which is wider (0.85 mm) than the abdomen, deeply cupped, thin, and with entire margins but no papillae or tubercles. The neck including the clitellum is 2.0 mm long; the abdomen 7.5 mm long.

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

The annuli are difficult to determine because of the translucency of the body-wall. None were detected on the oral or caudal suckers and there are no other superficial landmarks to indicate the constitution of these structures. The first two annuli are independent and apparently belong to somite V, these forming a narrow peduncle to the sucker. Somite VI is then apparently bimeric, but it may include the second annulus and hence be trimerous (see below). Somites VII and VIII are definitely trimerous, but the limits and subdivision of IX and X could not be determined with confidence, this region being greatly extended. The ganglion of VIII is situated 9/10; of IX, at 15/16; and so far as can be determined, of X, in the “21st” annulus, XI, in the “24th” annulus. A clitellum is usually formed in piscicolids by a posterior part of X, plus XI, XII, and the anterior part of XIII so that here it should probably include annuli “22” to “32” or “33”, but the determination and representation of annuli for IX and X are possibly in error. However, the crescentic transverse slit-like male genital aperture with simple lips is situated in the third interannular groove behind ganglion XI and the transverse female slit-like aperture with slightly raised incised lips is in the 5th interannular groove behind the male aperture and immediately posterior to or below the border of ganglion XII, so that the segmental positions are those commonly found, but the two apertures are separated relatively widely by 5 annuli. Somites XIII to XXIV inclusive are all clearly divided into 6 annuli of which the first and last, b₁ and b₆, in each segment are longer than the intervening four, b₂ to b₅, which are subequal. At the margins of the body the interlacing diagonal fibres of the external layer of the muscular envelope come into focus to show where the fibres cross as small oblongs (Fig. 4), three being present in the first and last annuli of a segment and only two in each of the intervening four. This is a most helpful guide to the annulation. The ganglia in this region are located slightly posterior to the middle of each segment being crossed by or posterior to the third (b₂/b₄) interannular groove. The testes are not strictly intersegmental but are generally displaced slightly anteriorly, and, in some cases, of a pair the one more so than the other. The transverse bands of colour are actually segmental; commencing with bands at XV or XIV and counting anteriorly, it is seen that the first band is over the posterior portion of the circumpharyngeal ganglionic mass, this band corresponds to segment VI and accordingly the first one or two annuli can be assigned to somite V as proposed above. Somite XXV is trimeric with the ganglion centrally placed. Ganglion XXVI is at XXV a₃; the segment XXVI is bimerous. Ganglion XXVII is at XXVI/XXVII, and the segment is also bimerous with the anus at XXVII/XXVIII. One annulus provides a broad basis to the caudal sucker and is posterior to XXVII. The caudal sucker is centrally attached, wider than the body (as 1.4:1), lacking tubercles or other adornment, and with a plain margin.

The circular mouth is posterior in the oral sucker. The retracted proboscis extends beyond the limit of VIII but does not reach ganglion IX. Oesophageal glands are large and few, there are about 10 in the vicinity of the posterior end of the pharynx and extending back to ganglion X. Clitellar glands are arranged principally in dorsal and ventral sheets internal to the muscular envelope and thus largely obscure the oesophagus and stomach in the entire specimen, but sections show that the oesophagus expands without a sphincter into a simple dilation in XIII which lies between and above the anterior ends of the ovaries and between the vesiculae seminales. There are further dilations in XIV, XV, XVI, XVII, XVIII, and

XIX, and these are not separated by sphincters excepting possibly the last two. The gastric pouches then are segmental dilations, and lack diverticula or other lateral subdivision, excepting the last which is extended posteriorly in the middle of XIX on either side to give rise to the large posterior caecum which forms a flattened elongate sac perforated in the middle of XX, XXI, and XXII by dorsoventral apertures which are somewhat irregular in form. The caecum ventral to the intestine extends to the posterior end of XXIV where it ends with a short right diverticulum which does not reach XXIV/XXV and a longer left diverticulum which extends to XXV a₃. The opening between the gastric pouch and the intestine is guarded by a sphincter. The intestine rests in a shallow groove on the dorsum of the posterior caecum, is tubular and divided by a constriction at the lever of each ganglion into intersegmental regions. The intestine commences with a short portion in XIX b₃/b₄ which constricts in XIX b₅ where it is followed by the first elongate chamber which is lobed anteriorly and reaches to ganglion XX where it is sharply constricted and enters the essentially tapering tubular second complete chamber in turn constricted at ganglion XXI. The third and fourth complete chambers are tubular, constricted at the ganglion XXII and at XXIII b₃, where another short chamber commences. This narrows abruptly at XXIII b₅ and terminates at XXIII b₅/b₆, where it communicates with the tubular rectum by an aperture controlled by a sphincter. The simple tubular rectum extends to XXVII/XXVIII, where it opens at the median dorsal anus. There is no postanal pocket on the rectum.

The male reproductive system consists of 5 pairs of relatively small subspherical testes which are not completely intersegmental but commonly displaced anteriorly either symmetrically, or not. The vas efferens opens from the ventro-lateral aspect of each testis to form vasa deferentia which are also ventro-lateral in their path. The testes are situated at XIV/XV, XV/XVI, XVI/XVII, XVII/XVIII, XVIII/XIX. The vasa deferentia extend anteriorly to the level of ganglion XIII where each expands into a seminal vesicle. The seminal vesicle extends laterally and dorsalwards to the level of ganglion XII, then narrows to form a stout sinuous epididymis which is on each side thrown into a few (3) vertical folds lateral and dorsal to the bursa and descends to join short ejaculatory ducts at the level of the male genital aperture. These ducts loop once ventrally reaching X/XI and then enter the anterior aspect of short wide cornua which join to form a large transverse bursa extended by a very definite small pouch posteriorly nearly to the middle of ganglion XII. The pars glandularis is extensive, the bulk of the glands being situated on the dorsal aspect of the bursa between the epididymi and extending also down the posterior face of the bursa. The ovaries are situated laterally in the line of the testes and are elongate bodies broadly rounded posteriorly at XIII/XIV and abruptly reduced at the level of ganglion XIII to continue as the short thin-walled oviducts which unite at about XII/XIII to form a small thin-walled atrium which extends anteriorly below the posterior portion of ganglion XII and opens by the female genital pore which is shortly posterior to this level. Sections show sperm-masses in the ovaries. Each such mass is an elongate body twisted on itself.

The clitellar gland cells are distributed between VII and XIX. There is the usual clustering of smaller gland cells in the neck—i.e., between VII and XI. Large clitellar gland cells extend from XIII to XIX, the most posterior cells being at XVIII/XIX. The ducts are not aggregated into distinct groupings but form dorsal and ventral sheets.

There are the usual twenty-one independent ganglia in the ventral nerve cord. The circumpharyngeal ganglionic mass is somewhat posterior, commences in the third annulus, and includes six ganglia, with ganglion VII closely following as the first free ganglion. There are four more ganglia anterior to the male genital pore. Ganglion XII is elevated from the ventral body-wall. Ganglion XIII is median in its segment; but ganglia XV to XXIII are slightly posterior to the middle level of their segments. Ganglia XXIV and XXV are median in their segments but ganglion XXVI is contiguous with ganglion XXV and located in XXV a₃. Ganglion XXVII is at XXVI/XXVII and separated from ganglion XXVI by a length of cord shorter than the ganglion itself so that it also is displaced anteriorly. The caudal ganglionic mass commences in the postanal annulus but the nerve supply to this annulus could not be determined.

External vesicles were not detected in the entire animal, but the examination of sections showed the ovarian sinus communicating anteriorly by a short channel which passed through the muscular envelope and expanded into a thin-walled vesicle. This is present at the level of ganglion XIII. Similar vesicles can be detected at the level of ganglion XIV and, but with less certainty in identification, back as far as segment XX. Another chamber of similar size and location is present at the level of ganglion XXII, but no connection to the lacunar system can be determined in this instance, so that while external vesicles are present the number may be 8, or 10, but a definite number cannot be given since in the posterior part of the body the sections are unfortunately somewhat too oblique. The most careful examination has not shown muscle fibres in the wall of the vesicles, so that these may not actually be pulsatile.