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Studies on New Zealand Hirudinea: Part II.Branchellion parkeri, a new Ichthyobdellid Leech

[Introduction]

Leeches of the genus Branchellion are generally known as ectoparasites of skates and rays, although as a rare exception B. torpedinis has been recorded on wrasse. A species of Branchellion occurs in New Zealand waters and was originally included in our fauna on the basis of specimens collected by Professor J. T. Parker, who exhibited stained and mounted material at a meeting of the Otago Institute in 1891. These leeches were collected from the common skate, and Parker suggested that should they turn out to be a new species it might be named B. rajae. They are referred to under this name in Hutton's Index Faunae Novae Zealandiae; but no recognizable description has been associated with this name, and, since the specimens mentioned are no longer available, B. rajae must be considered a nomen nudum. Professor Sir William Benham has sought these specimens, or page 4 their identifiable companions, but with no result other than the finding of a tube containing two specimens of Branchellion and labelled "Branchellion from Raia nasuta, T. J. Parker, 1881." These may well be the specimens referred to in the note on the exhibit of 1891, where it is stated "a single specimen had been found some years previously." I cannot distinguish these specimens from others which have come to hand in recent years; however, the correlation of these specimens with the name B. rajae is on no firm basis permitting the maintenance of the name, and, unless the stained and mounted specimen originally associated with the name comes to hand, this name regrettably must remain in its present status. Professor Sir William Benham has supplied me with two specimens from his own collection, taken from Raia sp.

Specimens of Branchellion which have been obtained from the vicinity of Wellington have been found as ectoparasites on dogfish, Mustelus antarcticus, brought to this laboratory for dissection. In one case, three specimens were found attached at the posterior end of the base of the first dorsal fin. When removed, there remained a shallow circular groove 5 mm. in diameter exactly matching the posterior sucker, and the angle at the posterior end of the base of the fin was found to be eroded. Other specimens have been collected during the sorting and handling of this host, but no other cases of attachment scars have been seen. We have not found a large colony such as the colony of "thirty or forty of the parasites in an area of 3 in. or 4 in. circumference," as seen on R. nasuta by Parker.

From the available literature, it seems that the genus Branchellion contains only five currently recognized species. Two of these, B. Torpedinis (v. Leigh-Sharpe, 1916) and B. orbinensis (v. Leigh-Sharpe, 1933) possess 33 pairs of gills. The other three species, B. borealis (v. Leigh-Sharpe, 1933), B. australis (v. Leigh-Sharpe, 1916), and B. ravenelii (v. Meyer, 1940), lack the first and last pairs of gills of the other two species, and accordingly have only 31 pairs of gills, which is also the case in the New Zealand specimens. B. borealis and B. australis are tuberculate, B. australis (from South Australian waters) having tubercles on all annuli of the neck, and always four, six, or eight tubercles on the abdominal annuli, while B. borealis (from Plymouth waters) has four tubercles on the dorsum of the a2 of the neck segments but none on the abdomen. B. Ravenelii and the New Zealand specimens lack tubercles and are close in superficial resemblance, but differ in many respects—in particular, the arrangement of the genital pores and ducts. The pores in B. ravenelii are relatively remote from one another, being situated in the middle of their respective segments—i.e., xi a2 and xii a2; the seminal vesicles are situated in xi and x, and connect to the atrium by a large, loosely convoluted duct. In the present material, the male and female pores are immediately adjacent, and there is a long, narrow, convoluted duct between the atrium and the seminal vesicle, which is situated in xii and xiii. This close page 5 approximation of the pores differs also from the arrangement of the pores in B. torpedinis, B. australis, and B. orbinensis, where the male pore is situated between two annuli; there is a full annulus intervening between this and the next, where the female pore is situated in the middle of the next annulus. B. borealis has an arrangement somewhat similar to that in the present material, the pores occurring on adjacent annuli, but is, of course, distinct in the possession of sensillae on the segments of the neck, which I have been completely unable to detect in living or preserved specimens from these waters. Finally, the present material is distinct from all other members of the genus, since the local material uniformly possesses only 10 pairs of pulsatile vesicles, whereas there are 11 pairs in the previously known species.

Additional to the currently recognized species, there are others in earlier literature which are poorly or inadequately described and essentially unrecognizable. Baird (1869) describes B. intybifolium (locality unknown) and B. lineare and B. punctatum from North Australia. B. intybifolium appears to be a 33-gilled species with irregular margins on the gills; B. lineare is from Mustelus, and the only distinctive recorded feature is that the neck is nearly equal in diameter to the width of the abdomen; B. punctatum from Myliobatis has "branchiform appendages larger on the posterior portion of the body. ..." None of these is recognizable in the present material.

Accordingly, the present material represents an undescribed species for which the name of B. parkeri is here proposed, although I am confident that if Parker's original exhibited specimen is ever located it will be found identical with this material, and the name B. rajae can be reintroduced, since it does not appear to be in any other way occupied.