ADDITIONAL RECORDS: Very common, found in 67 of 300 samples of forest soil and organic debris collected in tree fern forests and beech forests in New Zealand.

Solitary thalli in infected rotifers are ovoid to ellipsoid to cylindrical and 20-40 µm wide by 60-95 µm long (Fig. 9). At maturity each thallus produces a single exit tube to the exterior (Figs. 2, 11). No flagellate stage is produced in this species. The zoospore state has apparently been suppressed and the protoplasm cleaves directly into tightly packed, spherical cysts inside the thallus that now functions as a sporangium. At maturity of the thallus, cysts are expelled rapidly en masse and gather in a ball at the mouth of the solitary exit tube (Figs. 2, 11). Cyst balls vary considerably in size depending on the size of the contributing sporangium; they may remain attached to the sporangium or are released to float freely in the aqueous medium (Fig. 3).
There are two sizes of cysts, designated small (3.3-4.0 µm diam.) and large (5.5-6.5 µm diam.), but the cysts from one sporangium are all the same size. After expulsion from the sporangium, the cysts begin to germinate almost immediately (Figs. 4, 12). From each of the small cysts a 'slightly curved, elongate, tapering cell develops (Figs. 5, 6, 10). This cell is the equivalent to the so-called gun cell in H. mirabilis (Barron 1987) but is quite different in physical appearance. In H. elegans the gun cell is elongate, unbranched, and tapers to a very narrow apex. It is almost denticulate in appearance. At maturity the cyst is completely empty of contents and apparently dead, and the derivative cell has a vacuolated base containing an elongate tubular device running to the apex of the cell. Gun cells derived from small cysts (Figs. 6, 7, 10) in H. elegans are 13.5-17.2 µm long by 1.4-1.8 µm at their widest point and taper to a narrow (less than 1 µm) apex. All the cells in a cluster develop more or less simultaneously, and at maturity, a cluster of gun cells floats around passively in the aqueous matrix. With time the individual cysts come apart, and the gun cells separate and sink to the bottom. Unlike those of H. mirabilis, the gun cells of H. elegans do not attach to debris or the substrate but lie passively on the surface of the substrate until disturbed.
Larger cysts develop in an identical fashion to the small cysts (Figs. 7, 13) and produce gun cells that in all respects appear to be the same as those produced by the small cysts except they are 20-24 µm long by 2.6-3.2 µm at their broadest (Fig. 7). Large cysts, however, also produce a second type of gun cell that is a branched cell referred to as the Y-cell (Fig. 7, inset; Fig. 14).
Sporidia (Fig. 1) are broadly ellipsoidal to short cylindrical with a well-defined apiculus and are 4.0-5.0 by 2.2-3.3 µm. In general they are similar to sporidia reported for other species of Haptoglossa. Discharged gun cells are typical for Haptoglossa, with a slender everted tubular device containing a bladder-like swelling part way along the length (Fig. 8).

HABITAT: Endoparasitic in bdelloid rotifers.

Thalli 60-95 µm longi x 20-40 µm lati; thallus quisque proferens tubum singularem evacuandi; proferens nulla zooporangia; cystides expulsi rapide ut formant globum juxta os tubi evacuandi; cystides magnitudinum duarum; cystides parvi 3.3-4.0 µm in diametro; cystides magni 5.5-6.5 µm in diametro; cellae ejectantes e cystidibus parvis 13.5-17.2 µm longae x 1.4-1.8 µm latae; cellae ejectantes e cystidibus magnis 20-24 µm longae x 2.6-3.2 µm latae; cystides magni etiam proferentes cellas ejectantes et cruciatae; sporidia 4.0-5.0 µm longa x 2.3-3.3 µm lata.

In experiments with nematodes, none was observed to contain mature or developing thalli of H. elegans. In an earlier study (Barron 1989), it was found that all species of Haptoglossa except H. heterospora, which was not available for testing, attacked both rotifers and nematodes. Later I had the opportunity to test H. heterospora and found it parasitized both hosts (unpublished data).
Haptoglossa elegans is quite distinct from previously described species in this genus. No other species produces the elongate, unbranched, curved, tapering gun cell described for this species. All known Haptoglossa species produce only the branched gun cell as in Fig. 7 (inset). Also, all other Haptoglossa species except H. heterospora possess a zoosporic state.
In H. heterospora, however, the cysts are not expelled en masse as they are in H. elegans. Finally, all other species of Haptoglossa attack both rotifers and nematodes while H. elegans attacks only rotifers.

TYPE: Preserved material in Herbarium (OAC 10846); recovered from organic debris under a tree fern, Sprague Trail, Waitakere Range, North Island, New Zealand, November 1988.