[ref. ID; 4344 (Diana L. Lipscomb and Gavin P. Riordan, 1990)]

Subclass Haptoria Corliss, 1974
Order I. Haptorida Corliss, 1974
Suborder Helicoprorodotina Foissner & Foissner, 1988
Family Helicoprorodontidae Jankowski in Small & Lynn, 1985 (Helicoprorodon)
Family Actinobolinidae Kahl, 1930 (Actinobolina)
Suborder Vestibulifera
Family Balantidiidae Reichenow in Doflein & Reichenow, 1929 (Balantidium)
Family Isotrichidae Butschli, 1889 (Isotricha)
Family Buetschliidae Poche, 1913 (Alloiozona, Didesmis)
Suborder Acropisthiina Foissner & Foissner, 1988 (Fuscheria, Chaenea, Acropisthium)
Suborder Enchelyina Foissner & Foissner, 1988 (Enchelydium)
Suborder Dileptina Jankowski, 1978 (Dileptus)

Order II. Pleurostomatida Schewiakoff, 1896
Suborder Lacrymariidae nov. subord. (Lacrymaria, Lagnyophrya)
Suborder Didiniina Jankowski, 1978 (Didinium, Monodinium)
Suborder Pleurostomatina nov. subord.
Family Homalozoonidae Jankowski, 1980 (Homalozoon)
Family Spathidiidae Kahl in Doflein & Reichenow, 1929 (Spathidium)
Family Amphileptidae Butschli, 1889 (Litonotus, Loxophyllum)

Phylogenetic and taxonomic implications; The taxonomic revision of the haptorid ciliates supported by cladistic analysis is given below with the characteristics of each taxon. This discussion primarily addresses the classification of Foissner & Foissner (1988) which is the most recent and detained proposal.

Subclass Haptoria Corliss, 1974
Somatic monokinetid with overlapping postciliary microtubules in stacks 4 over 3, a laterally directed kinetodesmal fiber and two set of transverse microtubules. The oral structure consists of dikinetids in which the nonciliated, anterior kinetosome has a nematodesmata that is hexagonal to round in cross-section and a transverse ribbon supporting the cytopharynx. The ciliated, posterior oral kinetosome has a postciliary ribbon. Accessory of bulge microtubules arise perpendicular to the transverse microtubules lining the cytopharynx. Toxicysts are found within the circle of nematodesmata. Epiplasm is apparently absent and the alveoli are compressed. A dorsal brush is found on the anterior half of the cell body and it has pairs of clavate cilia in which the posterior kinetosome has a normal infraciliature but the anterior has only a nematodesmata.
Remarks; A few of the characters become modified or reduced in some taxa, especially symbiotic forms, but these remain the basic characters of the subclass. This definition is similar to that given by Foissner & Foissner (1988) with a few exceptions. They give some characters (uniform holotrichous ciliation, longitudinal kineties, convergent postciliary ribbons, closed cytostome that is usually apical and round to slit-like, tela corticalis and telokinetal stomatogenesis) that are also found outside the haptorids and are therefore pleisiomorphic and cannot be used to define the group. They give oralized somatic kinetosomes as a character of the subclass, but we find it is actually a character than defines a subgroup with in the haptorids and is not a character of the whole clade. Leipe & Hausmann (1989) create a new subclass, Ditransversalia, for ciliates with overlapping postciliary microtubules in a 4 over 3 double-row configuration and two sets of transverse microtubules. This subclass differs from the subclass Haptoria in that it would exclude Didinium, Monodinium, Actinobolina, Helicoprorodon and Dileptus. They are assuming that, since two transverse ribbons have not been described for these taxa, the 2nd transverse set is primitively absent. The position taken here and by others (Foissner & Foissner 1988, Grim 1987, Lynn & Nicholls 1985) is that they may not be absent but simply not yet discovered. We are persuaded that this may be the case because the 2nd set is difficult to find since it consists of only a few microtubules and these usually cannot be seen in the same section as the other set of transverse microtubules. The 2nd set of microtubules was unnoticed in many well-examined taxa until it was described by Williams et al. (1981) for Spathidium. It must be emphasized that Leipe & Hausmann's position is far from disproved and ours not yet proven. This issue will remain unresolved pending careful reexamination of all of these taxa.

Order Haptorida Corliss, 1974
Oralized somatic kinetosomes contribute both nematodesmata and transverse microtubules of the oral structure.
Remarks; This group corresponds best to the order Haptorida as defined by Foissner & Foissner (1988) but also includes Helicoprorodon, the buetschiliids, and the balantidiids.

Suborder Helicoprorodontina Foissner & Foissner, 1988
Haptorids with toxicysts found outside the oral area an oral microtubular elements rigidly held by fibrous material. (Helicoprorodon, Actinobolina).
Remarks; Helicoprorodon was traditionally classified as a prorodontid (Corliss, 1979). Small & Lynn (1985) placed it in its own family in a new order. Pharyngophorida, within the Haptoria. We agree with Foissner & Foissner's (1988) assessment that this order should be abandoned. According to Small & Lynn (1985), the Pharyngophorida is distinguished by an open cytopharynx but this is a variable character that is difficult to determine. In any case, the cytopharynx of Helicoprorodon is closed, not open as Small & Lynn state. Foissner & Foissner place Helicoprorodon in its own family in a new order, Pseudoholophryida, defined by having spiraling kineties around the oral area the ends of which are several oral dikinetids, and an aberrant or absent dorsal brush. This is based on Raikov & Kovaleva's (1980) interpretation of the oral structure. We have reexamined Helicoprorodon and found this interpretation incorrect. The oral dikinetids form a closed ring and are not continuous with the spiraling kineties. At this time, we recommended transferring the family Helicoprorodontidae into the order Haptorida because it has oralized somatic kinetosomes. Ultrastructural analysis of other pseudoholophrids to see if they also have oralized somatic kinetosomes contributing both nematodesmata and transverse microtubules to the oral structure will help solidify the taxonomy position of this group.

Suborder Vestibulifera de Puytorac et al., 1974
The chromatin is condensed in nondividing micronuclei. There is a secondary loss of oral kinetosomes, bulge microtubules and toxicyst. Oralized somatic kinetosomes form all parts of the oral structure. There are many concentric rings of nematodesmata around the mouth. (Balantidium, Isotricha, Alloiozona, Didesmis)
Remarks; In older classifications, the sister group to the Gymnostomatida was the Trichostomatida which included ciliates with uniform but asymmetrical body ciliation and a vestibule but no buccal ciliature. The Trichostomatida consisted of a wide variety of ciliate families such as the Colpodidae, Isotrichidae, Plagiopylidae and Balantidiidae. In recent years, this group has been spilt and lumped in various ways. The revision of de Puytorac et al. (1974) created a new subclass, the Vestibulifera, for three orders: the Trichostomatida (e.g. Plagiopyla, Balantidium, and Isotricha), the Entodiniomorphida (previously classified as Spirotricha) and the Colpodida. The family Buetschiliidae (e.g., Alloiozona and Didesmis) was described as being the most primitive prostomial gymnostome group because of the reduced oral structure and was given its own order, the Archistomatina (Corliss, 1979, de Puytorac et al. 1974). Small & Lynn (1985) elevate the trichostomes to a subclass containing two orders: the Vestibuliferida (Isotricha, Balantidium and their relatives); and the Entodiniomorphida with the suborders Blepharocorythina, Entodiniomorphina and Archiostomatina. They transferred the buetschiliids from the prostomes into this last suborder. The colpodids and plagiopylids were removed to the subphylum Cyrtophora. Foissner & Foissner (1988) transferred the buetschilliids to the Haptoria and the Trichostomes (sensu de Puytorac et al. 1974) were placed as the Haptoria's sister group. Leipe & Hausmann (1989) place the balantidiids within their subclass, Ditransversalia, which is approximately equivalent to the Haptoria. Our analysis indicates a close relationship between the balantidiids and buetschiliids and, because they have oralized somatic kinetosomes, they group within the order Haptorida. They have secondarily lost the accessory bulge microtubules, possibly because their endosymbiotic lifestyle does no require aligned toxicysts in the oral area. Nothing can be inferred from our analysis on the position of the entodiniomorphids, plagiopylids or colpodids.

Suborder Acropistiina Foissner & Foissner, 1988
Granular material fills the space between the outer tube wall of the toxicyst and the membrane that surrounds the toxicyst. The cilia are in furrows defined by extended cortical ridges. The tela corticalis is absent. (Chaenea, Acrospithium, Fuscheria)
Remarks; Acropisthium needs to be reexamined to determine if this suborder is indeed a monophyletic group.

Suborder Enchelyina Foissner & Foissner, 1988
The posterior kinetosome of the oral dikinetid is absent so that the oral structure consists of oral monokinetids homologous to the anterior oral kinetosome of other haptorids. In addition to the normal toxicyst, there is a unique, small, spindle-shaped toxicyst. The dorsal brush has zig-zag rows of clavate cilia. The endoplasmic reticulum that separate the endoplasm from the ectoplasm is interrupted only at kinetosomes. (Enchelydium)

Suborder Dileptina Jankowski, 1978
The oral area consists of a proboscis with oral dikinetids without nematodesmata anterior to the cytostome and ciliated monokinetids with nematodesmata posterior to the cytostome. (Dileptus)

Order Pleurostomatida Schewiakoff, 1896
Members of this order have two types of toxicysts and lack oralized somatic kinetosomes.

Suborder Lacrymariina nov. subord.
There are triangular, paired nematodesmata around the oral area. (Lacrymaria, Lagynophyra)

Suborder Didiniina Jankowski, 1978
Cilia in girdles around the cell rather than longitudinal rows. There are more oral dikinetids than somatic kineties. These oral dikinetids are parallel, not perpendicular to the somatic kineties. (Didinium, Monodinium)

Suborder Pleurostomatina nov. subord.
The oral area is a flattened slit. There are more oral dikinetids than somatic kineties and the line of oral dikinetids is perpendicular to the somatic kinety. (Spathidium, Homalozoon, Bryophyllum, Litonotus, Loxophyllum)
Remarks; Several authors have remarked on similarities between the spathidiids and pleurostomes (Leipe & Hausmann 1989, Saxena et al. 1978) although they have not been formally merged into a single taxon before. In conclusion, Fig. 24 shows our suggested changes to the classification of Foissner & Foissner (1988). This classification will certainly be modified further as other haptroids are studied. A natural grouping of the orders and suborders within the subclass Haptoria becomes ultrastructurally and as careful phylogenetic analysis grouping the taxa by apomorphic characters is undertaken.