Reclinomonas Flavin & Nerad, 1993 (ref. ID; 7277 original paper, 7295)
Family Histionidae (ref. ID; 7492, 7277)
The family Histionidae (International Code of Zoological Nomenclature)/Histionaceae (Internationl Code of Botanical Nomenclature) is proposed to accommodate both Histiona and Reclinomonas. The characters of the family are as follows: Biflagellated protists residing within a lorica and oriented with dorsal surface directed downward. Lorica of simple construction and not easily visible even using phase microscopy. Cells with two flagella, both of which have no mastigonemes. Membrane of the trailing flagellum modified as a flattened "wing-like" extension. Colorless organisms feeding upon bacteria. Engulfment of prey occurs in the ventral posterior half of the cell. Mitochondrial cristae tubular. Golgi apparatus absent or, if present, not prominent and comprised only of two to four cisternae.
The life cycle consists of two stages: a highly motile aloricate dispersal stage and a loricate feeding stage. The aloricate dispersal stage swims actively with the anterior flagellum providing the propulsive force and the posterior flagellum acting as a rudder. (ref. ID; 7277)
[ref. ID; 7277]
Diagnosis; Protists residing within a lorica with the dorsal surface directed downward. Lorica laterally compressed; outside surface studded with "nail-shaped" scales. Lorica composed of intertwined microfibrils and attached to the substrate by a stalk. Cell anchored to the lorica at the left anterior side with a cylindrical cytoplasmic appendage (epipodium) extending posteriorly approximately 1/3 of the body length. The right side of the cell raised into a prominent cytoplasmic lip reinforced at the margin by microtubules and a microfibrillar structure. Two flagella, both without mastigonemes, one directed upward and the other held along the longitudinal axis of the body and affixed to the posterior end near its tip. Membrane of the trailing flagellum modified as a flattened wing-like extension for most of the length. Subpellicular microtubules lining the longitudinal axis of the body under both the dorsal and ventral surfaces except in the region of food capture. Phagotrophic, eating bacteria, ingestion occurring in the posterior left half other the cell. Single, branched mitochondrion closely associated with the nucleus. Mitochondrial cristae tubular. Golgi absent. Two species. (ref. ID; 7277)
Basionym; Histiona campanula Penard, 1921. Penard described a new loricate flagellate which he assigned to the genus Histiona. He apparently had some reservations about his diagnosis since he stated, "the small Flagellate seems to belong to Histiona, a genus itself very little known." The new organism, Histiona campanula, differed significantly from the type species, Histiona velifera (Voight) Pascher, first described by Voight in 1901. (ref. ID; 7277)
Synonym; Stenocodon campanula Pascher, 1942. In 1942 Pascher, realizing that H. campanula did not belong within that genus, transferred it to the newly created genus Stenocodon. However, the type species for the genus, S. epiplankton, was quite distinct from Penard's flagellate. Stenocodon epiplankton differs from H. campanula in three major ways.
1. It is attached to the lorica by a cytoplasmic extension from the dorsal surface of the cell. 2. It has a thin cytoplasmic skirt that arises from the ventral surface of the cell. 3. It has flagella that are markedly different length and both are directed upward. Stenocodon appear to be related to both Histiona and Penard's flagellate, but its proper taxonomic assignment must await ultrastructural studies. The organism that we describe is very similar to Histiona but is placed in a separate genus along with H. campanula. Both genera should be placed in a new family incertae sedis within the Kingdom Protista.
Bourrely (1968) placed Histiona in the family Diacronetamataceae and considered it a prymnesiophyte. We agree with Mylnikov ((1989) that this is not an appropriate taxonomic home. Therefore the genus must be removed from this family and placed in a new family along with Reclinomonas. It may be necessary to also place Stenocodon within this family whe ultrastructural studies are completed. We feel that the placement of the family within a higher taxon, i.e. the Class Bicoecales as proposed by Mylnikov (1989), is premature. (ref. ID; 7277)
[ref. ID; 7295]
Trophic cells: Trophic cells reside in a hyaline lorica. The dorsal side of the cell is closely appressed to the lorica, the posterior end of the cell is not elevated with respect to the anterior end of the cell, there is no posterior ventral "sail," and the lorica bears spiny scales. Both lorica and scales are diffcult to observe with light microscopy. The species R. americana Flavin & Nerad, 1993, is known from three freshwater sites in the United Stated and one in New Zealand; the "freshwater species of Jakoba" referred to by Flavin & Nerad (1993) and Patterson (1990) is R. americana. (ref. ID; 7295)
Cysts: Walled cysts typically have an apical plug. (ref. ID; 7295)
- Reclinomonas americana Flavin & Nerad, 1993 (ref. ID; 7277 original paper) reported year? (ref. ID; 7492) reported author and year? (ref. ID; 4980)
- Reclinomonas campanula (Penard, 1921) Flavin & Nerad, 1993 n. comb. (ref. ID; 7277)
Syn; Histiona campanula Penard, 1921 (ref. ID; 7295)
- Reclinomonas echidna (ref. ID; 7295)
Reclinomonas americana Flavin & Nerad, 1993 (ref. ID; 7277 original paper) reported year? (ref. ID; 7492) reported author and year? (ref. ID; 4980)
Lorica not attached at an angle. (ref. ID; 7277)
- Light microscopy: In wet mounts the loricate flagellate appears as a half walnut shell (4x7 um), the convex dorsal side directed toward the base of the hyaline lorica. The single slender pedicel of the lorica is attached to the substrate. The anterior flagellum is arched over the body and moves steadily back and forth in an anterio-posterior direction. At times it displays an irregular thrashing motion. The second flagellum appears at all times attached posteriorly at its distal end, and vibrates like a bent wire across the ventral pocket. It is difficult to distinguish the lorica from the cellular lip. Empty loricas are more clearly seen by phase contrast, as pediceled cups. A single contractile vacuole empties about once per minute. The anteriorly located nucleus is often surrounded by mitochondria. It appears that there is a single mitochondrion. A slender cell process, seen extending upward from the ventral surface of the cell is believed to be an epipodial anchor to the hyaline lorica, although the latter cannot be discriminated by light microscopy. Oval swarmer cells without loricas are common in young cultures (up to 80% after 1 day), and move rapidly with one flagellum directed anteriorly and one held against the body along the ventrum of the cell. (ref. ID; 7277)
- Scanning electron microscopy: Figure 3 shows a lateral view comparable to that in Fig.1, with the convex dorsal surface of the lorica attached to a stalk(s), which is anchored in a clump of bacteria. Figures 4 and 5 illustrate the cup-like ventral surface, looking down through the opening in the lorica. The portion of the cytoplasmic lip that is toward the viewer in Fig.4 appears to have a thicker margin with a series of fine cytoplasmic extensions toward the posterior end. A slender epipodium passes to the rim of the lorica. Figure 5 shows a thin cytoplasmic wing associated with the recurrent flagellum (RF). Abundant mucus-like material surrounds the lorica. The swarmer cells are generally oval but when they have been under a coverslip for a time period, allowing them to slow down, they become more spherical in shape. Using interference contrast microscopy, the development of the RF in a ventral groove is clearly evident. The mitochondrion can be clearly visualized using phase contrast microscopy. In swarmer cells it often appears as a single sausage-shaped mass with one end adjacent to the nucleus. Figure 8 shows the orientation of anterior and RF, and the oval shape of a non-loricate swarmer cell. (ref. ID; 7277)
- Transmission electron microscopy: A section in the longitudinal plane reveals a cell with an abundance of vesicles, many related to phagocytosis. A vesicle that probably contains scale material is indicated. Tubular cristae characterize what appears to be a single convoluted mitochondrion, though we could not completely rule out the presence of more than one. The basal bodies generating the anterior and RF are oriented at an acute angle to each other. Broad arrays of subpellicular microtubules disseminate from the anterior region containing the basal bodies.
A transverse section shows the nucleus embraced by mitochondrial profiles. Subpellicular microtubular are closely packed under the plasma membrane of the convex dorsal surface, and also extend on the ventral side, but are not as tightly packed there. Microtubules are interrupted near the posterior left ventral side where food capture occurs. Figure 12 shows the winged RF, and the long narrow cytoplasmic lip that appears to be devoid of cytoplasmic material until it terminates in a swelling that contains microtubules as well as fibrous structures. Serial sections in this plane remain essentially unchanged through the cell (4 microns): the RF stays in the same orientation with the wing toward the ventral surface; the lip is more mobile. The distal attachment of RF to the cell posterior, deduced from light microscopy and scanning electron microscopy, has not been unequivocally identified in sections; occasionally the RF has appeared to lose its wing just before fusing with the plasma membrane.
A cell process, starting opposite the lip, appears to be the origin of the epipodium. Higher magnification also reveals cross-striations in the wing of the RF, and cross-links between subpellicular microtubules. Transverse sections of the anterior flagellum reveal an unmodified 9+2 axoneme (not shown here). No mastigonemes have been seen on either flagellum. About seven microtubules are seen in cross-section in the rim of the cytoplasmic lip where they are associated with a periodic array of fine filaments about 6 nm in diameter, two of which appear to be associated with each microtubule. The latter may be arranged in ribbons with their long axis parallel to that of the microtubules. The center to center spacing measures 39 nm between microtubules and 19 nm between filaments. The filaments are also seen as a pear-shaped cluster with a broader fibrous structure at the base, oddly resembling isolated striated flagellar roots (Salisbury et al. 1984). A more tightly packed periodic array of the fine filaments or ribbons, with a center-to-center spacing of 8-10 nm, is seen within the cell. Serial sections have shown that these filaments originate near the basal bodies. (ref. ID; 7277)
The organism we describe has other characteristics similar to those found in Colponema loxodes (Mignot & Brugerolle 1975), a flagellate of uncertain taxonomic affinity. The "wing" is large and of comparable size to that found in the organism described herein. It also appears to be supported by evenly spaced microfibrils, whereas in Colponema, the trailing flagellum is associated with a ventral groove, and is less well developed. The subplasmalemma microtubules of Colponema, although more sparse than those in the organism we describe, are oriented from the anterior to the posterior end of the cell. However, the orientation of the kinetosomes is at an acute angle in both organisms. Both have mitochondria with tubular cristae, ingest food at the ventral groove, and lack an oral apparatus. Colponema, however, differs in that the Golgi are well developed the anterior flagellum has mastigonemes in much the same manner as chrysophytes and bicosoecids, the mitochondrial profiles are peripheral and not closely associated with the nucleus, and it has toxicysts. However, since Colponema feeds on other flagellates it may need the toxicysts to inactivate its prey. This would not be necessary in Reclinomonas because its prey is bacteria. Colponema also has alveolar sacs beneath cell membrane that are not found in the organism we describe. Colponema appears to have a taxonomic position intermediate between that of chrysophytes and Reclinomonas.
The organism we described is most similar to Histiona (Mylnikov 1984, 1989). The two genera have a number of common structures. 1. They both have cytoplasmique appendage originating near the flagella; this appendage was referred to as the flagelliform process by Mylnikov (1989), but we adopt the term of Penard (1921), the epipodium, since it has priority. 2. Members of both genera have a very thin walled lorica that is virtually indistinguishable using phase contrast or interference optics. 3. Members of both genera have similar life histories; a highly motile swarmer stage gives rise to a sessile loricate feeding stage; in the swarmer stage the anterior flagellum lies in a groove and acts as a rudder, while in the feeding stage the trailing flagellum adopts a wing-like expansion that provides the feeding current. 4. Members of both genera have mitochondria with the tubular cristae; the mitochondria are closely associated with the nucleus (there appears to be only one mitochondrion in the organism we describe). The two genera differ in the following fashion: 1. Histiona has discobolocysts while the flagellate described herein does not. 2. Histiona has a long flexible ventral lip (i.e. the 'sail") not found in our flagellate. 3. Histiona has a poorly developed dictyosome with two to four cisternae while the organism we described has no obvious dictyosome. 4. Histiona does not have scales while the organism we described does.
Jakoba libera, also appears to be closely related to Histiona and the flagellate described herein. This organism has a wing-like extension of the posterior flagellum and has a raised lip reinforced with microtubules on the organism's right side. However, the mitochondrial cristae are reported to be flattened (Patterson 1990) rather than tubular as found in Histiona and Reclinomonas. In the above publication only a single micrograph details the mitochondria and from the micrograph it is not absolutely clear that the cristae are flattened. More recently, O'Kelly found that a freshwater species of Jakoba had tubular cristae. This species also was found to have cells with spines on the body surface. The nature of the species has not been reported. It is apparent that Jakoba is closely related to Histiona and the organism we describe. Patterson created the family Jakobidae to accommodate this new flagellate. We feel that the differences between Jakoba and Histiona and the organism we describe warrants creation of a separate family.
The organism that we describe appears to be most similar to Histiona campanula (Penard 1921). However, Penard's flagellate is quite distinct from the type species, H. velifera. The latter species, described by Voigt (1901), was reported to have only one flagellum. It was subsequently found by Nichols (1984) that both species of Histiona actually have two flagella, one of which is obvious at the light microscopic level and is directed upward. The second flagellum is held tightly against the body and is usually not visible with the light microscope. The anterior flagellum was found by Nichols (1984) not to have mastigonemes and the membrane of the trailing flagellum was reported to have flattened appearance. The flattened nature of the trailing flagellum is more clearly revealed in the shadow-cast preparations of Peterson and Hansen (1961) and more recent studies clearly confirm its presence (Mylnikov 1989). The lorica is transparent and details of its construction are similar to those reported here for Reclinomonas. (ref. ID; 7277)
Reclinomonas campanula (Penard, 1921) Flavin & Nerad, 1993 n. comb. (ref. ID; 7277)
Histiona campanula Penard, 1921 (ref. ID; 7295)
Lorica attached at an angle to the stalk. (ref. ID; 7277)