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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Goniomonas

Goniomonas Stein, 1878 (ref. ID; 4907, 5772, 6733)

Order Cryptomonadida Senn, 1900 (ref. ID; 4872)
Order Cryptophyceae Fritsch, 1927 (ref. ID; 4907)
Order Cryptophyceae Fritsch, 1927 (ICBN) (= Cryptomonadida Senn, 1900) (ref. ID; 5772)

[ref. ID; 4907]
Cell flattened with two antero-laterally inserted flagella and a row of extrusomes parallel to the truncate anterior margin. Previously, members of Goniomonas were called Cyathomonas, see Larsen & Patterson (1990) and Hill (1991) for discussion of nomenclature. (ref. ID; 4907)

[ref. ID; 5772]
Cryptophycean flagellates possessing an anterior transverse ring or line of ejectisomes and lacking plastidial complex and tubular, flagellar mastigonemes (Hill 1991; Kugrens & Lee 1991; Larsen & Patterson 1990). (ref. ID; 5772)
  1. Goniomonas amphinema Larsen & Patterson 1990 (ref. ID; 4907, 5772)
  2. Goniomonas pacifica Larsen & Patterson, 1889 (misspelling 1989?) (ref. ID; 4907) or 1990 (ref. ID; 4872, 5772)
  3. Goniomonas truncata (Fresenius, 1858) Stein, 1878 (ref. ID; 4907, 5772)
    Syn; Monas truncata Fresenius, 1858 (ref. ID; 5772)

Goniomonas pacifica Larsen & Patterson, 1889 (misspelling 1989?) (ref. ID; 4907) or 1990 (ref. ID; 4872, 5772)

Descriptions

7.3 um, range 5-8.3 um. Observed at several occasions, surface ridges indistinct but appearance largely in agreement with original description. (ref. ID; 4872)

Remarks

Length range was given in the original description as 8-10 um (Larsen & Patterson 1990), but an extended range of 5-15 um is given by Vors (1992). Surface grooving not well marked and can be difficult to see. (ref. ID; 4872)

Goniomonas truncata (Fresenius, 1858) Stein, 1878 (ref. ID; 4907, 5772)

Synonym

; i>Monas truncata Fresenius, 1858 (ref. ID; 5772)

Descriptions

Cell flattened, outline tending to ovate, rounded posteriorly, obliquely truncate anteriorly. Two nearly indentical flagella about half as long as cell length emerge from small antero-lateral depression. Four to six densely packed refractile extrusomes located parallel to anterior margin of cell. Nucleus usually situated mid-laterally to the side where flagella emerge, contractile vacuole lateral at opposite side of cell. In some cells 2-4 more or less conspicuous, slightly oblique longitudinal stripes present on the periplast, in other cells no stripes visible. Sometimes swimming with flagella directed forward; sometimes in contact with substrate either motionless or gliding with one flagellum trailing. (ref. ID; 4907)

Comments

There is some difficulty in identifying individuals of Goniomonas observed in this study to species. Three species of Goniomonas are usually recognized: G. truncata, G. pacifica Larsen & Patterson, 1889 and G. amphinema Larsen & Patterson, 1990. While G. amphinema clearly differs from the other two because of its very unequal flagella one of which trails during movement, G. truncata and G. pacifica have been difficult to separate. Larsen & Patterson (1990) described G. pacifica to be different from G. truncata because of its distinct and well defined pattern of periplast striation, and probably smaller size. Two further characters for distinguishing between the two species were suggested by Hill (1991) namely length:breadth ratio (lower in G. pacifica than in G. truncata), and extrusome number (higher in G. pacifica than in G. truncata). The value of the last character is questionable since extrusomes may be ejected from the cell. Most of these character are difficult to apply in practice. Size is obviously not a good character because ranges overlap. The original description of G. truncata suggests smaller cells than G. pacifica. The two characters suggested by Hill (1991) are not clear; firstly because Hill does not state whether he suggests the two additional characters on the basis of own observations or on the basis of the illustrations of G. pacifica in Larsen & Patterson (1990). Secondly because no exact values for the two distinguishing parameters are suggested. Pattern and distinctness of periplast striation seem to be the most applicable characters. When Larsen & Patterson (1990) described G. pacifica, longitudinal ridges had never been observed in G. truncata. The faint stripes, observed by Skuja (1939) in G. truncata, are clearly different from the strong striation Larsen & Patterson (1990) observed in G. pacifica. Earlier workers may, however, have overlooked the longitudinal ridges on G. truncata because their microscopes were not equipped with phase contrast to differential interference contrast. In order to evaluate the different characters, character states from different papers are listed in Table 1. Only the studies of Vors (1992, 1993) contain observations of both G. truncata and G. pacifica. The only character used by Vors to distinguish between the two species was the distinctness of the periplast ridges (Vors, pers. com.). According to the figures of Vors (1992, 1993), the two species were almost similar with respect to pattern of surface striation and number of extrusomes. The literature is clearly ambiguous with respect to criteria that may allow G. truncata to be distinguished from G. pacifica. Distinctness of periplast striation has been regarded at the most reliable character, but "how distinct" the striation must be to make the organism a G. pacifica as opposed to a G. truncata is not clear. In the present study all types of transitional forms from specimens with very conspicuous ridges, forms with faint striation and to cells without any visible stripes were found. With respect to size, length:breadth ratio and number of extrusomes the organisms seen in this study fit G. truncata better (longer, thinner, and fewer) than G. pacifica. We have therefore chosen to assign all the observed specimens to G. truncata. Clearly, the genus is in need of further study to firmly establish species boundaries. (ref. ID; 4907)

Measurements

Length 8-12 um, length:breadth ratio: 1.2-1.8. (ref. ID; 4907)
Cell length 3-10 um (8-25 um). (ref. ID; 5772)