Main Content
< Top page

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Henoceros

Henoceros Milne, 1916

Order Philodinavida: Family Philodinavidae (ref. ID; 6565)

Synonym Monoceros Milne, 1916 (ref. ID; 1345, 3137)

ref. ID; 1923

Corona consists of 2 small, circular areas, elevated above ventral surface of head only at anterior margin. Littoral species. (ref. ID; 1923)

ref. ID; 3137

The wheel-organ is completely stunted, or it is very slightly indicated on the ventral side of the head. On the ventral side of the head behind the rostrum are two insufficiently developed wheel-discs. The anterior borders of them extend somewhat beyond the surface of the body, and they look like the lateral borders, which incline slowly backwards towards the body level, provided with short wheel-cilia. The posterior borders of the discs are without cilia, and these into the level of the body. The foot is stout. Instead of the two lateral spurs only a central, strong somewhat mobile knob is developed, which projects over the rest of the foot like a roof. (ref. ID; 3137)
  1. Henoceros caudatus Hauer, 1937/38 (ref. ID; 1345) or 1938 (ref. ID; 3137)
  2. Henoceros falcatus (Milne, 1916) (ref. ID; 1345, 1923, 2227, 2685, 2810, 3137, 6939, 7795)
    Syn; Monoceros falcatus Milne, 1916 (ref. ID; 1345, 3137)

Henoceros caudatus Hauer, 1937/38 (ref. ID; 1345) or 1938 (ref. ID; 3137)

Descriptions

In the middle of the posterior border of the lanal segment a long backwards pointing knob. (ref. ID; 3137)

Henoceros falcatus (Milne, 1916) (ref. ID; 1345, 1923, 2227, 2685, 2810, 3137, 6939, 7795)

Synonym

Monoceros falcatus Milne, 1916 (ref. ID; 1345, 3137)

Descriptions

Without knob on the dorsal side of the rump. (ref. ID; 3137)

This species has not been found and recorded in the literature since it was first described by Milne (1916). This author mentioned that the species is small and of a pale glaucous colour. The corona is inconspicuous and reduced to thin discs. The rostrum is well developed with strong cilia. On the ventral side of the post-rostral segment there is a double arrangement of thin discs which project slightly right and left. The dorsal antenna is short compared to that of Philodinavus paradoxus. There is no eye-spot. The egg has an oval shape. The foot is stout, and it has a clear characteristic feature at the posterior end: four great sickle-shaped toes and one large spur. In living specimens, each toe can move independently of the others. The structure of the trophi differs from that in the other member of the same family (Philodinavidae). It has a simple and symmetric design. Rami, unci and manubria are long and narrow. There are two separate rami on the outer sides of which rest the unci, which are hinged to the two manubria shown at their sides. Milne's description reports that the fulcrum is cut into two symmetrical and minute rods lying between the ends of the unci and rami. However, Remane (1929-1933) redescribed these rods as basal-apophyses or subunci. Milne (1916) also mentioned the presence of a plate with fine striae between the rami and manubria indicating a link to Philodina trophi. However, these observations cannot be confirmed with light microscopy. Further description awaits scanning microscope analyses. (ref. ID; 6939)

Habitats

The habitat of H. falcatus seems to be streams and rivers as both Milne's and my findings demonstrate. (ref. ID; 6939)

Examined materials

The specimens were collected in the stream Oberer Seebach, lower Austria (47 degrees 51'N, 5 degrees 04'E) while performing drift experiments between August and December 1994. (ref. ID; 6939)

Measurements

Total length: 285 µm, dorsal antenna: 5 µm; egg length: 60 µm; trophi length: 13-14 µm, toes: 18-20 µm. (ref. ID; 6939)