The World of Protozoa, Rotifera, Nematoda and Oligochaeta
Encentrum
Encentrum Ehrenberg, 1838
Class Monogonontaet: Order Ploimida: Family Dicranophoridae (ref. ID; 6806)
Synonym Encentroides Sudzuki, 1960 (nov. syn.) (ref. ID; 2019); Parencentrum Wiszniewski, 1953 (ref. ID; 1345, 3688)
ref. ID; 1663
Corona oblique. One eyespot, or eyespots absent. Rostrum conspicuous. Retrocerebral sac present or absent. Rami never with shearing teeth. Unci weak and needle-like. Chiefly littoral. (ref. ID; 1663)
ref. ID; 1923
Many species is in brackish water. Wiszniewski (1953) removed 5 species with stiff, transversely plicated cuticle to Parencentrum. (ref. ID; 1923)
ref. ID; 3334
The members of this genus are cylindrical and usually illoricate or only partially loricated. The mastax has protrusible forcipate trophi. There is a small, intercalating piece between the manubrium and each uncus (the intra-mallei), and subcerebral glands are present (cf. Dicranophorus). Eyes are not usually present. The foot ends in two small toes. A very active, predatory group. (ref. ID; 3334)
The trunk convex in the lateral view, highest part little posteriorly situated apart from the middle. The body surface soft but not sticky. The head small and shout with short rostrum. The trochus oblique. No eye. No dorsal antenna. The mastax forcipate in type. The incus strongly ankylosed at the tip and only separable under the strong pressure by cover glass. The rami smooth, provided with no remarkable projection nor special window-like structure at the base. No comb-like structure at the inner sides, except for one large soft tooth as in Dicranophorus nikor or D. aquila at the upper 1/3 the rami, and two fine terminal teeth like Wierzejskiella at the tip of each ramus. The unci not divided into two parts, two spines at the tip, and one projection at the inner side of the uncus in the middle. The intramallei nearly globular, without lamella. The manubria long almost straight, small window-like structure at the both extremities. The fulcrum straight, slender, with one apophysis at both sides of the free end. The vitellarium with 8 nuclei. The tail-like projection very short. One annulation at the base of the foot. The foot very short, not separated clearly from the trunk. The foot glands without reservoir. The toe short and straight about 1/9 the body length. (ref. ID; 3536)
Measurements
Total length 110-120, height 50-55, toe 8-12 long, mastax 20x18, rostrum 4-5 long, manubria 8x2, fulcrum 8-9, unci 8-9, rami 10-12 inner teeth at the rami 4 µm. (ref. ID; 3536)
Marine rotifer. Encentrum bidentatum (Lie-Pettersen) has a large head with an almost frontal corona. There is a long, stiff bristle on each side of the mouth. The abdomen is curved dorsally, flattened ventrally, and compressed laterally. The foot is conical. There is no further visible segmentation. The toes are short, with swollen bases and acute tips. The large mastax can be pushed forward outside the head and the trophi can protrude through the large opening with the pair of tongs which can open through 180 degrees to seize the prey. This grabbing action is very vigorous. All parts of the trophi are long and slender. The rami are nearly straight, each with two anterior teeth pointing inwards at right angles to the rami. The fulcrum has no distal extension. The unci are needle-like and little curved. The intramallei are long and extended anteriorly. The manubria are curved and the ends are little extended. The oesophagus is long and extensible. The gastric glands have flexible stalks. The ganglion contains two refractive globules. The dorsal antenna is situated just in front of the neck fold. (ref. ID; 3573)
Comments
The species here described is certainly identical with the species described by Lie-Pettersen (1906) as Pleurotrocha bidentata. The specimens correspond exactly in the shape of the body and toes and in the outline of the internal organs. Lie-Pettersen's drawing of the trophi is somewhat inaccurate, but it does not disagree with the main outlines of my drawing. The specimens were also collected in the same area and mainly from the same type of habitat. The specimens found by van Hofsten (1912) on the Swedish west coast and identified as Diglena bidentata (Lie-Pettersen) do not belong to this species; neither the figure nor the description bears any marked resemblance to it. Remane (1929) first mentioned E. bidentatum as an unsatisfactorily known species, but reproduced von Hofsten's figure. In an appendix he gave a new record of the species from shore-pools in the bay of Kiel. His description is brief, without a figure, but enough to show that his specimens were not E. bidentatum. Sick (1933) also recorded it from shore-pools in the same area, but with no further description. This must have been the same species as that recorded by Remane (l.c.). (ref. ID; 3573)
Type locality
Lie-Pettersen records Encentrum bidentatum from rock-pools and (sub)littoral algae. (ref. ID; 3573)
Encentrum bryocola (E. bryocolum) Sudzuki, 1964 (ref. ID; 2019, 2105 original paper, 3536)
Descriptions
The general features of the body closely related to a species E. antarcticum. The main difference due to lateral feature of the body besides the structure of the mastax. The rami with small post lateral alurae at the base. The rami and unci strongly ankylosed to from "meso-unci" at each tip. The intramallei with lamelle. The manubria curved at the distal end. The fulcrum straight, needle-shaped, with one apophysis at the free end. (ref. ID; 3536)
Measurements
The body 80 long, 44 µm high. The mastax 22x15, uncus 5, meso-uncus 2.5x5 µm. The manubria 16, fulcrum 7, rami 8 µm. The amictic egg 70-75x50-55 µm. (ref. ID; 3536)
This species has a mastax very similar to that of E. marinum but can be recognized by the lack of eyespots and the presence of salivary glands. In contrast to E. marinum, this species is mainly a predator which was found to contain nematodes and gastrotrichs (Chaetonotus) in the stomach. (ref. ID; 1511)
Marine rotifer. Encentrum flexilis is elongated and very flexible. The specimens examined were somewhat contracted but very characteristic in shape. The head is small and consists of two segments. The corona is oblique. The rostrum is short and rounded anteriorly. The anterior part of the abdomen is highly curved dorsally, almost straight ventrally, and extended laterally. The posterior part is almost conical, with three segments. The foot is short and oblique ventrally. The toes are short and conical. The trophi are relatively small. Each of the rami is shaped like a cresent, with two teeth anteriorly. The hindmost teeth are situated dorsally to the others, crossing inwards from the outer edge of the rami. The fulcrum is curved ventrally, with no distal extension. The unci have a small tooth in the middle and terminate in slender tips. The intramallei are small and spherical, with slender processes pointing obliquely backwards. The manubria are curved, with somewhat extended ends. The oesophagus is short. The stomach fills the dorsal extension of the abdomen. The intestine is relatively long. The pedal glands are large compared with the foot. The dorsal antenna is situated just in front of the neck fold. (ref. ID; 3573)
Comments
Encentrum flexilis bears a certain resemblance to the specimens wrongly identified as Diglena bidentata by von Hofsten (1912), but on the basis of his figure and description, it is impossible to be definite. (ref. ID; 3573)
Body smooth and spindle shaped. Foot broad, two segmented. Gastric glands narrowing posteriorly into long stalks opening into the stomach. Rami with 3 strong pincers and with a tooth in the inner margin. Unci two-segmented. The body is spindle shaped, fairly slender, convex dorsally, and slightly concave ventrally. The outline of the body is fairly constant. The lorica is relatively smooth and the animal is transparent. A dorsal antenna is present about two-thirds from the anterior end of the head. The head is short, distinctly separated from the trunk by a neck, and slightly deflexed. The corona is slightly oblique and the rostrum is small. The abdomen is fairly long, deepest in the middle, and tapers gradually. There are no definite constrictions dividing the trunk into sections, except for a well marked, circular fold posteriorly. The foot is two segmented and both segments are wider than long and are retractable. In the extended condition, the foot is clearly separated from the trunk. The toes are fairly long, about 1/10th of the total length, stout, slightly decurved, and are distinct at the base. Into the toes open two large, multinucleate, two-segmented pedal glands that extend into the trunk. The distal segment of the pedal glands is smaller than the club-shaped proximal segment. The ganglion is large and extends beyond the neck fold. No eye spots are present. The gastric glands are fairly large, narrowing posteriorly into long stalks opening into the stomach. There is a definite to constriction between stomach and intestine. The germovitellarium has eight large, conspicuous nuclei. The bladder is medium sized and more or less round in shape. The trophi are forcipate type, elongate. The fulcrum is slightly shorter than the rami and stout; in lateral view, it is sickle shaped and very wide where it joins with the rami. The rami are broad at the base and have three strong pincers at the tips; the median opening is pyriform. The inner margins of the rami have a strong, shape tooth. No alulae are present on the rami. The unci are relatively short and two segmented. The distal smaller segment is pointed and the proximal segment is more or less parallel sided. The unci are connected to the manubria by fairly strong and stout intramallei. The manubria are very long, twice as long as the rami, strongly curved and knobbed posteriorly. (ref. ID; 2601)
Comments
The main diagnostic features used in the identification of species of Encentrum are based on the morphology of the trophi. Encentrum spinosum Koch-Althaus, 1962 and Encentrum mucronatum (Wulfert, 1936) share some of the characters of the trophi of E. graingeri. They all have strong teeth on the inside of the rami and also possess long, strong pincers at the tip for grasping food; however, E. spinosum has two pincers and E. mucronatum four, whereas E. graingeri has three. Further, the lorica of E. spinosum has distinct longitudinal and transverse folds, which are less developed in E. mucronatum, while E. graingeri has a smooth lorica. The total length of E. graingeri ranges from 170 to 225 µm. In comparison, E. spinosum has a total length of 160 µm, and E. mucronatum is much larger with size range of 300-420 µm. Taxonomy of the large genus Encentrum has long been both neglected and avoided by rotifer workers for many reasons. The difficulty is obtaining well-preserved specimens and specialist literature has deterred some, and the flexible lorica makes good preparations almost impossible to produce. Koste (1978) lists 59 valid species of Encentrum, with another 30 species that he has been unable to place because of inadequate data or meagre descriptions and illustrations. Subsequently Tzschaschel (1979) has described a number of species of Encentrum from the interstitial system of the North Sea island of Sylt. Only two species have so far been reported from Canada (Chengalath 1984). The genus with its numerous species is, therefore, badly in need of a revision. (ref. ID; 2601)
Etymology
This species is named for Dr. E.H. Grainger, Arctic Biological Station, Ste-Anne-de-Bellevue, Quebec, in recognition of this work in Arctic biological oceanography and in gratitude for collecting the rotifer specimens. (ref. ID; 2601)
To this much-disputed species, hitherto recorded from marine and brackish water habitats only. It should be added that von Hofsten declares that Levander's name is a synonym for Diglena pachida Gosse, but this view is not shared by Harring, who dismissed D. pachida as insufficiently described whilst accepting Levander's name as valid pending further investigation. De Beauchamp, writing later, seems to take the same view as von Hofsten. If Gosse's figures of his species could be relied upon, there would be little doubt of the two names referring to distinct species. He draws the toes about twice as long as they are in any of the specimens referred to above. (ref ID; 3217)
The animal is easily recognized at low magnification due to its habit of raising the hind part of the body and spreading the toes while creeping on the bottom of the Petri dish. The salinity range is wide, it has been recorded from all salinities raging from freshwater to fully marine conditions. Voigt (1957) mentions that the stomach often is coloured yellow, brown or green indicating that the animal is a herbivore. (ref. ID; 1511)
Marine and brackish water. (ref. ID; 3573)
Measurements
Length of body 190; length of toes 26 µm. (ref. ID; 2285)
Encentrum mnium Berzins, 1982 (ref. ID; 2019, 4606 original paper)
Descriptions
Stout body. Very slowly movement. Head large with a very stout rostrum, and no eyes. Posterior part of the body with segment. Short foot with 2 sharp, somewhat ventrally bent toes. Trophi stout. Rami with a sharp termination, and with a broad but thin alulae. Unci with 3 sections. (ref. ID; 4606)
Type locality
For three individuals from moss from Bambala. (ref. ID; 4606)
Measurements
Total length 240; toe 18; trophy 32 µm. (ref. ID; 4606)
Very contractile form. Can be very long and slender when swimming. The figure shows the resting position. Very rapid movements. The body ends with a small prolongation at the foot. Toes thin and sharp. Segmentation of the body is not visible. Also the limit between head and body is insignificant. Rami with thickened termination, and a broad alulae. Manubrium with a crutch on the upper end. Unci with three segment. Eyes lacking. (ref. ID; 4606)
Type locality
Two individuals in moss at Bombala. (ref. ID; 4606)
Measurements
Total length 260; toe 20; trophy 30 µm. (ref. ID; 4606)
The toes have their small tips withdrawn. The trophi differ somewhat from Wulfert's figure: the rami have two broad teeth each, and the unci have each a short and a long tooth. Between the intramallei are the same structure as found by Schulte (1959) and Donner (1964). The species seems to vary considerably in size and shape. Donner (1943) has described two forms as var. armatus and var. externum, but the latter is later held not to be a separate variety as intermediates between it and the typical form have been observed (Donner 1964). (ref. ID; 3572)
Measurements
Total length of specimen in extended position 440; length of toes 30; length of trophi 48 µm. (ref. ID; 3572)
This species resembles E. villosum rather much and they can hardly be distinguished at low power magnification. The former species can be recognized on the mastax which has alulae. As E. villosum it feeds on flagellates and blue-green algae and the colour of the stomach resembles that of the former species. (ref. ID; 1511)