Diagnostic characters: Body bilateral, or asymmetrical by local
prolongations; usually compressed or flattened laterally, the left
side more convex than the right. The essential feature is the
position and character of the mouth. This is either a long slit
extending from the anterior end well down the ventral surface, or the
posterior part only of a ventral furrow remains open as a round or
elongate mouth some distance from the anterior end. The entire mouth
region of the body is usually drawn out into an elongate tapering
proboscis which is generally curved dorsally at the extremity.
An oesophagus is short or absent altogether; when present it is
supported by a stiff buccal armature. Cilia are uniform about entire
body or limited to the flat right side. Food is swallowed.
1. a. Proboscis easily distinguished 2
from the main body
b. Proboscis not marked off from Genus *_Loxophyllum_
main body; body flat;
both surfaces striated
2. a. Mouth runs the entire length Genus _Amphileptus_
of proboscis; entire body
uniformly ciliated
b. Mouth runs the entire length Genus *_Lionotus_
of proboscis; body flat; right
side only is ciliated
c. Proboscis much drawn out, Genus _Dileptus_
flexible; mouth at its base
* Presence at Woods Hole indicated by asterisk.
Genus LOXOPHYLLUM Dujardin '41.
(Duj. '41; Wrzesniowski '69; Quennerstedt '65; '67; Cohn '66; Entz
'84; Gourret & Roeser '88; Bütschli '88; Shevyakov '96.)
The body is flat and somewhat leaf-shape, flexible, and elastic. The
anterior end is somewhat proboscis-like and flexible, but is not
sharply demarcated as in _Lionotus_. The central portion of the body
is developed into a more or less arched dorsal mass, which usually
contains the nuclei and contractile vacuoles. As a result of this
local thickening, the body is surrounded by a thin hyaline margin.
This, however, may be absent on the right side in some species. The
mouth reaches from the anterior extremity to a short distance from
the end, and usually approaches the left edge. An anus is present
near the posterior end of the dorsal swelling. Trichocysts are
numerous on the ventral surface, and often on the dorsal surface,
where they are inclosed in minute papilla-like swellings.
Cilia-distribution controverted. Maupas and Bütschli hold that
ventral surface alone is ciliated; others (Kent and Dujardin) that
cilia are uniformly distributed. The entire body, dorsal and ventral
surfaces alike, are uniformly striated. The contractile vacuole lies
posteriorly, on the right side and in the dorsal swelling. In the
fresh-water form _L. meleagris_, it is connected with a long canal
whose swellings are frequently taken for additional contractile
vesicles (Bütschli); in the marine form described below the canal is
not developed and a series of vacuoles takes its place; these are
all contractile. The macronucleus may be single, double, quadruple,
band-formed, or rosette-formed. Movement is steadily progressive and
peculiarly gliding. Fresh and salt water.
Loxophyllum setigerum Quenn. '67.
Synonyms: _Litosolenus armatus_ Stokes '93; _Litosolenus verrucosa_
Stokes '93.
The body is flattened, irregular in outline, obtusely pointed
anteriorly, the point being turned to the right; rounded posteriorly.
The left edge is nearly straight, the right considerably arched with
a few setæ on the posterior half. Contractile vacuoles are numerous,
dorsal in position and on the right side. The macronueleus is beaded,
the several spheres connected.
Variety armatum (Cl. & Lach.) Fig. 32.
Under the name _Litosolenus armatus_, Stokes described a form from
brackish water near New York, which should unquestionably be referred
to the genus _Loxophyllum_, and I believe to Quennerstedt's species
_setigerum_. While the latter possesses only a few setæ, the former
has a number of them, and Stokes described his species as having a
variable number. For this reason I include the Woods Hole form under
the tentative name _armatum_, as a variety of Quennerstedt's _L.
setigerum_. The flat margins are distinctly striated longitudinally,
and faintly marked radially, on the dorsal surface. Longitudinal
elevated striæ also run the length of the dorsal hump and upon the
entire ventral surface. The ventral surface is alone ciliated. Upon
the edges of the flat border are sharp-pointed, colorless, spine-like
processes, situated at equal distances around the entire periphery
except at the anterior end. Each spine is thick at the base and
tapers to a full point which is curved upward--_i. e._, dorsally
(fig. 32, a, b). The entire body is plastic and contractile, turning
its leaf-like edge readily over objects upon which it creeps. The
cilia are fine and uniform, with a tendency to lengthen in the oral
region.
Length 100µ; greatest width assumed on contraction 85µ; when normal
about 50µ.
[Illustration: Fig. 32.--_Loxophyllum setigerum_, var. _armatum_. a,
b, c, ventral, dorsal, and lateral aspects.]
Genus LIONOTUS Wrzesniowski '70.
(Incorrectly called _Litonotus_ by many. Entz '84; Gruber '84;
Bütschli '88; Kent '81; Schewiakoff '89; Shevyakov '96.)
The body is elongate and somewhat lance-shaped, widest at the central
part and tapering to a point at the anterior end. The posterior end
may be similarly tapered or rounded. The anterior end frequently
proboscis-like, flat, and flexible, while the entire body is more or
less elastic and contractile. The right side is flattened and alone
provided with cilia, while the left side of the body proper is
arched; on the left side of the proboscis is a row of coarse cilia
resembling an adoral zone, and a row of trichocysts. A long peristome
stretches down the thin, ventral side of the proboscis, and the mouth
proper is situated at the junction of the proboscis and body; the
mouth, as a rule, is invisible. The ciliated right side alone is
striated in the majority of species. The contractile vacuole may be
single or multiple, usually in the posterior region of the body and
dorsal in position. The macronucleus is usually double, rarely single
or quadruple, but may occasionally break into numerous smaller
pieces. Movement, free-swimming or gliding, with especial tendency
to get under clumps of foreign matter.
Fresh and salt water.
Lionotus fasciola Ehr. Fig. 33.
Synonyms. _Amphileptus fasciola_ Ehr. '38; Dujardin '41; Lachmann
'56; Cohn '66, Diesing '65.
_Loxophyllum fasciola_ Claparède & Lachmann '58;
Balbiani '61.
_Loxophyllum duplostriatum_ Maupas '83. Shevyakov '96.
Body frequently brown or brilliant yellow in color, somewhat sigmoid
in form with tapering anterior end, the extremity of which is turned
dorsally. The proboscis is about half the entire length and is not
sharply marked from the rest of the body but tapers gradually, its
base being equal to the diameter of the body at its middle point. The
body is slightly contractile and the posterior end is carried to a
rounded point, but not into a distinct tail. Unlike the fresh-water
variety, this one has no hyaline margin nor hyaline caudal region,
and the contractile vacuole is double or multiple on the dorsal side
near the posterior end. Cilia are present only on the under (right)
side, with, however, a row of large cilia marking the course of the
elongate mouth, upon its left side. The right side is striated, the
left arched and without markings. The endoplasm is finely granular
with, however, larger food particles in the process of digestion,
while specimens are occasionally seen with the natural form
completely lost through distortion caused by over-large captures (Cf.
also Wrzesniowski '70, p. XXIII, fig. 32). Movement continuous, slow,
and gliding; very little tendency to jerking movements. Macronucleus
double, both parts spherical, and placed in about the center of the
larger part of the body; closely approximated but not, as Schewiakoff
described, connected. In conjugation, a large form unites with a
smaller one, the mouth parts being connected. Details of conjugation
and macronuclei not made out. Length 200µ to 600µ.
[Illustration: Fig. 33.--_Lionotus fasciola_.]