Length 104; greatest diameter 36.

I was much surprised to find this form swimming about freely in the water; its mouthless condition showed it to belong to the family of parasites, the _Opalinidae_. As the name indicates, however, this species is an ectoparasite upon the gills, and Stein gave the name _branchiarum_ to a fresh-water form parasitic upon _Gammarus pulex_.

The Woods Hole form is so strikingly similar to the figure of _G.

branchiarum_ that, although the name was given to a fresh-water form, it obviously applies to this marine variety. One important difference is the presence of only one contractile vacuole in the marine form.

[Ill.u.s.tration: Fig. 44.--_Anoplophrya branchiarum_.]

KEY TO FAMILIES OF HETEROTRICHIDA.

Cilia cover the body 1

Cilia reduced to certain 2 localized areas

1. _Polytrichina_.

a. The mouth terminates a long Family _Plagiotomidae_ peristomial furrow having an adoral zone along the entire left edge

b. Peristomial area a broad Family _Bursaridae_ triangular area ending in mouth

c. Peristomial depression short; Family _Stentoridae_ limited to the anterior end; its plane at right angles to the long axis of body; surface of peristome striated and ciliated; no undulating membranes

2. _Oligotrichina_.

a. Peristome without cilia; cilia Family _Halteriidae_ limited to one or more girdles about body

One marine genus *_Strombidium_

b. Thecate forms; the body is Family _Tintinnidae_ attached by a stalk to the cup; within the adoral zone is a ring of cilia.

c. The peristomial depression is Family _Ophryoscolecidae_ deep and funnel-like; cuticle thick, with posterior spine-like processes.

* Presence at Woods Hole indicated by asterisk.

KEY TO THE MARINE GENERA OF PLAGIOTOMIDae.

Diagnostic characters: The peristome is a narrow furrow which begins, as a rule, close to the anterior end and runs backward along the ventral side, to the mouth, which is usually placed between the middle of the body and the posterior end. A well-developed adoral zone stretches along the left side of the peristome, and is usually straight.

1. Body cylindrical; size medium; Genus _Metopus_ peristome long and turns sharply to the left at the extremity

2. No torsion in the peristome; Genus _Blepharisma_ undulating membrane is confined to the posterior part of peristome

3. No peristomial torsion; Genus _Spirostomum_ body highly contractile; no undulating membrane

KEY TO THE MARINE GENERA OF BURSARIDae.

Diagnostic characters: The body is usually short and pocket-like, but may be elongate. The chief characteristic is the peristome, which is not a furrow, but a broad triangular area deeply insunk and ending in a point at the mouth. The adoral zone is usually confined to the left peristome edge, or it may cross over to the right anterior edge.

1. The anterior half of the body Genus _Balantidium_ tapers to nearly a point in front; the peristome is narrowest at the apex; the mouth is the entire peristome base.

2. The anterior end does not taper; Genus *_Condylostoma_ the peristome is widest at the end of the body; the mouth is clearly defined.

* Presence at Woods Hole indicated by asterisk.

Genus CONDYLOSTOMA (KONDYLOSTOMA Bory de St. Vincent 1824) Dujardin '41

(Dujardin '41; Claparede & Lachmann '58; Stein '59, '67; Cohn '66; Quennerstedt '67; Wrzesniowski '70; Butschli '76, '88; Kent '81; Maupas '83; Shevyakov '96.)

Colorless and more or less flexible animals of medium size. The general form is elongate and cylindrical or somewhat smaller anteriorly. The posterior end is broadly rounded, the anterior end somewhat truncate and oblique. The peristome is broad and triangular, the base of the triangle being the entire anterior end of the body.

The entire length of the peristome is one-fourth or less of the body length. The mouth is large and placed at the apex of the peristomial triangle and opens into a comparatively small oesophagus. The right edge of the peristome is lamellate and bears a clearly defined undulating membrane. The adoral zone is well developed upon the left edge of the peristome, from which it pa.s.ses around anteriorly to the right edge. The surface of the peristome is free from cilia, but the rest of the body is uniformly coated with small active cilia.

Contractile vacuoles are not safely determined. Butschli thinks there is probably one terminal vacuole, but some observers deny this (_e.g._ Maupas). Others describe them on the dorsal side of the posterior end (Quennerstedt). The macronucleus is long and beaded and placed upon the right side. Micronuclei are numerous and scattered along the macronucleus. The a.n.u.s is terminal and dorsal. Food consists of large and small particles. Movement rapid, free swimming, alternating with resting periods; in some cases an undulating or wriggling movement is seen, showing clearly the flexibility of the body. Fresh and salt water.

Condylostoma patens Muller. Fig. 45.

The body is elongate, somewhat sac-like, five or six times as long as broad, plastic, and frequently contains brightly colored food granules. The triangular peristome takes up the greater part of the anterior end, and the mouth is situated at the sharper angle of the triangle, about one-fourth of the total length from the anterior end.

The cuticle is longitudinally striated, the lines having a slightly spiral course. They are not closely set, and fine cilia are thickly inserted along their edges. The endoplasm is granular and viscous.

The motile organs consist of an adoral zone of membranelles, which stretch along the left edge of the peristome and the front edge of the body. The right edge of the peristome supports an undulating membrane. The nucleus is moniliform and extends the full length of the left side; a number of micronuclei are distributed along its course (Maupas).

Length 400; diameter at widest part 105. Maupas gives the length from 305 to 495; and Stein 376 to 564. Very common.

For a more extended account of the structures, see the excellent description by Maupas '83.

[Ill.u.s.tration: Fig. 45.--_Condylostoma patens_.]

KEY TO THE MARINE GENERA OF STENTORIDae.

Diagnostic characters: The peristome is relatively short and limited to the front end of the animal, so that its plane is nearly at right angles to that of the longitudinal axis of the body. The adoral zone of cilia either pa.s.ses entirely around the peristome edge or ends at the right-hand edge. The surface of the peristome is spirally striated and provided with cilia. Undulating membranes are absent.

1. Peristome circular in outline; Genus _Stentor_ limited to the anterior end

2. The peristome is drawn out into two Genus _Folliculina_ wing-like processes; tube-dwelling

Genus STROMBIDIUM Cl. & Lach. '58.

(Stein '67; Butschli '73; Fromentel '74; Kent '81; Gruber '84; Entz '84; Maupas '83. Butschli '88.)

Small, colorless (except for ingested food) animals with characteristic springing movements. The form is usually constant, but in some cases may be plastic like _Astasia_; it is usually globular or conical, the posterior end being more or less pointed, the anterior end broadest. The latter is surrounded by a complete circle of the adoral zone, the oral end of which pa.s.ses into a peristomial depression which extends deep into the middle of the body. The mouth, with a very small oesophagus, lies at the bottom of the inturned peristome. The region surrounded by the adoral zone is frequently drawn out into an anterior process, occasionally bearing a pigment ma.s.s. The ventral surface in some cases bears cilia, which may be distributed or restricted to a row of large cilia. Trichocysts are usually present and may be widely spread, limited to the posterior region, or arranged in a girdle about the middle. The contractile vacuole is simple, and posterior in position. The macronucleus is spherical and usually central in position. Movement is rapid swimming, combined with resting and floating periods, the latter usually terminated by a sudden leap.

Fresh and salt water; more common in the latter.