The animals of this genus are transparent, subcylindrical, smooth, gelatinous bodies encircled by bands of white muscular fiber. They strikingly exemplify alternation of generations. They occur in two distinct conditions, one being solitary, the other consisting of animals united in chains. The solitary individuals are about an inch long, and have two long processes at the posterior end. These single animals reproduce by budding, and form series of individuals in small chains, the animals being arranged in two rows. The chains grow to the length of a foot or more, and contain twenty to thirty pairs of salpas. Each of these connected individuals produces in turn a single egg, which becomes a single Salpa, and this again, like its grandmother, reproduces by budding. Thus the animals are alike only in alternate generations. The naturalist Chamisso, who discovered the relationship between the two forms, expressed it as follows: a Salpa mother is not like its daughter or its mother, but resembles its sister, its grandmother, and its granddaughter. The single zoöids liberate many colonies during the summer, which grow rapidly, and in the autumn the chains are exceedingly abundant. The Salpa chains swim about with a serpentine movement, and are beautiful, delicate objects with their transparent bodies banded with white, tinged with pink, and streaked with blue.
SIMPLE ASCIDIANS
These are solitary and usually fixed; they are never free-swimming, and when in colonies each animal has a distinct test. All the larger ascidians, or sea-squirts, belong to this group.
Genus Molgula
Body more or less globular, membranous, attached or free; orifices on very contractile tubes.
M. manhattensis. Nearly globular when the tubes are contracted; usually covered with bits of eel-grass, seaweeds, sand, etc.; surface a [pg476] little rough; color olive-green. The animal is often attached to rocks, more frequently to eel-grass and seaweeds, and is sometimes so crowded as to form large clusters. Found from Maine to North Carolina.
M. pellucida. Body nearly globular, about an inch in diameter, smooth, clean, and translucent, the intestine showing through the test. The two tubes are large, swollen at the base, and divergent. The animal lives free in the sand, and is found from Massachusetts to North Carolina.
M. arenata. Body somewhat compressed laterally; test thin and covered completely with sand, which is closely adherent; about three quarters of an inch in diameter; tubes short and wide apart. Found on shelly and sandy bottoms of bays and sounds.
Genus Cynthia
The animal is attached, the body coriaceous, and the orifices four-lobed. Frequently associated in groups, the individuals often differing in color.
C. pyriformis. Body globular, or oblong when extended; hard, velvety, whitish surface, with pink cheeks; orifices on prominent protuberances on the upper surface. It lives in clear, deep water on rocks, and is sometimes found at low-water mark on the northern New England coast. Commonly called the sea-peach. (Plate LXXXV.)
C. partita. Body oblong; attached; test horny and wrinkled; rusty-brown; apertures square, on prominent tubes marked with triangular spots of white and purple; diameter one inch. Found on the piles of wharves and on shelly bottoms in shallow water; also on the under side of stones when they are much flattened.
C. carnea. Test low and flat, with a thin margin; adherent by a very broad base; orifices small, square, slightly prominent; red or flesh-color. Found in deep water on stones and shells on the northern New England coast.
Genus Boltenia
Body more or less globular, on a long stem; fixed; orifices on the side.
B. clavata. Body long, wrinkled, leathery, on a long stalk, resembling the flower of lady's-slipper (Cypripedium); two cross-shaped orifices wide apart on the side; yellowish in color; attached to stones in deep water, but sometimes washed ashore in storms. The stalks are often covered with polyzoans and hydroids. (Plate LXXXV.)
Genus Ascidia
Test gelatinous or cartilaginous; attached; it grows in bunches under stones at low-water mark. Sometimes it is variously [pg477] colored, but otherwise it is repulsive in aspect. The apertures are wide apart; one orifice is eight-lobed, the other six-lobed.
| PLATE LXXXV. ASCIDIANS. | |
|---|---|
| 1, Ascidia callosa. | 5, Cynthia placenta. |
| 2, Botryllus Schlosseri. | 6, Glandula fibrosa. |
| 3, Cynthia pyriformis. | 7, Cynthia condylomata. |
| 4, The same, enlarged. | 8, Boltenia clavata. |
| 9, Cynthia echinata. | |
A. amphora. Form usually globular, but more or less irregular; substance something like rubber. Found of all sizes adhering in clusters to stones, shells, and piles, and usually covered with marine growths. The color is grayish-brown.
A. callosa. Body depressed, usually oval, but varying in shape; thick, fleshy, translucent; surface uneven; apertures dark purple and prominent. Found at low tide adhering to stones and shells. (Plate LXXXV.)
COMPOUND ASCIDIANS
Ascidians of this group form fixed colonies, and are embedded in gelatinous material, the animals having a common test, but not being united by any internal union. The colonies thus formed are flat and incrusting, or are branched and lobed, or sometimes elevated on stalks. The zoöids are in some cases dotted irregularly over the entire surface, in others are in rows, or again are in groups. They have various colors—purple, yellow, blue, gray, and green. They are common on eel-grass, the piles of wharves, the bottoms of boats, and so on.
Genus Botryllus
B. gouldii. This species forms thick, fleshy, translucent incrustations, often several inches in length and a quarter of an inch wide, over eel-grass, the piles of wharves, and other objects. Sometimes, at the end of summer, small objects are completely covered with the luxuriant growth of this compound ascidian. The zoöids form circular or elliptical groups, often as many as fifteen surrounding each orifice, looking like minute stars. The colonies vary in color. Often on the same stem of eel-grass will be found separate colonies varying in this respect. In some the ground-color will be olive-green specked with white, while the zoöids are purple, marked with other colors; again the arrangement is quite different.
Genus Amaræcium
A. pellucidum. A massive compound ascidian, smooth, translucent, and gelatinous, which forms large, hemispherical, complex, irregular masses six inches or more in diameter. It is usually covered by adhering sand. The mass consists of club-shaped lobes, which rise from a common base. Each lobe contains a central orifice around which long, slender zoöids, sometimes an inch long, are grouped. These masses are so abundant in some places that they cover the bottom for considerable spaces. They are found in deep water from Cape Cod to North Carolina. [pg479]
INDEX
Heavy-faced type is used to indicate names of classes, orders, genera, etc.; heavy-faced numerals to indicate the place where the fullest description is given