Bryozoan

“ Every bryozoan in a colony remains throughout its life a separate animal, shut off from its fellows by a wall of limestone and leading an independent existence. Nevertheless, in the species pattern it assumes, each colony acts as if it were a single organism.
Moreover, a phenomenon unique in nature, every individual appears to be two and in some species three animals in one. Each leads its own life and dies its own death at its own time. ”

“ Bryozoans are colonial animals that are often referred to as “sea mats.” They have been called this because they are commonly found matted on shells, rocks, fossils, and other objects. The living animal is quite small, has a tentacle-bearing ridge surrounding the mouth, and secretes a tiny cup-like exoskeleton composed of calcareous or chitinous material. ”

“ While crabs, butterflies, and birds have evolved through many and varied ancestral forms, the tiny Bryozoans, or, being interpreted, moss-animals, seem throughout all past ages to have found a niche for themselves where strenuous and active competition is absent. Year after year, century upon century, age upon age, they have lived and died, almost unchanged down to the present day. When you look at the tiny animal, troubling the water and drawing its inconceivably small bits of food toward it upon the current made by its tentacles, think of the earth changes which it has survived. ”

“ The weaving process may be very rapid. A colony, starting with a single free-swimming larva, may cover as much as 100 sq. feet. Such colonies have been found on a single stone. They often are found on mollusk shells. At present the bryozoans are economically important chiefly as a menace to the oyster industry. Once they have covered an abandoned shell, oystermen believe, no other oyster will make use of it. About their only other importance to man comes from the fact that some fresh-water species may clog water pipes by their rapid growth. ”

“ The shales carrying these remains are highly charged with other fossils, among which are fragments of fishes, Beyrichia, Leperditia, Phacops, Homalonotus, Orthoceras, Nautilus, Loxonema, Pleurotomaria, Bellerophon, Platyostoma, numerous species and genera of lamellibranchiata, with a few species of brachiopods and bryozoans.
Associated with numerous specimens of E. punctata are frequently found mandibles or jaws of the form represented in Figs. ”

“ The real bottom animals are mainly fixed—sponges, hydroids, sea anemones, bryozoans, brittle-stars, crinoids, brachiopods, holothurians, worms and mollusks. They are nowhere numerous remote from a shore, and below 2,500 fathoms are very scarce, to judge by the results of dredging. Their food comes wholly from the surface, apparently, some catching it as it falls and others sucking it out of the ooze. Moving about among these, and feeding on them, is a scanty population of snails, squids, crabs, and fishes, making their living upon or close to the bottom ”

“ The best collecting will, of course, be found where the rocks have been sufficiently weathered.
Fig. 8. Sketch of typical crinoidal limestone from the Pennsylvanian of north Texas.
Typical invertebrate fossils are foraminifera (principally fusulinids) , corals (especially the solitary or “horn” corals) , brachiopods, bryozoans (the lacy and branching types are most common) , pelecypods, gastropods (exhibiting a variety of coiling) , cephalopods (nautiloids and goniatites predominate) , and crinoids, which in many areas are found in thick crinoidal limestones (fig. 8) . ”

“ This extremely graceful form is common on Bryozoa at Woods Hole. The cup is shaped like a wine glass and is specifically characterized by a cup-formed membrane upon which the animal rests. The animal thus has the appearance of being suspended on the edge of the cup. The stalk is slender and about 4 times the length of the body. The tentacles are all capitate and distributed, and about 2-1/2 times the body length. They sway back and forth very slowly. The nucleus is spherical and central in position. The contractile vacuole lies near the periphery. ”

“ The animal can extend its tentacula and protrude the mouth from the cell, but the rest of the body is incapable of extension or contraction. These polypifera increase by germination. In their organization, they so closely approach the mollusca, that in recent zoological systems they are placed in that class. The ciliated character of their tentacula has also led to their being named Cilio-branchiata. But as it is desirable in a work of this elementary nature to avoid conflicting opinions as much as possible, the fossil Bryozoa will be considered as corals, in the general sense of that term. ”

“ From the friable arenaceous limestone beds of Maestricht, which abound in corals, fine specimens of a delicate species are occasionally procured. Wond. p. 320, fig. 5, shows the character of this fossil zoophyte.
Fossil Bryozoa.
FOSSIL BRYOZOA.
The second class of Polypifera, the Bryozoa or Polyzoa, are of a much higher order of organization than those which have engaged our attention. The body is not symmetrical, « 266 » nor capable of contraction and expansion, as in the Anthozoa: it consists of a digestive cavity or sac, which is bent on itself and open at both extremities. ”

“ These lace weavers are the bryozoa, or moss animalcules—one of the oldest, most abundant and least known forms of animal life. They have much the same habits as the corals, but the two limestone secreting creatures are not even remotely related. The weavers are far higher in the scale of evolution than the island builders. Their family associations long have been in dispute. They have been associated with the rotifers and mollusks and even with some unknown ancestral form leading to the vertebrates. ”

“ Minute Mollusca, both bivalve and univalve, uncouth-formed Crustacea, tiny Starfishes, and especially Annelida, will pretty certainly reward the investigator. The last-named Class occurs in remarkable abundance and variety; while if, after you have gone round the glass, noticing particularly the very edge of the surface-line, you pass your eye, assisted by the lens, carefully over the surfaces of the bits of stone, you will probably find many more creatures, such as tube-dwelling Annelides, the smaller Zoophytes, and several species of the delicate Bryozoa. ”

“ The Molluscoidea, to which phylum belong the Bryozoa and Brachiopoda, would be but imperfectly understood from a morphological standpoint but for the vast number of fossil forms. The Brachiopoda have been estimated to have less than 150 living species, while probably more than 6,000 fossil species have been described. Of the 31 families only 7 have living representatives. We are dependent, therefore, largely on the fossil forms for our knowledge of the morphology of this class. ”

“ The bodies of the animals are soft and polype-like, and are furnished at one end with a circle of tentacles, covered with rows of cilia, by which the water is changed for respiration, and particles of food are brought to the mouth. The tentacles can be protruded or withdrawn at the will of the animal. The Bryozoa are what are called compound animals, each individual body having its own set of organs; yet the whole are connected together.
The two species figured are very common. Flus ́tra foliácea (Pl. IX. fig. 27) is found everywhere upon the sea-shore. The polypidom has cells upon both sides ”

“ No less than 130 species of bryozoa have been found in the Coralline Crag, and some belong to genera unknown in the living creation, and of a very peculiar structure; as, for example, that represented in Fig. 127, which is one of several species having a globular form. Among the testacea the genus Astarte (see Fig. 128) is largely represented, no less than fourteen species being known, and many of these being rich in individuals. There is an absence of genera peculiar to hot climates, such as Conus, Oliva, Fasciolaria, Crassatella, and others. ”

“ In dealing with the fossil species it is often impossible to make use of those characters which are of primary importance in the recognition of recent species. The fossil thallus is usually too intimately associated with the surrounding rock to admit of any use being made of external form as a diagnostic feature. The size and form of the cells must be taken as the chief basis on which to determine specific differences. In the absence of conceptacles or reproductive organs it is not always easy to distinguish calcareous algae from fossil Hydrozoa or Bryozoa. ”

“ Nor is it impossible that some modern bivalves of the Brachiopod group may be scarcely modified descendants even of Palæozoic species.
Perhaps some of the most remarkable facts in connection with the permanence of species and varietal forms are those furnished by that magnificent flora which burst in all its majesty on the American continent in the Cretaceous period, and still survives among us even in some of its specific types, I say survives; for we have but a remnant of its forms living, and comparatively little that is new has probably been added since. ”

“ Supposing these to be all, it is remarkable that we have no Protozoa or Corals or Echinoderms, and that the types of Brachiopods and Crustaceans are of comparatively modern affinities. Passing upward through another 1,000 feet of barren sandstone, we reach a zone in which no less than five genera of Trilobites are found, along with Pteropods and a sponge. Thus it is that life comes in at the base of the Cambrian in Wales, and it may be regarded as a fair specimen of the facts as they appear in the earlier fossiliferous beds succeeding the Laurentian. ”

“ Although the Brachiopoda, or "Lamp-shells," are not true mollusca, they are not very far removed from them, and are so often to be found in cabinets that it will not do to pass them over, especially since in past times they were very abundant, an enormous number occurring in the fossil state. Only eight genera are now living. ”

“ In favour of the theory of the simultaneous life of the host and the parasite, the theory of the growth of the Algæ in recent times must be advanced and the presence of sea-water and of animal tissue of a low vitality assumed. In addition there is the fact that a portion of a Brachiopod included in a sandy matrix within the coral, and not continuous with coral-structures, contains the tubes. Moreover the crystalline mass of the interstices of the coral, although it holds mechanically abundance of spores, does not present tubes or any evidence of growth. ”

“ Passing from the Azoic rocks, in the northern part of the State of New York, through the Potsdam region, to Trenton Falls, southwardly to the Helderberg Mountains near Albany, and eastwardly to Niagara, the immense number of fossil shells, particularly Brachiopods (Fig. 145) , attracts the attention of the traveler. The Brachiopods of the present seas are few and far between, whereas the sea of that most ancient period was characterized by shells of this order; the remains of other Mollusca are found, but much less abundantly as compared with those of Brachiopods. ”

“ Separate pieces of the leaves of many plants, as of the begonia, produce buds from which the whole plant may grow out.
An aptitude for reproduction like that in plants exists in many cœlenterates, worms, and tunicates. The polyps of hydroids and of bryozoa, the stolons of an ascidian (Clavellina lepadiformis) , may give rise to buds in many places, and these grow up into the perfect hydroid, bryozoon, or ascidian. ”

“ With this preliminary caution, we may regard the carboniferous fauna as peculiarly rich in marine species. The sea-bottoms swarmed with stone-lilies, cup-corals, and net-like bryozoa, mingled with the various tribes of molluscan life—the brachiopods with their long ciliated arms; the bivalves and gastropods with their coloured shells that recall some of the most familiar objects of our shores; and the cephalopods with their groups of siphonated chambers, straight as in the orthoceras, or gracefully coiled as in the goniatite. ”

“ Tube may be compared with tube in all its parts; but fossilization has produced appearances in the spores and conidia which suggest distinction between the recent and the fossil kinds of Algæ. Nevertheless the general character of the re- productive resting spores and the conidia arising from the vegetative part of the organism remain much the same. The large tubes in the palæozoic coral and Brachiopod, or whatever else Calceola may be, would at first sight indicate a different species of parasite from those which formed the smaller penetrations ”

“ The Flustra are marine Bryozoa, whose skin in hardening forms a thin shell of horny or cellular appearance; their little cells, more or less horny, are grouped symmetrically, somewhat like the cells in a bee-hive. Sometimes they form a crust which covers the algæ and other submarine bodies; sometimes they form ribbon-like stems. In some species the cells are only found on one side; in others they occupy both. Their orifices are extremely small, and defended by spines quite microscopic (Fig. 123) . ”

“ Mr. Clark, one of my assistants, has made very good drawings of all its stages of growth, and of various other hydroid medusae peculiar to this coast. Mr. Stimpson, another very promising young naturalist, who has been connected with me for some time in the same capacity, draws the crustacea and bryozoa, of which there are also a good many new ones here. ”

“ The orifices of the cells are surrounded with teeth, and are usually furnished below with a very long bristle—the polypidom appearing to the naked eye as a white hairy crust. In the variety figured, the long bristles are replaced by a spine; and this is not uncommon.
The polypidoms of the Bryozoa form interesting microscopic objects, the cells being furnished with variously arranged spines and punctures or dots. In some the cells are erect and arranged in rows upon the branches of a plant-like stem, while in others they are scattered irregularly over a creeping filament. ”