The connexion of the Pterobranchia with the Polyzoa is in the highest degree questionable.
Milne-Edwards removed the Polyzoa; the group was soon further thinned by the exclusion of the Protozoa on the one hand and the Entozoa on the other; while in 1848 Leuckart and Frey clearly distinguished the Coelenterata from the Echinodermata as a separate sub-kingdom, thus condemning the usage by which the term still continued to be applied to these two groups at least.
These attempts, however, to perpetuate the usage were finally discredited by Huxley's important Lectures on Comparative Anatomy (1864), in which the term was finally abolished, and the "radiate mob" finally distributed among the Echinodermata, Polyzoa, Vermes (Platyhelminthes), Coelenterata and Protozoa.
The corals are few in number, but the Molluscoida (Polyzoa) are more numerous in species and individuals.
Lime is, in fact, absorbed to an enormous extent by fishes, molluscs, crustacea, calcareous algae and sponges, starfishes, sea-urchins and feather stars, many polyzoa and a multitude of protozoa (mainly the foraminifera).
Brachiopods have been at various times placed with the Mollusca, the Chaetopoda, the Chaetognatha, the Phoronidea, the Polyzoa, the Hemichordata, and the Urochordata.
The suggestion to place Brachiopods with the Polyzoa, Phoronis, Rhabdopleura and Cephalodiscus, in the Phylum Podaxonia made in Ency.
Orders: Ciliati (Rotifera), Denudati (Hydroids), Vaginati (Anthozoa and Polyzoa), Natantes (Crinoids).
Classes: Polyzoa, Brachiopoda, Tunicata.
Certain additional small groups should probably be recognized as independent lines of descent or phyla, but their relationships are obscure - they are the Mesozoa, the Polyzoa, the Acanthocephala and the Gastrotricha.
POLYZOA, in zoology, a term (introduced by J.
The correctness of this association is questionable, and the Polyzoa are here treated as a primary division or phylum of the animal kingdom.
With these exceptions, the existing Polyzoa are marine forms, occurring from between tide-marks to abyssal depths in the ocean.
The Polyzoa are colonial animals, the colony (zoarium) originating in most cases from a free-swimming larva, which attaches itself to some solid object and becomes metamorphosed into the primary individual, or "ancestrula."
The form of the colony may thus be a good generic character, or, on the contrary, a single genus or even species may assume a variety of different forms. While nearly all Polyzoa are permanently fixed to one spot, the colonies of Cristatella and Lophopus among the Phylactolaemata can crawl slowly from place to place.
It is one of the most remarkable facts in the natural history of the Polyzoa that a single zooecium may be tenanted by several polypides, which successively degenerate.
The lophophore is a simple circle in all Polyzoa except in the Phylactolaemata, where it typically has the form of a horse shoe outlined by the bases of the tentacles.
The most singular of the external appendages found in the Polyzoa are the avicularia and vibracula of the Cheilostomata.
This appears to indicate B that the Polyzoa are remotely allied to other phyla in which this type of larva prevails, and in particular to the Mollusca and Chaetopoda, as well as to the Rotifera, which are regarded as persistent Trochospheres.
- For general accounts of the structure and development of the Polyzoa the reader's attention is specially directed to 12, 14, 6, 25, I, 2, 17, 26, 18, 23, 3, in the list given below; for an historical account to i; for a full bibliography of the group, to 22; for fresh-water forms, to 1-3, 7-10, 17; for an indispensable synonymic list of recent marine forms, to 15; for Entoprocta, to to, II, 24; for the classification of Gymnolaemata, to 21, 1 4, 4, 13, 20; for Palaeontology, to 27, 22.
References to important works on the species of marine Polyzoa by Busk, Hincks, Jullien, Levinsen, MacGillivray, Nordgaard, Norman, Waters and others are given in the Memoir (22) by Nickles and Bassler.
Fresh-water Polyzoa," Ray Soc. (1856).
(4) Busk, "Report on the Polyzoa," "Challenger" Rep. pt.
(12) Harmer, "Polyzoa," Cambr.
(19) Lankester, art, "Polyzoa," Ency.
(27) Ulrich, "Fossil Polyzoa," in Zittel's Text-book of Palaeontology, Eng.
Thus we regard Rotifers as an independent stem branching off at the outset of the rise from the Platode type to higher Invertebrata The Polyzoa (q v), which in many ways recall Rotifers, appear to be equally independent.
The Polyzoa or Bryozoa, which has been both added to and again removed from the Mollusca between Cuvier's date and the present day.
Henri Milne-Edwards in 1844 demonstrated the affinities of the Polyzoa with the Molluscan class Brachiopoda, and proposed to associate the three classes Brachiopoda, Polyzoa and Tunicata in a large group " Molluscoidea," co-ordinate with the remaining classes of Cuvier's Mollusca, which formed a group retaining the name Mollusca.
By subsequent writers the Polyzoa have in some cases been kept apart from the Mollusca and classed with the " Vermes "; whilst by others they have, together with the Brachiopoda, been regarded.as true Mollusca.
Such forms he distinguished as Coelentera, and showed that they had no special affinity with echinoderms, polyzoa, &c. He divided the Coelentera into a group Hydrozoa, in which the sexually produced embryos were usually set free from the surface of the body, and a group Actinozoa, in which the embryos are detached from the interior of the body and escape generally by the oral aperture.
Spicules of sponges and fragments of other organisms, such as molluscs, polyzoa, foraminifera and brachiopods, often occur in flint, and may be partly or wholly silicified with retention of their original structure.
The development of Phoronis was supposed by Caldwell (2) to furnish the explanation of the relations of the surfaces in Brachiopoda, Polyzoa and perhaps the Sipunculoid Gephyrea, in which the ontogenetic evidence is less clear.
The comparative study of the development does not support the hypothesis that the Polyzoa (q.v.) are comparable with Phoronis.
There are, indeed remarkable similarities between the external characters of the Phylactolaematous Polyzoa and the Phoronidea, and notably between their lophophores.
But a serious objection to the comparison is that the development of Phylactolaemata can be explained by supposing it to be a modification of what occurs in other Polyzoa, while it appears to have no relation whatever to that of Phoronis.
Most observers consider that Actinotrocha is a highly modified Trochosphere, and this would give it some claim to be regarded as distantly related to the Entoproct Polyzoa and to other groups which have a Trochosphere larva.
The skeletons of many other organisms, such as Polyzoa and Mollusca, contribute to coral masses but cannot be included in the term "coral."
At one time they were referred by some to the Polyzoa (Bryozoa), and later, by almost general consent, to the Hydroida (Calyptoblastea) among the Hydrozoa (Hydromedusae).
Some Red Algae find a home in the gelatinous substance of Flustra, Alcyonidium and other polyzoa, only emerging for the formation of the reproductive organs.
Increase of knowledge has now, however, established the conclusion that the agreement of structure supposed to obtain between Polyzoa and true Mollusca is delusive; and accordingly they, together with the Brachiopoda, were removed from the Molluscan phylum by Lankester in his article in the 9th edition of this work (on the which present article is based).