Freshwater Sponges, Hydroids & Polyzoa Part 3

Its bottom is muddy and it contains few water-plants, although in some places the water-plants that do exist are matted together to form floating islands on which trees and bushes grow. The fauna, at any rate as regards mollusca and microscopic organisms, is remarkably poor, but two species of polyzoa (_Fredericella indica_ and _Plumatella fruticosa_) and one of sponge (_Trochospongilla pennsylvanica_) grow in considerable abundance although not in great luxuriance.

_The Himalayas._

BHIM TAL[H] is a lake situated at an alt.i.tude of 4500 feet in that part of the Western Himalayas known as k.u.maon, near the plains. It has a superficial area of several square miles, and is deep in the middle. Its bottom and banks are for the most part muddy. Little is known of its fauna, but two polyzoa (_Plumatella allmani_ and _Lophopodella carteri_) and the gemmules of two sponges (_Spongilla carteri_ and _Ephydatia meyeni_) have been found in it.

[Footnote H: The fauna of this lake and of others in the neighbourhood has recently been investigated by Mr. S. W.

Kemp. See the addenda at the end of this volume.--_June 1911._]

NOMENCLATURE AND TERMINOLOGY.

The subject of nomenclature may be considered under four heads:--(I.) the general terminology of the various kinds of groups of individuals into which organisms must be divided; (II.) the general nomenclature of specimens belonging to particular categories, such as types, co-types, etc.; (III.) the nomenclature that depends on such questions as that of "priority"; and (IV.) the special terminology peculiar to the different groups. The special terminology peculiar to the different groups is dealt with in the separate introductions to each of the three parts of this volume.

(I.)

No group of animals offers greater difficulty than the sponges, hydroids, and polyzoa (and especially the freshwater representatives of these three groups) as regards the question "What is a species?" and the kindred questions, "What is a subspecies?" "What is a variety?" and "What is a phase?" Genera can often be left to look after themselves, but the specific and kindred questions are answered in so many different ways, if they are even considered, by different systematists, especially as regards the groups described in this volume, that I feel it necessary to state concisely my own answers to these questions, not for the guidance of other zoologists but merely to render intelligible the system of cla.s.sification here adopted. The following definitions should therefore be considered in estimating the value of "species," etc., referred to in the following pages.

_Species._--A group of individuals differing in constant characters of a definite nature and of systematic[I] importance from all others in the same genus.

[Footnote I: "What characters are of systematic importance?"

is a question to which different answers must be given in the case of different groups.]

_Subspecies._--An isolated or local race, the individuals of which differ from others included in the same species in characters that are constant but either somewhat indefinite or else of little systematic importance.

_Variety._--A group of individuals not isolated geographically from others of the same species but nevertheless exhibiting slight, not altogether constant, or indefinite differences from the typical form of the species (_i. e._, the form first described).

_Phase._--A peculiar form a.s.sumed by the individuals of a species which are exposed to peculiarities in environment and differ from normal individuals as a direct result.

There are cases in which imperfection of information renders it difficult or impossible to distinguish between a variety and a subspecies. In such cases it is best to call the form a variety, for this term does not imply any special knowledge as regards its distribution or the conditions in which it is found.

I use the term "form" in a general sense of which the meaning or meanings are clear without explanation.

(II.)

The question of type specimens must be considered briefly. There are two schools of systematists, those who a.s.sert that one specimen and one only must be the type of a species, and those who are willing to accept several specimens as types. From the theoretical point of view it seems impossible to set up any one individual as the ideal type of a species, but those who possess collections or are in charge of museums prefer, with the natural instinct of the collector, to have a definite single type (of which no one else can possibly possess a duplicate) in their possession or care, and there is always the difficulty that a zoologist in describing a species, if he recognizes more than one type, may include as types specimens that really belong to more than one species.

These difficulties are met by some zoologists by the recognition of several specimens as paratypes, all of equal value; but this, after all, is merely a terminological means of escaping from the difficulty, calculated to salve the conscience of a collector who feels unwilling to give up the unique type of a species represented by other specimens in his collection. The difficulty as regards the confounding of specimens of two or more species as the types of one can always be adjusted if the author who discovers the mistake redescribes one of the species under the original name and regards the specimen that agrees with his description as the type, at the same time describing a new species with another of the specimens as its type. Personally I always desire to regard the whole material that forms the basis of an original description of a species as the type, but museum rules often render this impossible, and the best that can be done is to pick out one specimen that seems particularly characteristic and to call it the type, the rest of the material being termed co-types. A peculiar difficulty arises, however, as regards many of the sponges, coelenterates, and polyzoa, owing to the fact that they are often either compound animals, each specimen consisting of more than one individual, or are easily divisible into equivalent fragments. If the single type theory were driven to its logical conclusion, it would be necessary to select one particular polyp in a hydroid colony, or even the part of a sponge that surrounded a particular osculum as the type of the species to which the hydroid or the sponge belonged. Either by accident or by design specimens of Spongillidae, especially if kept dry, are usually broken into several pieces. There is, as a matter of fact, no reason to attribute the peculiarly sacrosanct nature of a type to one piece more than another.

In such cases the biggest piece may be called the type, while the smaller pieces may be designated by the term "schizotype."

The more precise definition of such terms as topotype, genotype, _et hujus generis omnis_ is nowadays a science (or at any rate a form of technical industry) by itself and need not be discussed here.

(III.)

In 1908 an influential committee of British zoologists drew up a strenuous protest against the unearthing of obsolete zoological names (see 'Nature,' Aug. 1908, p. 395). To no group does this protest apply with greater force than to the three discussed in this volume. It is difficult, however, to adopt any one work as a standard of nomenclature for the whole of any one of them. As regards the Spongillidae it is impossible to accept any monograph earlier than Potts's "Fresh-Water Sponges" (P. Ac. Philad., 1887), for Bowerbank's and Carter's earlier monographs contained descriptions of comparatively few species. Even Potts's monograph I have been unable to follow without divergence, for it seems to me necessary to recognize several genera and subgenera that he ignored. The freshwater polyzoa, however, were dealt with in so comprehensive a manner by Allman in his "Fresh-Water Polyzoa" (London, 1856) that no difficulty is experienced in ignoring, so far as nomenclature is concerned, any earlier work on the group; while as regards other divisions of the polyzoa I have followed Hincks's "British Marine Polyzoa" (1880), so far as recent researches permit. In most cases I have not attempted to work out an elaborate synonymy of species described earlier than the publication of the works just cited, for to do so is a mere waste of time in the case of animals that call for a most precise definition of species and genera and yet were often described, so far as they were known earlier than the dates in question, in quite general terms. I have been confirmed in adopting this course by the fact that few of the types of the earlier species are now in existence, and that a large proportion of the Indian forms have only been described within the last few years.

MATERIAL.

The descriptions in this volume are based on specimens in the collection of the Indian Museum, the Trustees of which, by the liberal manner in which they have permitted me to travel in India and Burma on behalf of the Museum, have made it possible not only to obtain material for study and exchange but also to observe the different species in their natural environment. This does not mean to say that specimens from other collections have been ignored, for many inst.i.tutions and individuals have met us generously in the matter of gifts and exchanges, and our collection now includes specimens of all the Indian forms, named in nearly all cases by the author of the species, except in those of species described long ago of which no authentic original specimens can now be traced. Pieces of the types of all of the Indian Spongillidae described by Carter have been obtained from the British Museum through the kind offices of Mr. R. Kirkpatrick. The Smithsonian Inst.i.tution has sent us from the collection of the United States National Museum specimens named by Potts, and the Berlin Museum specimens named by Weltner, while to the Imperial Academy of Sciences of St. Petersburg we owe many unnamed but interesting sponges. Dr. K. Kraepelin and Dr. W.

Michaelsen have presented us with specimens of most of the species and varieties of freshwater polyzoa described by the former in his great monograph and elsewhere. We owe to Dr. S. F. Harmer, formerly of the Cambridge University Museum and now Keeper in Zoology at the British Museum, to Professor Max Weber of Amsterdam, Professor Oka of Tokyo, and several other zoologists much valuable material. I would specially mention the exquisite preparations presented by Mr. C. Rousselet.

Several naturalists in India have also done good service to the Museum by presenting specimens of the three groups described in this volume, especially Major H. J. Walton, I.M.S., Major J. Stephenson, I.M.S., Dr.

J. R. Henderson and Mr. G. Matthai of Madras, and Mr. R. Shunkara Narayana Pillay of Trivandrum.

The following list shows where the types of the various species, subspecies, and varieties are preserved, so far as it has been possible to trace them. I have included in this list the names of all species that have been found in stagnant water, whether fresh or brackish, but those of species not yet found in fresh water are enclosed in square brackets.

+-----------------------------------------------------------------------+ | INDIAN SPONGILLIDae. | | | +---------------------------------+----------------------+--------------+ | NAME. | TYPE IN COLL. | MATERIAL | | | | EXAMINED. | +---------------------------------+----------------------+--------------+ | _Spongilla lacustris_ subsp. | Ind. Mus. | Type. | | _reticulata_ | | | +---------------------------------+----------------------+--------------+ | _Spongilla proliferens_ | " " | " | +---------------------------------+----------------------+--------------+ | _Spongilla alba_ | Brit. and Ind. Mus. | Schizotype. | +---------------------------------+----------------------+--------------+ | [_Spongilla alba_ var. | Ind. Mus. | Type | | _bengalensis_] | | | +---------------------------------+----------------------+--------------+ | _Spongilla alba_ var. | Brit. Mus. | {Specimens | | _cerebellata_ | | {compared | | | | {with type. | +---------------------------------+----------------------+--------------+ | _Spongilla cinerea_ | Brit. and Ind. Mus. | Schizotype. | +---------------------------------+----------------------+--------------+ | [_Spongilla travancorica_] | Ind. Mus. | Type. | +---------------------------------+----------------------+--------------+ | _Spongilla hemephydatia_ | " " | " | +---------------------------------+----------------------+--------------+ | _Spongilla crateriformis_ | U.S. Nat. Mus. | Co-type. | +---------------------------------+----------------------+--------------+ | _Spongilla carteri_ | Brit. and Ind. Mus. | Schizotype. | +---------------------------------+----------------------+--------------+ | _Spongilla carteri_ var. | Ind. Mus. | Type. | | _mollis_ | | | +---------------------------------+----------------------+--------------+ | _Spongilla carteri_ var. | " " | " | | _cava_ | | | +---------------------------------+----------------------+--------------+ | _Spongilla carteri_ var. | " " | " | | _lobosa_ | | | +---------------------------------+----------------------+--------------+ | _Spongilla fragilis_ subsp. | " " | " | | _calcuttana_ | | | +---------------------------------+----------------------+--------------+ | _Spongilla fragilis_ subsp. | Amsterdam Mus. | Co-type. | | _decipiens_ | | | +---------------------------------+----------------------+--------------+ | _Spongilla gemina_ | Ind. Mus. | Type. | +---------------------------------+----------------------+--------------+ | _Spongilla cra.s.sissima_ | " " | " | +---------------------------------+----------------------+--------------+ | _Spongilla cra.s.sissima_ var. | " " | " | | _cra.s.sior_ | | | +---------------------------------+----------------------+--------------+ | _Spongilla bombayensis_ | Brit. and Ind. Mus. | Schizotype. | +---------------------------------+----------------------+--------------+ | _Spongilla indica_ | Ind. Mus. | Type. | +---------------------------------+----------------------+--------------+ | _Spongilla ultima_ | " " | " | +---------------------------------+----------------------+--------------+ | _Pectispongilla aurea_ | " " | " | +---------------------------------+----------------------+--------------+ | _Ephydatia meyeni_ | Brit. and Ind. Mus. | Schizotype. | +---------------------------------+----------------------+--------------+ | _Dosilia plumosa_ | " " " " | " | +---------------------------------+----------------------+--------------+ | _Trochospongilla latouchiana_ | Ind. Mus. | Type. | +---------------------------------+----------------------+--------------+ | _Trochospongilla phillottiana_ | " " | " | +---------------------------------+----------------------+--------------+ | _Trochospongilla pennsylvanica_ | U.S. Nat. Mus. | Co-type. | +---------------------------------+----------------------+--------------+ | _Tubella vesparioides_ | Ind. Mus. | Type. | +---------------------------------+----------------------+--------------+ | _Corvospongilla burmanica_ | Brit. and Ind. Mus. | Schizotype. | +---------------------------------+----------------------+--------------+ | _Corvospongilla lapidosa_ | Ind. Mus. | Type. | +---------------------------------+----------------------+--------------+ | INDIAN COELENTERATES OF STAGNANT WATER. | +---------------------------------+----------------------+--------------+ | HYDROZOA. | | | +---------------------------------+----------------------+--------------+ | _Hydra oligactis_ | Not in existence. | | +---------------------------------+----------------------+--------------+ | _Hydra vulgaris_ | " " | | +---------------------------------+----------------------+--------------+ | [_Syncoryne filamentata_] | Ind. Mus. | Type. | +---------------------------------+----------------------+--------------+ | [_Bimeria vest.i.ta_] | ? Not in existence. | | +---------------------------------+----------------------+--------------+ | [_Irene ceylonensis_] | {Hydroid in Ind.} | Hydroid type | | | {Mus., Medusa} | | | | {in Brit. Mus.} | | +---------------------------------+----------------------+--------------+ | ACTINIARIA. | | | +---------------------------------+----------------------+--------------+ | [_Sagartia schilleriana_] | Ind. Mus. | Types. | +---------------------------------+----------------------+--------------+ | [_Sagartia schilleriana_ | " " | " | | subsp. _exul_] | | | +---------------------------------+----------------------+--------------+ | INDIAN POLYZOA OF STAGNANT WATER. | +---------------------------------+----------------------+--------------+ | ENTOPROCTA. | | | +---------------------------------+----------------------+--------------+ | [_Loxosomatoides colonialis_] | Ind. Mus. | Types. | +---------------------------------+----------------------+--------------+ | ECTOPROCTA CHEILOSTOMATA. | | | +---------------------------------+----------------------+--------------+ | [_Membranipora lacroixii_] | ? Paris Mus. | | +---------------------------------+----------------------+--------------+ | [_Membranipora bengalensis_] | Ind. Mus. | Types. | +---------------------------------+----------------------+--------------+ | ECTOPROCTA STENOSTOMATA. | | | +---------------------------------+----------------------+--------------+ | [_Bowerbankia caudata_ subsp. | Ind. Mus. | Types. | | _bengalensis_] | | | +---------------------------------+----------------------+--------------+ | _Victorella bengalensis_ | " " | " | +---------------------------------+----------------------+--------------+ | _Hislopia lacustris_ | ? Not in existence. | | +---------------------------------+----------------------+--------------+ | _Hislopia lacustris_ subsp. | Ind. Mus. | " | | _moniliformis_ | | | +---------------------------------+----------------------+--------------+ | ECTOPROCTA PHYLACTOLaeMATA. | | | +---------------------------------+----------------------+--------------+ | _Fredericella indica_ | Ind. Mus. | Type. | +---------------------------------+----------------------+--------------+ | _Plumatella fruticosa_ | Not in existence. | | +---------------------------------+----------------------+--------------+ | _Plumatella diffusa_ |?Philadelphia Acad.[J]| | +---------------------------------+----------------------+--------------+ | _Plumatella allmani_ | Not in existence. | | +---------------------------------+----------------------+--------------+ | _Plumatella emarginata_ | " " | | +---------------------------------+----------------------+--------------+ | | {Hamburg and} | One of the | | _Plumatella javanica_ | {Ind. Mus. } | types. | +---------------------------------+----------------------+--------------+ | | {Brit. and Ind.} | One of the | | _Plumatella tanganyikae_ | {Mus. } | types. | +---------------------------------+----------------------+--------------+ | _Stolella indica_ | Ind. Mus. | Type. | +---------------------------------+----------------------+--------------+ | _Lophopodella carteri_ | Brit. Mus. | " | +---------------------------------+----------------------+--------------+ | _Lophopodella carteri_ var. | Ind. Mus. | " | | _himalayana_ | | | +---------------------------------+----------------------+--------------+ | _Pectinatella burmanica_ | Ind. Mus. | " | +---------------------------------+----------------------+--------------+

[Footnote J: I have failed to obtain from the Philadelphia Academy of Science a statement that the type of this species is still in existence.]

The literature dealing with the various groups described in the volume is discussed in the introductions to the three parts. Throughout the volume I have, so far as possible, referred to works that can be consulted in Calcutta in the libraries of the Indian Museum, the Geological Survey of India, or the Asiatic Society of Bengal. The names of works that are not to be found in India are marked with a *. The rarity with which this mark occurs says much for the fortunate position in which zoologists stationed in Calcutta find themselves as regards zoological literature, for I do not think that anything essential has been omitted.

It remains for me to express my grat.i.tude to those who have a.s.sisted me in the preparation of this volume. The names of those who have contributed specimens for examination have already been mentioned. I have to thank the Trustees of the Indian Museum not only for their liberal interpretation of my duties as an officer of the Museum but also for the use of all the drawings and photographs and some of the blocks from which this volume is ill.u.s.trated. Several of the latter have already been used in the "Records of the Indian Museum." From the Editor of the "Fauna" I have received valuable suggestions, and I am indebted to Dr. Weltner of the Berlin Museum for no less valuable references to literature. Mr. F. H. Gravely, a.s.sistant Superintendent in the Indian Museum, has saved me from several errors by his criticism.

The majority of the figures have been drawn by the draftsmen of the Indian Museum, Babu Abhoya Charan Chowdhary, and of the Marine Survey of India, Babu Shib Chandra Mondul, to both of whom I am much indebted for their accuracy of delineation.

No work dealing with the sponges of India would be complete without a tribute to the memory of H. J. Carter, pioneer in the East of the study of lower invertebrates, whose work persists as a guide and an encouragement to all of us who are of the opinion that biological research on Indian animals can only be undertaken in India, and that even systematic zoological work can be carried out in that country with success. I can only hope that this, the first volume in the official Fauna of the Indian Empire to be written entirely in India, may prove not unworthy of his example.

Indian Museum, Calcutta Oct. 23rd, 1910.

PART I.

FRESHWATER SPONGES

(SPONGILLIDae).

INTRODUCTION TO PART I.

I.

THE PHYLUM PORIFERA.

The phylum Porifera or Spongiae includes the simplest of the Metazoa or multicellular animals. From the compound Protozoa its members are distinguished by the fact that the cells of which they are composed exhibit considerable differentiation both in structure and in function, and are a.s.sociated together in a definite manner, although they are not combined to form organs and systems of organs as in the higher Metazoa.

Digestion, for instance, is performed in the sponges entirely by individual cells, into the substance of which the food is taken, and the products of digestion are handed on to other cells without the intervention of an alimentary ca.n.a.l or a vascular system, while there is no structure in any way comparable to the nervous system of more highly organized animals.

The simplest form of sponge, which is known as an olynthus, is a hollow vase-like body fixed at one end to some solid object, and with an opening called the osculum at the other. The walls are perforated by small holes, the pores, from which the name Porifera is derived.

Externally the surface is protected by a delicate membrane formed of flattened cells and pierced by the pores, while the interior of the vase is covered with curious cells characteristic of the sponges, and known as choanocytes or collar-cells. They consist of minute oval or pear-shaped bodies, one end of which is provided with a rim or collar of apparently structureless membrane, while a flagellum or whip-like lash projects from the centre of the surface surrounded by the collar. These collar-cells are practically identical with those of which the Protozoa known as Choanoflagellata consist; but it is only in the sponges[K] that they are found constantly a.s.sociated with other cells unlike themselves.