48 



SPONGES 



Classification. 



Classi- The phylum Parazoa or Spongix consists of two main 

 fication. branches, as follows : 



Branch A. MEG A MASTIC'- Branch B. MICROMASTIC- 



TORA. TOR A. 



Class CALCAREA, Grant Class I. MYXOSPONGI.E, 



Order 1. Homoccda, Pol. Haeckel. 



Order 2. Heterocala, Pol. Order l.ffalisarcina. 



Order 2. Chondrosina. 



Class II. SILICISPONGI^E. 



Sub-class i. HEXACTINELLIDA, 



O. Schmidt. 



Order 1. Lyssacina, Zittel. 

 Order 2. Diciyonina, Zittel. 



Sub -class ii. DEMOSFONGIJE, 



Sollas. 

 Tribe a. Monaxonida. 



Order 1. Monaxona. 



Order 2. Ceratosa, Grant. 



Tribe b. Tetractinellida, 



Marshall. 



Order \.-Choristida, Sollas. 

 Order 2. Lithistida, O.S. 



Position By the possession of both sexual elements and a complex histo- 



in animal logical structure, and in the character of their embryological devt-1- 



kingdoin. opment, the sponges are clearly separated from the Protozoa ; on 



the other hand, the choanoflagellate character of the endoderm, 



which it retains in the flagellated chambers throughout the group 



without a single exception, as clearly marks them off from the 



Metazoa. They may therefore be regarded as a separate phylum 



derived from the choanoflagellate Infusoria, but pursuing for a 



certain distance a course of development parallel with that of the 



Metazoa. 



Different views have been propounded by other authors. Savile 

 Kent regards the sponges as Protozoa (10} ; Balfour suggested that 

 they branched off from the Metazoan phylum at a point below the 

 Ccelentera, and considered them as intermediate between Protozoa 

 and Metazoa ; Schulze regards them as derived from a simple 

 ancestral form of Ccelentera (23) ; Marshall advocates the view that 

 they are degraded forms derived from Ccelenterates which were 

 already in possession of tentacles and mesenteric pouches (14). 



As a phylum the Spongix are certainly divisible into two branches, 

 one including the Calcarea and the other the remaining sponges, 

 which Vosmaer has termed Non-Calcarea, and others Plethospongite. 

 Since, however, the choanocytes of the Calcarea are usually, if not 

 universally, larger than those of other sponges, we may make use 

 of this difference in our nomenclature, and distinguish one branch 

 as the Mcgamastidora (fiaaTlKTwp, "scourger") and the other as 

 the Micromastictora. 



Branch A.MEGAMASTICTORA. 



Sponges in which the choanocytes are of comparatively large 

 size, 0'005 to 0'009 mm. in diameter (Haeckel, 6). 



Class CALCAREA. 



Calcarea. Megamastietora in which the skeleton is composed of calcareous 

 spicules. 



Order 1. HOMOOELA. Calcarea in which the endoderm consists 

 wholly of choanocytes. Examples : Leucosolenia, Bwk. ; Homo- 

 derma, Lfd. 



Order 2. HETEROCOJLA. Calcarea in which the endoderm is dif- 

 ferentiated into pinnacocytes, which line the paragastric cavity 

 and excurrent canals, and choanocytes, which are restricted to special 

 recesses (radial tubes or flagellated chambers). Examples : Sycon, 

 O.S. ; Grautia, Fl. ; Leuconia, Bwk. 



Branch B. MICROMASTICTORA. 



(Non-Calcarea, Vosmaer; Plethospongise, Sollas.) Sponges in 

 which the choanocytes are comparatively small, 0'003 mm. in 

 diameter. 



Class I. MYXOSPONGLS. 



Myxo- Micromastictora in which a skeleton or scleres are absent. 



spongiie. Order 1. HALISARCINA. Myxosponyiie in which the canal system 

 is simple, with simple or branched Sycon or eurypylous Rhagon 

 chambers. An ectosome sometimes and a cortex always absent. 

 Examples: Halisarca, Duj.; Oscarella, Vosm. ; Bajalus, Lfd. 



Order 2. CHONDROSINA. Myxospongise, in which the canal 

 system is complicated, with diplodal Rhagon chambers and a 

 well-developed cortex. Example : Chondrosia, O.S. 



The Halisarcina are evidently survivals from an ancient and 

 primitive type. The simplicity of the canal system is opposed to 

 the view that they are degraded forms ; we may therefore regard 

 the absence of scleres as a persistent primary and not a secondary 

 acquired character. They are as interesting, therefore, from one 



Subdivi- 



groups. 



point of view (absence of scleres) as the Ascons are from another 

 (undifferentiated endoderm). With the Chondrosina the case is 

 different ; they differ only from Chondrilla and its allies by the 

 absence of asters ; these differ only from the Tethyidse by the 

 absence of strougyloxeas ; and we may very reasonably assume that 

 in these three groups we have a series due to loss of characters, the 

 Chondrillw being reduced Tcthyidee, and the Chondrosina reduced 

 Chondrillss. Still, as Huxley has well remarked, "classification 

 should express not assumptions but facts " ; and therefore till we 

 are in possession of more direct evidence it will be well to exclude 

 the Chondrosina from the SilicispongiK. 



Class II. SlLICISPONGLffi. 



Micromastictora possessing a skeleton or scleres which are not 

 calcareous. 



Sub-class i. HEXACTINELLIDA. 



Silicispongias characterized by sexradiate silicious spicules. Hexmti- 

 Canal system usually simple, with Sycon chambers. Sponge nettida. 

 differentiated into ecto-, choano-, and endo-some. 



Order 1. LYSSACINA. Huxaclincllida in which the skeleton is 

 formed of separate spicules, or, if united, then by a subsequent not a 

 contemporaneous deposit of silica. Examples : Euplectella, Owen ; 

 Asconema, S. Kent ; Hyalonema, Gray ; Rossella, Crtr. 



Order 2. DICTYONINA. Hexactincllida in which sexradiate 

 spicules are cemented together by a silicious deposit into a con- 

 tinuous network pan passu with their formation. Examples : 

 Farrea, Bwk. ; Eurete, Marshall ; Aphrocallistes, Gray ; Myliiisia, 

 Gray ; Dactylocalyx, Stutchbury. 



The Hcxactinellida are a very sharply denned group, impressed 

 with marked archaic features. No other Silicispongise possess, so 

 far as is known, so simple a syconate canal system. The oldest 

 known fossil sponge is a member of the Lyssacina (7 and 24), viz., 

 Protospmigia, Salter, from the Menevian beds, Lower Cambrian, 

 St David's Head, Wales. The group is almost world- wide in distri- 

 bution, chiefly affecting deep water, from 100 to 300 fathoms, but 

 often extending into abyssal depths ; occasionally, however, though 

 rarely, it frequents shallow water (Cystispongia superstcs dredged off 

 Yucatan in 18 fathoms). 



Sub-class ii. DEMOSPONGLffi. 



Silicispongix in which sexradiate spicules are absent. Detno- 



Tribea. MOXAXOXIDA. spongi* 



Demospongise in which the skeleton consists either of silicious 

 spicules which are not quadriradiate, or of horny scleres or in- 

 cluded foreign bodies, or of one or more of these constituents in 

 conjunction. 



Order 1. MONAXONA. The skeleton is characterized by either 

 uniaxial or polyaxial spicules. Examples : Amorphina, 0. S. 

 ("crumb of bread" sponge); Spongilla, Link, ("freshwater" 

 sponge) ; Chalina, Bwk. ; Tcthya, Lmk. 



Order 2. CERATOSA. The skeleton consists of horny scleres 

 which never include "proper" spicules, or of introduced foreign 

 bodies, or of both these in conj unction. Examples : Darwinclla, 

 F. Miiller ; Euspongia, Bronn (the "bath" sponge). 



Tribe 6. TETRACTINELLIDA. 



Demospongix possessing quadriradiate or trisene spicules or 

 Lithistid scleres (desmas). 



Order 1. CHORISTIDA. Tetractinellida with quadriradiate or 

 triame spicules, which are never articulated together into a rigid 

 network. Examples: Tetilla, 0. S. ; Thenea, Gray ; Geodia, Lmk. ; 

 Dcrcitus, Gray. 



Order 2. LITHISTIDA. Tetractinellida with branching scleres 

 (desmas), which may or may not be modified tetrad spicules, arti- 

 culated together to form a rigid skeleton. Trisene spicules may or 

 may not be present in addition. Examples : Thconclla, Gray ; Coral- 

 listes, O.S. ; Azorica, Crtr.; Vetulina, O.S. 



This large sub-class embracesthe great majority of existing sponges. 

 Its external boundaries are fairly well denned, its internal divisions 

 much less so, as its various orders and families pass into each other 

 at many points of contact. Although there does not appear to be 

 much resemblance between a Lithistid sponge, such as Theonella, 

 a Monaxonid such as Amorphina, and an ordinary "bath" sponge 

 (Euspongia), yet between these extremes a long series of inter- 

 mediate forms exists, so nicely graduated as to render their dis- 

 ruption into groups by no means an easy task. If the delimitation 

 of orders is difficult, that of genera is often impossible, so that 

 they are reduced to assemblages depending on the tact or taste of 

 the author. Thus Polejaeff states that with a single exception 

 " none of the genera of Ceratosa are separable by absolute charac- 

 ters." The chief spicules of Monaxona are uniaxial, often accom- 

 panied by characteristic microscleres. Although distinguished as a 

 group by the absence of quadriradiate or triune spicules, two ex- 

 ceptions are known in which these occur (Triccntrion, Ehlers, and 

 Acarnus, Gray) ; these, however, present unusual characters which 

 suggest an independent origin. The canal system of Monaxona has 

 not yet been fully investigated ; it appears usually to follow the 



