SUM 'I. ASS I 



HYDROZOA HYDRO*! KI >rs.\ K 



109 



Sub-Class 1. HYDROMEDUSAE. Vogt. 1 



Sessile or free-.w'im nnn<i, ux/ml/i/ branching r///o//?'rx, //-///t dimorpkici /////////>-, "//</ 

 jmli/ji* : tin 1 In tier frequently become liberated in the form of small, free- 

 xirimnting ifedhtsat, ?///// non-lobate umbrellas composed of a hyaline, gelatinous 



Six orders of ////</////"///.<//, ;iro recognised 7///'//v//-/>^, Hydrotor&llinae, 

 Tnbulnri<n; CampamUariae, Trachymedtuae, and Siplwnophorae. But of these only 

 the HydrocurnlHiiiH'. Tnbnl<iriin>, and Campanulariae secrete durable, calcareous, or 

 chitinous structures. 



Order 2. HYDROCORALLINAB. Moseley. * 



Xiihnl i/olyps secreting at the base a dense calcareous skeleton, traversed at intervals 

 ifo series of vertical tubes, into which the dimorphic zooids can be retracted. 



The Hydrocorallinae comprise the two recent groups Milleporidae and Stjilnx- 

 which were universally regarded as true corals until Louis Agassi/ and 

 Moseley proved their relationship to the Hydrozoa. 



Millepora, Lin. (Fig. 193). Massive, foliately expanded, encrusting, or 

 ^branching polyparia (coenosteum), often attaining considerable size. Upper 

 sin face punctured by round open- 

 ings of the larger tubes (gastro- 

 pwes), between which are the 

 mouths of numerous smaller 

 tubes (dactylopores). The skeleton 

 i- composed of a network of 

 juiastomosing calcareous fibres, 

 traversed by a system of tortuous 

 canals. The gastropores lodge 

 the larger, nutritive polyps, and 

 the dactylopores the smaller, food- 

 procuring zooids ; the latter have 

 no mouth, but are provided with 

 short, clavatc tentacles on their 



, . . 



sides, and their tubes commum- 



-.1 +V> rv,4^v,, 1 



CatC With the Vermiform CanalS. 



Zooidal tubes tabulate, but non- 

 sept ate. The genus is an important reef -builder of the present day, but occurs 

 only sparsely in the fossil state. Earliest known forms appear in the Eocene. 



A s'///A/.s/6'/-, Gray. Branching polyparia composed of a network of fibrous, 

 rose-coloured coenenchyma, in which are situated calicular depressions that are 



1 . 1 II ni,i, t, ./. (,'., Monograph of the Gymuoblastic or Tubularian Hydroids ; Ray Society, 1371-72. 

 S!, imixnm, (/., Ueber fos-sile Hydrozoen au.s der Faniilie der Coryniden (Palaeontographica, Bd. 

 XXV.), 1877. Ueber triasische Hydrozoen vom ostlicheii Balkan (Sitzungsl)er. Wiener Akad. 

 in.it li. phys. Classc, Bd. CII.), 1893. Canavari, M., Idrozoi Titoniani appartenanti alia Fainiglia 

 delle Ellipsactinidi (Mem. Comitato Geol. vol. IV.), 1893. Nichol^m. II. A., Monograph of the 

 British Stromatoporoids (Palaeontographical Society), 1886-92. Bargatzki, A., Die Stromatoporen 

 iU-s rlicinischfii Devons. Bonn, 1881. 



/, 11. .\'., Philosophical Transactions Royal Society, vol. 167, 1878. 



FIG. 193. 



Millepora nnilosa, Esp. Recent. A, Upper surface of coeno- 

 steuin, showing gastropores, /,-, and daetyloi>ores, c, *<>/! . /;, Ver- 

 tical sect inn, /., ^astropores with tabulae, t ; c, Vermiform canals 

 coiimiunicatiny with dactylopores, so/j (after Steinmann). 



