MARINE ZOOLOGY 



2. Medusa 



Gelatinous, bell or disc-shaped, transparent, 

 often with radiating or marginal streaks of 

 brilliant colours ; not colonial ; free-swim- 

 nming, often in large shoals. 



The smaller medusae are produced by lateral 

 budding from various Hydroid stocks, es- 

 pecially such forms as Podocoryne, Syncoryne, 

 Perigonimus, Bougainvillea, Corymorpha, 

 Clytia, Obelia, and Campanularia. Wher- 

 ever these Hydroids occur their medusa may 

 be obtained either from the Hydroids them- 

 selves at the proper season, or with a muslin 

 net at the surface of the sea. Other medusae 

 may also be found whose larval or Hydroid 

 phases are not yet determined. 



The larger medusae, which are so frequently 

 cast ashore after strong sea-breezes in the 

 summer months, do not always exhibit a 

 similar alternation of stages in their life-history ; 

 but Aurelia and Chrysaora are known to be 

 produced by a remarkable process of succes- 

 sive fission from minute hydra-like polyps 

 which form extensive colonies on lold oyster- 

 shells and similar objects. 



My present list of local medusae is very brief 

 from the scantiness of existing records. 



A. Hydromeduste 

 I. Obelia, sp. 



The medusa of Obelia is readily recognized 

 by its perfectly flat and disc-shaped umbrella, 

 its short quadrate manubrium, its numerous 

 short marginal tentacles (24 to 114, according 

 to age), and its eight marginal otocysts, as 

 well as by its brilliant phosphorescence. It 

 varies in diameter from i to 6 mm. according 

 to age. 



Under the name Eucope lucifera, Schultze 

 records a number of small medusae derived 

 from Obelia colonies which were taken in a 

 surface net oflF Cromer during the Pommerania 

 cruise. Haeckel has attempted to refer the 

 various described types of Obelia medusae to 

 their respective Hydroid stocks, basing his 

 distinctions on the length of the tentacles and 

 manubrium relatively to the umbrella radius, 

 and on the position of the ovaries on the 

 radial canals, i.e. whether in the proximal, 

 middle or distal thirds of the course of the 

 canals. As some of these differences are 

 known to be due to growth-changes, it is 

 doubtful how far they can be relied upon as 

 specific characters. The only safe plan of 

 identification will be to rear the medusse of 

 various Obelia colonies to maturity in aquaria, 

 until the characters of several species are 

 known at successive ages. 



B. Discomedusa 



2. Aurelia aurita (Linn.). 



Umbrella very slightly arched ; margin 

 beset with numerous very short tentacles and 

 notched at eight equidistant points ; transparent, 

 the ovaries showing through as four horse-shaped 

 masses of a violet or purplish colour. Com- 

 mon close around our coasts. The Pom- 

 merania met with this and the next species in 

 all parts of the North Sea, but the individuals 

 found far from shore were scattered and of 

 small size. 



3. Cyanea capillata (Linn.). 



Umbrella slightly arched, disc-shaped ; 

 margin divided as in Aurelia, but beset with 

 long slender tentacles. Colour usually 



yellowish brown or reddish yellow. Common 

 all round the North Sea. The beautiful blue 

 Cyanea Lamarckii is far rarer than the preced- 

 ing species, and has not yet been recorded for 

 Norfolk. 



C. Lucernarians 

 Sheringham has been reported as a good 



locality for Lucernarians, but I have no record 

 of the species found there. A minute long- 

 stalked Lucernarian obtained on the Norfolk 

 coast by Mr. Geldart appears to be a young 

 specimen of Depastrum cyathiforme, but the 

 record needs confirmation. 



II. CTENOPHORA 



Jeliyfishes devoid of a muscular umbrella 

 and provided with eight vertical (meridional) 

 rows of iridescent paddles. 



1 . Pleurohrachia pileus, Modeer. 



Shape ovoid ; size usually ^ to | inch. 

 Provided with a pair of flexible fringed retrac- 

 tile tentacles. Off Cromer and in Yarmouth 

 harbour, common (P.). 



2. Berce, probably ovata, Eschscholtz. 

 Shape cylindrical ; size usually from i to 3 



inches. No tentacles. Off Cromer, rare (P.). 



III. ANTHOZOA 



Sea Anemones and Corals 



Nomenclature : Gosse, British Sea Anemones 

 and Corals, i860. 



I. Alcyonium digitatutn. 



Commonly known as ' dead men's fingers,' 

 'cow's pap,' etc. Abundant in the deeper 

 waters, but not recorded nearer than twenty 

 miles north-west of Cromer (P.), though doubt- 

 less often cast ashore. 



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