Scyphomedusae of the German Bight
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| License | CC Attribution - NonCommercial - NoDerivatives 3.0 Germany: You are free to use, copy, distribute and transmit the work or content in unchanged form for any legal and non-commercial purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
| Identifiers | 10.3203/IWF/C-1803eng (DOI) | |
| IWF Signature | C 1803 | |
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| Production Year | 1991 |
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| IWF Technical Data | Film, 16 mm, LT, 204 m ; F, 19 min |
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Transcript: English(auto-generated)
01:04
In the coastal zones of the German Bight, the large siphon medusae commonly occur in the zooplankton. The rocky island of Heligoland offers a natural biotope for the sessile polyps. These are mainly found on various hard substrates in shallow water.
01:27
After strobeleting from the polyps, the apherae have developed into medusae. These can achieve diameters of several decimeters. In calm weather, they make their appearance near the surface of the sea, drifting together by wave action and currents.
01:49
The siphozoa are represented in the pelagic zone of the German Bight by five species. According to their mode of life, they differ in morphology, behaviour and seasonal occurrence.
02:03
This species has markings on the upper surface of the bell resembling a compass card. Chrysoaura hysocella, the sea nettle, often occurs in large numbers during the summer and autumn months. Characteristic features of chrysoaura are very long tentacles and oral arms.
02:29
The massive bell is filled with gelatinous mesoglia, containing cells. The sea nettle belongs to the order semiostomy, in which the manubrium is prolonged to form four pleated, pennant-like folds, the oral arms.
02:47
Along the reddish midrib of the oral arm, two folds of tissue arise and unite to form a frilly, marginal fold.
03:00
The tentacles of the sea nettle are inserted in the margin of the umbrella. They are arranged in eight bunches of three. A peripheral sensory organ, or ropallium, is located between each bunch of tentacles.
03:22
The female gonads are visible as milky yellow areas within the bell. In them, the eggs develop to form ciliated planular larvae, which are then released into the surrounding water. Chrysoaura is a protandric hermaphrodite. This young specimen has developed only male gonads.
03:43
The female sex organs will not mature until later. The male gonads, whitish testicular buds, are mainly produced in the central stomach.
04:01
In the sea nettle, the stomach opens into sixteen broad gastric pouches. The gastric filaments in the central stomach secrete digestive enzymes. Testicular buds can grow directly on the transparent gastric filaments.
04:24
The buds can also be found scattered in the adjacent gastric pouches. They are covered with spermatogenic follicles. The gastric pouches are separated from one another by narrow septa.
04:42
At the umbrella margin, either a tentacular bunch or a ropallium is allocated alternately to the pouches. Statoliths are lodged in the tip of each club-shaped ropallium. It responds to movements of the umbrella margin with a pendulum action.
05:00
Sensory receptors on the stalk of the club register the deflection of the pendulum. The tentacles, shown here in the contracted state, are liberally provided with nematocysts. They serve the purpose of prey capture.
05:20
In quest of food, the sea nettle swims through the water with its contractile tentacles relaxed. In the extended state, they can comb a large volume of water in search of prey.
05:49
Chrysaora feeds mainly on larger zooplankton such as hydro medusae or, as here, comb jellies.
06:02
Captured by the nematocysts, the prey animals cling to the tentacles, which contract. The prey is then taken up towards the bell and transferred to the mouth by the oral arms. A repetition of the process, capture of the prey, contraction of the tentacles, transfer of prey to the oral arms.
06:41
The broad oral arms encircle the prey organisms, here, hydro medusae. Digestion of the prey can already occur in the oral arms before the food is transferred to the gastric cavity. A further representative of the semiostomyae is the blue lion's mane jelly, Cyanea lamarchiae.
07:12
Young medusae can already be encountered in the plankton during the winter months. Though its diet resembles that of the sea nettle, Cyanea shows a different predatory behaviour pattern.
07:29
The medusae interrupts its active swimming movements and sinks passively while spreading its tentacles in a net-like fashion.
07:44
The oral arms in this species are short and densely folded. The tentacles are inserted in eight groups. They emerge from the sub-umbrella at the margin of the coronal muscle. Cyanea may have up to 500 tentacles.
08:07
The blue-tinted umbrella distinguishes adult specimens from the virulent red stinging jelly. The slightly pinkish gonads surround the oral arms.
08:22
In mature specimens, they are highly developed and project from the sub-umbrella like rupture sacs. The common jellyfish or moon jelly, Aurelia aurita, is also classified among the semiostomyae.
08:46
The first Ephyrae already strobolate from the polyps in the winter and develop to medusae during the spring. Aurelia's morphology is modified in accordance with its different feeding habits. The moon jelly can feed on micro-plankton, which it captures over its whole body surface, particularly the X-umbrella.
09:15
The marginal tentacles of Aurelia are short and very numerous.
09:24
The digestive cavity is produced into a wide-ranging system of branching canals. Currents caused by cilia action inside them ensure an even distribution of nutritive substances and elimination of excreta.
09:40
Through the translucent X-umbrella, four ear-shaped gonads are visible, which give the animal its Latin name. They lie on the floor of the gastric pouch above the subgenital pits. These are present in both semiostomyae and rhizostomyae.
10:02
Aurelia is dioecious like most siphomedusae. The oral arms of the female possess deep grooves, in which the ripe eggs are deposited. In these brood pouches, the fertilized eggs develop into ciliated planular larvae.
10:29
The abundant larvae give the oral arms of brooding females a brownish coloration.
10:47
Rhizostoma octopus is the only representative of the rhizostomyae inhabiting the pelagic zone of the German bite. Like the sea nettle, it makes its appearance in the summertime.
11:03
The massive, mushroom-shaped bell is devoid of tentacles. It can reach a diameter of up to 60 centimeters. In adaptation to its micro-planktonic style of feeding, the manubrium has become highly differentiated.
11:20
It is divided into eight branched oral arms, which are reinforced with colloidal cartilage. Above the oral arms, a ring of scapulates originates directly from the manubrium.
11:42
The oral arms and scapulates are traversed by a densely branched system of canals, which open into the environment via a large number of pores. The original single-mouth opening has developed into a polystomatous condition.
12:01
Through the smooth terminal appendage of each oral arm, a central canal opens to the exterior. The individual pores are surrounded by tentacular processes, called digitals. They form the frilled, saktorial mouths.
12:28
Prey organisms captured by the saktorial mouths, such as these Artemia larvae, are enveloped in mucus.
12:42
They pass through the pores into the adjacent canals. The food particles flow into the central canal and are transferred to the stomach cavity in the bell.
13:02
Food residues are also transported in the canal system and voided via the pores to the outside. The scapulates at the top of the oral arms also serve for food uptake.
13:21
The pulsations of the umbrella margin produce a water current which sweeps the food organisms in their direction. The small lapids on the rim of the umbrella are provided with numerous papillae containing nematocysts. These papillae are distributed over the entire surface of the umbrella.
13:47
The thin margins of the bell allow a view of the gastrovascular system. In Rhizostoma, it forms a fine network of canals. The peripheral sensory organs resemble those of other cyphermidusae in form and function.
14:06
They possess a sensory pit containing chemoreceptors. Above the ropallium, it is recessed into the X umbrella as a saddle-shaped depression.
14:20
More highly developed sensory organs are restricted to the medusa generation. They represent a form of adaptation to the animal's pelagic mode of life. In the German bite, there are, however, cyphozoans which retain the sessile habit of the polyps throughout their life cycle.
14:42
Their habitats are the algae-covered areas of the seabed near the coast, like the intertidal rocky foreshore off Heligoland. The tidal pools, which remain filled at ebb tide, are the habitat of Craterolophus tethys, the tethys cup jelly.
15:05
Here, it attaches to various species of brown, red or green algae. It is a member of the storo medusae. Its body is differentiated into a medusoid upper section and a polypoid peduncle, ending in a pedal disc.
15:24
This secretes an adhesive substance which anchors the animal to its substrate. The margin of the cup-shaped umbrella is prolonged into eight short adradial arms, bearing at their ends rigid capitate tentacles.
15:45
The tentacle caps are armed with nematocysts. A ropalloid, or adhesive body, is located in the indentation between two arms. It is a modified tentacular primordium. In Craterolophus tethys, it is, however, only a rudiment.
16:03
The peripheral sense organs of the pelagic medusae are absent in the stalked jellies. At the base of the funnel-shaped sub-umbrella is the forelobed manubrium.
16:21
Craterolophus tethys feeds on snails, mollusks and small crustaceans. Here, it is voiding the undigested remains of a shrimp. The paired gonads with their whitish germ glands can be seen shining through the sub-umbrella.
16:43
As these sessile jellyfish do not develop into pelagic medusae, they remain confined to one particular location.
17:00
They can be encountered all year round among the algae of the Heligoland foreshore. On account of their differing seasonal occurrence, the pelagic medusae of the cipher zones are also a permanent feature of the marine fauna in the German Bight.