Morphology and Reproduction of Hydrozoa
This is a modal window.
The media could not be loaded, either because the server or network failed or because the format is not supported.
Formal Metadata
| Title |
| |
| Alternative Title |
| |
| Author | ||
| License | No Open Access License: German copyright law applies. This film may be used for your own use but it may not be distributed via the internet or passed on to external parties. This film contains music to which the collecting society GEMA holds the rights. | |
| Identifiers | 10.3203/IWF/C-1687eng (DOI) | |
| IWF Signature | C 1687 | |
| Publisher | ||
| Release Date | ||
| Language | ||
| Other Version | ||
| Producer | ||
| Production Year | 1989 |
Technical Metadata
| IWF Technical Data | Film, 16 mm, LT, 186 m ; F, 17 1/2 min |
Content Metadata
| Subject Area | ||
| Genre | ||
| Abstract |
| |
| Keywords | ||
| IWF Classification |
Transcript: English(auto-generated)
00:33
Morphology and reproduction of the hydrozoa. Besides the anthozoa, which have never had medusae,
00:47
here for example, Itasia, three more classes of diploblastic animals which normally produce medusae are included in the phylum Cnidaria. Today the ciphozoa are considered to be the phylogenetically most basal class. The cipho polyps exhibit tetramerous symmetry evidenced
01:07
by the four gastric septae and the four septal funnels. The polyps produce ephyrae by strobilation, a modified transverse division. Those ephyrae grow up to medusae which have no velum.
01:31
They serve for spreading and sexual reproduction. The cubozoa are separated from
01:43
the ciphozoa. Their polyps exhibit radial symmetry. The cubomedusae are products of a metamorphosis. The tetramerous symmetry becomes visible during this process and remains in the medusae. The third class of metagenetic cnidarians are the hydrozoa
02:12
in which the polyps are radially symmetric. Hydro medusae are born by budding. A typical medusae is radially symmetric, in many cases tetra-radial, shown here by the radial canals.
02:26
In general, a velum is present. The hydrozoa are the most polymorphic class of metagenetic cnidarians. The ficate hydroids have a well-developed chitinous exoskeleton, the so-called periderm. The annulations of the periderm provide useful taxonomic characters.
02:47
The hydro-thesae contain the polyps which can stretch out the tentacles or retreat into the theca. These of the size we see here are not present in all genera of thecates.
03:03
The so-called athicates lack a protecting hydro theca for retraction of the polyp. The periderm ends below the hydrants in clava multicornis, shown here,
03:22
just above the stolons. The very variable tentacles of the polyps can be filiform. In this type, the nematocysts are scattered over the whole length of the tentacle. The capitate tentacles are mostly shorter and end in a knob-like battery of sting cells.
03:47
Both types can occur side by side on one polyp, like in Cladonema. The capitate tentacles
04:05
surrounding the mouth catch the prey, while the filiform ones at the basal part of the hydrants serve for sensory purposes. The just stretching tentacles of Gonothyria are arranged in one whorl. The single whorl of tentacles and the trumpet-shaped or conical
04:23
hyper-stone are characteristic for thecates. In the ontogenesis of most thecates, all tentacles develop simultaneously. The young polyp of Irenae viridula, however, completes the whorl
04:50
of tentacles later. The bases of the tentacles in this species are connected by an intertentacular web called the umbrella. The ontogenesis of the tentacles of the athecates follows another
05:11
pattern. They are developed one after another, and new single tentacles are added during growth of the polyp. Among the athecates there are species with two whorls of tentacles,
05:46
and species with tentacles scattered over most of the hydrants, sometimes filiform ones as in lava, or capitates as in Korine tubulosa. Only a few hydrazone species have solitary polyps.
06:08
They can multiply by asexual budding. The liberated bud again is a solitary polyp. In some
06:24
species, buds of the polyps do not differentiate but are mobile. They continue development into polyps if they reach a favorable growth location. Most of the hydrazone
06:45
species are colonial. In stolonial colonies, the main expansion is horizontal and the hydrants arise direct from the common hydro riser. Other species have erect colonies with an upright
07:03
ramified hydrocollis bearing the polyps. In the plumulary, the organization of the colony is feather-like, hence more complicated. Many species have a distinct polymorphism with division
07:33
of labor. The essential tasks such as catching prey, feeding, propagation, and defense are
07:40
distributed among different shaped polyps. In the genus Thecocodium, we find special gastrozooids. They have a very elastic mouth. Nematocysts are only arranged around the mouth opening. The feeding individuals lack tentacles but are able to produce medusa buds if conditions
08:14
are favorable. Therefore, they are called gastrogonozooids. In the colony, those polyps
08:25
are in the minority. About 10 times more small polyps with tentacles are present. In the species Thecocodium penicillatum, the tentacles form a bunch. In the species quadratum, the four or seldom five tentacles form an oral whirl. These macozooids are considerably smaller
08:44
than the gastrogonozooids. The catching and defensive individuals show a solid core of entoderm cells. If they have caught some prey, the gastrozooids bend down to take over
09:08
and ingest it. On buxinum shells inhabited by hermit crabs, a spinous brownish covering is
09:44
to be found. This is the skeleton of a hydrozoan colony. Between these spines, the polyps of Hydractynia echinata find a degree of protection against predators. Besides the siphonophora, this species has reached the culmination of polymorphism in hydrozoa. There are polyps which
10:06
only serve propagation and others for feeding with a well-developed whirl of tentacles.
10:24
Defensive individuals are the spiral zooids without mouth and tentacles but a gastric cavity.
10:41
The more slender tentacular zooids have a solid entoderm, no mouth and no tentacles. Medusae of the hydrozoa are borne by budding but are still capable of feeding. The medusae are radially symmetric, mostly with four radial canals. From the bell margin
11:04
a velum projects inwards and demarcates a sub-umbrella cavity useful for increasing the repulsion. Originally there are four marginal tentacles which secondarily can increase considerably in number.
11:23
Around the margin runs the ring canal. So-called tentacle bulbs are to be seen where the radial canals communicate with the ring canal. The canal system serves distribution of pre-digested food to the places of requirement. Besides the statocysts,
11:47
occasionally ocelli are placed at the bell margin as in Ratchea octopunctata. Very rarely the medusa generation can propagate asexually. Above the eight-mouth tentacles,
12:06
Ratchea produces buds which develop into gonads if the temperature is higher than six degrees Celsius. But below six degrees they become medusae. As mentioned before, hydrozoans produce
12:28
medusae budding at the hydrants or, as in Loicatiara, from the stolons.
12:43
Under culture conditions the medusae become mature in three or four months. The fertilized eggs develop into planulae which after settling grow out to a new polyp. This regular alternation between a sessile asexual and a planktonic
13:01
sexual generation is called metagenesis. In many species the complete metagenesis is reduced to a varying degree. Such a reduction can be observed in the species Lovenae. Besides hydro-thesae with feeding polyps, the gonangia develop inside special
13:22
gonothesae. Below a tissue operculum the gonophores are budding from a central axis, the blastostyle. Sperms and eggs, as shown here, develop inside the gonophores. When the gonads
13:51
become mature the gonophores are pushed out of the gonothesae and, in this case, are called mechanidia. In these fixed eumidusae, the umbrella of the degenerate medusa and vestigial
14:05
tentacles are still to be seen. The sexes are separate but without sexual dimorphism. The males, shown here, release their sperm into the water. Fertilization and development of the moving planulae takes place inside the female gonophores. A higher degree of
14:27
reduction of the gonophores is reached in clover multicornis. Development of gonophores starts with small buds on the body wall of the hydranth below the tentacles.
14:43
The male ones become styloids. In the outer gonophores the white mass of sperm can already be seen. Blue cryptomedusoids with two eggs each are characteristic for the females.
15:03
Fertilization occurs inside the female gonophores. The long orange planulae of this species also develop inside. The highest degree of reduction of metagenesis is reached in hydra. In this genus gonads appear with only a few accessory cells in the ectoderm of the hydranth.
15:24
Hydra oligactis at first produces sperm recognizable as a white mass in the bulges of the body wall. Later the same individual produces eggs. Hydra oligactis is therefore a protoandric hermaphrodite. Hydra has no planktonic stages so it can even colonize
15:42
flowing waters.