| Obelia geniculata | |
|---|---|
 | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Cnidaria |
| Class: | Hydrozoa |
| Order: | Leptothecata |
| Family: | Campanulariidae |
| Genus: | Obelia |
| Species: | O. geniculata |
| Binomial name | |
| Obelia geniculata (Linnaeus, 1758) | |
Obelia geniculata is a species of cnidarian belonging to the family Campanulariidae. [1] Its common name is the Knotted Thread Hydroid. [2]
The species has cosmopolitan distribution. [1]
Estimates of divergence times and distinctive haplotypes provide evidence of glacial refugia around Iceland and southeastern Canada. In one study, O. geniculata was first documented in these areas in the 1990s but were later found in Massachusetts and Japan in the 2000s. There are three reciprocally monophyletic clades of Obelia, one branch for the North Atlantic, one for Japan, and one for New Zealand. [3] There seems to be an ancestral haplotype that occurs in the North Atlantic populations from Massachusetts, New Brunswick, and Iceland. The population from Woods Hole, MA shows less genetic diversity than the New Brunswick population. The more recent expansion of these haplotypes demonstrates the southward movement of hydroid populations, possibly due to climate change. The North Atlantic populations contain ancestral haplotypes, which differ from the populations in Japan and New Zealand. Pacific populations have more haplotype diversity than all four of the North Atlantic populations, which indicates that the North Atlantic population is more recently established than the Pacific population. [3] The minimum estimated age of the New Brunswick population is between 47 and 143 thousand years old. Including the Massachusetts population, this number is between 82 and 150 thousand years, but Iceland has the oldest estimated population with the minimum age ranging from 68 to 204 thousand years old. [3]
Obelia are distinguishable from others in Campanulariidae from their size in length and diameter, as well as their smaller hydrothecal cusps and relatively thinner perisarc thickness. Some morphological traits are hard to distinguish across species, so observing a combination of these traits will help with identification. Other useful observable characteristics are branching pattern of colonies and length of trophosome. There are variations and exceptions to these, which makes identification even more difficult. [4] O. geniculata is characterized by a thicker perisarc with more variation that other species of Obelia. O. longissima have longer first and second order branches, in addition to a greater variation in hydrothecal cusp length than others in the genus. O. bidentata differs from the previous species due to their more cylindrical and longer hydrothecal cusps. [4]
O. geniculata have two distinct forms – polyp and medusa, also known as hydranths and gonangia, respectively. [5]
The horizontal portion of the hydranth is called the hydrorhiza. [6] The hydrorhiza is the structure that attaches to the other hydranths as well as the substrate. For O. geniculata, the substrate is almost always leaves of plants since it is an epiphytic organism. [7] The vertical portion or main stalk of the hydranth form is called the hydrocalus, and it has two layers – the coenosarc and the perisarc. The coenosarc is the internal tube, containing the coelenteron, and the perisarc is the external layer secreted by the ectoderm. The mesoglea is located between these two layers. O. geniculata are distinguished from other Obelia species by the thickness of the perisarc; the perisarc on O. geniculata is much thicker than other species. [8] Branches of the hydranth stem from the hydrocalus, and each has a zooid at the end. There are two types of zooids: gastro-zooids and blastostyles. Gastro-zooids are feeding buds and make up the majority of the buds in the colony. The manubrium is hollow, contains the mouth, and is located at the distal end of the body and is surrounded by approximately 24 feeding tentacles. The hydrotheca is at the base of the gastro-zooid. It is a form of the perisarc. Blastostyles have no tentacles or mouth, a gonotheca instead of a hydrotheca, and a reduced coelenteron. [6] [9] [10] [11]
The gonangia is the result of the medusa buds being released from the hydranth blastostyles. [12] The body plan of the gonangia is fairly simple: the main body is shaped like a convex umbrella, with the manubrium hanging from the concave underside. The mouth is at the terminal end of the manubrium. In a newly-formed gonangia, there are 16 tentacles, but that can increase as they develop more. The mouth leads into the coelenteron, similarly to the hydranth, which then branches into 4 radial canals. The canals take the food around the entire body of the gonangia for full digestion. The endoderm of the gonangia is the inner lining to the canal system. The mesoglea can be found in the manubrium in between the endo- and ectoderm. The gonangia is also able to produce bioluminescence through a photoprotein called obelin. [13] For O. geniculata, the fluorescence is blue (λmax = 495 nm).
O. geniculata have no systems for excretion, circulation, or respiration. Both waste excretion and oxygen intake occur from gas exchange across the body surface. [6]
O. geniculata reproduce asexually through the budding of blastostyles. When the medusa buds are ready to be released from the blastostyle, the lateral wall will burst at the distal end. When the buds are free-floating, they are then classified as the gonangia. [9] [6] [12]
Gonangia reproduce sexually through broadcast spawning. Male and female gonangia will release their sperm and eggs into the water, and fertilized zygotes undergo complete cleavage until they become planular larvae. These planulae will then swim through the water until they find their spot on the substrate, and eventually grow into hydranths. [9] [6] [12]
Colonies of O. geniculata are sessile, so they feed through suspension feeding. In the polyp stage, feeding hydranths use their tentacles to bring food towards their mouths. Research has shown that the mouth opening and tentacle contraction are both governed by spontaneous electrical potentials, rather than knowingly. [10] The ends of the tentacles have nematocysts, which help in catching and stunning prey. [14] O. geniculata are typically voracious predators, and can consume a wide variety of bacteria, crustacean zoopankton, and icthyplankton. [15] [14] O. geniculata gonangia have also been seen to digest fecal pellets. [16] In situations of food stress, where the colonies are not getting enough food to sustain themselves, some research has shown that hydranths can create more gastro-zooids to increase the chances of getting food. [5] In areas of upwelling, O. geniculata are more abundant because of the increase in food availability. [16]
O. genicula are classified as epiphytic, meaning they encrust on plants in the water. Since they have a cosmopolitan distribution, meaning they are found basically everywhere, this can be hard for agriculture. In Korea, colonies of O. geniculata were found to infest areas of Saccharina japonica , a kelp that is widely consumed by humans in China and Japan. When there is too much O. geniculata encrusted on the kelp, it is no longer deemed suitable for human consumption by degrading the taste and quality. [17] [18] In Spain, O. geniculata was the most abundant epiphyte on two other types of kelp - Undaria pinnatifida and Saccharina latissima.
Cnidaria is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water and marine environments, including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are a decentralized nervous system distributed throughout a gelatinous body and the presence of cnidocytes or cnidoblasts, specialized cells with ejectable flagella used mainly for envenomation and capturing prey. Their bodies consist of mesoglea, a non-living, jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Cnidarians are also some of the few animals that can reproduce both sexually and asexually.
Hydra is a genus of small freshwater hydrozoans of the phylum Cnidaria. They are native to the temperate and tropical regions. The genus was named by Linnaeus in 1758 after the Hydra, which was the many-headed beast of myth defeated by Heracles, as when the animal has a part severed, it will regenerate much like the mythical hydra's heads. Biologists are especially interested in Hydra because of their regenerative ability; they do not appear to die of old age, or to age at all.
Hydrozoa is a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genera within this class live in freshwater habitats. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria.
Obelia is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyp and medusa stages in their life cycle. Hydrozoa belongs to the phylum Cnidaria, which are aquatic organisms that are relatively simple in structure with a diameter around 1mm. There are currently 120 known species, with more to be discovered. These species are grouped into three broad categories: O. bidentata, O. dichotoma, and O. geniculata. O. longissima was later accepted as a legitimate species, but taxonomy regarding the entire genus is debated over.
Gonionemus is a genus of hydrozoans that uses adhesive discs near the middle of each tentacle to attach to eelgrass, sea lettuce, or various types of algae instead of swimming. They are small and hard to see when hanging onto swaying seaweed. Nevertheless, they are capable of swimming when necessary. The bell is transparent, revealing the four orange to yellowish-tan gonads that lie along most of the length of the four radial canals. The pale yellow manubrium has four short, frilly lips. Up to 80 tentacles line the bell margin, with about an equal number of statocysts. Copepods are a favored prey.
Medusozoa is a clade in the phylum Cnidaria, and is often considered a subphylum. It includes the classes Hydrozoa, Scyphozoa, Staurozoa and Cubozoa, and possibly the parasitic Polypodiozoa. Medusozoans are distinguished by having a medusa stage in their often complex life cycle, a medusa typically being an umbrella-shaped body with stinging tentacles around the edge. With the exception of some Hydrozoa, all are called jellyfish in their free-swimming medusa phase.
Turritopsis dohrnii, also known as the immortal jellyfish, is a species of small, biologically immortal jellyfish found worldwide in temperate to tropic waters. It is one of the few known cases of animals capable of reverting completely to a sexually immature, colonial stage after having reached sexual maturity as a solitary individual.
Clytia gregaria, sometimes referred to as the gregarious jellyfish, is a small species of hydrozoan in the family Campanulariidae. It is one of the most abundant hydrozoans of the Pacific Northwest, particularly during late spring and summer.
Hydroidolina is a subclass of Hydrozoa and makes up 90% of the class. Controversy surrounds who the sister groups of Hydroidolina are, but research has shown that three orders remain consistent as direct relatives: Siphonophorae, Anthoathecata, and Leptothecata.
Leptothecata, or thecate hydroids, are an order of hydrozoans in the phylum Cnidaria. Their closest living relatives are the athecate hydroids, which are similar enough to have always been considered closely related, and the very apomorphic Siphonophorae, which were placed outside the "Hydroida". Given that there are no firm rules for synonymy for high-ranked taxa, alternative names like Leptomedusa, Thecaphora or Thecata, with or without the ending emended to "-ae", are also often used for Leptothecata.
Narcomedusae is an order of hydrozoans in the subclass Trachylinae. Members of this order do not normally have a polyp stage. The medusa has a dome-shaped bell with thin sides. The tentacles are attached above the lobed margin of the bell with usually a gastric pouch above each. There are no bulbs on the tentacles and no radial canals. Narcomedusans are mostly inhabitants of the open sea and deep waters. They can be found in the Mediterranean in large numbers.
A gonophore is a reproductive organ in members of the Hydrozoa which produces gametes. It is a sporosac, a medusa or any intermediate stage. The name is derived from the Greek words γόνος and -φόρος.
Bougainvillia aberrans is a marine invertebrate, a species of hydroid in the suborder Anthomedusae. It was first described by Dale Calder in 1993. They have four radical clusters of marginal tentacles. Bougainvillia aberrans is found in Bermuda in the western North Atlantic Ocean.
Eudendrium ramosum, sometimes known as the tree hydroid, is a marine species of cnidaria, a hydroid (Hydrozoa) in the family Eudendriidae of the order Anthoathecata.
Porpita prunella is a marine species of hydrozoan organisms within the family Porpitidae. It consists of colonies of zooids. Very little is known about this species, as there have been no confirmed sightings since its discovery in 1801 and naming by Haeckel in 1888. Being in the chondrophore group, it is likely that its behaviour is similar to the other species of the genera in the family. However there are also serious doubts as to its very existence as a separate species and may in fact be a synonym for Porpita porpita instead.
Obelia dichotoma is a broadly distributed, mainly marine but sometimes freshwater, colonial hydrozoan in the order Leptothecata that forms regular branching stems and a distinctive hydrotheca. O. dichotoma can be found in climates from the arctic to the tropics in protected waters such as marches and creeks but not near open coasts like beaches in depths up to 250m. O. dichotoma uses asexual and sexual reproduction and feeds on mainly zooplankton and fecal pellets. Obelia dichotoma has a complex relationship with the ecosystem and many economic systems.
Clava is a monotypic genus of hydrozoans in the family Hydractiniidae. It contains only one accepted species, Clava multicornis. Other names synonymous with Clava multicornis include Clava cornea, Clava diffusa, Clava leptostyla, Clava nodosa, Clava parasitica, Clava squamata, Coryne squamata, Hydra multicornis, and Hydra squamata. The larvae form of the species has a well developed nervous system compared to its small size. The adult form is also advanced due to its ability to stay dormant during unfavorable periods.
Zancleidae is a family of cnidarians belonging to the order Anthoathecata.
Lensia is a genus of hydrozoans belonging to the order Siphonoporae and the family Diphyidae. This genus is colonial and consists of many different types of highly specialized zooids. The genus Lensia was first established in 1932 by Dr. Arthur Knyvett Totton, who would also describe and add another 11 species during his career. As of March 2023, the genus consists of only 26 described and accepted species and an additional seven uncertain species, according to the World Register of Marine Species.
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