Species
Hydrozoa
IUCN
NCBI
EOL Text
Despite their protective stinging cells, hydrozoans are prey for many types of predators. A variety of snails and worms graze on polyps and stolons, as do some fish and crustaceans. Fish also consume medusae and pelagic colonial hydrozoans, as do some sea turtles (especially leatherbacks), ctenophores, and other cnidarians, including larger hydrozoans.
A variety of predators have the ability to consume the stinging cells of hydrozoans without triggering them. These predators then sequester the stinging cells in their body to defend them against their own predators. Nudibranchs are particularly well known for this ability, but some species of ctenophores, turbellarian flatworms, and priapulids can store cnidocysts as well.
Nearly all hydrozoans protect themselves with their cnidocysts. Some colonial species have specialized polyps that grow large tentacles armed with dense batteries of these stinging cells or grow large rigid spines. Many colonial polyps secrete a rigid protective layer over stolons and polyp tubes. This layer is often made of chitin, some groups produce a mineral skeleton. Free-swimming medusae cannot use rigid protection, but do defend themselves with stinging cells. There is evidence that some also contain toxic compounds that discourage predators from eating them. Most hydrozoan medusae also follow the diel migration pattern common to many planktonic organisms -- sinking below the limit of light penetration to avoid visual predators during the day, and then rising towards the surface at night in pursuit of prey.
Known Predators:
- leatherback sea turtle (Dermochelys coriacea)
- Nudibranchia
- Ctenophora
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Rights holder/Author | ©1995-2013, The Regents of the University of Michigan and its licensors |
Source | http://animaldiversity.ummz.umich.edu/accounts/Hydrozoa/ |
Animal / predator
adult of Velutina plicatilis is predator of Hydrozoa
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Source | http://www.bioimages.org.uk/html/Hydrozoa.htm |
Hydrozoa (Hydroids) preys on:
Crangon
Mysidae
Gammaridae
Hyperiidae
Caprellidae
Isopoda
Based on studies in:
USA, Northeastern US contintental shelf (Coastal)
This list may not be complete but is based on published studies.
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Rights holder/Author | Cynthia Sims Parr, Joel Sachs, SPIRE |
Source | http://spire.umbc.edu/fwc/ |
Hydrozoa (Hydroids) is prey of:
Pollachius pollachius
Merluccius bilinearis
Urophycis regia
Urophycis tenuis
Urophycis chuss
Gadidae
Melanogrammus aeglefinus
Hemitripterus americanus
Myoxocephalus octodecemspinosus
Leucoraja erinacea
Leucoraja ocellata
Amblyraja radiata
Macrozoarces americanus
Anarhichas
Tautogolabrus adspersus
Sebastes marinus
Pleuronectes ferrugineus
Scophthalmus aquosus
Paralichthys dentatus
Glyptocephalus cynoglossus
Hippoglossina oblonga
Pleuronectes americanus
Hippoglossoides platessoides
Hippoglossus hippoglossus
Mustelus canis
Squalus acanthias
Lophius americanus
Based on studies in:
USA, Northeastern US contintental shelf (Coastal)
This list may not be complete but is based on published studies.
License | http://creativecommons.org/licenses/by/3.0/ |
Rights holder/Author | Cynthia Sims Parr, Joel Sachs, SPIRE |
Source | http://spire.umbc.edu/fwc/ |
All hydrozoans have tactile and chemical sensing structures. Some also have eyespots that detect light, and/or statocysts that detect gravity. They communicate mainly by chemical signals. Some free-swimming hydrozoans, including many siphonophores have bioluminescent structures. It's not known what function these serve. It is unlikely that they communicate with other hydrozoans (their light sensors are too simple for this). Possibly they are lures for prey or have some predator defense function.
Communication Channels: visual ; chemical
Other Communication Modes: photic/bioluminescent ; pheromones
Perception Channels: visual ; tactile ; chemical
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Rights holder/Author | ©1995-2013, The Regents of the University of Michigan and its licensors |
Source | http://animaldiversity.ummz.umich.edu/accounts/Hydrozoa/ |
Hydrozoans have a complex life cycle, usually with two or three morphologically different stages. The classic cycle starts with fertilized eggs developing into small, free swimming larvae called planulae, which may be able to enter a dormant resting state to resist unsuitable environmental conditions. Planulae transform into sessile polyps, usually attached to substrate, but free-floating in some groups. Polyps duplicate themselves asexually by budding, often producing colonies of hundreds or thousands of polymorphic individual polyps. Polyps produce "adult" sexually-reproducing medusae by budding. Medusae are solitary, free-swimming, dieocious. They release sperm and eggs into the water, where fertilization occurs. This is the basic cycle, but there is an enormous range of variations. In nearly half of species (e.g. Hydra) the the medusa stage is entirely suppressed; polyps produce gametes directly. In others the medusa are formed, but never detach from the parent polyp, and produce gametes while still attached. In some cases these fused combinations form elaborate structures. In other taxa the polyp stage is suppressed, and planulae transform directly into tiny medusae, or form a polyp, produce a medusa, and resorb the polyp. Numerous taxa have suppressed the planula as well.
Development - Life Cycle: metamorphosis ; colonial growth
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Rights holder/Author | ©1995-2013, The Regents of the University of Michigan and its licensors |
Source | http://animaldiversity.ummz.umich.edu/accounts/Hydrozoa/ |
Hydrozoans are mostly broadcast spawners. In some species only sperm is shed, and eggs are retained on the parent. Eggs release sperm-attracting compounds.
Mating System: polygynandrous (promiscuous)
Hydrozoan polyps reproduce asexually by budding, creating daughter polyps, medusae, or both. In some species medusae reproduce asexually as well, by fission or budding. Medusae (if present in the life cycle) or polyps produce gametes. Most hydrozoan species are dioecious, a few are sequential hermaphrodites. Eggs and sperm are most often released into the water column and fertilization is external. In some species eggs are retained and fertilized internally, in which case embryos may be releases as larvae or retained until even more developed.
Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sequential hermaphrodite; sexual ; asexual ; fertilization (External , Internal ); ovoviviparous ; oviparous
Most hydrozoan species have minimal parental investment. Eggs and sperm are released into the water, and left to survive on their own. In a few species, eggs are retained in special structures on the parent, and the embryos are retained as brood, developing to the planula or even young polyp stage. In the latter case we have no information on whether the young are nourished by their parent, or just protected.
Parental Investment: no parental involvement; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female)
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Rights holder/Author | ©1995-2013, The Regents of the University of Michigan and its licensors |
Source | http://animaldiversity.ummz.umich.edu/accounts/Hydrozoa/ |
recent & fossil
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Rights holder/Author | This work is licensed under a Creative Commons Attribution-Share Alike 4.0 License |
Source | http://www.marinespecies.org/aphia.php?p=taxdetails&id=1337 |
Barcode of Life Data Systems (BOLD) Stats
Specimen Records:2856
Specimens with Sequences:2059
Specimens with Barcodes:1544
Species:402
Species With Barcodes:297
Public Records:1557
Public Species:259
Public BINs:380
The Hydrozoa is a subgroup of cnidarians containging approximately 3700 species. It is a diverse group with a variety of life cycles, growth forms, and specialized structures. Like many cnidarians, hydrozoans have both polyp and medusa stages in their life cycle. They are distinguished from other groups by their complex life cycle, by the growth of medusae from buds rather than strobilae or from metamorphosis, by the presence of a velum inside the bell of the medusa, and by the production of gametes from ectodermal, rather than endodermal, tissue. Most hydrozoans are marine, and hydrozoan species are found in nearly every marine habitat type; a very few species live in freshwater. Most hydrozoans form colonies of asexual polyps and free-swimming sexual medusae. Colonies are usually benthic, but some, notably the siphonophores, are pelagic floaters. Colonial polyps often have some division of function, with certain polyps specialized for defense, feeding, or reproduction. Most hydrozoans are predators or filter-feeders, though a few have symbiotic algae (zooxanthellae), in the same way that other other groups of cnidarians do.
Better-known hydrozoans include Portuguese man-o-wars (Physalia physalis), the freshwater genus Hydra, fire coral (Milleporidae), and by-the-wind sailors (Velella velella).
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Rights holder/Author | ©1995-2013, The Regents of the University of Michigan and its licensors |
Source | http://animaldiversity.ummz.umich.edu/accounts/Hydrozoa/ |