Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help
Researched by | Nicola White | Refereed by | Dr Richard S.K. Barnes |
Authority | (Berrill, 1948) | ||
Other common names | - | Synonyms | Clavopsella navis (Millard, 1959), Rhizorhagium navis (Millard, 1959), Pachycordyle navis (Millard, 1959) |
A simple hydroid consisting of an erect, unbranched stem, up to 5 mm in height, with a single terminal polyp (hydranth) . Each upright stem rises from a creeping stolon (hydrorhiza). The stem is sheathed by a chitinous sheath, the perisarc. The perisarc is often wrinkled, especially near the base, and terminates below the hydranth. The hydranth bears 8 to 16 tentacles in 2 to 4 alternating whorls, depending on hydranth size. It is creamy white in colour, with hints of pink around the mouth of the hydranth. The reproductive bodies (gonophores) are borne on short stalks in an irregular spiral below the hydranth.
The systematic status of this species was revised by Stepanjants et al. (2000) who placed Clavopsella navis and Clavopsella quadrangularia in the new genus Thieliana. Subsequent revision by Schuchert (2004, 2007; cited in Calder, 2012) placed the species in the genus Pachycordyle. Pachycordyle navis was subsequently synonymized with Pachycordyle michaeli (WoRMS, 2021).
Phylum | Cnidaria | Sea anemones, corals, sea firs & jellyfish |
Class | Hydrozoa | White weeds, sea firs, sea beard and siphonophores; hydroids |
Order | Anthoathecata | |
Family | Bougainvilliidae | |
Genus | Pachycordyle | |
Authority | (Berrill, 1948) | |
Recent Synonyms | Clavopsella navis (Millard, 1959)Rhizorhagium navis (Millard, 1959)Pachycordyle navis (Millard, 1959) |
Typical abundance | Data deficient | ||
Male size range | 0.39-1.29mm | ||
Male size at maturity | |||
Female size range | Very small(<1cm) | ||
Female size at maturity | |||
Growth form | Turf | ||
Growth rate | Data deficient | ||
Body flexibility | |||
Mobility | |||
Characteristic feeding method | No information, Passive suspension feeder, Predator | ||
Diet/food source | |||
Typically feeds on | |||
Sociability | |||
Environmental position | Epifaunal | ||
Dependency | - | ||
Supports | - | ||
Is the species harmful? | Data deficient |
Size refers to length of hydranth.
Physiographic preferences | Isolated saline water (Lagoon) |
Biological zone preferences | Data deficient |
Substratum / habitat preferences | Macroalgae |
Tidal strength preferences | Weak < 1 knot (<0.5 m/sec.) |
Wave exposure preferences | Very sheltered |
Salinity preferences | Reduced (18-30 psu) |
Depth range | |
Other preferences | No text entered |
Migration Pattern | Non-migratory / resident |
Reproductive type | Gonochoristic (dioecious) | |
Reproductive frequency | ||
Fecundity (number of eggs) | 2-10 | |
Generation time | Insufficient information | |
Age at maturity | ||
Season | Insufficient information | |
Life span | Insufficient information |
Larval/propagule type | - |
Larval/juvenile development | |
Duration of larval stage | No information |
Larval dispersal potential | No information |
Larval settlement period |
The MarLIN sensitivity assessment approach used below has been superseded by the MarESA (Marine Evidence-based Sensitivity Assessment) approach (see menu). The MarLIN approach was used for assessments from 1999-2010. The MarESA approach reflects the recent conservation imperatives and terminology and is used for sensitivity assessments from 2014 onwards.
Intolerance | Recoverability | Sensitivity | Evidence/Confidence | |
High | None | Very High | Very low | |
Pachycordyle navis lives attached to algae, so would be removed with the algae upon substratum loss. There would be no recovery of the population because only two extant populations of Pachycordyle navis are known: Widewater lagoon, Sussex and Kiel Canal, Germany. | ||||
Intermediate | Low | High | Very low | |
The species would be affected by smothering if the algae on which it lives is completely covered in the sediment. If the algae protrudes sufficiently above the sediment the hydroid may escape the effects of smothering. | ||||
Intermediate | Very low / none | High | Very low | |
Pachycordyle navis is likely to have some tolerance to siltation as it inhabits lagoons where siltation frequently occurs. The algae on which the species lives will also lift the hydroid above the accumulation of silt. However, the heath of the host algae may be adversely affected by siltation. | ||||
No information | ||||
Intermediate | None | Very High | Very low | |
The species is vulnerable to desiccation because it is soft bodied and has no protection from the drying effects of sun and wind. Some of the population may be sheltered from desiccation if they are present on the underside of the algal frond. However, if the whole population is destroyed recoverability would be non-existent because only two populations of Thieliana navis occur worldwide. | ||||
Intermediate | None | Very High | Very low | |
The species is vulnerable to emergence because it is soft bodied and has no protection from desiccation. Some of the population may be sheltered from desiccation if they are present on the underside of the algal frond. However, if the whole population is destroyed recoverability would be very low because only two populations of Pachycordyle navis occur worldwide. | ||||
No information | ||||
Tolerant | Not relevant | Not sensitive | Very low | |
The species would probably not be affected by a change in water flow because it is permanently attached to the algae and may be able to withstand high water flow rates because they have been transported long distances on ships hulls. | ||||
No information | ||||
No information | Not relevant | No information | Very low | |
The temperature resistance of the Pachycordyle navis is not known. | ||||
No information | ||||
Low | Moderate | Low | Very low | |
The species is unlikely to be affected by a change in turbidity as it is not dependant on light availability and it would not interfere with its feeding. However, the host algae may be adversely affected by a reduction in light availability. | ||||
No information | ||||
Tolerant | Not relevant | Not sensitive | Very low | |
A change in wave exposure is unlikely to occur in a lagoon unless one of the lagoon boundaries is breached. The species would probably not be affected by an increase in wave exposure because it does not present a large surface area to wave action. However, it's host algae may be intolerant of wave exposure and may be washed away. | ||||
No information | ||||
No information | Not relevant | No information | Very low | |
Insufficient | ||||
No information | Not relevant | No information | Very low | |
Insufficient | ||||
High | Low | High | Very low | |
The species and its host algae are flexible so will 'give' under abrasion. However, they occur on top of the sediment and would probably be removed, along with surface substratum by a passing scallop dredge (or equivalent force). The impact is likely to be equivalent to substratum loss. Therefore, an intolerance of high has been recorded. | ||||
High | None | Very High | Very low | |
Pachycordyle navis is permanently attached to algae and would be unable to re-attach itself if removed. If the whole population is destroyed recoverability would be very low because only two populations of Pachycordyle navis occur worldwide. |
Intolerance | Recoverability | Sensitivity | Evidence/Confidence | |
No information | Not relevant | No information | Very low | |
Insufficient | ||||
No information | Not relevant | No information | Not relevant | |
Insufficient | ||||
No information | Not relevant | No information | Not relevant | |
Insufficient | ||||
No information | Not relevant | No information | Not relevant | |
Insufficient | ||||
No information | Not relevant | No information | Not relevant | |
Insufficient | ||||
No information | Not relevant | No information | Not relevant | |
Evidence suggests that the species is tolerant of fully saline conditions because it can survive on ships hulls. The species must be tolerant of reduced salinity because it occurs in lagoons but the tolerance of the species to very reduced salinities is not known. | ||||
No information | ||||
No information | Not relevant | No information | Not relevant | |
Insufficient |
Intolerance | Recoverability | Sensitivity | Evidence/Confidence | |
No information | Not relevant | No information | Not relevant | |
Insufficient | ||||
No information | Not relevant | No information | Not relevant | |
Insufficient | ||||
No information | Not relevant | No information | Not relevant | |
Insufficient | ||||
No information | Not relevant | No information | Not relevant | |
Insufficient |
Wildlife & Countryside Act | Schedule 5, section 9 |
UK Biodiversity Action Plan Priority | |
Species of principal importance (England) |
National (GB) importance | Not rare/scarce | Global red list (IUCN) category | - |
Native | - | ||
Origin | - | Date Arrived | 1973 |
Anonymous, 1999s. Saline lagoons. Habitat Action Plan. In UK Biodiversity Group. Tranche 2 Action Plans. English Nature for the UK Biodiversity Group, Peterborough., English Nature for the UK Biodiversity Group, Peterborough.
Barnes, R.S.K., 1994. The brackish-water fauna of northwestern Europe. Cambridge: Cambridge University Press.
Boero, F., 1984. The ecology of marine hydroids and effects of environmental factors: a review. Marine Ecology, 5, 93-118.
Eno, N.C., Clark, R.A. & Sanderson, W.G. (ed.) 1997. Non-native marine species in British waters: a review and directory. Peterborough: Joint Nature Conservation Committee.
Gili, J-M. & Hughes, R.G., 1995. The ecology of marine benthic hydroids. Oceanography and Marine Biology: an Annual Review, 33, 351-426.
Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]
Millard, N.A.H., 1975. Monograph of the Hydroida of Southern Africa. Annals of the South Africa Museum, 68, 1-513.
Reise, K., Gollasch, S. & Wolff, W.J., 1999. Introduced species of the North Sea coasts. Helgoland Meeresuntersuchungen, 52, 219-234.
Sheader, M. & Sheader, A., 1990. A survey of Widewater saline lagoon to determine the current status of the site, with special reference to Ivell's sea anemone, Edwardsia ivelli. Preliminary Report, Peterborough. Nature Conservancy Council. NCC CSD Report 1176.
Sommer, C., 1992. Larval biology and dispersal of Eudendrium racemosum (Hydrozoa, Eudendriidae). Scientia Marina, 56, 205-211. [Proceedings of 2nd International Workshop of the Hydrozoan Society, Spain, September 1991. Aspects of hydrozoan biology (ed. J. Bouillon, F. Cicognia, J.M. Gili & R.G. Hughes).]
Stephanjants, S.D., Timoshkin, O.A., Anokhin, B.A. & Napara, T.A., 2000. A new species of Pachycordyle (Hydrozoa, Clavidae) from Lake Biwa (Japan), with remarks on this and related Clavid genera. Scientia Marina, 64 (Suppl. 1), 225-236.
NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.
OBIS (Ocean Biodiversity Information System), 2023. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2023-03-25
This review can be cited as:
Last Updated: 24/06/2005