The Marine Life Information Network

Information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles


Growth form

Unitary An organism composed of a single functional entity i.e. a tree, a plant, a worm, a crab etc.  It may or may not be equivalent to 'individual'.
Modular An organism in which the zygote develops into a discrete unit which then produces more units like itself, forming a colony or modular structure, e.g. bryozoans and sea squirts.
The main visible parts of organism stand straight and above the substratum.
Arborescent / Arbuscular Having the shape or characteristics of a tree.
Forest A dense stand of large plants in which the upper branches (trees) or laminae (macroalgae) overlap to form a canopy that shades the under story of flora and fauna.
Shrub Having a very short stem with branches near the ground (Thompson, 1995).
Turf The lowest stratum of erect branching or filiform species.
Forms or resembles a crust over a substratum or other organisms.
Crustose soft Forming or resembling a crust (Thompson, 1995) that yields to the touch or pressure e.g. the gelatinous colonies of Botryllus schlosseri or soft cushions of sponges such as Halichondria sp.
Crustose hard Forming or resembling a crust (Thompson, 1995) that is solid or resistant to touch or pressure e.g. the encrusting coralline algae or sea mats.
Cushion A mass or pillow of soft material.
Mat A dense mass which blankets the substratum.
Vermiform unsegmented Worm-like where the external surface is divided into a chain of rings or 'annuli' by furrows giving the appearance of segments (Barnes et al., 1993).
Vermiform segmented Worm-like with the body divided into semi-independent, serially repeated units (Barnes et al., 1993) e.g. Annelida.
Vermiform annulated Worm-like where the external surface is divided into a chain of rings or 'annuli' by furrows giving the appearance of segments (Barnes et al., 1993).
Accretion Build up or accumulation of sediment.
Algal gravel Maerl; twig-like unattached (free-living) calcareous red algae, often a mixture of species and including species which form a spiky cover on loose small stones - 'hedgehog stones'.
Anchor-shaped E.g Ceratium spp.
Articulate Jointed, arthrous (Holmes, 1979).
Bivalved Characteristically a shell of two calcareous or chitinous valves joined by a flexible ligament.
Bullate / Saccate Balloon or sac-like (Prescott, 1969).
Capitate / Clubbed Enlarged or swollen at the apex, with a ‘head’, clubbed. (Prescott, 1969).
Chains Formed of chains of individuals.
Clathrate Latticed (Holmes, 1979).
Cone (conical) Cone shaped e.g. Limpet -shaped, patelliform, (adapted from Stachowitsch, 1992).
Cylindrical Straight sides and a circular section (Thompson, 1995).
Dendroid Branching irregularly – similar to that of a root system (Prescott, 1969).
Digitate Having parts arranged like fingers on a hand (Holmes, 1979).
Faunal beds Dense aggregation of animals that visually dominate the seabed or shore such as brittlestars (e.g. Ophiothrix fragilis) or mussels (e.g. Mytilus edulis).
Filiform / Filamentous Slender and thread-like (Kozloff, 1996).
Flabellate Flabellate, shaped like a fan, fanlike (Brusca, 1980).
Flaccid Soft, limp, flabby (Brusca, 1980).
Foliose Bearing leaves or leaf-like structures; having the appearance of a leaf.
Funnel shaped Shaped like a funnel.
Globose Approximately spherical / ovoid / globular (Brusca, 1980).
Lanceolate Lance shaped and usually elongate (Brusca, 1980).
Massive Large, heavy or solid (OED, 1990).
Medusiform / Medusoid Disk, bell or umbrella shaped and often gelatinous (Barnes et al., 1988).
Penicillate Brush like (Prescott ,1969).
Pinnate Branching like a feather – an elongate main axis with lateral branches or lobes (Prescott, 1969).
Pisciform Fish shaped
Radial Symmetrical about any plane passed perpendicular to the oral/aboral axis (Barnes et al., 1993).
Reticulate In the form of a mesh or net (Prescott, 1969).
Stellate Arranged like a star.
Strap-like / Ribbon-like In the form of a strap or ribbon.
Tadpole Having the body form of a tadpole i.e. consisting of a round head with a tail.
Turbinate Whorled (Brusca, 1980).
Whip-like Long and thin like a whip.


  • Barnes, R.S.K., Calow, P. & Olive P.J.W., 1993. The invertebrates: a new synthesis. Oxford: Blackwell Science Ltd.
  • Brusca, R.C., 1980. Common intertidal invertebrates of the Gulf of California. University of Arizona Press.
  • Holmes, S., 1979. Henderson’s dictionary of biological terms. 9th ed. London: Hendersons.
  • Kozloff, E.N., 1996. Marine invertebrates of the Pacific Northwest. Seattle: University of Washington Press.
  • Prescott, G.W., 1969. The algae: a review. Sunbury-upon-Thames: T. Nelson and Sons Ltd.
  • Stachowitsch, M., 1992. The invertebrates: an illustrated glossary. Chichester: John Wiley & Sons, Inc.
  • Thompson, D., (ed.) 1995. The Concise Oxford Dictionary of Current English. 9th ed. London: Oxford University Press.