MarLIN Glossary

Glossary items

pallial line

The mark on the inside of a bivalve shell at the position of attachment of the mantle. It is normally concentric and joins the anterior and posterior adductors muscle scars. It may be indented by the pallial sinus, and exceptionally in is made up of a series of separate muscle scars (Tebble, 1976).


Singular of 'palps'.


In Pycnogonida, the second pair of appendages on the body between the chelifores and oviger (Stachowitsch, 1992).


A minute rounded, nipple-like, protuberance on a part or organ of the body (OED, 1990)


Plural of 'papilla'.


Plural of 'papule'.


A small, solid elevation of the skin (Hayward & Ryland, 1995).

paralytic shellfish poisoning

A serious illness affecting organisms with higher nervous systems (vertebrates) caused by eating shellfish which have themselves consumed toxin-producing micro-organisms (usually certain phytoplankton species) and have bioaccumulated the toxins.


Quantity constant in case considered, but varying in different cases (Thompson, 1995). An arbitrary constant, as distinguished from a fixed or absolute constant. Any desired numerical value can be given to a parameter. The term is also used to describe a definable characteristic of an item, device or system (Considine, 1976). A variable in terms of which it is convenient to express other interrelated variables which may then be regarded as being dependent upon the parameter (Chambers & Chambers, 1971).


Plural of 'parapodium'.


1) Lateral appendage of segments in annelids, supported by aciculum and bearing chaetae. Composed of two lobes, the dorsal notopodium and ventral neuropodium. May also bear gills and cirri in some species of annelid. 2) One of two lateral lobes of the posterior division of the foot in gastropod molluscs, which may be used to cover the shell or as a swimming organ (Stachowitsch, 1992).


An organism that lives in or on another living organism (the host), from which it obtains food and other requirements. The host does not benefit from the association and is usually harmed by it. (cf. commensalism, mutualism, symbiosis).


A form of asexual multiplication in which the ovum develops into a new individual without fertilization (Barnes et al., 1993).


Of sediment particles - the main characteristic for classifying rock-derived sediments. By granulometric analysis (q.v.), it is possible to distinguish: clay (< 0.004 mm); silt (0.0625-0.004 mm); sand (0.0625 mm - 1 mm); granules (2-4 mm); pebbles (4 mm - 64 mm); cobbles (64-256 mm), and boulders (> 256 mm) (based on Wentworth, 1922). The MNCR habitat classification combines or subdivides these categories to separate substratum types in a biologically meaningful way (see descriptions in this glossary and Hiscock, 1990).

particle-size distribution

Percentage (by weight) of sediment particles of each grain-size fraction.

Particularly Sensitive Sea Area

An area that needs special protection through action by IMO because of its significance for recognised ecological or socio-economic or scientific reasons and which may be vulnerable to environmental damage by maritime traffic (IMO, 1991).

pear shaped

In the shape of a pear.


A pure organic soil, the result of plant material accumulating in waterlogged conditions (from Fitter & Manuel, 1986).


Rock particle 16-64 mm in diameter (from Hiscock, 1990, based on Wentworth, 1922.)


Relating to the lower front or chest region of an animal (OED, 2005).


Of Echinodermta (echinoderms); a pincer or grasping organ. The simplest are formed by two adjacent spines, while most are stalked and have a head composed of three calcareous valves, controlled by muscles (Southward & Campbell, 2006).


Plural of 'pedicellaria'.


1) Of Crustacea - a stalk like part of the body (Barnes et al., 1993). 2) Of Brachiopoda - a fleshy cuticle covered stalk by which the brachiopod attachesitself to the substratum (Stachowitsch, 1992). 3) Of Isopoda - Proximal division of antennule or antenna. Typically consists of three segments in antennule, five segments in antenna (Stachowitsch, 1992). 


With the body borne on a stalk (see peduncle).

peeler crab

A recently-moulted crab, normally a shore crab Carcinus maenas, which is still soft-shelled and suitable for use by anglers as bait.


Inhabiting the open sea, excluding the sea floor.

pelagic zone

The open sea and ocean, excluding the sea bottom. Pelagic organisms inhabit such open waters.


Brush like (Prescott,   1969).


The segmented upper body of Malacostraca crustaceans, split into eight segments (Barnes et al., 1993).


In amphipods, one of seven segments between the head and the abdomen (adapted from Stachowitsch, 1992).


Forked limbs of Malacostaca crustaceans, used for locomotion and feeding (Barnes et al., 1993).


Proteinaceous outer layer of the shell, which is sometimes thick or sometimes almost transparent depending on the species.  It frequently flakes off or is eroded and is not retained in dead shells (Tebble, 1976).


The chitinous exoskeleton of a hydroid (Cornelius, 1995).


The continued presence of species or communities at a location (usually inferring in spite of disturbance or change in conditions) (cf. 'constancy', 'stability', 'resilience').

photic zone

The surface layer of the sea or a lake having sufficient light penetration for photosynthesis; cf. dysphotic zone (from Lincoln et al., 1998).


Thriving in conditions of strong light (cf. 'sciophilous').


The biochemical process that utilizes radiant energy from sunlight to synthesize carbohydrates from carbon dioxide and water in the presence of chlorophyll and other photopigments (based on Lincoln et al., 1998).


Plural of 'Phylum'


A major taxonomic division containing one or more classes.


(as prefix, e.g. phytobenthos, phytoplankton) Pertaining to plants.


Planktonic plant life: typically comprising suspended or motile microscopic algal cells such as diatoms, dinoflagellates and desmids (based on Lincoln & Boxshall, 1987).


Branching like a feather - an elongate main axis with lateral branches or lobes (Prescott, 1969).


In the shape of a fish.


Organisms which drift in the water column and have limited powers of locomotion in comparison with the horizontal water movements. Many benthic animals have planktonic larvae which act as a dispersive phase. (See also holoplankton, meroplankton). (Based on Hawkins & Jones, 1992.) (Cf. 'nekton').

plankton bloom

1) A seasonal increase in the abundance of plankton. 2) A superabundance of one or more species of planktonic organism, often resulting in a discoloration or opacity of the water, or of macroalgae; can be a consequence of eutrophication.


Feeding at least in part on materials captured from the plankton (cf. lecithotrophic) (Barnes et al., 1993).


Describes an animal which feeds on plankton (Lincoln et al., 1998).


The segmented lower body of Malacostraca crustaceans, split into six segments (Barnes et al., 1993).


In crustaceans the individual segments which make up the pleon.


In crustaceans, it is a limb eminating from the abdominal area (Hayward & Ryland, 1995).


Plural of 'pleopod'.


Isopoda - Terminal structure of body formed by fusion of one or more abdominal segments (pleonites) with telson (Stachowitsch, 1992). 


Buoyant organisms subject to wind drift. (Baretta-Bekker et al., 1992).

pock mark

A relatively small depression in the sea-floor, formed by expulsion of gas and/or liquid through the seabed displacing sediment and leaving a crater (based on Dando et al., 1991) (cf. 'bubbling reef').

pocket beach

A beach contained within bounding headlands; a cove (based on Pethick, 1984).


A term used of organisms having body fluids that conform to external changes in salinity (from Lincoln et al., 1998).


A relatively short, relatively shallow fjord, with a sill at its entrance at a depth less than that of the pycnocline (q.v.) (based on Earll & Pagett, 1984).

pollution (marine)

"The introduction by man, directly or indirectly, of substances or energy into the marine environment (including estuaries) resulting in such deleterious effects as harm to living resources, hazards to human health, hindrance to marine activities including fishing, impairment of quality for use of seawater and reduction of amenities." (Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection - GESAMP, 1995).


The Class Polychaeta (Phylum Annelida) are a group of truly segmented worms, characterized by extensions of each segment called 'parapodia' that bear bundles of bristles, hence the term 'many bristled' or 'poly' 'chaeta'. Cf. bristleworm.


A general term for members of the Class Polychaeta (Phylum Annelida).


Plural of 'polychaete'.


Pertaining to brackish water having a salinity between 18 ‰ and 30 ‰ (from McLusky, 1993).


Occurrence of different forms (usually morphological) of individuals of the same species.


The internal organs of bryozoans, including the nervous system, muscles, lophophore and digestive tract (Stachowitsch, 1992).


Plural of 'polypide'.


All individuals of one species occupying a defined area and usually isolated to some degree from other similar groups (from Lincoln & Boxshall, 1987).


The setting of traps (pots) on the seabed to fish for lobsters, crabs, etc. (see also 'creeling').

precautionary principle

A principle underlying the concept of sustainable use of resources, which implies that:
a) Prudent action be taken in the absence of scientific certainty;
b) The balance of the burden of proof between the requirement to prove significant damage and the requirement to show no irreversible harm be encouraged;
c) Environmental well-being be given legitimate status and best-practice techniques be developed (from WWF, 1994).


An organism that feeds by preying on other organisms, killing them for food (Lincoln et al., 1998).


Generally most anterior of the bones forming gill cover (Abercrombie et al., 1973).


The mechanism through which an activity has an effect on any part of the ecosystem. The nature of the pressure is determined by activity type, intensity and distribution (Robinson et al., 2008).


Bivalved shell formed by larva prior to metamorphosis. It may be possible to distinguish an earlier, smaller prodissoconch I from a later, larger prodissoconch II that encloses the entire animal (Stachowitsch, 1992) (see 'protoconch').


Any part of an organism, produced sexually or asexually, that is capable of giving rise to a new individual (Lincoln et al., 1998).


The segment of a decapod crustacean leg which is immediately below the claw.


A condition of hermaphroditism in plants and animals where male gametes mature and are shed before female gametes mature (Holmes, 1979).


Any organism belonging to the kingdom Protista, including bacteria, protozoans, unicellular algae and fungi, regarded as distinct from plants and animals (from Makins, 1991).


The first shell laid down by the veliger larvae of gastropods (Barnes, 1980) (see 'prodissoconch').


A condition of hermaphroditism in plants and animals where female gametes mature and are shed before male gametes mature (Holmes, 1979).


paralytic shellfish poisoning.


A horizontal boundary layer in the water column at which water density changes sharply with depth, as a result of either a halocline or a thermocline, or both acting together. See 'stratification'.


The general term for members of the Class Pyncogonida (Phylum Chelicerata).


The Class Pycnogonida (Phylum Chelicerata) have slim bodies divided into a head and a segmented trunk with eight, often slender, legs that give them a superficial resemblance to true spiders, e.g. %Nymphon gracile%.


Plural of 'pycnogonid'.


The last (terminal) non-segmental part of a segmented animal (e.g. Annelida) which usually bears the anus (Ruppert & Barnes, 1994).

pyloric caeca

Blind sacs attached to the section of the intestinal tract immediately following the stomach (Hayward & Ryland, 1995).