Radial – radiating from the apex or umbone to the outer margin.

Radiation – the increase in numbers of a new species and its spread into new habitats.

Radula – ribbon-shaped membrane with transverse rows of many small hard teeth, attached to floor of the inner mouth of molluscs (except bivalves) and used in rasping food.

Raised – projecting above the surface.

Ramus – a branch e.g. of an appendage.

Range – the natural geographical limits in which a species occurs, including migratory pathways.

Recessed – shorter than adjacent structures.

Repress – to prevent the natural or normal occurrence (abundance) of (an organism).

Reef – an organic, wave resistant, shallow-water structure.

Resilium – elastic, cartilage lodged in the chondrophone; internal part of the ligament.

Respiration – the energy releasing oxidation of organic material.

Reticulate – netted.

Retractile – capable of being drawn back or in.

Rheobiontic – occurring only in flowing water.

Rheophilous – occurring mainly in flowing water, but may also be found in standing water.

Rib, riblet – continuous ridge, usually radial or axial.

Rostrum – also called beak or snout, a forward extension of the upper jaw.

Rugose – wrinkled.

Sailing – raising the flukes vertically into the wind for an extended period and moving through the water as if sailing.

Salinity – total amount of dissolved solids in sea water.  Measured in parts per thousand.

Salp – transparent, barrel-shaped or fusiform free-swimming tunicates.

Saprophilic – usually occurring in organically polluted water, accompanied by brief periods of dissolved oxygen concentrations below 5.0 mg/l, pH changes of up to 2 units, and/or temperatures exceeding 25 C; also present in limited numbers in clean water habitats.

Saprophobic – restricted to waters that have not been polluted organically.

Saprophytes – organisms that feed by uptake of dissolved organic materials.

Saproxenous – occurring mainly in clean water habitats but also tolerant of some organic enrichment if the dissolved oxygen concentration remains above 5.0 mb/l and pH and temperature are not adversely altered.

Scar – striated impression in inner surface of shell marking point of attachment of muscle(s) closing the valves.

Sclerotized – hardened.

SCUBA – self contained underwater breathing apparatus.

Scythe – a mowing implement with a long, curving blade.

Seamount – an isolated underwater mountain of volcanic origin, rising more than 1,000 m above the ocean floor and usually 1,000 to 2,000 m below the ocean surface.

Secondary production – production by heterotrophs.

Serrated, serrulate – sharply toothed or notched; finely or minutely serrate.

Sessile – attached to the substratum.

Seston – suspended particulate matter in water.

Setae – bristle or stiff hairlike structures.

Sexual dimorphism – the differences in size, shape, or color between males and females that occur in any population.

Shoulder – upper edge of the whorl, next to the suture.

Simple – without branches or subdivisions.

Sinistral – twisting to the left.  Anti-clockwise.

Sinuate – wavy; S-shaped.

Sinus – cavity or indentation.

Siphon – extensible fleshy tube through which the mollusc takes in or emits water.

Songs – the complex pattern of low-frequency grunts, squeals, whistles, wails, and chirps such as those produced by male humpback whales.  The songs have predictable patterns, although, in the case of humpbacks, they change over time.

Spermaceti – the high-quality oil found in the melon of the sperm whale.  It was once used to make fine candles and later, industrial lubricant.

Spicules – skeletal needle like structures as in sponges.

Spiral – parallel to the sutures; along the whorl or coil.

Splash guard – in some whales it is the raised area in front of the blow-hole that prevents water entering when the nasal plug is retracted for breathing.

Spyhopping – raising the head vertically out of the water, usually while stationary then sinking below the surface without much splash.

Stellate – star-shaped.

Stenobathic – having a limited range of depth tolerance.

Stenohaline – having a limited range of salinity tolerance.

Stenothermal – having a limited range of temperature tolerance.

Stranding – the coming to land, either dead or alive, of a cetacean.  A mass stranding involves 3 or more animals with strandings of up to 400 recorded.  Species usually found in deep waters away from coastlines, such as pilot, false killer, melon-headed, and sperm whales strand most often; coastal species, such as humpback and southern right whales, rarely strand.

Striate – crossed by lines or grooves.

Styliform – dagger shaped.

Sub – almost, nearly; e.g. sub-truncate: nearly cut off squarely at tip; subovate; almost egg-shaped.

Subequal – approximately or almost equal in size or length.

Sublittoral zone – also called continental shelf, the area extending from immediately below the littoral zone to the edge of the continental slope.

Substrate – a surface on which the organism feeds.

Substratum – a surface of seabed, lakebed or riverbed.

Succession – the orderly process of change from a pioneer community to a climax community.

Suction feeding – feeding by using the tongue and throat muscles to create a rapid inrush of water that sucks up nearby prey.

Suture – line of junction between whorls.

Symbiosis – where organisms live together to their mutual benefit.

Symbiotic relationship – a situation in which plants or animals of different species live together in a mutually advantageous relationship.

Sympatric – with overlapping geographical distributions.

Taxon – a kind of organism; any taxonomic unit of classification e.g. species, genus, family, order, etc.

Taxonomy – the science of classifying all living things by arranging them in groups according to the relationship of each to the others.

Telson – the posterior end of the body of higher crustaceans.

Test – the hard exoskeleton of small animals.

Thermocline – zone of rapid vertical temperature change in water.

Thermohaline – pertaining to density currents.

Thread – thin connecting ridge.

Tidal Bore – high, breaking wave that advances up an estuary as the tide rises.

Tide – cyclic rising and falling of the ocean due to gravitational pulls of the moon, sun and earth.

Tooth – a small projection; interlocking projections of the bivalve hinge; those near the umbone are cardinal teeth; those on either side are the lateral teeth.

Tooth raking – aggressive interaction in toothed whales resulting in linear scars left by teeth.

Toxic – poisonous.

Transverse – across; crosswise.

Trifid – split into 3 branches or processes.

Trigonal – three-sided; triangular.

Trophic level – feeding level. Link in food chain.

Trucate – square-ended; opposite to rounded.

Truncate – cut off squarely at tip.

Tsunami – “Tidal” or seismic wave.

Tube feet – small, fleshy, sucker-like, locomotory appendages of echinoderms.

Tubercles – circular bumps on the surface of the skin along the flippers and dorsal fins of some cetaceans.

Tubule – a soft, fleshy projection.

Tunicate – marine chordate animals with a thick covering layer, including sea squirts; of the subphylum Urochordata.

Turbid – thick or opaque with suspended materials; roiled; muddy.

Turnover – mixing of water due to lack of a pycnocline.