As two pigmented taxa attributed to the class Chrysophyceae had been discovered (Lackey, 1939; Scagel & Stein, 1961) with apparently similar organization to the Choanoflagellida this group of protista was included in the Revised Check-list of British Marine Algae (Parke & Dixon, 1964) following Bourrelly (1957). The group was placed in the class Craspedophyceae erected by Chadefaud (1960) and a first revision of the genus and species list was included in the Check-list of British Marine Algae - Second Revision (Parke & Dixon, 1968).

The order Isochrysidales was erected by Pascher in 1910 to accommodate chrysomonads with two equal flagella. It was based on the family Hymenomonadaceae (Senn, 1900) and included such genera as Synura Ehrenberg (later shown to be heterokont and therefore incorrectly placed here; Hovasse, 1949; Manton, 1955), Wyssotzkia Lemmermann and Hymenomonas Stein. Papenfuss (1955) used the name in a similar sense but encompassing also the coccolithophorids, while those genera with two equal flagella and a ‘short third flagellum’ ((Prymnesium Massart, Platychrysis N. Carter, Chrysochromulina Lackey) were placed in the order Prymnesiales. Subsequently it was demonstrated that members of the Isochrysidales and Prymnesiales differ from other chrysomonads in that the two true flag-ella are smooth with no coarse hairs (‘mastigonemes’) and that the third appendage found in genera of the latter order is a unique structure, termed the ‘haptonema’ by Parke, Manton & Clarke (1955). On the basis of these observations, Christensen (1962) erected a new class, the Haptophyceae (now referred to by the typified name Prymnesiophyceae; Hibberd, 1976 a), to contain the two orders although Bourrelly (1968) preferred to retain them within the Chrysophyceae whilst recognizing their unique status by the erection of a sub-class, the Isochrysophycidae.

Tube-dwelling diatoms are found in a variety of habitats, from marine to fresh water on different types of substrata; rock, wood, plant and animal. I have described species as tube-dwelling (Cox, 1975 b) if they produce mucilage which is consolidated into a tubular structure around the cells, yet within the mucilage tube individual cells move and divide. The tube is usually attached to the substratum at its base and is extended apically by the secretion of more mucilage by the enclosed diatoms. Tube volume thus increases to accommodate the increased endotubular diatom population. The presence of tube-dwelling diatoms on rocky shores has been recorded by some workers (Aleem, 1949, 1950; Castenholz, 1963, 1967; Hopkins, 1964), while Castenholz (1963, 1967) correlated seasonal and distribution patterns of some littoral species with their response to light intensity and day-length. Carter (1932,1933) described the algal flora, including several tube-dwelling species, of two salt marshes but little work has been done on tube-dwelling diatoms occurring in estuaries. During the course of a study on the biology of these diatoms (Cox, 1975 ft) variation in their distribution at two Severn Estuary sites prompted an investigation into their distribution in the estuary as a whole. Diatom distribution was recorded with reference to the geographical location in the estuary and to the position on the shore at two sites lower down the estuary (Clevedon and Weston-Super-Mare).

On 11 August 1976 an observant yachtsman noted an unfamiliar alga between Misery Point and Warren Point at the mouth of the River Yealm. Suspecting that it might be ‘Japweed’ he collected a piece and took it to Mr B. W. P. Sparrow of the International Marine Coatings Laboratory who contacted the Marine Biological Association, where Dr Boalch confirmed that it was a part of a fertile plant of Sargassum muticum, the first to be recorded from the Plymouth area (see Fig. 1).

In spite of the controversy surrounding the accidental introduction of the Japanese seaweed Sargassutn muticum (Yendo) Fensholt onto two continents, the startling south-ward expansion of its range on the Pacific coast of North America (Norton, 1977 a), and the failure of an eradication campaign on the south coast of England, surprisingly little is known about the ecology of this species. Work has recently begun in both southern California and Britain (Nicholson et al. 1977; Lewey & Farnham, 1977). Unfortunately the ecological studies in Britain have been hampered by the conflicting aims of trying to study the plant and at the same time trying to eradicate it.

Mesodinium rubrum is a marine planktonic holotrich ciliate of extremely wide geographical distribution which has often been found to be associated with ‘red water’ phenomena (Taylor, Blackbourn & Blackbourn, 1971). It has mainly been recorded from extremely neritic locations such as bays and fjords; away from the coast it is usually associated with regions of upwelling and in such conditions the blooms have been recorded as extending over areas as large as 100 square miles (Ryther, 1967). Fifty instances of the occurrence of M. rubrum are usefully summarized by Taylor et al. (1971).

The study reported here stems from experiments performed upon cirripedes and bivalve molluscs exposed to fluctuating sea water concentrations. It is obvious that these two groups of benthic organisms are capable of shutting themselves off to a greater or lesser degree from the external environment by opercular or shell valve closure, thus avoiding the osmotic stresses associated with exposure to lowered salinity levels. With the development by Davenport, Gruffydd & Beaumont (1975) of an apparatus to deliver fluctuating salinity regimes to experimental animals in a repeatable, routine manner, it has become possible to establish the sea-water concentrations at which such mechanisms operate.

A map of the Looe Estuary in south-east Cornwall is shown in Fig. 1. As it flows to the western branch of the estuary, the West Looe River passes through the Herodsfoot mining area which lies about 5 km above Sowden's Bridge. By Cornish standards, this was a productive area for lead and Dewey (1921) gives the output of Herodsfoot mine as 13470 tons of metal between 1848 and 1884 and more than 17 tons of silver between 1853 and 1884.

The intertidal phyllodocid polychaete Eulalia viridis (O. F. Müller) is widely regarded as a predator as stated, for example, by Newell (1970). This assertion is based on statements made by several authors, e.g. Moore & Kitching (1939), Glynne-Williams & Hobart (1952), Connell (1961), and Kensler (1964, 1967), who have reported E. viridis foraging over rocky substrates at low tide in daylight and in some cases have observed the insertion of the proboscis between the opercular plates of a barnacle and the subsequent ingestion of the soft tissues. The capture of a large chironomid by E. viridis has been recorded by Connell (1961). This was considered sufficient evidence for stating that E. viridis is a predator attacking living barnacles and other intertidal animals. Moore & Kitching (1939) further suggested that E. viridis might be as important a predator on barnacles as Thais lapillus (L). On the other hand Michel (1970) regarded E. viridis as a scavenger feeding on dead and decaying animals. There is evident disagreement about the feeding habits of E. viridis and consequently of its role in the population ecology of the community of which it forms a part. Examination of its feeding behaviour has been undertaken to clarify the situation.

The observations of Schlieper (1929) established the lugworm Arenicola marina (L.) as an osmoconformer which remains virtually isosmotic with the external medium over a wide range of salinities. In a recent comprehensive review of salt and water balance in lugworms, Oglesby (1973) describes ‘the extensive swelling associated with transfer of lugworms to lower salinities’, and ‘when maintained in salinities lower than about 50% s.w. in the laboratory, lugworms are rendered incapable of such vital physiological activities as burrowing and burrow ventilation’. Under these conditions, lugworms exhibit little or no ability to regulate their volume or water content.

The taxonomy and distribution of sipunculan species in the shallow-water zone (< 200 m depth) of European seas are fairly well-documented. One notable exception is Phascolosoma intermedium, a small-sized species described by Southern (1913 a) from material dredged off the west coast of Ireland at 44–143 m depth. Since its description, no further specimens of P. intermedium have been reported in the region and the species was not considered by Stephen (1960) in his synopsis of the British species.

The spermatophore in the Copepoda is an elongated flask-shaped object produced by the male copepod in which are contained the sperm and associated secretions. The male must attach the spermatophore to the female genital segment in such a position that the opening to the neck of the spermatophore, through which the sperm come out, is in contact with the opening of the female cavity. Placement of the spermatophore elsewhere, in such a manner that connexion with the female genital cavity is not achieved, may not cause fertilization and will waste sperm.

A population of the two species, Nephtys hombergii Savigny and N. caeca Fabricius, has been studied for a period of 3 years. Three separate but related aspects of the biology of these species have been investigated; gametogenesis (Olive, 1976a, and in preparation), reproductive endocrinology (Olive, 1976 a, b) and the life-history and population structure which is the subject of the present report. Nephtys species are particularly interesting for studies of this kind since Kirkegaard (1970) described rings in the teeth of N. hombergii which were thought to represent annual growth rings. Estcourt (1975) has found that these rings can be used to age the nephtyid species Aglaophamus verrilli in New Zealand which is a slow growing species living to at least 5 years of age. The degree of overlap between the successive generations, as indicated by the rings in the teeth, emphasizes how difficult age analysis of populations with this type of growth is without additional information of this kind. This problem is particularly acute in long lived polytelic (= iteroparous, Gadgil & Bossert, 1970) species. Olive (1975) has discussed the problem with reference to Eulalia viridis and other recently investigated polychaetes but it is not peculiar to Polychaeta as, for instance, Lewis & Bowman (1975) have shown in a particularly detailed study of populations of Patella vulgata.

The polychaete Capitella capitata (Fabricius) has become well known amongst marine biologists as an indicator of polluted conditions, especially those due to organic enrichment. Reish (1959) mapped zones in a polluted harbour and correlated the presence of C. capitata with the polluted region. Bellan (1967) and Cognetti (1972) drew similar conclusions and Henriksson (1969) describes the species as a bacterial pollution indicator. Pearson (1975) records its presence in areas enriched by pulp mill effluents and Rosenberg (1972, 1973) notes its importance in the pioneer community developing after the closure of a pulp mill.

The ability of the slipper limpet Crepidula fornicata L. to feed on suspended particles carried into the mantle cavity by cilia on the gill has attracted attention for many years since the feeding mechanism was described by Orton (1912). Subsequent studies were made on the possible origins of this mode of feeding (Yonge, 1928, 1938), and later Werner (1951, 1952, 1953, 1955, 1959) made more detailed observations on the mechanisms by which particles are retained by the animal. He showed that coarse particles are strained by means of a mucus filter covering the inhalant aperture to the mantle cavity, whilst the majority of the medium and fine particles are entangled by a second mucus filter secreted by an endostyle and which lies against the frontal surface of the gill (for review, see Jørgensen, 1966; Newell, 1970).

Preliminary feeding experiments (Morris, Ferguson & Raymont, 1973) showed that Neomysis integer was capable of incorporating dietary labelled [1-14C]fatty acids (16:04 18:1,18:2,18:3) into its lipid. Radioactivity was observed in all the major fatty acids of Neomysis, including the polyunsaturated fatty acids. Neomysis could also convert dietary 14C-labelled starch into lipid, producing a range of fatty acids, including long-chain polyunsaturated acids, incorporated in both triglycerides and phospholipids. During these metabolic conversions, the mysid was observed to incorporate more radioactive14C into the phospholipid fraction with increase in the experimental feeding period.

Information on the littoral fauna of Rockall (lat. 57° 36′ 20” N, long. 13° 41′ 32” W) is limited to the report by Crisp (1956) on a collection made during the occasion of the annexation of Rockall to the British Crown in 1955. An historical survey (Fisher, 1956) reveals that only once previously has a marine biological (phycological) collection been taken from the rock, during a landing from the French’ Pourquoi-Pas ?’ in 1921 (Charcot, 1921; Hamel, 1922).

Members of the small suborder Runcinacea have recently been reviewed and efforts have been made to group new findings (Burn, 1963; Baba, 1967; Miller & Rudman, 1968). The following structures served for the classification: gills alone (Baba, 1967), gills, radula, gizzard-plates and shell (Burn, 1963). According to this classification a more detailed subdivision became necessary. Two proposals brought forward by Burn (1963) and Baba (1967) are in discussion (see below). Two new genera Runnica and Pseudoilbia (Miller & Rudman, 1968) have not as yet been definitely placed in a family. As a consequence of this grouping some of the former members of the genus Runcina have been moved to another genus, e.g. Runcina elioti (Baba, 1937) to Runcinida (Burn, 1963) by reason of four or five gills surrounding the anus in a semi-circle, and Runcina setoensis (Baba, 1954; Ghiselin, 1963) to Metaruncina setoensis (Baba, 1967) because of its single gill and a greatly reduced radula (compare Table 1).

The prosobranch snail, Hydrobia ulvae, lays eggs on the shells of neighbouring individuals where they are held together and protected by a covering of sand grains. The eggs develop within this egg mass, hatching as veliger larvae for which there are several descriptions (Henking, 1894; Thorson, 1946; Pilkington, 1971; Fish & Fish, 1974). It is clear that there is considerable variation in the size, pigmentation and swimming behaviour of veligers from different localities. The material used in the present study was from a population of snails in the Dovey estuary, Wales, which have free-swimming veliger larvae similar to those described by Thorson (1946). These have a single whorl to the shell; a shell length at hatching of 140–170 µm; a semi-lunate band of purplish black pigment on each velar lobe; a narrow band of pigment between the eyes and black pigment associated with the hindermost part of the intestine. In contrast, those from Ply-mouth hatch with one and a half shell whorls and a colourless velum (Lebour, 1937; Pilkington, 1971); a shell length of 340–390 µm and show complete suppression of the pelagic phase, the velar cilia being short and incapable of lifting the larva off the bottom (Pilkington, 1971). It has been suggested by Pilkington (1971) that the differences in size and swimming behaviour might be the result of the Plymouth larvae hatching at a later stage. The present account is the result of investigations into the effects of temperature and salinity on the survival of embryos to hatching and the duration of embryonic development.

Brood protection is characteristic of the Spirorbinae although the mode of protection differs widely between species (Bailey, 1969; Knight-Jones, Knight-Jones & Vine, 1972). The way in which these protected eggs are successfully fertilized has been a subject of speculation (Gee & Williams, 1965; Franzen, 1956; Potswald, 1968). Individuals of the Spirorbinae are simultaneous hermaphrodites and the possible role of self-fertilization in their reproduction has been considered (Gee & Williams, 1965; Potswald, 1968). In the past, these problems have been discussed with the tacit assumption that no spermatheca is present in the Spirorbinae.