I bought back to Lichfield a sample of water/material from the beach at Bognor Regis and today looked at this under my Leitz Laborlux 11 microscope.
Small piece of red algal seaweed.
These are most probably Red Algae, or Rhodophyta. From Wikipedia (https://en.wikipedia.org/wiki/Red_algae), Rodophyta means ‘rose plant’. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species . The majority of species (6,793) are found in the Florideophyceae (class), and mostly consist of multicellular, marine algae, including many notable seaweeds. Approximately 5% of the red algae occur in freshwater environments with greater concentrations found in the warmer area. There are no terrestrial species, which is assumed to be traced back to an evolutionary bottleneck where the last common ancestor lost about 25% of its core genes and much of its evolutionary plasticity.
The red algae form a distinct group characterized by having eukaryotic cells without flagella and centrioles, chloroplasts that lack external endoplasmic reticulum and contain unstacked (stoma) thylakoids, and use phycobiliproteins as accessory pigments, which give them their red color. Red algae store sugars as floridean starch, which is a type of starch that consists of highly branched amylopectin without amylose, as food reserves outside their plastids. Most red algae are also multicellular, macroscopic, marine, and reproduce sexually. The red algal life history is typically an alternation of generations that may have three generations rather than two.
See also https://www.countrylife.co.uk/nature/a-simple-guide-to-british-seaweed-how-to-spot-it-how-to-cook-it-159632 for simple guide to UK seaweeds.
x4 objective showing the tendrils of seaweed – individual cells are seen:
x10 objective – the individual cells now look like bones in the hand:
x40 objective showing structure in an individual cell – cell wall surrounds the cell and their are clear differences between the terminal ends of the cell and its middle part:
Sediment at bottom of pool in sand adjacent to wooden structure on shore.
x10 objective showing sand grains with some attached green algal growth:
x10 objective showing plant matter on top of sand grain:
x40 objective showing green algal seaweed attached to edge of sand grain:
x40 objective showing microscopic algal plant matter on a sand grain:
x40 objective – close up of green algal free floating plant cell pairing: