At a cellular level, there appear to be two main " designs " of eyes, one possessed by the protostomes ( molluscs, annelid worms and arthropods ), the other by the deuterostomes ( chordates and echinoderms ).
42.
When the first thorough examination of " Opabinia " in 1975 revealed its unusual features, it was thought to be unrelated to any known phylum, although possibly related to a hypothetical ancestor of arthropods and of annelid worms.
43.
He argues that the supposed " radula " is nothing of the sort; he classifies " Odontogriphus " as a basal lophotrochozoan, in other words close to the last common ancestor of molluscs, annelid worms and brachiopods.
44.
Grouping animals with these body plans resulted in four " embranchements " or branches ( vertebrates, molluscs, the articulata that he claimed were natural ( arguing that insects and annelid worms were related ) and zoophytes ( radiata ) ).
45.
Fragmentation, also known as splitting, as a method of reproduction is seen in many organisms such as filamentous cyanobacteria, molds, lichens, many plants, and animals such as sponges, acoel flatworms, some annelid worms and sea stars.
46.
The male incubates the eggs, usually four, in a nest on the ground or floating for about 20 days . All three species live in reedy swamps, and their diet consists of annelid worms and other invertebrates, which they find with their long bills.
47.
"Spriggina "'s affinity is currently unknown; it has been classified as an annelid worm, a rangeomorph-like frond, a variant of " Charniodiscus ", a proarticulatan, or an arthropod perhaps related to the trilobites, or even an extinct phylum.
48.
Originally it was known from only one specimen, but 189 new finds in the years immediately preceding 2006 made a detailed description possible . ( ) As a result, " Odontogriphus " has become prominent in the debate that has gone on since 1990 about the evolutionary origins of molluscs, annelid worms and brachiopods.
49.
Later, more specific similarities were discovered : for example, the Distal-less gene was found in 1989 to be involved in the development of appendages or limbs in fruit flies, the fins of fish, the wings of chickens, the parapodia of marine annelid worms, the ampullae and siphons of tunicates, and the tube feet of sea urchins.
50.
The cladogram they presented showed the halkieriids split into three groups : one as " aunts " of brachiopods, animals whose modern forms have bivalve shells but differ from molluscs in having muscular stalks and a distinctive feeding apparatus, the lophophore; the second group of halkieriids as " aunts " of both " Wiwaxia " and annelid worms; and the earliest halkieriids as " great aunts " of all of these.
