Polychaete Worms

Vermes is an obsolete taxon used to group all non-arthropod invertebrates together.  Here the Class Annelides has now been promoted to the Phylum Annelida.  The order Polychaetae errantes is now classified as the Class Polychaeta.  The Annelida are the segmented worms (arguably some memberts have lost segmentation) with the polychaetes being the bristle-worms, both the formal and informal names refer to the many rigid bristles which extend from each segment’s parapodia.  This chart shows adult sand worms (1, 2, 3 & 9) but the group also include burrowing and tube building worms.  Annelids have a closed circulatory system which is highlited in the by the vessels (red), a partitioned through-gut (yellow) and cephalisation (concentration at the anterior end) of sensory organs (6 & 8).

Peanut Worms (Sipunculids and Echiurans)

The now obsolete taxon of Vermes once encompassed all non-arthropod invertebrates.  This wall chart compares two different phyla of worm; sipunculids and echiurans.  Both groups have previously been classified with in the Annelida despite their lacking the segmentation and bristled parapodia characteristic of this group. They are now both classified as seperate phyla within a group known as the Lophotrochozoa based on both larval development (14 & 15) and ribosomal DNA evidence.  A typical sipunculid (peanut worm) has an introvertible anterior region often with a crest of tentacles (1, 2, & 3). Different species burrow into sediments, rocks or calcified organic structures with the anterior end protruding. Echiurans are found in soft sediments with a long proboscis extending to the surface of the sediment where organic particles settle down onto a ciliated gutter which moves food to the mouth via the proboscis (10).

Tusk Shells (Scaphopoda)

The Scaphopoda, or tusk shells, are a basal form of mollusk which filter feed on detritus and foraminifera from the surface of soft sediments.  The muscular foot (1P) anchors the anterior end of the body in the sediment while the apical (narrow) end protrudes the surface.  Water is drawn into the mantle cavity, which has no gills, via the apical opening using cillia.  Food particles are sorted from sediment before a muscular contraction ejects  the water back out the same opening.  This diagram shows an adult laterally within its shell (1) and ventrally without a shell (2) where blue represents nervous tissue, red is blood vessels, green is gonad and yellow is the digestive system which is shown isolated in higher magnification (3).  Further illustrations show a detailed progression of development (4-11).

Bryozoans (Ectoprocts) & Entoprocts

This wall chart shows the colonial nature of the so called moss animals. Note the position of the anus on many of the adults as this feature is their namesake; those with the anus within the crown of tentacles are Entoprocta (ento – within; proct – anus) those with the anus outside of the crown of tentacles are Ectoprocta (ecto – outside; procta – anus).There is large debate about the relationships of the two groups Ectoprocta and Endoprocta.  There are many similarities in superficial structures and morphology, however these similarities often mask dissimilarities such as the feeding crown of tentacles (lophophore/lophophore-like structure) which operates in opposing directions between the two groups.  Molecular data suggests these two are distinct phyla however many skeptics still class them together within Bryozoa.

Anodonta cygnea (freshwater mussel)

Commonly used as an examplar of it’s family, this fresh water mussel has a wide range across the whole of northern europe from the British Isles across to Siberia and down to Northern Africa.  There are many synonyms for this one species.  The top diagram shows the musculature of the mussel including the anterior and posterior adductor muscles used to keep the valves together (A.Ad & P.Ad), retractor muscles used to retract the foot (A.R & P.R) and the foot protractor muscle (Pr).  The middle diagram is of the scarring from muscles left behind in a shell once the soft tissue has been removed.  The bottom diagram focuses on the dorsal edge of the mussel to show the pericardium (Pc) a clear window which reveals the heart (Au & V) and the Keber’s organ, also known as the Organ of Bojanus (O.Bj).

Mytilus / Pecten

Generalised internal structures of two bivalve genera Mytilus (mussels) and Pecten (scallops) with left valve removed.  Structures are not labelled but easy to describe from the illustrations are the gut (yellow tubes with bulbous swellings), adductor muscle (large round pink structure with brown dots), gill (green on Mytilus grey on Pecten with lines running perpedicular to the length of the structure).

Gastropod Larvae

This chart compares development of a generic gastropod larva (fig. I & II) illustrating the velum and formation of the mantle cavity and operculum.  The third image is the larva of a sea butterfly, the classification of which remains confused to this day.  Sea butterflies were thought to be similar to sea angels because of their flapping appendages developed from the food however these two groups are now thought to be quite different.  Note the position of the forming mantle cavity relative to the operculum and velum between I & III, the sea butterfly has not undergone torsion.