The circulatory system and a new cell type of the cephalocarid crustacean Hutchinsoniella macracantha
The circulatory system of Hutchinsoniella macracantha consists of a tubular heart in thoracic segments 1–6, a dorsoposterior channel, and body fluid (“haemocoelic”) sinuses. The heart, which is possibly closed anteriorly, has three paired ostia dorsolaterally in thoracic segments 2–4. The heart wall is formed by two cellular layers: an inner myocardium and an outer epicardium. The myofibrils are o