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Taxon
Eudendrium racemosum (Cavolini, 1785)
Nomenclature
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Family: EudendriidaeGenus: Eudendrium
SUMMARY
Colonies of moderate height, ranging from 30-70 mm, main stems unfascicled or with one supplementary fascicular tube. Primary branches long, particularly those in the proximal stem region, secondary branches bearing hydranth pedicels. Branches with a few spiral annulations at origin; groups of annulations sometimes at irregular intervals along branch, perisarc otherwise smooth.
Hydranths large, with an open trumpet-shaped and sometimes fluted hypostome (preserved material), surrounded by 27-30 tentacles, a contraction groove and an indistinct nematocyst ring in the proximal region. A cnidophore (Weismann 1881) present in 20% of hydranths, arising just above the contraction groove, usually on hydranths in the proximal region of the branch. The cnidophore is usually thicker than the tentacles and often several times the length of the hydranth, the distal end thickly armed with nematocysts.
Female gonophores borne in clusters of up to 10 on a wrinkled blastostyle below a hydranth with a reduced number of partially-atrophied tentacles. Spadix of female bifurcated in early stages of development, the bifurcation remaining until the egg reaches maturity.
Nematocysts of two kinds present:
— Small microbasic euryteles, capsule 6.5-7 x 2-3 µm, shaft 5-6 µm, very abundant in tentacles.
— Atrichous isorhizas, capsule bean-shaped, 9-11 x 3.5-4 µm wide, thread moderately long, finely spinous, loosely coiled inside capsule when undischarged. Moderately common around hypostome and very abundant on cnidophore.