Omalosecosa ramulosa (Linnaeus, 1767)


Erect branching structure developing into planar or three-dimensional structures.

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This species might get confused with other erect branching species such as Palmiskenea skenei and Porella compressa. It should be distinguishable by branching pattern, presence of the large hooked avicularium and habitat preference.


Colonies grow into a branched, stagshorn-like growth, 30-40mm in height and yellow to orange in colour. The branches are cylindrical and tapering towards the growing tip; they divide dichotomously in one or more planes. Often this gives rise to a fan shaped structure, but frequently several branches arise from the encrusting base to develop a three-dimensional rounded shape. This distinctive branching pattern gives rise to a common name ‘Monkey-puzzle’ bryozoan, after the South American tree. Autozooids are arranged in alternating longitudinal series, disposed around the axis of the branch. They are oval, convex and separated by shallow grooves. They measure 0.6-0.9x0.3-0.6 mm. The frontal shield of the zooids is smooth and fine-grained; there are a few inconspicuous marginal pores. The primary orifice is wider than long, the proximal edge is shallowly concave. The peristome is very deep, with a large, round latero-suboral pseudospiramen. This is adjacent to a large avicularium that is enfolded by the peristome and extends into an elongated hollow spike. These spikes give the colony a characteristic appearance with the naked eye. The avicularium has an elongated triangular rostrum; it is strongly hooked. It has a complete crossbar, with a small median columella and no palate.


Colonies grow up to 30-40mm in height and diameter.


This species is common around all British coasts. It occurs as far south as Mauritania and the western Mediterranean up as far north as western Norway. It has not been recorded in the Arctic.


This species encrusts shell, stones and other live substrate such as erect hydroids or bryozoans (Cellaria species). It is a sublittoral species, occurring from the kelp zone down to 80m or so.


The ovicell of this species is prominent, spherical, finely granular and without pores. There is a narrow rim around its aperture. Embryos have been observed in March and August to November in the western Mediterranean and in July and August at Lundy, Bristol Channel.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith