Fig. 4

Small colonies of I cf. suecica. a Young ancestrula. b Ancestrula with one long primary cystid appendage, development of next primary cystid appendage (opposite direction) delayed. c Ancestrula with two primary cystid appendages. d Ancestrula with primary cystid appendages developing at an acute angle with developing bud in an advanced state (top), no breakthrough of borehole aperture yet. Lateral cystid appendage developing to the right of primary cystid appendage. e Ancestrula and autozooid after breakthrough of borehole aperture. Lateral cystid appendage developing to the left from primary cystid appendage near autozooid. f Tentacle crown of ancestrula with eight tentacles (one tentacle obscured from view). g Autozooids do not display enantiomorphism; all appear on the same side of the primary cystid appendage. h Schematic of sinistral and dextral borehole aperture deflection along the primary cystid appendage. Arrow indicates direction of growth from the ancestrula. i Same colony. Lateral cystid appendages develop only after development of first autozooids. Secondary cystid appendage developing from ancestrula below substrate surface (double arrowheads) then visible just below surface with tubulets and anastomose with lateral primary cystid appendage (asterisk) with developing bud. Lateral and paired lateral cystid appendages in section of colony. Autozooids neighbouring ancestrula are enantiomorphic. Abbreviations: ab – advanced bud, anc – ancestrula, az – autozooid, b – bud, lca – lateral cystid appendage, pcy – primary cystid appendage, plca – paired lateral cystid appendage, scy – secondary cystid appendage, sp – boring sponge, t – tentacle