This work expands the scope of chemobrionic chemistry to produce biopolymer-intercalated inorganic tubes that structurally and chemically resemble both oceanic hydrothermal vent tubules and the scaffolds of tubular sponges. The sponge-mimetic tubules (SMTs) are formed by seeding calcium chloride into a solution of concentrated sodium silicate–potassium phosphate containing solubilized biopolymers of the cyanobacterial origin. A carbonation step to increase the calcium carbonate content in the SMTs was optimized. Incorporation of biopolymers into the fabric of the SMTs was confirmed by energy-dispersive X-ray microanalysis and infrared spectroscopy and the mineral components identified by X-ray diffraction. SMT morphology was characterized by scanning electron microscopy. Experiments testing the hypothesis that biohybrid hydrothermal tubules in Paleoproterozoic oceans served as sites where unicellular eukaryotes colonized and evolved into early ocean sponges were performed: the compatibility of the SMTs with marine cells was demonstrated by live cell imaging of Pyrocystis lunula seeded onto alginate-incorporated SMTs. The choanoflagellate cell line Salpingocea rosetta, considered the ancestor of sponge choanocytes, was seeded onto alginate SMTs. Live cell imaging and confocal laser scanning microscopy confirmed the viability of the cells and actively feeding choanoflagellate cell assemblies on the SMTs were captured by video microscopy. The findings suggest that these hydrothermal vent models can support diverse eukaryotic life and validate the theory of a chemobrionic-linked origin of ocean sponges. The potential of using SMTs for tissue engineering was explored by using them as scaffolds for 3D cell culture of human fibroblasts.