Sponge mesenchymal cells secrete and organize the mineral and the organic skeleton (collagen) according to its phylogenetic lineage. Haliclona spicules are siliceous oxeas, smooth, fusiform, and slightly curved, with acerate or hastate tips. The ectosomal skeleton is easily detachable, formed by a slightly disorganized tangential reticulation of oxeas. It is isotropic, predominantly paucispicular, and has two to five spicules adjacent to one another. The amount of collagen is low in both the choanosome and ectosome, mostly concentrated in the nodes joining the spicule tips, acting as a cement to sustain the reticulation. Collagen also bases the Haliclona epithelial layer.

Sponges have the ability to fully regenerate from small number of aggregated cells. The morphogenetic program to mount a sponge body does not require embryonic development. Asexual reproduction by fragmentation and generation of stem cell aggregates contributes significantly to sponge straggling. Sexual reproduction in sponges does not count with a specific germinative lineage, and two somatic stem cell types, the choanocyte and the archeocyte, undergo meiosis to generate spermatozoa and oocyte, respectively. Nurse cells forming brooding chambers and intense phagocytic activity accessorize the internal development of Haliclona embryos. Parenchymula larvae are released and set the substrate after some days, initiating the metamorphosis.

Early sponges diverged from the metazoan lineage and have a genetic repertoire representative of our common ancestor. Sponges do not possess a neural system, neither specialized cells to conduct cell depolarization, but have neural toolkits that were probably coopted for it. Sensitive epithelial cells and myoepithelial cells conducting waves of generalized cell depolarization and contraction constitute the neural toolkit present in sponges. Their genomes have pre‐ and postsynaptic genes. Secondary loss of neural system is another possibility, and the genes for synapsis might serve another secretory propose in sponge, but secondary loss is not commonly accepted.

Sponge integuments have primitive characteristics. Epithelial cells at the outer most cell layer covering the body have junctional‐like complexes and collagen fibers underlying the epithelial layer, suggesting homology with bilaterian epithelia. The subdermal layer (subectosome) under the outermost epithelium (exopinacoderm) has water canals and lacunae. The subectosome has delicate connection between the ectosome and the choanosome. Porocytes are modified exopinacocytes for water to enter the subdermal canals and lacunae. The osculum is the exhalant opening at the exopinacoderms with connection to endopinacoderm. Isolated epithelial cells bearing stereocilia were reported lining the osculum.

The phylum Porifera groups originally filter‐feeding pore‐bearing animals, with carnivore sponges lacking the filtering system. Demospongiae is the class comprising sponges with silica spicule, but it is different from the Homoscleromorph. Sponge taxonomy is based on the morphology and arrangement of spicules, which are highly homoplasics. Molecular studies have importantly contributed to refine sponge taxonomy. Haplosclerida display (or partially) triangular meshes of diactinal (two‐rayed) spicules with sides of one spicule length (i.e. isodictyal reticulation). The genus Haliclona has variable morphology and consistency (erect, tube‐shaped, and branching forms, soft and fragile, and firm and elastic).