Entoprocts have two reproductive modes: sexual reproduction via a larval stage and asexual budding. For sexual reproduction, sperms released into the water enter the female reproductive tract and fertilize the eggs in the ovaries or oviducts. During the passage of the zygote along the oviducts, they are covered with the secretion from the eosinophilous glands, forming a loose membrane. Cement glands then secrete stalks that adhere to the wall of the brood chamber in the anus by which the embryos get attached to (Brusca and Brusca, 2003).  Some females brood their fertilised eggs in the ovary, providing nutrition to the developing embryos from their placental cells. When they develop into trochophore-like larvae, they are released into the water column. The planktonic duration and dispersal distance of larvae remains unknown (Sugiyama et al., 2010). Most entoproct species are hermaphrodites, with colonial forms having either hermaphroditic or dioecious zooids where colonies may contain one or both sexes (Brusca and Brusca, 2003). In particular, Barentsiidae are reported to have three contrasting modes of sex: (1) comprehensively gonochronistic at both zooid and colony levels, (2) hermaphroditic at the colony level with gonochric zooids and (3) simultaneously hermaphroditic the zooid level (Wasson, 1997). On the other hand, Loxosomatidae species are generally protandrous hermaphrodites, with a discrete male stage followed by a female phase (Nielsen, 1971).

Asexual reproduction in entoprocts occurs through budding. Gut and atrial epithelium develop from ectodermal invaginations while the ectoderm of the bottom of the atrium give rise to ganglion and protonephridia (Nielsen, 2013). In Barentsiidae, colonial growth occurs by budding at the base of zooids, on various branches of the stalk or from the growing tips of stolons as zooids. Some even make hibernacula, which are thick-walled mono-or multilocular resting cytes at the ends of the short stolons that form zooids at germination (Nielsen, 2013). On the contrary, Loxosomatidae produce buds at a pair of laterofrontal or frontal areas of the stomach and release them from the parental calyx when all the organs are fully developed (Sugiyama et al., 2010). Surprisingly, some species of Loxosomella  and Loxosoma bud even at the larval stage. It is said that the larval epithelium above the prototroph gives rise to the buds, which detach from the larval body when fully grown. The body then disintegrates (Nielsen, 2013). These liberated buds can swim slowly with their tentacle cilia (Atkins 1932, Nielsen 1989), but their dispersal distance remains unknown (Sugiyama et al., 2010).

Entoproct embryonic development is indirect with more or less typical trochophore larvae and follows the holoblastic, spiral cleavage pattern of protostomes, with the mesoderm originating from the 4d mesentoblast (Nielsen, 2013). At about the 56-cell stage, nonsynchronous divisions produce five quartets of micromeres, leading to the formation of a coeloblastula and gastrulation by invagination. When the embryos have fully developed, they are usually released as free-swimming, feeding larvae, with long pelagic planktotrophic phase. Like other trochophore larvae, entoproct larvae have equatorial ciliary bands used for feeding on suspending particles, apical and ventral sensory tufts, pigment-cup ocelli serving as light-sensing organs, digestive organs and a pair of protonephridia for waste excretion. When released into the water column, these larvae have the ability to orient themselves and sense specific settlement cues. When prompted to settle, they attach by the coronal ciliary band and undergo metamorphosis where the body mass experiences unequal growth to direct the ventral, vestibular surface away from the substrate (Brusca and Brusca, 2003). Moreover, some entoprocts also produce lecithotrophic or benthic crawling larvae with a large well-developed, ciliated, ventral foot, which have a free period of only a few hours.

Specifically, the trochophores of Barentsiidae retract the ventral side and attach to the substratum by secretions from the glandular cells above the contracted prototroch. The internal organs rotate 180 degrees along the dorsoventral axis, with the mouth, anus and gut turning to face the vestibular surface in front and the atrium opens with a series of surrounding small tentacles (Nielsen, 2013). This is followed by the differentiation of the stalk into a muscular basal section and a non-muscular distal section as well as the formation of the circulatory organ at the top. The cuticle above the atrium is shedded and small tentacles develope (Nielsen, 1971). On the other hand, the larvae of some Loxosomatidae species do not rotate when adhering to the substratum. For example, in some Loxosomella species, the larvae settle with glandular cells around the frontal organ, followed by metamorphosis through a retraction of the foot, a constriction of the prototroph and a reopening of the atrium surrounded with new tentacles (Nielsen 2013). Some, such as Loxosomella polita and Loxosomella vivipara, even produce an correctly oriented asexual buds that later becomes the adult upon settling (Nielsen, 1971). Other species with free-swimming larvae produce adult buds precociously that are formed earlier while the larvae are still in the brood chamber. They are held inside the larvae and are released by rupture of the body wall of larvae prior to settling (Shank, 2001). A reconstruction of the larva of a species each from the Barentsiidae and Loxosomatidae families are shown in Figure 4.

Though small and sessile, entoprocts exhibit various interesting behaviour, including locomotion and regeneration. While most movement in entoprocts happens in larval dispersal since they get attached to a substate with their foot after settlement, some adult individuals in the Loxosomatidae family can capable of movement, including gliding over, crawling on, detaching from and reattaching to the substratum with their foot, even after adulthood (Iseto 2002, Iseto & Hirose 2010). This has been observed in some Loxosomella species dwelling inside the tubes of marine annelids (Ramel, 2012). 

The structure of the body wall in entoprocts is pseudocoelomate throughout the stalk, stolon, calyx and tentacles, consisting of one-layered epithelium with microvilli that penetrate the layer of crossing collagenous filaments (Nielsen, 2013). The calyx and stalk are clothed with a thin cuticle that does not extend over the ciliated portion of the tentacles and the vestibule. In Barentsiidae, the stalks and stolons have a thickened cuticle with chitin (Nielsen, 2013). Beneath the cuticle lies the epidermis of mostly cuboidal cells that scatter over the body surface. The epidermis is taller on the inner surface of the tentacles and heavily ciliated along the vestibular groove. The inner side of the epidermis contains musculature in the form of longitudinal bands. Though sparsely present in the calyx, they serve to retract or extend the tentacles, forming a sphincter that contracts the crown and curling the tentacles into the vestibule. Other muscles located within the stalk provide the ability to bend. As entoprocts do not have persistent body cavity, their pseudocoel is filled with mesenchyme cells and occupies the space between the body wall and digestive tract in the calyx as well as the interior of tentacles, stalks and stolon. The pseudocoel of tentacles contains free amoeboid cells while the pseudocoel of the stalk and stolon contains long tube cells. The pseudocoel of the calyx is separated from that of the stalk by the septum and cells blocking the central hole in the septum. Body support is provided by the mesenchyme and cuticle (Brusca and Brusca, 2003). 

Furthermore, entoprocts contain sense organs that include sensory tactile nerve cells. They consist of one or more bristles that proceed from a nerve cell to the epidermis. These unicellular tactile receptors are concentrated on the outer surface of the tentacles and along the calyx margin. In Loxosomatidae, ciliated papillae form the lateral sense organs that are located on the sides of the calyx near the oral end. Each consists of bristles lined by a ganglion connected to the subenteric ganglion through a nerve (Brusca and Brusca, 2003).

Entoprocts are sessile filter feeders. Using the ‘catch-up principle’, they extract small food particles from currents created by the compound cilia of the tentacles that form downstream-collecting ciliary bands (Riisgaard et al., 2000). Larger food particles are captured by a sticky substance secreted by the glandular cells in the tentacles. As entoprocts are oriented with the dorsal side attached to the stalk and ventral side away from the substratum, water currents pass from dorsal to ventral. The lateral cilia trap the food, cover it with mucus and move it to the frontal cilia. It is then transported to the ciliated vestibular food groves at the base of the tentacular ring where additional ciliary tracts carry the food to the mouth. The food is further moved into the gut by the cilia lining the buccal tube and muscular contractions of the esophagus, which lead to a spacious stomach from which a short intestine extends to the r ectum located within the anal cone. Food is then mixed with digestive enzymes inside the stomach by a tumbling action through the ciliary currents and is held by an intestinal-rectal sphincter muscle in the intestine where absorption takes place (Brusca and Brusca, 2003). Barentsiidae species are said to not share the ingested nutrients like ectoprocts and hydroids (Dipper, 2016). A comparative diagram between Barentsiidae and Loxosomatidae of the feeding apparatus inside the calyx is shown in Figure 6.

Zooids have one or two pairs of gonads beneath the vestibular surface (Brusca and Brusca, 2003). The gonads are sacciform bodies situated ventral to the liver region of the stomach and close to the ganglion and they have short gonoducts that lead to the pore opening to a brood chamber (Verma, 2001). In hermaphroditic species of Barentsiidae and Loxosomatidae, the pair of testes are located posterior to the pair of ovaries. From each gonad, a short duct protrude medially and meets its partner to connect to the ventral side of the calyx through a common gonopore. The sperm duct unites with the oviduct of that side before the formation of the common gonopore, which is located behind the nephridiopore. The gonoducts are covered with eosinophils unicellular glands or glandular epithelium. Ripe sperms with flagella are stored in the seminal vesicle in the common sperm duct while developing eggs stay in the brood chamber (Verma, 2001). The brood chamber is a depression formed from the calyx surface between the elevation of the nephridiopore and the anal cone.