INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM METAZOA

SUBKINGDOM EUMETAZOA

DIVISION TRIPLOBLASTICA, OR BILATERIA

SUBDIVISION SPIRALIA

PHYLUM ENTOPROCTA (KAMPTOZOA)

Entoproctans are microscopic (up to 5 mm in height) sessile aquatic animals, predominantly marine. Only the genus *Umatella* has successfully colonized freshwaters. Around 150 species are known, with two species inhabiting the Black and Azov Seas. The species *Umatella gracilis* was passively introduced from North American rivers into Europe via ship hulls—specifically into the Tisza and Dniester rivers, where it was eventually discovered.

These are colonial, rarely solitary organisms, whose bodies consist of a calyx and a stalk. A true body coelom is absent, and the spaces between Organs are filled with parenchyma. Both the Mouth and the anus are located within the tentacular crown. The excretory system is protonephridial. Development proceeds via metamorphosis.

Most entoproct species form small, delicate colonies consisting of a basal web-like stolon system that encrusts the substrate (such as stones and shells), and individual zooids 2–3 mm in height that project upward.

Morphology. The body is cup-shaped; one pole bears a crown of tentacles (ranging from 6 to 36) surrounding a depression of the calyx known as the atrium. A contractile stalk is situated at the opposite pole, anchoring the animal to the substrate or to the colonial stolon (Fig. 159). In solitary species, the distal end of the stalk features a gland with an adhesive secretion used for substrate attachment.

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Fig. 159. Fragments of Kamptozoa colonies (from Abrikosov):

a — Pedicinella cernua; b, c — Arthropodaria kowalevski, extended and flexed, respectively:

1 — calyx; 2 — stalk; 3 — colonial stolon

Integument. A cutaneous-muscular sac is absent. The tentacles are covered with ciliated epithelium, while the rest of the body surface bears a thin cuticle underlain by the hypodermis.

Musculature is poorly developed: there are isolated smooth Muscles that move the tentacles and the stalk. When disturbed, the stalk bends and presses the calyx against the substrate; it straightens out due to the elasticity of the cuticle. This behavior gave rise to the name used in Russian-language literature: *Kamptozoa* translates as bending animals.

The body cavity is absent, and the intervals between organs are filled with parenchyma (Fig. 160).

Fig. 160. Longitudinal section through the calyx of Pedicinella cernua (from Abrikosov):

1 — anus; 2 — brood chamber; 3 — parenchyma; 4 — Ovary; 5 — nerve ganglion; 6 — mouth; 7 — Esophagus; 8 — Stomach;

9 — stalk; 10 — intestine; 11 — egg emerging from the genital pore; 12 — rectum; 13 — tentacle

Digestive System. The mouth opening is located within the atrium, leading to a narrow ectodermal esophagus that expands into an endodermal stomach surrounded by glandular Cells. The Stomach lies transversely across the body and transitions into a narrow midgut. This is followed by an ectodermal hindgut that opens via the anus on the opposite side of the atrium. Thus, the complete digestive tract forms a loop, with both the mouth and the anus opening inside the tentacular crown—hence the alternative name for these animals, Entoprocta (meaning those with the anus opening internally within the crown). Functionally, these animals are suspension feeders (filter feeders). The tentacles generate Water currents that drive food particles into the atrium, where the mouth is situated.

The excretory system consists of a pair of typical protonephridia that open via a single unpaired pore into the atrium.

Gas exchange (Respiration) occurs across the tentacles.

The Nervous system consists of a single nerve ganglion, from which nerves extend to the tentacles and the stalk. Specialized Sense Organs are absent; isolated sensory cells (sensillae) are scattered throughout the body, with a particularly high concentration on the tentacles.

Reproductive System. Most kamptozoans are gonochoric, although hermaphroditic species also occur.

The FEMALE REPRODUCTIVE SYSTEM consists of a pair of sac-like Ovaries and a pair of oviducts that merge into a single unpaired duct opening into the atrial cavity. The latter Functions as a brood pouch where the larvae develop. The Male Reproductive System has a similar Structure.

Reproduction. Spermatozoa are released into the surrounding water and enter the female's atrial cavity, where egg Fertilization takes place. Cleavage is spiral. Postembryonic development proceeds through metamorphosis. The egg hatches into a larva (Fig. 161) that bears resemblance, on the one hand, to the trochophore larva of Annelids and, on the other, to the larva of bryozoans (see below). The structure of the larva, particularly its nervous system, is more complex than that of the adult animal. It swims freely, then settles on a substrate, and undergoes dramatic transformations while metamorphosing into an adult individual.

Fig. 161. Larva of *Pedicinella cernua* (after Abrikosov):

1 - frontal organ; 2 - aboral organ; 3 - stomach; 4 - hindgut; 5 - anus; 6 - atrium; 7 - mouth; 8 - prototroch

All entoprocts are characterized by asexual reproduction via budding. In colonial forms, the buds do not detach; instead, a long stalk develops between the bud and the parent Organism, creeping along the substrate and giving rise to new buds to form a colony. These animals possess a high capacity for regeneration: they can easily restore not only lost body parts, but even the entire body from a tiny fragment.