INVERTEBRATE ZOOLOGY IN THREE VOLUMES - BOOK 2 - G.I. Shcherbak - 1996

PHYLUM KAMPTOZOA, OR ENTOPROCTA

CLASS KAMPTOZOA, OR ENTOPROCTA

Most species of kamptozoans form small, delicate colonies consisting of a basal network (stolon) that covers the substrate (stones, shells, etc.). Individual zooids, 2–3 mm in height, rise upward from this base.

The body of kamptozoans is calyx-shaped. One pole bears a simple ring of tentacles surrounding a depression in the calyx, the atrium; the opposite pole features a contractile stalk by which the animal attaches to the substrate or the colony's stolon (Fig. 38). At the end of the stalk, There is a gland with an adhesive secretion.

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Fig. 38. Portions of Kamptozoa colonies:

a - Pedicellina cernua; b - Arthropodam kowalevski extended; c - bent

1 - calyx; 2 - stalk; 3 - stolon

A Skin-muscular sac is absent. The tentacles are covered with ciliated epithelium, while the rest of the body surface is covered by a thin cuticle underlain by the hypodermis. Muscles are sparse. There are individual smooth muscles that move the tentacles and the stalk, which, when disturbed, bends and presses the calyx against the substrate; the stalk straightens out due to the elasticity of the cuticle. This is the Water/144.html">Origin of the animals' name: the word kamptozoa translates as "those that bend."

Kamptozoans lack a body cavity; the spaces between Organs are filled with parenchyma (Fig. 39).

Fig. 39. Cross-section through the calyx of Pedicellina cernua:

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 opening; 12 - rectum; 13 - tentacle

In terms of their feeding mechanism, kamptozoans are filter feeders. The tentacles sweep water containing food particles into the atrium, where the mouth is located. The mouth leads into a narrow esophagus (ectodermal foregut), which expands into an entodermal stomach surrounded by glandular Cells; this is followed by a narrower section—the midgut—and an ectodermal hindgut that opens via the anus at the opposite end of the atrium. Thus, the gut forms a loop, and both the mouth and the anus open within the ring of tentacles. This gives rise to the second name of these animals, Entoprocta (meaning "inside-anus" in Greek), referring to those whose anus opens inside the tentacular crown.

The excretory system consists of a pair of typical protonephridia that open via a single unpaired pore into the atrium. Circulatory and respiratory systems are absent. Respiration occurs through the tentacles. The Nervous system consists of a single nerve ganglion from which nerves extend to the tentacles and stalk. Special Sense Organs are absent. Isolated receptors are scattered all over the body, being particularly abundant on the tentacles.

Most kamptozoans are dioecious, although hermaphroditic species also occur. The FEMALE Reproductive System consists of a pair of sac-like Ovaries and a pair of oviducts,

which merge into an unpaired duct opening into the atrial cavity. The latter acts as a brood pouch where the larvae develop. The Male Reproductive System has a similar Structure. Spermatozoa are released into the surrounding water and enter the female atrial cavity, where Fertilization of the egg takes place.

Egg Cleavage is spiral. Embryonic development shares features that link it to that of Annelids: the arrangement of individual blastomeres, the mode of Gastrulation, the closure of the slit-like blastopore, and The formation of the mouth at its anterior edge. The kamptozoan larva resembles the trochophore of annelids.

In the most thoroughly studied genus, *Pedicellina*, the larva consists of upper and lower hemispheres, separated by a band of cilia known as the prototroch; at the upper pole, there is an apical (aboral) sensory organ—a small papilla with sensory cilia, beneath which lies the nerve ganglion (Fig. 40).

Fig. 40. Trochophore larvae of kamptozoans:

a - Pedicellina cernua; b - Loxosomella bannen; 1 - frontal organ; 2 - aboral organ; 3 - stomach; 4 - hindgut;

5 - anus; 6 - atrium; 7 - mouth; 8 - prototroch; 9 - FOOT

The mouth is located on one side of the lower hemisphere, and the anus on the opposite side. A small depression, the atrial cavity, forms between them. The larva has a primary body cavity with mesenchymal cells scattered within it; there is a pair of protonephridia opening into the atrium. Interestingly, the larva possesses a more complex nervous system than the adult animal. In addition to the aboral sense organ and its associated ganglion mentioned previously, a frontal organ of similar structure and its associated ganglion lie anterior to the mouth, directly beneath the prototroch. Both ganglia are connected by paired nerves.

After swimming in the water Column for some time, the larva settles on the substrate with its oral side. During this process, the edges of the upper hemisphere above the prototroch gradually draw together toward a single point to form a stalk base, while the prototroch and all Organs of the lower hemisphere end up enclosed within a closed atrial cavity. A stem grows above the base, and the upper part of the larva, together with the atrial cavity, forms the calyx. The atrium, along with the mouth, anus, intestine, and protonephridia, rotates by 180°. Following this, the mouth and anus face upward, while the atrial cavity remains enclosed. Inward-directed tentacle rudiments appear on the fold of the atrial cavity. The atrial cavity breaks open, and the tentacles extend outward. The prototroch, aboral organ, and ganglion degenerate.

There are species (family Loxosomatidae) in which the larva has an elongated shape, dorsoventrally flattened, with its apical organ shifted forward and a pair of eyes present (Fig. 40). Such a larva initially crawls and then attaches to the substrate by its anterior end, where the frontal organ is located.

All Kamptozoa exhibit asexual reproduction in the form of budding. In solitary forms (family Loxosomatidae), buds form symmetrically at specific sites on the calyx and detach immediately (Fig. 41). In colonial forms, the buds do not separate; a long stolon forms between the bud and the parent, creeping along the substrate, upon which new buds are initiated, thus forming a colony.

Fig. 41. Budding in Loxosomella annelidicola:

1 - hindgut; 2 - tentacles; 3 - buds at various developmental stages; 4 - coelom; 5 - esophagus; 6 - mouth

Regeneration of lost parts occurs very easily in Kamptozoa: amputated tentacles and even entire calyces are rapidly restored.

The phylogenetic position of Kamptozoa within the animal kingdom remains a subject of debate. For a long time, they were grouped together with Bryozoa into a single taxon (Tentaculata) and classified as the class Entoprocta, based on THE POSITION OF the anus inside the tentacle crown, in contrast to Bryozoa (Ectoprocta), in which it lies outside the tentacles. Some scientists consider Kamptozoa to be a group close to lower worms (rotifers, gastrotrichs) that underwent modification associated with the transition to a sessile lifestyle. However, the features of their embryonic development, larval structure, and metamorphosis provide grounds for allying Kamptozoa with trochophore-bearing animals, viewing their level of Organization as the most primitive within this animal group (parenchyma, absence of a coelom, Circulatory system, etc.).