Comprehensive Description

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General Description

(from Coe, W. R. (1905). Nemerteans of the west and northwest coasts of America.. Bull. Mus. comp. Zool. Harv.. 1-318)
Body rather slender, rounded anteriorly, flattened in the intestinal region. Head changeable in shape, often wider than parts immediately following; pointed, rounded or emarginate in front, according to state of contraction. Proboscis pore ventral, near tip of snout; mouth immediately behind brain.
Cephalic furrows represented only by a pair of very inconspicuous transverse grooves just back of head. Cerebral sense organs wanting, but a pair of large and very highly developed lateral sense organs lies in the vicinity of the nephridial openings, as in Tubulanus. Ocelli wanting.
Intestine without regularly paired, lateral diverticula, although the epithelium is thrown into conspicuous folds which often simulate actual diverticula.

Body musculature consists of a strong longitudinal layer and two circular layers. Of the latter the outer circular muscles remain very thin throughout the body, while the inner become massively developed in the nephridial region, back of which they terminate abruptly, except for a few delicate fibers which continue to the posterior end of the body. The longitudinal muscles are highly developed throughout the body. A very massive layer of longitudinal muscles lies between the proboscis sheath and intestinal canal. These muscles are thickest immediately behind the nephridia, and join the main longitudinal muscular layer posteriorly to the end of proboscis sheath. Proboscis sheath extends through about half the length of the body. Proboscis composed of two muscular layers--an inner circular and an outer longitudinal layeroutside or between which is a firm basement membrane or layer of connective tissue. Proboscis cavity separated into three chambers, of which the anterior is bulb-like in some states of contraction and resembles the middle chamber of the proboscis of some of the Hoplonemerteans, although it is without armature.Nephridia much as in Tubulanus linearis. Blood vascular system consists of very large cephalic lacunae and a pair of large lateral vessels. These latter lie intern al to the inner circular layer in the esophageal region ; farther back they pass outside this laver and lie between it and the longitudinal muscles, while in the intestinal region they become imbedded in the longitudinal muscles.

Brain shaped much as in Tubulanus and similarly situated immediately beneath the basement layer of the integument. Lateral nerves likewise situated between the outer circular muscles and the basement membrane, although in the nephridial region,and throughout all the body more posteriorly, the nerves sink inward among the longitudinal muscles, carrying at least a portion of the very thin circular layer with them. By this means the nerve cords may come to lie well toward the inner border of the longitudinal muscles, although still situated to some extent outside the very thin layer of circular muscles.

Sexual glands develop as small pouches lying in the longitudinal muscles on the dorsal side of the body.

The massive band of longitudinal muscles between the proboscis sheath and the intestinal canal, most highly developed posterior to the nephridial region; the position of the lateral blood spaces internal to the inner circular muscles in the anterior esophageal region; the pouch-like outfoldings of the intestine, which are not true diverticula, however; the structure of the proboscis; the enormous cephalic blood lacunae ; the extremely thin basement membrane ; the total absence of cerebral sense organs ; the anastomosing fibers of the integument ; these may be enumerated as some of the more striking peculiarities of the present genus.With Bergendal's genus Callinera are many similarities, but the differences are even more pronounced than is the case with Tubulanus.


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© Ritger, Rebecca

Source: Nemertea

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