Ijima and Kaburaki, 1916
Overview
Diagnosis: Procerodes lacteus (Ijima and Kaburaki, 1916) can be distinguished from other procerodids by the following combination of features: (1) distinct tentacles at the front end, (2) absence of pigmentation, (3) numerous testes, extending from the ovaries into the hind end of the body, (4) oviducts opening separately into the diverticulum, (5) long and slender ejaculatory duct, 6) presence of eye lenses.
Habitus: Preserved specimens 2-4 mm long and 1 mm wide. The body is slender; the body margins run almost parallel, gradually converging to form an obtusely pointed hind end. In the anterior part of the body the margins converge towards a slight constriction in front of the eyes. The anterior margin is convex, whereas the head shows two distinct auricles. The eyes are spaced rather wide apart. The animals are milky white, due to the lack of pigmentation.
Alimentary System
The slender pharynx is about one-third of the body length. The mouth opening is situated at the hind end of the pharyngeal pocket.
The anterior ramus of the intestine extends anterior to the eyes and gives off a pair of forked, lateral diverticula. Behind the brain the anterior trunk rise gives to 7-8, bi-or trifurcated lateral diverticula. Each of the posterior intestinal rami gives off 10-15 lateral diverticula. The posterior gut trunks do not communicate.
Male Reproductive System
There are 44-58, dorsally situated testes on either side of the body (In Kaburaki's figure there are depicted 44 testes on one side of the body and 50 on the other side, while in the text he mentioned a number of 58 on either side of the body). The testes extend from behind the ovaries into the hind end of the body.
At about the hind end of the pharynx, the vasa deferentia enlarge to form false seminal vesicles. Behind the mouth opening these ducts curve dorso-medially, meanwhile narrowing, penetrate the penis bulb and, subsequently, unite in the upper part of the bulb to form the ejaculatory duct. The latter opens at the tip of the penis papilla. Penis glands, which lie outside the bulb, discharge their secretion into the ejaculatory duct.
The small and conical penis papilla has a vertical orientation. It is situated in a spacious male atrium which communicates via a pronounced constriction with the common atrium.
Female Reproductive System
The paired ovaries are situated directly behind the brain. The oviducts arise from the postero-lateral surface of the ovaries and run laterally to the ventral nerve cords. Behind the gonopore the oviducts curve medially and, subsequently, open separately into the diverticulum of the bursal canal. This diverticulum receives the openings of numerous shell glands.
The spherical copulatory bursa is lined with large, cuboidal cells. The bursa is surrounded by "fine circular and longitudinal muscles". The bursal canal runs obliquely towards the common atrium. The canal is lined with cuboidal cells and surrounded by a subepithelial layer of circular muscles, overlain with a layer of longitudinal muscles.
Eyes
The pigment cups contain 3 or 4 retinal cells and a well developed, ellipsoidal lens.
Ecology
Specimens have been collected from under stones.
Distribution
Type locality: Between Yukanki and Meleya on Sakhalin, i.e. on the southern part of that island. The species is known only from its type locality.
Material Examined and Type Material
The type material has been lost, and no new material has become available. The detailed account of this species published by Kaburaki (1922) formed the major source of information for the present description.