Xironogiton
Xironogiton Ellis, 1919 (ref. ID; 1923)
Superclass Clitellata: Class Branchiobdellida (ref. ID; 6638)
Family Branchiobdellidae (ref. ID; 6451, 6456)
ref. ID; 1923
Without setae; with posterior sucker; pharynx with dorsal and ventral chitinous jaws; commensal on crayfish. With two pairs of testes in segments 5 and 6. Body with appendages. Accessory sperm tube present. Body flattened, posterior end enlarged so that the body is racket- or spatula-shaped, anterior nephridia opening to the outside through separate pores. (ref. ID; 1923)
- Xironogiton cassiensis Holt, 1974 (ref. ID; 6651)
- Xironogiton fordi Holt, 1974 (ref. ID; 6651)
- Xironogiton instabilis (Moore, 1893) (ref. ID; 6651)
- Xironogiton instabilis (ref. ID; 6451, 6456)
- Xironogiton instabilius instabilius (Moore, 1894) (ref. ID; 1923)
- Xironogiton instabilius oregonensis Ellis, 1919 (ref. ID; 1923)
- Xironogiton kittitasi Holt, 1974 (ref. ID; 6651)
- Xironogiton occidentalis Ellis, 1919 (ref. ID; 1923) or 1920 (ref. ID; 6651)
- Xironogiton victoriensis Geld. & H., 1990 (ref. ID; 6638, 6651)
Descriptions
The spermatozoon of X. instabilis has a tapering, helical acrosome that makes 1.5 revolutions. The acrosome tube has a characteristic wall of uneven thickness all along its length and the posterior end has a small acentric aperture. In longitudinal section this appears as an internal lip or shelf (= limen; Jamieson 1983) of varying length. The acrosome vesicle makes contact with the plasma membrane only through the open anterior tip of the tube. The vesicle fills the anterior half of the tube, and there is a deep invagination from the vesicle's base. The posterior margin of the vesicle extends posteriorly into a short secondary tube. The vesicle invagination and the secondary tube surround the anterior half of the acrosomal rod. The posterior half of the rod is often bent to one side, and is surrounded by part of the elongated electron-lucent material that fills the rest of the acrosome tube (= basal chamber; Jamieson 1983). The nucleus is helical, with a pitch of 0.7 µm, and tapers from a diameter of 0.33 µm posteriorly to 0.15 µm anteriorly; both ends are concave. The nucleus is followed by four mitochondria slightly twisted around the central axis of the spermatozoon. The tail consists of a flagellum and an end-piece. The flagellum starts with a centriolar area in which it is possible to see the remnants of the centriole. The latter loses its conventional appearance during spermiohistogenesis (M. Ferraguti, unpublished data), to give rise in the mature spermatozoa to a short electron-dense ring in which a ninefold symmetry can be recognized. A central apparatus, similar to that of the flagella, passes through the center of the centriole remnant and ends in contact with the mitochondria. The main portion of the flagellum contains a prominent central sheath surrounding the central tubules, multiple-like heads, and pairs of glycogen granules along the external length of the axoneme. The tail ends in a tapering end-piece which is composed of homogeneous electron-dense material and devoid of any axonemal structure. (ref. ID; 6456)
Descriptions
Two teeth of the longest pair in the upper jaw separated by only 1 tooth; if 2 long teeth are contiguous, the inner one is the longer. Holt (1949) believes that this form does not possess a true accessory sperm tube. (ref. ID; 1923)
Descriptions
Two teeth of the longest pair in the upper jaw separated by 2 teeth; if 2 long teeth are contiguous, the outer one is usually the longer. (ref. ID; 1923)
Descriptions
Glandular concave discs near the lateral margin of the ventral surface of segments 8 and 9; body usually spatula-shaped. (ref. ID; 1923)
Descriptions
Because of the dorsoventral flattening of segments of the posterior body, the ental tip of the tubular, glandular atrium is located between the mid-line and the lateral margin of the body. The gland traverses across the segment and then bends ventrad before merging into the muscular atrium. Deferent lobes and a prostate are absent. The muscular atrium is about one quarter length of the glandular atrium. The muscular tube extends into the subspherical, muscular bursa to from a protrusible penis. The length of the pyriform spermatheca is about half the height of the flattened segment, and is therefore considered small in relation to all other branchiobdellidan spermathecae. (ref. ID; 6638)