Reproductive biology

Kinorhynchs are dioecious, with external sexual dimorphic characters (AT and penile spines in males, and LTAS in females). Sexes copulate with spermatophore transfer; fertilization is internal. Mature ovaries commonly develop a single large oocyte. Fertilized eggs (60-80 microns) are attached to sand grains or detritus. Cleavage has not been observed. The early embryo in the egg shows no segmentation. Just before hatching, the juvenile kynorhynch has 11 segments: the head with scalids, the neck with placids, and nine trunk segments, which are not divided into sternal and tergal plates. The time required for development from oviposition to hatching is about 10 days. At the time of hatching, the juvenile straightens and simultaneously everts its head, thus tearing open the egg envelope. Kinorhynchs have a direct development through five to six juvenile stages, each derived from a molt.

Just after hatching, the first juvenile can feed on diatoms and detritus. The first molt establishes a 12-segmented juvenile. All trunk segments are discernible in the third stage, but the complete separation of the most posterior segments becomes evident in the fourth or fifth stages.

To distinguish various juvenile stages of kinorhynchs, terms previously proposed for some invalid genera are used. In Cyclorhagida, two morphological states of juveniles are designated: "Centropsis," with MTS and "Habroderes," having LTS and without MTS. In Homalorhagida, there are three morphological states of juveniles: "Centrophyes," with MTS; "Hyalophyes," with LTS and without MTS; and "Leptodemus," without any terminal spines. Cyclorhagids with MTS usually have series of only "Centropsis" stages. In Echinoderidae, first three "Centropsis" stages are usually followed by three "Habroderes" stages. In Pycnophyidae, three 11 Centrophyes" or

"Leptodemus" stages are usually followed by three "Hyalophyes" stages or there are only "Leptodemus" stages.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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