Reproductive biology

The sexes are separate in Concentricycloids, and the disclike body of the species, and the radial arrangement of gono-pores (female) and penial projections (male), makes it mechanically possible, although somewhat unlikely, for one female to be serviced by five males, or alternatively, five females could surround one male, or an alternate male/female chain of reproductively active individuals might occur.

Oocytes are ovoid and become increasingly yolk-filled with growth. The largest develop towards the blind end of the gonad, and measure up to 0.00709 in (180 pm) in length.

Spermatozoa are streamlined, elongate cells over 0.00106 in (27 pm) long and composed of a finely tapered segmented astrodome, tail attachment area, free flagellum, nucleus, and a single, elongate mitochondrion posterior to the nucleus.

The two Xyloplax species are dioecious and sexually dimorphic: males are smaller than females. Different reproductive strategies are adopted by each species: X. medusiformis is an intra-ovarian, non-placental, viviparous species, and X. turnerae is presumed to be capable of depositing fertilized eggs externally. In X. medusiformis, reproduction is asynchronous between the 10 gonads—not all gonads show equal development of oocytes. The developing juveniles are clearly recognizable as cone-shaped or flattened individuals with developing tube feet, a well-developed ectoneural nerve, and a vestigial gut (which is lost in immediate prenatal specimens).

No larval stages have been observed, but it is likely that they exist in X. turnerae, as developmental stages have not been observed in the ovaries of that species.

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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