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Holland, LZ, Miller RL.  1994.  Mechanism of Internal Fertilization in Pegea-Socia (Tunicata, Thaliacea), a Salp with a Solid Oviduct. Journal of Morphology. 219:257-267.   10.1002/jmor.1052190305   AbstractWebsite

The ovary of the salp Pegea socia (Bose, 1802) is located at the end of an atrial diverticulum. The ovary consists of a single oocyte encased in a layer of follicle cells and is connected to the atrial epithelium by an oviduct. Transmission electron microscopy shows that the oocyte lacks a vitelline layer, cortical granules, and yolk granules and that the oviduct lacks a continuous lumen. What previous authors thought was a lumen is a line of dense intercellular junctions running down the center of the oviduct. The sperm nucleus in this species, as in other salps, is elongate. The tubular mitochondrion spirals about the sperm nucleus giving it a corkscrew-shape appearance. Sperm reach the ovary when the oocyte is still at the germinal vesicle stage. Many sperm swim up the atrial diverticulum and burrow through the cells of the atrial epithelium, oviduct, and follicular epithelium. Thus oviduct shortening, which occurs when the oocyte is in the meiotic divisions, is evidently unrelated to sperm moving up the oviduct. All previous authors, who argued either that a continuous lumen is necessary for sperm to move up the oviduct or that sperm bypass the oviduct, were incorrect. (C) 1994 Wiley-Liss, Inc.

Holland, PWH, Garcia-Fernandez J, Holland LZ, Williams NA, Holland ND.  1994.  The Molecular Control of Spatial Patterning in Amphioxus. Journal of the Marine Biological Association of the United Kingdom. 74:49-60. AbstractWebsite

The embryology of amphioxus (Chordata: Cephalochordata) has features in common with vertebrate embryology, reflecting a dose phylogenetic relationship between the two taxa. Amphioxus differs from vertebrates, however, in having less complex organogenesis and cranial morphogenesis, and less specialization along the anteroposterior body axis. Here we illustrate this by describing the embryology of an amphioxus species, Branchiostoma floridae. To gain further insight into the origins, evolutionary divergence and comparative embryology of these taxa, we are comparing the molecular control of embryonic development in amphioxus and vertebrates. For these analyses, we are focusing on homeobox genes: a diverse multigene family implicated in developmental control in many Metazoa. We report the results of PCR-based experiments which reveal that the amphioxus genome has homeobox genes from several recognized gene classes. The PCR experiments also suggest that amphioxus has fewer 'Hox' and 'Msx' class homeobox genes than do vertebrates. We suggest, therefore, that amphioxus may be a living descendant from an intermediate stage in the evolution of homeobox gene family complexity, and the complexity of vertebrate developmental control. The pattern of gene expression during embryogenesis has been described for one amphioxus homeobox gene of the Hox class. This gene is primarily expressed in the presumptive neural tube of amphioxus neurulae, later embryos and larvae, in a spatially-restricted manner. The expression data lead us to suggest that Hox genes are involved in the control of spatial patterning in the neural tube of amphioxus; the data are also interpreted as giving insight into possible homology between the amphioxus and vertebrate body plans.

Holland, LZ.  1996.  Muscle development in amphioxus: Morphology, biochemistry, and molecular biology. Israel Journal of Zoology. 42:S235-S246. AbstractWebsite

This review concerns the structure and biochemistry of muscle in amphioxus. Most work has focused on the segmented swimming (axial) muscles. These muscles derive from the medial wall of the somites, which arise as evaginations from the gut wall. The myotomal muscle cells of amphioxus, unlike those of vertebrates, never fuse, but remain mononucleate, contain only one myofibril, and span the entire length of the myotome. The muscle cells are very thin and lack a T-tubule system. There are two, maybe three, types of fibers. Innervation is via muscle tails, which contact the basal lamina of the nerve cord. The notochord is also composed of striated muscle cells, which similarly send muscle tails to the nerve cord. Less is known about the biochemistry of muscle. The notochord, like molluskan catch muscle, contains paramyosin. Among the muscle-specific proteins sequenced are alkali myosin light chain, troponin C and sarcoplasmic calcium-binding proteins, calcium-vector protein, and its target protein calcium vector-target protein. The only muscle regulatory factors identified are two MyoD proteins. Almost nothing is known about muscle enzymes in amphioxus.