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The embryo of the grass shrimp, Palaemonetes pugio, is surrounded during development by a protective extracellular coat designated as the embryonic coat (EC). At hatching, this EC is composed of four embryonic envelopes (EE), each of which is composed of multiple layers. The outermost layer of the EC, the outer investment coat (OIC), is derived primarily, if not completely, from pleopods of the female. The first envelope (EE1) forms as a bilayered envelope, EE1a and EE1b, immediately after oviposition. The OIC becomes closely associated with EE1 and remains in close contact with EE1 until hatching occurs. An additional layer, EE1c, is added to the inner side of EE1 between 3 and 5 d after oviposition. Three more embryonic envelopes, EE2, EE3, and EE4, are formed between the embryo and EE1 by 7 d after oviposition. Formation of embryonic envelopes continues until 10 d after oviposition; by this time each envelope is morphologically distinct in composition, with "outer" and "inner" sides clearly identifiable. All but the innermost embryonic envelope (EE4) are shed by the embryo about 6 h before hatching. Permeability of the EC during the 12-d incubation period is found to decrease between 0 and 5 d after oviposition, and then increase until hatching. Fluorescently labeled lectins react positively with the OIC, indicating the presence of glucose and N-acetylglucosamine residues. Thus, the palaemonid EC is a dynamic structure throughout embryonic development.

Thyroid proliferative lesions are rather common in bony fishes but disagreement exists in the fish pathology community concerning diagnostic criteria for hyperplastic versus neoplastic lesions. To simplify the diagnosis of proliferative thyroid lesions and to reduce confusion regarding lesion interpretation, we propose specific criteria for distinguishing hyperplastic from neoplastic lesions. Development of these criteria was based on the examination of a large series of proliferative lesions from Japanese medaka (Oryzias latipes), lesions from other small fish species, and a reexamination of the 97 cases of proliferative thyroid lesions from bony fishes deposited in the Registry of Tumors in Lower Animals. Specific diagnostic criteria are provided for all lesion categories including follicular cell hyperplasia (simple, nodular, or ectopic), adenoma (papillary or solid), and carcinoma (well- or poorly differentiated). These criteria should assist fish pathologists in describing and categorizing naturally occurring proliferative lesions from wild fishes, lesions that develop in laboratory fishes due to suboptimal culture practices or water quality, those in fishes used in toxicological assays, and captive aquarium fishes.