Early embryonic development and external features of developing embryos of the caddisfly, Nemotaulius admorsus (trichoptera: Limnephilidae)

Formative processes of the blastoderm, germ disk, embryonic membranes, and germ band in the trichopteran Nemotaulius admorsus are described. Successive external changes of developing embryos are also described, chiefly on the basis of SEM data. The blastoderm is very thin, and a circular germ disk forms in its ventro-posterior region about 32 hr after oviposition. Embryonic membranes are completed by fusion of amnio-serosal folds extending from the margin of the germ disk. The germ disk then differentiates into a long germ band in situ. This process is similar to that of other trichopterans of the suborder Integripalpia (e.g., Neophylax concinnus and Neoseverinia crassicornis), but differs from that of Stenopsyche griseipennis (suborder Annulipalpia) in which the germ band and embryonic membranes are formed by deep invagination of the germ disk. The germ band or embryo, as in other trichopteran species, assumes a completely superficial position throughout development. The following description summarizes its external differentiation. An egg tooth develops at the top of the head capsule. Antennal rudiments become small as development advances. In the maxillary segment, the lacinial and galeal lobes are indistinguishable and united into one laciniogaleal complex. Thoracic appendages develop considerably during the embryonic period. Pleuropodia are formed in the first abdominal segment. Two pairs of appendage-like swellings, a ventral and a medial pair, arise in each of the first eight abdominal segments, and homologies of these swellings and pleuropodia are discussed. Terminal hooks originate from the bilateral projections of the telson. Tracheal invaginations appear in the mesothoracic, metathoracic, and the first eight abdominal segments, but their openings or spiracles close later. Embryonic membranes rupture after revolution, and thus the secondary dorsal organ is formed.