Brachyura larvae
Identification

For the purposes of this chapter, only the first zoea and the megalopa are included. However, a key to staging of zoeae is provided (see page Bl.10 Key to recognize zoeal larvae of major decapod groups ). In general, the identifications are largely based on gross morphological features and relative size, and mostly only figures of the whole animal are presented. In some cases, however, this may not be satisfactory for proper identification. See pages Bl.11 Identification of first zoea of Brachyura and Bl.12 Identification of megalopa of Brachyura for introductions to the identification keys for brachyuran first zoea and megalopa respectively.

Editor's note: the only key available is a key to families for first zoea, which starts at Page 1697: Brachyura larvae: first zoea. Further identification of the zoae has to be carried out then by comparising characters listed in the family tables 5-13 (Table 5 First zoeae of Dromiidae to Table 13 First zoeae of Portunidae). Identification of megalopal stages entirely must be carried out by comparising characters in the concerned family tables 15-19 (Table 15 Mgp Dromiidae Latreilliidae Calappidae Leucosiidae to Table 19 Mgp Pinnotheridae Grapsidae Gecarcinidae Ocypodidae).

The reader must also bear in mind that for some species not all larval stages are known and that for others, larvae are totally unknown. As well, it should be kept in mind that most descriptions are based on laboratory rearing and that all species exhibit some morphological variability. Thus, descriptions and illustrations may deviate from the specimens being compared. Consequently, when scientific reliability is essential, identifications of specimens should be verified by consulting with experts in the field or by cross-checking with the original description using the appropriate references cited. This may in many cases necessitate the dissection of appendages from the body to help in the identification. A brief protocol follows for anyone wishing to pursue this route.

—Dissecting and mounting
Dissection will necessitate the use of very fine-tipped needles. While the finest insect pins may be satisfactory for relatively large specimens, best results are obtained by using tungsten wire that is electrolytically sharpened in a 10% KCl solution and fastened onto a probe. For this a microscope transformer can be conveniently used, with one cable attached to an electrode (e.g. a nail) immersed in the solution, the other cable with the tungsten wire at the tip also being dipped into the liquid as low voltage is applied from the transformer. The voltage, emersion time, and depth of wire dipped, are manipulated until the desired shape is obtained.

With the specimen in water on a depression microscope slide, the larval carapace and abdomen should be separated before dealing with the appendages. This is done by using one needle to hold the carapace in place while gently pushing the abdomen away at its point of insertion until it detaches from the carapace. By piercing the carapace with one needle, the other needle can then be used to separate appendages at their point of attachment, starting from the posterior end of the larva. A stain, such as Chlorazol Black, can be added to increase contrast when necessary. For temporary mounts, the dissected parts are pipetted onto a flat microscope slide and a coverslip is applied. A sealant, such as clear fingernail polish, can be applied to the edges to help prevent evaporation. For the preparation of more permanent mounts the reader is referred to Koomen and Von Vaupel Klein (1995). A good compound microscope with 10x, 40x and 100x objectives is required to examine the dissected appendages. A microscope equipped with phase contrast or Nomarski differential interference contrast would be preferable in order to facilitate the determination of critical features such as hair-like setae.