CONTRIBUCIONES CARCINOLOGICAS. l. EL PRIMER ESTADIO ZOEA EN GECARCINUS LATERALIS (FREMINVILLE) (BRACHYURA GECARCINIDAE) PROCEDENTE DE VERACRUZ, MEXICO

Resumen

For the first time, now, we are going to make a description of the initial zoeal stage of Gecarcinus lateralis (Freminville) obtained in vitro.
As far as possible, the Snodgrass concept of a triple division of Decapoda will be followed  in the description of this organism.
Some of the varied structures in this larva are undifferentiated, nevertheless, it is possible to establish an homology of the structure between the larvae and the adult, taking into consideration three tagmatae: the protocephalon, the gnathothorax and the abdomen. Each one of these has a particular organization and includes some of the appendages with their particular anatomy and characteristic setation. The protocephalon includes the labrum, the eyes, the first and second antennae, the ocular plate and the epistome. In the somites of the gnathothorax and the abdomen the following regions can be distinguished: tergal, pleural and sternal. The gnathothorax includes the mandibles, the first maxillae, the second maxillae, the first maxillipeds, the second maxillipeds and the carapace with its rostral spine, dorsal spine, lateral spines and the branchiostegal folds. The abdomen includes five segments and the bifurcated telson. The following are the principal characteristics of each of the appendages that might possibly have a taxonomical value: the eyes are sessile and compound with corneal and peduncular areas. The first antennae or antennules are conical, each one having in its distal end three aesthetes and one seta. The second antennae have two rows of spines on the endopodite, and one seta. lt also has one seta and two spines on the exopodite, one of which is very small. The mandibles have incisor and molar processes. The first maxillae have constantly six spines on the coxal endite, five spine on the basal endite and six setae on the three-jointed endopodite. The second maxillae have variable setation on the protopodial endites but the setation of the endopodite or palpus and on the exopodite or scaphognathite is very constant; there are four or five setae on the proximal lobe of the coxal endite; two to four setae on the distal lobe of the coxal endite; three to five setae on the proximal lobe of the basal endite; three or four setae on the distal lobe of the basal endite; the endopodite or palpus maxillar is bilobed and in each one of these lobes there are two setae; on the exopodite or scaphognathite there are four plumose setae. The first maxillipeds have constant setation on all parts except on the distal half of the protopodite; the proximal half of the protopodite bears four setae, one of which is outstanding; on the distal half of the protopodite there are four to six setae; the exopodite bears in its distal end four natatory setae, each one has one medial articulation. The general setation of the second maxilliped is very constant. Except for one occasional seta, found on the base of the protopodite, there are usually three setae on it. The endopodite is incompletely divided into four articles, each one bears in order from proximal to distal end: one, one, three and three setae; the exopodite bears in its distal end four natatory setae with medial articulation. The abdomen has five segments, in addition to the telson; the general form of the abdomen is important from the taxonomic point of view. On the first abdominal segment there are two dorsal setae; on the second and third abdominal segments there are two lateral knobs; on the forked telson there are six posteromedian setuled spines.
The chromatophores were studied in preserved material, they were found as following: one in the labrum, one in the antennules, two in each eye, one in the first maxillae, one in the first maxilliped, two in the second maxilliped being one of them very inconstant. In the carapace there are two chromatophores near the posterolateral margin of the branchiostegal fold. In the inside of the body there is a big melanic zone between 
the dorsal part of the stomodaeum and the heart. In the abdomen there are two chromatophores in each segment along the gut; the last pair is between the fifth segment and the telson.