FISHERY BULLETIN: VOL. 86, NO. 2 



shallow waters of the northern Gulf of Mexico 

 near Grande Terre, LA, in May 1982 and held in 

 a small aquarium at room temperature. After the 

 eggs hatched, the zoeal larvae were given fresh 

 seawater and newly hatched Artemia nauplii 

 daily. Exuviae as well as dead and some living 

 megalopae were preserved in 70% ethanol. Draw- 

 ings were made with the aid of a Wild^ M-5 

 stereoscope and a Wild M-11 compound stereo- 

 scope, both with camera lucida; accuracy was ver- 

 ified with a Nikon Optiphot. Measurements were 

 made with an ocular micrometer. Ten laboratory- 

 reared megalopae were examined, measured, dis- 

 sected, and compared with megalopae from field 

 collections made in 1973 off south Texas. Com- 

 parisons with M. mercenaria are based on 

 laboratory-reared M . mercenaria megalopae from 

 two females collected on 13 August 1987 from the 

 Indian River system, north of Ft. Pierce, FL. Eggs 

 of these two females hatched on 21 August 1987, 

 and the megalopa stage was first reached after 17 

 days in mass culture aquaria (30%o salinity, 

 25°C, 12h:12h light/dark regime). Descriptions of 

 setation for all appendages proceed from proximal 

 to distal. Specimens examined under the scan- 

 ning electron microscope (SEM) were prepared 

 according to procedures outlined by Felgenhauer 

 (1987) but without postfixation in osmium tetrox- 

 ide and with 100% ethanol, rather than amyl ac- 

 etate, as the transitional fluid. Sibling megalopae 

 and field collections have been deposited in the 

 U.S. National Museum of Natural History, 

 catalogue No. USNM 229962 (laboratory- 

 reared M. adina), USNM 229961 (field-collected 

 M. adina), and USNM 229963 (laboratory-reared 

 M. mercenaria). 



RESULTS 



Carapace (Figs., lA, B, C, 3 A).— Length 1.67 

 mm, width 1.45 mm (A'^ = 10). Subquadrate, with 

 2 lateral prominences on each side; dorsoven- 

 trally thick, with minute tubercle centrally lo- 

 cated. Posterior border fringed with numerous 

 short setae; lateral margin with few scattered 

 setae. Rostrum ventrally deflexed, nearly verti- 

 cal, with deep medial depression, rounded anteri- 

 orly. Angular interorbital prominences extend 

 ventrally between orbit and antennule. Chroma- 

 tophores variable in placement, but almost al- 

 ways found in areas indicated in Figure IB. 



Eyes (Figs. lA, B, C, 3A). — Large, exposed; eye- 

 stalks sometimes with 2 or 3 short, simple ante- 

 rior setae, always with posterodorsal chroma- 

 tophore. 



Abdomen (Fig. lA, B). — Subequal in length to 

 carapace. All pleura with rounded posterolateral 

 angles. All somites with sparse setae dorsally; 

 somites 2-5 always with elongated chroma- 

 tophores. 



Telson (Fig. IG). — Broadly rounded with vari- 

 able setation, occasionally with pair of small pos- 

 terior spines (as in Figure IB). 



Antennule (Fig. IK). — Biramous; peduncle 3- 

 segmented, with variable setation. Basal seg- 

 ment of peduncle large, bulbous, always with 

 large chromatophore; middle segment subcylin- 

 drical with 0-2 distal setae; distal segment ovoid 

 with scattered short setae. Lower ramus 

 1-segmented with 6-8 setae; upper ramus 

 5-segmented with aesthetascs arranged in tiers, 

 usually 0, 7, 8, 6, 4 subterminal plus 3 terminal, 

 with short setae sometimes present on segments 

 2 and 4 (note: all aesthetascs not illustrated). 



Antenna (Fig. IJ). — Flagellum 12-segmented 

 (sometimes 11), with 3 peduncular articles and 8 

 or 9 flagellar articles (see Rice, in press, for cor- 

 rect number of antennal segments in megalopae); 

 setation variable, usually 2, 3, 2, 0, 0, 2, 4, 0, 4 or 

 5, 1, 4, 4. 



Mandibles (Fig. 2F). — Asymmetrical, with 

 broadly rounded spade-shaped cutting edges; palp 

 2-segmented with setation 0, 11-14. 



Maxillule (Fig. 2E). — Protopodite with 1 or 2 

 long plumose setae on posterodorsal margin; en- 

 dopodite 2-segmented with setation 1, 2 subtermi- 

 nal plus 2 terminal; basal endite with 29-35 

 spines and setae; coxal endite with 13-16 spines 

 and setae. 



Maxilla (Fig. 2D).— Scaphognathite with 70-78 

 fringing setae and 0—6 setae on blade; endopodite 

 unsegmented with or 1 distolateral seta and 4 or 

 5 basal plumose setae; basal endite bilobed with 

 setation variable, usually 8-10, 9-11; coxal en- 

 dite bilobed with setation usually 7, 9 or 10. 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Maxilliped 1 (Fig. 20). — Exopodite 2-seg- 

 mented, with setation 2 or 3, 5-7. Endopodite 



290 



