44 
Fishery Bulletin 115(1) 
A 
Figure 1 
Locations of the longitudinal axes used for prep- 
aration of thin sections indicated by red arrows 
for (A) the eyestalk of spot shrimp (Pandalus 
platyceros) and (B) the dorsal ossicle (urocar- 
diac and mesocardiac) of red king {Paralithodes 
camtschaticus) and southern Tanner {Chionoece- 
tes bairdi) crabs, as illustrated with the ossicle of 
a southern Tanner crab. Red king and southern 
Tanner crabs and spot shrimp were collected in 
Alaska during 2013-2014 for this study of a di- 
rect age-determination method. 
ed at the time of collection. Shell condition, a subjec- 
tive index of epibionts and wear on the exoskeleton, 
was noted because it has proven useful for evaluating 
differences in the recency of molting in crab species 
(Jadamec et al., 1999; Donaldson and Byersdorfer, 
2002). Crab gastric mills and shrimp eyestalks were 
dissected, cleaned, and preserved in a mixture of eth- 
anol, glycerol, and distilled water (with a volume ra- 
tio of 70:4:26). 
Structures were embedded in cold cure epoxy resin 
and sectioned longitudinally (Fig. 1) with a diamond- 
bladed IsoMet Low Speed Saw (Buehler, Lake Bluff, 
IL) at the University of New Brunswick in Saint 
John, New Brunswick, Canada. Several serial sec- 
tions (with thickness of 160-180 pm) were prepared 
per structure and mounted with epoxy individual- 
ly on slides, polished by hand with dry, 0.3-pm-grit 
lapping film, covered with 90% ethyl alcohol, and 
viewed under transmitted light with a CX41 Olym- 
pus compound microscope (Olympus Corp., Tokyo) at 
100-400X magnification. All cuticular layers were ex- 
amined throughout the thin sections, and bands were 
recognized as alternating (bipartite) translucent and 
opaque zones in the endocuticle of crab mesocardiac 
ossicles and shrimp eyestalks. Photographs were tak- 
en with a DP72 Olympus digital camera (Olympus 
Corp.) attached to the microscope. 
Examination of exuviaS gastric structures 
Two female red king crab were captured by divers in 
southeast Alaska and 3 male southern Tanner crab 
were captured by pot and trawl gear near Kodiak, 
Alaska, in 2014. Female red king crabs were immature 
and grasped by males in situ (precopulatory guarding 
of mate), indicating that the pubertal molt to matu- 
rity was imminent. All crabs were held in aquaria with 
flow-through seawater at ambient seawater tempera- 
ture and monitored daily until they molted. After ec- 
dysis, the exuvial gastric mill structures were removed 
and photographed. At 1 week after the molt, the whole 
stomach was dissected from the crab, and the gastric 
mill structures were photographed for comparison with 
the same structures from the exuviae. 
Results 
Histological examination of the cuticle 
The eedocuticular layer was visually differentiated 
from other cuticular layers in the mesocardiac ossicles 
of red king and southern Tanner crabs (Fig. 2) and in 
the eyestalks of spot shrimp (Fig. 3) after ossicles were 
stained with Masson’s trichrome. The epicuticle, exocu- 
ticle, and membranous layers were clearly visible in 
thin sections of crab mesocardiac, where red indicated 
the membranous layer and epicuticle (Fig. 2). Lamellar 
structure, of alternating light and dark stained bands, 
were more discernible in the mesocardiac of a southern 
Tanner crab (Fig. 2B) and the exo- and endocuticle of 
the eyestalk of a spot shrimp (Fig. 3B) than in the me- 
socardiac of a red king crab (Fig. 2C) at similar mag- 
nification. The cuticle layers of the eyestalks of spot 
shrimp tended to separate during histological section- 
ing (Fig. 3A). 
