FISHERY BULLETIN: VOL. 7L NO. 3 



The opercular bones in adults are structur- 

 ally similar in both species except that the 

 posterodorsal margin of the opercle may be 

 more deeply indented in C. arctifrons. 



Hypobranchial Region 



Branch iostegal rays may become ossified by 

 4 mm in both species, although the total of 

 seven may not be stained until 6 mm (Leonard, 

 1971a, Figure 26). The unpaired urohyal, 

 which lies beneath the branchiostegals, ossifies 

 at around 6 mm in E. ))iicrostomus and 7 mm 

 in C. arctifrons. The interhyal is next, followed 

 by the hypohyals, ceratohyal, and epihyal 

 which ossify at about the same time. These 

 bones usually become ossified at a smaller size 

 in E. microstomus (Table 7). The basihyal 

 ossifies after metamorphosis (Figures 10, 11). 



Structural similarity between the two species 

 is great. The first three branch iostegal rays 

 appear to be supported by the ceratohyal and 

 the remaining four by the epihyal in both 

 species. 



Additional Comments 



The first bones to ossify in the branchio- 

 cranium are of dermal origin. Except for the 

 quadrate and articular, which form the angle 

 of the jaws, the only bones ossified in larvae 

 of 4-5 mm in both species are dermal bones. 

 These bones become ossified at about the same 

 size in both species (Table 7). They include the 

 premaxillary, maxillary, dentary, ectopterygoid, 

 preopercle, opercle, branchiostegal rays, cleith- 

 rum, and supracleithrum. Ossification of cart- 

 ilage bones follows. 



The parasphenoid, a dermal bone of the 

 neurocranium, is also prominent in 4-mm 

 stained larvae of both species. This bone ex- 

 tends from the ethmoid region to the basi- 

 occipital in the basicranial region of the neuro- 

 cranium (Figure 9). 



In the smallest stained specimens, pharyngeal 

 teeth in the form of sharp pointed cones, may 

 be seen clearly. Together with the parasphenoid 

 and the cleithrum, they are prominent features 

 in 4-mm larvae t)f both species. They are still 

 apparent in 12-mm larvae (Figure 9). 



The sequences of ossification of bones dis- 

 cussed are the same for E. microstomus and 

 C. arctifrons. Most bones become ossified at 

 an earlier stage in E. microstomus. Major 

 differences are the preopercular spines of E. 

 microstomus and the small size at which the 

 larger jaw of C. arctifrons becomes evident. 



OCCURRENCE AND SPAWNING IN 

 THE CHESAPEAKE BIGHT 



Adults of E. m,icrostomus and C. arctifrons 

 occur throughout the Chesapeake Bight from 

 Cape Henlopen, Del., to Cape Hatteras. Their 

 distribution is limited by depth. E. microsto- 

 mus is found in waters shallower than 37 m 

 (20 fm) while C. arctifrons occurs in depths 

 >37 m (Figure 12). Slight distributional overlap 

 may occur around depths of 37 m. Adults of 

 both species are present in the bight throughout 



Figure 12. — Distribution of adult Etropits microstomus 

 and Citharichlhys arctifrons in the Chesapeake Bight. 

 The 37-m (20-fm) and 183-m (100-fm) depth contours 

 are emphasized. [From data collected by Virginia Insti- 

 tute of Marine Science in 1966. No tows were made be- 

 yond 183 m (100 fm).] 



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