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Fishery Bulletin 107(2) 
dorsal-fin spines are not longer than the third or fourth, 
and the two rows of ctenoid scales below the dorsal fins 
extend onto the caudal peduncle (Bolin, 1936; Mecklen- 
burg et al., 2002). 
This study is the first to identify and describe the 
larval and juvenile stages of I. borealis. Previous de- 
scriptions were based on misidentified specimens or 
were made at a more conservative generic level because 
of difficulty distinguishing among species of Icelinus 
and between Icelinus and other sympatric cottid larvae. 
Larvae of Icelinus quadriseriatus from the coast of Cali- 
fornia are currently the only Icelinus larvae described 
(Feeney, 1987). Larvae tentatively identified as I. borea- 
lis in early literature were misidentified as Ruscarius 
meanyi based on a pelvic-fin ray count of 1, 2 — a count 
diagnostic of Icelinus but also occurring rarely in R. 
meanyi (Blackburn, 1973; Richardson, 1977; Richardson 
and Pearcy, 1977; Richardson and Washington, 1980; 
Washington, 1981; Begle, 1989). Current literature has 
continued to identify larvae of Icelinus at the generic 
level; however, Matarese et al. (1989, 2003) have cau- 
tiously identified illustrations as I. borealis. Icelinus bo- 
realis has cautiously been identified at the species level 
because three other species of Icelinus with unidentified 
larvae (I. burchami, I. filamentosus, and I. tenuis), and 
other unidentified cottid larvae (e.g., Icelus) are also 
found in the Gulf of Alaska. 
Uniformity between larval Icelinus and other cottid 
larvae is noted in the assignment of phenetic groups 
based on shared larval characters (e.g., preopercular 
spine pattern, body shape, and pigmentation) (Rich- 
ardson, 1981). Icelinus is included in phenetic group 2, 
which includes Paricelinus, Triglops, Icelus (tentative- 
ly), and Chitonotus, and is characterized by a slender 
body shape, pointed snout, and four prominent pre- 
opercular spines (Richardson, 1981). Further study of 
phenetic groups has increased the size of group 2, the 
“ Myoxocephalus group,” to include a total of 13 genera 
(Matarese et al., 1989; Moser et al., 1996). The Myoxo- 
cephalus group includes the genera previously included 
in group 2 as well as the genera Myoxocephalus, Rus- 
carius, Ascelichthys, Orthonopias, Enophrys, Radulinus, 
Gymnocanthus, and Synchirus (Matarese et al., 1989; 
Moser et al., 1996). Members of the Myoxocephalus 
group have four preopercular spines and are defined by 
a unique larval character, namely a bony preopercular 
shelf (Moser et al., 1996). 
Larvae of Icelinus are reported to be the most fre- 
quently collected larval cottids in the Northeast Pacific 
Ocean and Bering Sea. Although collected in large num- 
bers, the size range of specimens is limited, which has 
hindered compiling the developmental series necessary 
for description. Increased ichthyoplankton sampling 
conducted in the Bering Sea in the 1990s has provided 
the specimens necessary to describe larvae of I. borealis 
using meristic counts and morphological characters, 
including pigmentation and preopercular spination. 
This study presents an illustrated developmental series 
and general aspects of osteological development for I. 
borealis. 
Methods 
A total of 53 specimens (7.4-51.7 mm standard length 
[SL] ) collected during AFSC research cruises in the 
Bering Sea and Gulf of Alaska between 1979 and 2002 
were examined (Fig. 1). Specimens were collected at 
depths to 400 m, primarily using 60-cm bongo nets 
and Methot trawls. Specimens were initially preserved 
in 5% formalin buffered with sodium borate, then later 
transferred to 70% ethanol. Nineteen specimens were 
cleared and stained using the method of Potthoff (1984). 
Twenty-two adult Icelinus borealis specimens were radio- 
graphed to verify the vertebral count of 35-36 recorded 
in literature. 
Specimens were grouped using the series method, 
by positively identifying juveniles using known adult 
characteristics then linking those specimens to progres- 
sively smaller specimens using shared characteristics 
(Neira et al., 1998). Larvae were identified using re- 
ported generic characters for Icelinus including 35-36 
vertebrae (myomeres) and four distinct preopercular 
spines, if developed. Illustrated Icelinus (tentatively 
identified as I. borealis ) from Matarese et al. (1989) 
were also used to compare general morphological and 
pigment characters. 
Meristic counts are reported for ossified elements 
using cleared and stained or radiographed material. 
Morphometric measurements were taken following 
Richardson and Washington (1980) using a digital 
image analysis system with Image Pro Plus, vers. 4.5 
software (Media Cybernetics, Inc., Silver Spring, MD). 
Both body length and proportional measurements are 
in SL unless otherwise noted. Developmental termi- 
nology follows Kendall et al. (1984). Nomenclature de- 
scribing caudal-fin development follows Matarese and 
Marliave (1982). 
Only melanistic pigmentation is described. Nomencla- 
ture describing pigment pattern follows Busby and Am- 
brose (1993). The term “band” refers to an aggregation 
of melanophores oriented vertically; “bar” refers to an 
aggregation that is oriented horizontally. Illustrations 
were rendered using a camera lucida attached to a dis- 
secting stereomicroscope. 
Material examined 
Larvae: 53 specimens examined, 7.4-51.7 mm. UW 
105110, 1 (16.7 mm), Bering Sea, 52°35.9'N, 173°25.6W, 
137 m depth, 2 August 1997, FV Vesteraalen\ UW 105111, 
1 (13.4 mm), Bering Sea, 56°31.9'N, 166°25.4'W, 88 m 
depth, 16 July 1994, RV Miller Freeman ; UW 105113, 2 
(14.4-15.1 mm), Bering Sea, 56°30.6'N, 168°60.0'W, 95 
m depth, 23 July 2001, TS Oshoro maru; UW 105114, 
1 (12.1 mm), Bering Sea, 54°59.7'N, 166°58.9'W, 100 
m depth, 19 July 1995, TS Oshoro maru\ UW 105116, 
1 (14.5 mm), Bering Sea, 56°59.6'N, 170°00.4'W, 62 m 
depth, 25 July 1996, TS Oshoro maru\ UW 105117, 2 
(13.4-14.3 mm), Bering Sea, 57°01.1'N, 171°00.2'W, 94 
m depth, 25 July 1996, TS Oshoro maru\ UW 105119, 
2 (14.3—16.3 mm), Bering Sea, 55°00.9'N, 166°01.4'W, 
