Hawaiian Barnacle- — UTINOMI 
47 
TABLE 2 
Differences in Details of Structure Between Balanus amphitrite hawaiiensis and 
B. amphitrite communis 
DETAILS OF 
STRUCTURE 
B. amphitrite hawaiiensis 
B. amphitrite communis 
Ground color of shell. .. 
Glossy white 
Rather reddish white, darkened with 
bluish tint in upper part 
Outside of parietes 
Only dark violet longitudinal stripes 
sharply defined; those in middle and 
along both sides indistinct or reduced 
(Fig. la) 
Pale or dark violet longitudinal stripes 
crossed by the same colored or red- 
dish transverse stripes on the whole 
area 
Inside of parietes 
Strongly ribbed up to the sheath; ribs 
flat on roof and finely denticulate on 
both sides but not bifurcate distally 
(Fig. lb) 
Slightly ribbed near base; ribs low, with 
slight denticulation at base which 
may extend as bifurcate secondary 
ribs; a few shorter riblets often in- 
terseptally (Fig. 1 c) 
Parietal tubes 
Numerous (about 16 in rostrum), nar- 
row and square at base (Fig. lb) 
Few (about 9 in rostrum), large and 
rectangular at base (Fig. 1 c) 
Radii.... 
Very broad, flat, with almost level sum- 
mits, forming an angle of about 
100°-110° with the interlocking 
margin (Fig. la) 
Narrow, slightly sunken, with very ob- 
lique summits, forming an angle of 
about 140° with the interlocking 
margin 
Rostrum 
Apex usually incurved 
Apex often turned outwards when iso- 
lated 
Scutum 
Depression below adductor ridge deep, 
oblongly circumscribed (Fig. 2b) 
Depression below adductor ridge shal- 
low, lengthened along adductor ridge 
(Fig. 2d) 
Tergum. 
Spur very broad, over 14 width of the 
valve, short, either rounded or trun- 
cate distally and separated from basi- 
scutal angle by less than its own 
width; crests for depressor muscles 
strongly developed, typically 5 (Fig. 
2a) 
Spur longer than wide, with more or less 
hatchet-shaped end, separated from 
basi-scutal angle by its own width 
which is less than 14 that of the 
valve; crests for depressor muscles 
not so strong, exceeding 5 in num- 
ber (Fig. 2c) 
Labrum 
Multidenticulate on each side of a me- 
dian notch (Fig. le) 
3 teeth, or with a smaller additional one, 
on each side (Fig. Id) 
of this subspecies, compared with the typical 
communis , will help to a certain extent in later 
identifications. 
NATIVE SEA AND HABITAT 
From these data of occurrence, it is very likely 
that the subspecies hawaiiensis (= denticulata ) 
is not a local variant restricted to such a small 
area of special environments as the Suez Canal, 
but nowadays is very widely distributed in cir- 
cumequatorial tropical and temperate areas in 
all oceans. 
Its native habitat is probably the Hawaiian 
Islands in the mid-Pacific tropical sea. From this 
mid-Pacific area it may have spread much earlier 
and more rapidly in all seas than did the Aus- 
tralasian barnacle, Elminius modestus Darwin, 
in European and South African waters. It is sup- 
posed that the first establishment of this Ha- 
waiian barnacle took place from the tropical 
west Pacific, such as the Philippines and For- 
mosa, lying along the North Equatorial Current, 
where it is directed westerly, although the most 
probable means of migration may have been at- 
tachment on the hulls of ships. 
In these tropical and subtropical areas the 
