9. THE CLASS CRUSTACEA
323
It has also been found in the tubes of Chaetopterus variopedatus, from
Molgula robusta, in the pharynx of Bostrichobranchus pilularis and on
Asterias vulgaris. It was originally described by Say (1818) as inhabiting
" the muricated Pinna of our coast."
Descriptions. Mature female (Fig. 2 16) with suborbicular carapace,
13.7 mm long, 14.3 mm wide, thick and firm but not hard, convex;
surface uneven, covered with short and deciduous tomentum ; gastrocardiac area higher than and separated by depressions from branchiohepatic area ; front slightly advanced, approximately one-fifth width of
carapace, subtruncate in dorsal view, slightly bilobed ; orbits small,
subcircular ; eyes spherical ; antenna longer than width of orbit ;
antennule large, obliquely transverse ; buccal mass roughly quadrangular, crescentic, much broader than long ; ischium and merus of
external maxilliped united ; propodus larger than carpus ; dactyl narrow,
curved, spatulate, attached near middle of propodus, reaching to near
extremity of propodus ; chelipeds moderately stout, articles subcylindrical, more or less pubescent ; carpus elongate ; palm thick, blunt
edged, increasing in size distally ; fingers stout, fitting closely together
with tips hooking past each other ; immovable finger nearly horizontal ;
dactyl with tooth near base fitting into sinus with tooth at either side
on immovable finger ; walking legs slender, hairy above and below ;
second pair longest but shorter than chelipeds ; first three dactyls
falcate, shorter than propodi; last leg shortest, turned forward and
upward, with long dactyl of same length as propodus. Obscure brown
in color,
Young females resemble dark-colored males except in shape of
abdomen and characteristics of appendages ; free-swimming, measuring
up to 6.2 mm in length. More mature females symbiotic with hosts
(usually pelecypods) ; light colored, measuring from 3.3 mm in length ;
long hair persists on such small- and medium-sized females.
Mature male (Fig. 217) with flat subcircular carapace, 9.1 mm long,
8.7 mm wide, harder than female ; regions superficially defined, more
by color than by structural prominence, light areas mostly elevated,
usually allowing pubescence to wear ; gastric, cardiac, and branchial
regions separated by broad, shallow confluent indentations ; front
broad, prominent, depressed, slightly lobed, approximately one-third
width of carapace ; orbits subcircular, eyes large ; antenna somewhat
longer than width of orbit; chelipeds shorter than in female, hands
stouter ; walking legs wider, especially propodal articles of first three
legs ; posterior surface overlaid with thin fringe of hairs attached near
upper margin ; last leg relatively shorter than in female, not reaching
propodus of third leg, dactyl more like third leg than in female;
323
It has also been found in the tubes of Chaetopterus variopedatus, from
Molgula robusta, in the pharynx of Bostrichobranchus pilularis and on
Asterias vulgaris. It was originally described by Say (1818) as inhabiting
" the muricated Pinna of our coast."
Descriptions. Mature female (Fig. 2 16) with suborbicular carapace,
13.7 mm long, 14.3 mm wide, thick and firm but not hard, convex;
surface uneven, covered with short and deciduous tomentum ; gastrocardiac area higher than and separated by depressions from branchiohepatic area ; front slightly advanced, approximately one-fifth width of
carapace, subtruncate in dorsal view, slightly bilobed ; orbits small,
subcircular ; eyes spherical ; antenna longer than width of orbit ;
antennule large, obliquely transverse ; buccal mass roughly quadrangular, crescentic, much broader than long ; ischium and merus of
external maxilliped united ; propodus larger than carpus ; dactyl narrow,
curved, spatulate, attached near middle of propodus, reaching to near
extremity of propodus ; chelipeds moderately stout, articles subcylindrical, more or less pubescent ; carpus elongate ; palm thick, blunt
edged, increasing in size distally ; fingers stout, fitting closely together
with tips hooking past each other ; immovable finger nearly horizontal ;
dactyl with tooth near base fitting into sinus with tooth at either side
on immovable finger ; walking legs slender, hairy above and below ;
second pair longest but shorter than chelipeds ; first three dactyls
falcate, shorter than propodi; last leg shortest, turned forward and
upward, with long dactyl of same length as propodus. Obscure brown
in color,
Young females resemble dark-colored males except in shape of
abdomen and characteristics of appendages ; free-swimming, measuring
up to 6.2 mm in length. More mature females symbiotic with hosts
(usually pelecypods) ; light colored, measuring from 3.3 mm in length ;
long hair persists on such small- and medium-sized females.
Mature male (Fig. 217) with flat subcircular carapace, 9.1 mm long,
8.7 mm wide, harder than female ; regions superficially defined, more
by color than by structural prominence, light areas mostly elevated,
usually allowing pubescence to wear ; gastric, cardiac, and branchial
regions separated by broad, shallow confluent indentations ; front
broad, prominent, depressed, slightly lobed, approximately one-third
width of carapace ; orbits subcircular, eyes large ; antenna somewhat
longer than width of orbit; chelipeds shorter than in female, hands
stouter ; walking legs wider, especially propodal articles of first three
legs ; posterior surface overlaid with thin fringe of hairs attached near
upper margin ; last leg relatively shorter than in female, not reaching
propodus of third leg, dactyl more like third leg than in female;