294
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Humes (195413) from the intestine of the quahaug, Mercenaria mercenaria, the recurved mussel, Brachidontes recurvus ( = Mytilus recurvus),
and the ribbed mussel, Modiolus demissus granosissimus, collected
near Grand Isle and Grand Terre, Barataria Bay, Louisiana.
Description. Adult female (Fig. 192) reddish to brownish orange ;
egg sacs whitish to greenish blue (depending on age of embryos) ; total
length of body (from anterior end to tips of rami) 4.017-5.850 mm
(average 4.875 mm), width 0.343-0.414 mm (average 0.377 mm) a t
anterior border of somite bearing second pair of legs; five pairs of
dorsolateral thoracic projections of subequal length ; abdomen elongate
and slender, terminating in two small caudal rami which extend posteriorly and bear four small spines ; no distinct cuticular division between thoracic and abdominal somites but segmentation suggested by
arrangement of internal muscles ; first antenna with four segments,
each of three distal ones armed with an aesthete and several setae or
spines, basal segment large with scattered spines and a group of fine
spinules along anterior border ; second antenna of four segments, the
terminal one in the form of a chitinized hook curving slightly towards
midline of body ; mandibles absent ; first maxilla as circular base from
which two setae arise ; second maxilla with three podomeres, basal
one elongated and largest, middle one short, distal one spatulate and
fringed with row of slender setae ; maxillipeds lacking but with chitinous
thickenings a t their positions ; head 0.342 mm long x 0.418 mm wide ;
ratio of length to width is 0.924; all four pairs of swimming legs
biramous; first leg with rami of two podomeres, expanded on their
outer margins to form a wide lamella, first exopodite podomere with single
seta on outer distal corner, secondexopodite podomere with three terminal
setae, endopodites unarmed ; second leg similar to first but with outermost terminal exopodite reduced in size ; third and fourth legs with only
two terminal setae; fifth leg absent; openings of oviducts strongly
chitinized and with transverse rod across aperture ; egg sacs 1.28 mm
x 0.15 mm, contain about forty-five to fifty-five eggs, extend beyond
ends of caudal rami.
Adult male (Fig. 193) reddish to brownish orange but paler than
female ; total length 2.379-2.574 mm (average 2.472 mm), width,
measured as in female, is 0.272-0.340 mm (average 0.319 mm) ; dorsolateral thoracic processes reduced to indiscernible humps ; abdomen
elongate, without distinct segmentation, terminates in caudal rami as
in female ; first and second antennae and first and second maxillae like
those of female ; mandibles absent ; maxilliped well developed, consisting of large subtriangular basal podomere and terminal podomere
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Humes (195413) from the intestine of the quahaug, Mercenaria mercenaria, the recurved mussel, Brachidontes recurvus ( = Mytilus recurvus),
and the ribbed mussel, Modiolus demissus granosissimus, collected
near Grand Isle and Grand Terre, Barataria Bay, Louisiana.
Description. Adult female (Fig. 192) reddish to brownish orange ;
egg sacs whitish to greenish blue (depending on age of embryos) ; total
length of body (from anterior end to tips of rami) 4.017-5.850 mm
(average 4.875 mm), width 0.343-0.414 mm (average 0.377 mm) a t
anterior border of somite bearing second pair of legs; five pairs of
dorsolateral thoracic projections of subequal length ; abdomen elongate
and slender, terminating in two small caudal rami which extend posteriorly and bear four small spines ; no distinct cuticular division between thoracic and abdominal somites but segmentation suggested by
arrangement of internal muscles ; first antenna with four segments,
each of three distal ones armed with an aesthete and several setae or
spines, basal segment large with scattered spines and a group of fine
spinules along anterior border ; second antenna of four segments, the
terminal one in the form of a chitinized hook curving slightly towards
midline of body ; mandibles absent ; first maxilla as circular base from
which two setae arise ; second maxilla with three podomeres, basal
one elongated and largest, middle one short, distal one spatulate and
fringed with row of slender setae ; maxillipeds lacking but with chitinous
thickenings a t their positions ; head 0.342 mm long x 0.418 mm wide ;
ratio of length to width is 0.924; all four pairs of swimming legs
biramous; first leg with rami of two podomeres, expanded on their
outer margins to form a wide lamella, first exopodite podomere with single
seta on outer distal corner, secondexopodite podomere with three terminal
setae, endopodites unarmed ; second leg similar to first but with outermost terminal exopodite reduced in size ; third and fourth legs with only
two terminal setae; fifth leg absent; openings of oviducts strongly
chitinized and with transverse rod across aperture ; egg sacs 1.28 mm
x 0.15 mm, contain about forty-five to fifty-five eggs, extend beyond
ends of caudal rami.
Adult male (Fig. 193) reddish to brownish orange but paler than
female ; total length 2.379-2.574 mm (average 2.472 mm), width,
measured as in female, is 0.272-0.340 mm (average 0.319 mm) ; dorsolateral thoracic processes reduced to indiscernible humps ; abdomen
elongate, without distinct segmentation, terminates in caudal rami as
in female ; first and second antennae and first and second maxillae like
those of female ; mandibles absent ; maxilliped well developed, consisting of large subtriangular basal podomere and terminal podomere