216
(1) setose cercopods, i.e. with a set of plumose setae
along their inner and lateral borders; these cercopods
are clearly articulated to the telson, and are not confluent dorsomedially; the anus is terminal (Fig. 7 E); and
(2) spinose cercopods, i.e. with spines replacing the
setae on the distal half; these cercopods are sclerotized,
fused with the telson, and confluent dorsomedially; the
anus is shifted to a subterminal, ventral position (Fig.
7 F).
Female genital tract
In general, the female genital apparatus of the Anostraca consists of (1) a pair of ribbon-like ovaries situated
on both sides of the gut, (2) a pair of oviducts (ventral
outgrowths of the ovaries) with lateral pouches, (3)
two pairs of shell glands (4) an ovisac, and (5) a brood
pouch.
Embryologically, and although the ovaries and
oviducts are derived from the mesoderm, the ovisac
and shell glands are considered to be of ectodermal
origin (Linder, 1959; Criel, 1992). The genital segments are ventrally modified into a genital atrium; this
is the so-called brood pouch (Linder, 1959; Martin,
1992) which, by invagination of the cuticular epithelium (Linder, 1959), forms the ovisac (Linder, 1959;
Martin, 1992) (= uterus (Claus, 1886; Criel 1980;
1992)), inside of which the oocytes are fertilized,
and later shelled by secretions of the shell glands.
In adult Streptocephalus females, different stages of
the ovarian cycle can be recognized under a stereoscopic microscope without dissecting the specimen.
The type and extension of the ovaries, however, is
only precisely seen when they are in the ripening egg
(vitellogenesis) stage. This stage is the longest of the
ovarian cycle and corresponds to the period of the
reproductive cycle when the ovisac contains eggs or
cysts (Brendonck, 1991; pers. obs.). Most field samples usually contain some females with this ovarian
stage represented. Claus (1886) and Valousek (1952),
Munuswamy & Subramoniam (1985), and Brendonck
(1991) reported on S. torvicornis, S. dichotomus, and
S. proboscideus with uniramous ovaries. This type of
uniramous ovary is developed in most species of the
genus. They normally extend from the genital segment
1 to the abdominal segment 6 (Fig. 8 A-C). On the
other hand, biramous ovaries are found only within
a group of North American species. The maximum
extension of both anterior and posterior rami is variable within and among species (Maeda-Martinez et al.,
1995; this volume). In both types of ovaries, the connection between ovary and oviduct is located in the
first genital segment (Fig. 8 A, C, E). In females with
uniramous ovaries, a suspensory ligament attached to
thoracic segment 11 is normally observed in lieu of
the anterior branch of the biramous ovary (Fig. 8 C).
A peculiarity noticed in females of S. dichotomus, S.
proboscideus, and S. torvicornis are the long and elastic diverticula (lateral pouches) of the oviducts. When
filled with oocytes, they extend into the lumen of the
abdomen (Valousek, 1952; Brendonck, 1991; Murugan, pers, comm.; pers. obs.). It remains to be seen,
however, whether this is a general feature of Streptocephalus females.
Family Streptocephalidae Daday, 1910
Diagnosis. Male antennae two-jointed; basal joints
somewhat coalesced; apical joints, in ventral position,
laterally directed to some extent, then curved inward.
Basal joints with a stout distal outgrowth, consisting of
a cylindrical, robust, unigeniculated or bigeniculated
peduncle, and terminating in a scleroid cheliform structure (hand). Maxillae with one distal seta. Eleven pairs
oflimbs; one praeepipodite. Seminal vesicles not clearly defined. Vas deferens forming a variable loop dorsally directed in the first genital segment. Penes ventrally
projected; basal parts not rigid, non-retractile; apical
parts long, retractile, and usually with two longitudinal
rows of spines (three in one species).
Genera. The Streptocephalidae contains only one
genus.
Remarks. Except for (1) the modified apical joint,
(2) the cheliform structure or hand of the distal outgrowth, and (3) morphology oflthe retractile penes, all
of the diagnostic features are shared with the family Thamnocephalidae. These similarities, as Linder (1941) pointed out, suggest a close relationship
between these two families.
Streptocephalus Baird, 1852
Diagnosis. As for family.
Type species. S. torvicornis (Waga, 1842).
Species. Fifty-eight species can be recognized as
valid (Belk & Brtek, 1995; this volume). They are
distributed in North America, Europe, Africa, Arabia,
(1) setose cercopods, i.e. with a set of plumose setae
along their inner and lateral borders; these cercopods
are clearly articulated to the telson, and are not confluent dorsomedially; the anus is terminal (Fig. 7 E); and
(2) spinose cercopods, i.e. with spines replacing the
setae on the distal half; these cercopods are sclerotized,
fused with the telson, and confluent dorsomedially; the
anus is shifted to a subterminal, ventral position (Fig.
7 F).
Female genital tract
In general, the female genital apparatus of the Anostraca consists of (1) a pair of ribbon-like ovaries situated
on both sides of the gut, (2) a pair of oviducts (ventral
outgrowths of the ovaries) with lateral pouches, (3)
two pairs of shell glands (4) an ovisac, and (5) a brood
pouch.
Embryologically, and although the ovaries and
oviducts are derived from the mesoderm, the ovisac
and shell glands are considered to be of ectodermal
origin (Linder, 1959; Criel, 1992). The genital segments are ventrally modified into a genital atrium; this
is the so-called brood pouch (Linder, 1959; Martin,
1992) which, by invagination of the cuticular epithelium (Linder, 1959), forms the ovisac (Linder, 1959;
Martin, 1992) (= uterus (Claus, 1886; Criel 1980;
1992)), inside of which the oocytes are fertilized,
and later shelled by secretions of the shell glands.
In adult Streptocephalus females, different stages of
the ovarian cycle can be recognized under a stereoscopic microscope without dissecting the specimen.
The type and extension of the ovaries, however, is
only precisely seen when they are in the ripening egg
(vitellogenesis) stage. This stage is the longest of the
ovarian cycle and corresponds to the period of the
reproductive cycle when the ovisac contains eggs or
cysts (Brendonck, 1991; pers. obs.). Most field samples usually contain some females with this ovarian
stage represented. Claus (1886) and Valousek (1952),
Munuswamy & Subramoniam (1985), and Brendonck
(1991) reported on S. torvicornis, S. dichotomus, and
S. proboscideus with uniramous ovaries. This type of
uniramous ovary is developed in most species of the
genus. They normally extend from the genital segment
1 to the abdominal segment 6 (Fig. 8 A-C). On the
other hand, biramous ovaries are found only within
a group of North American species. The maximum
extension of both anterior and posterior rami is variable within and among species (Maeda-Martinez et al.,
1995; this volume). In both types of ovaries, the connection between ovary and oviduct is located in the
first genital segment (Fig. 8 A, C, E). In females with
uniramous ovaries, a suspensory ligament attached to
thoracic segment 11 is normally observed in lieu of
the anterior branch of the biramous ovary (Fig. 8 C).
A peculiarity noticed in females of S. dichotomus, S.
proboscideus, and S. torvicornis are the long and elastic diverticula (lateral pouches) of the oviducts. When
filled with oocytes, they extend into the lumen of the
abdomen (Valousek, 1952; Brendonck, 1991; Murugan, pers, comm.; pers. obs.). It remains to be seen,
however, whether this is a general feature of Streptocephalus females.
Family Streptocephalidae Daday, 1910
Diagnosis. Male antennae two-jointed; basal joints
somewhat coalesced; apical joints, in ventral position,
laterally directed to some extent, then curved inward.
Basal joints with a stout distal outgrowth, consisting of
a cylindrical, robust, unigeniculated or bigeniculated
peduncle, and terminating in a scleroid cheliform structure (hand). Maxillae with one distal seta. Eleven pairs
oflimbs; one praeepipodite. Seminal vesicles not clearly defined. Vas deferens forming a variable loop dorsally directed in the first genital segment. Penes ventrally
projected; basal parts not rigid, non-retractile; apical
parts long, retractile, and usually with two longitudinal
rows of spines (three in one species).
Genera. The Streptocephalidae contains only one
genus.
Remarks. Except for (1) the modified apical joint,
(2) the cheliform structure or hand of the distal outgrowth, and (3) morphology oflthe retractile penes, all
of the diagnostic features are shared with the family Thamnocephalidae. These similarities, as Linder (1941) pointed out, suggest a close relationship
between these two families.
Streptocephalus Baird, 1852
Diagnosis. As for family.
Type species. S. torvicornis (Waga, 1842).
Species. Fifty-eight species can be recognized as
valid (Belk & Brtek, 1995; this volume). They are
distributed in North America, Europe, Africa, Arabia,