REPRODUCTION, DEVELOPMENT AND LIFE-HISTORY TRAITS
403
in these cysts until after spawning, possibly as a
mechanism for reducing sperm dilution (Eckelbarger
et al., 1998).
Bronsdon et al. (1993, 1997) contrasted the reproductive patterns of two epizoic anemones, Amphianthus inornata which lives attached to gorgonians at depths between 2100 and 2300 m, and
Kadosactis commensalis, which lives on sea cucumbers between 4500 and 4900 m. The shallower
species breeds seasonally, releasing eggs in the spring,
whereas the deeper-dwelling species has asynchronous
breeding and probably spawns throughout the year.
A species pair of zoanthid anemones which live
epizoically on hermit crabs have also been studied
at similar depths. In this case, however, the shallow
species (Epizoanthus paguriphilus at 770–1065 m) and
the deep one (Epizoanthus abyssorum at 3749 to
4400 m), are both continuous breeders (Muirhead et al.,
1986).
Van-Pra¨ et and Duchateau (1984) and Van-Pra¨ et
(1990) also provided evidence for seasonal reproduction in an abyssal sea anemone, Paracalliactis
stephensoni. The timing and duration of reproduction
has also been related to depth and seasonal flux of
organic matter in congeneric actinians of the genus
Phelliactis (Van-Pra¨ et et al., 1990). Both species are
dioecious and produce large eggs. Phelliactis hertwigi
lives between 719 and 1448 m in the Porcupine
Seabight and produces an egg 180 mm in diameter.
Gametogenesis takes 8–9 months and spawning occurs
in October or November of each year. Phelliactis
robusta lives at a greater depth (1600–2173 m) in
the Bay of Biscay and produces a slightly larger
egg (220 mm). Its gametogenesis takes 15–19 months
and it spawns in April or May. These contrasting
life cycles appear to be correlated with differences
between the two habitats in the timing and intensity
of phytodetritus flux (Van-Pra¨ et et al., 1990). Despite
intense recent interest in deep-sea scleractinian corals
such as Lophelia pertusa, there are no published
data on the reproduction of these species, although
fecundity appears to be very low (Waller and Tyler,
pers. comm.).
Embryogenesis and larval development
Brooded planula larvae of two deep-water hydrocorals, Cryptohelia pudica and Errina labiata, were
observed by Moseley (1881) during the Challenger
expedition. Both male and female gametes of hydrozoans, actinians and octocorals were also described by
the Challenger authors (von K¨ olliker, 1880; Hertwig,
1882; Allmann, 1883). Danielssen and Koren (1884)
reported a developing embryo from inside the polyp of
Umbellula encrinus, but no evidence of brooding has
been reported since and it has been suggested (Tyler
et al., 1995) that the earlier workers mistook a parasitic
flatworm for an embryo.
The only study of larval biology in a deep-water
cnidarian is of the alcyonacean Anthomastus ritteri
from California (Cordes et al., 2001). A large individual of this species broods more than 4000 yolky
embryos in its gastrovascular cavity. Larvae are released as fully formed demersal planulae capable of
settlement within two days, but also capable of delaying
metamorphosis for more than four months (Cordes
et al., 2001).
Other phyla
Porifera
Hexactinellids dominate the sponge fauna of bathyal
and abyssal depths, yet hexactinellid larvae have been
described for only a single species from relatively
shallow water, and embryos have only been observed
in a few cases (M. Maldonado and C.M. Young,
unpublished observations). Witte (1996) described
reproduction in three deep-sea demosponges from
2300 m in the Norwegian Sea. One of these reproduced
seasonally, the onset of yolk formation correlating
closely with the maximum flux of particles collected
in sediment traps.
Nemertea
Seven species of pelagic nemertean worms living at
depths between 250 and 3250 m in the eastern Pacific
had eggs substantially larger (0.5–1 mm diameter) than
those typical of shallow-water nemerteans (Norenburg
and Roe, 1998). Females tended to be larger than
males, and the sex ratio was apparently biased toward
females in all but one species. The polystyliferan nemerteans in this assemblage transfer yolk to the oocytes
through cytoplasmic bridges attached to nurse cells,
a vitellogenic mechanism unknown among shallowwater nemerteans. Reproduction was iteroparous in all
species, though only two species of the genus Phallonemertes showed evidence of seasonal reproductive peaks
(Norenburg and Roe, 1998).
Echiura
Selenka (1885) reported multiple dwarf males attached to a single female of the echiuran worm Bonellia
403
in these cysts until after spawning, possibly as a
mechanism for reducing sperm dilution (Eckelbarger
et al., 1998).
Bronsdon et al. (1993, 1997) contrasted the reproductive patterns of two epizoic anemones, Amphianthus inornata which lives attached to gorgonians at depths between 2100 and 2300 m, and
Kadosactis commensalis, which lives on sea cucumbers between 4500 and 4900 m. The shallower
species breeds seasonally, releasing eggs in the spring,
whereas the deeper-dwelling species has asynchronous
breeding and probably spawns throughout the year.
A species pair of zoanthid anemones which live
epizoically on hermit crabs have also been studied
at similar depths. In this case, however, the shallow
species (Epizoanthus paguriphilus at 770–1065 m) and
the deep one (Epizoanthus abyssorum at 3749 to
4400 m), are both continuous breeders (Muirhead et al.,
1986).
Van-Pra¨ et and Duchateau (1984) and Van-Pra¨ et
(1990) also provided evidence for seasonal reproduction in an abyssal sea anemone, Paracalliactis
stephensoni. The timing and duration of reproduction
has also been related to depth and seasonal flux of
organic matter in congeneric actinians of the genus
Phelliactis (Van-Pra¨ et et al., 1990). Both species are
dioecious and produce large eggs. Phelliactis hertwigi
lives between 719 and 1448 m in the Porcupine
Seabight and produces an egg 180 mm in diameter.
Gametogenesis takes 8–9 months and spawning occurs
in October or November of each year. Phelliactis
robusta lives at a greater depth (1600–2173 m) in
the Bay of Biscay and produces a slightly larger
egg (220 mm). Its gametogenesis takes 15–19 months
and it spawns in April or May. These contrasting
life cycles appear to be correlated with differences
between the two habitats in the timing and intensity
of phytodetritus flux (Van-Pra¨ et et al., 1990). Despite
intense recent interest in deep-sea scleractinian corals
such as Lophelia pertusa, there are no published
data on the reproduction of these species, although
fecundity appears to be very low (Waller and Tyler,
pers. comm.).
Embryogenesis and larval development
Brooded planula larvae of two deep-water hydrocorals, Cryptohelia pudica and Errina labiata, were
observed by Moseley (1881) during the Challenger
expedition. Both male and female gametes of hydrozoans, actinians and octocorals were also described by
the Challenger authors (von K¨ olliker, 1880; Hertwig,
1882; Allmann, 1883). Danielssen and Koren (1884)
reported a developing embryo from inside the polyp of
Umbellula encrinus, but no evidence of brooding has
been reported since and it has been suggested (Tyler
et al., 1995) that the earlier workers mistook a parasitic
flatworm for an embryo.
The only study of larval biology in a deep-water
cnidarian is of the alcyonacean Anthomastus ritteri
from California (Cordes et al., 2001). A large individual of this species broods more than 4000 yolky
embryos in its gastrovascular cavity. Larvae are released as fully formed demersal planulae capable of
settlement within two days, but also capable of delaying
metamorphosis for more than four months (Cordes
et al., 2001).
Other phyla
Porifera
Hexactinellids dominate the sponge fauna of bathyal
and abyssal depths, yet hexactinellid larvae have been
described for only a single species from relatively
shallow water, and embryos have only been observed
in a few cases (M. Maldonado and C.M. Young,
unpublished observations). Witte (1996) described
reproduction in three deep-sea demosponges from
2300 m in the Norwegian Sea. One of these reproduced
seasonally, the onset of yolk formation correlating
closely with the maximum flux of particles collected
in sediment traps.
Nemertea
Seven species of pelagic nemertean worms living at
depths between 250 and 3250 m in the eastern Pacific
had eggs substantially larger (0.5–1 mm diameter) than
those typical of shallow-water nemerteans (Norenburg
and Roe, 1998). Females tended to be larger than
males, and the sex ratio was apparently biased toward
females in all but one species. The polystyliferan nemerteans in this assemblage transfer yolk to the oocytes
through cytoplasmic bridges attached to nurse cells,
a vitellogenic mechanism unknown among shallowwater nemerteans. Reproduction was iteroparous in all
species, though only two species of the genus Phallonemertes showed evidence of seasonal reproductive peaks
(Norenburg and Roe, 1998).
Echiura
Selenka (1885) reported multiple dwarf males attached to a single female of the echiuran worm Bonellia