167
10 Nautilus
10.2 Reproductive Biology
Nautiluses do not fully mature until at least 12–15 years (Saunders 1983; Dunstan
et al. 2011b). They have long embryonic periods of 10–12 months (Okubo et al.
1995; Uchiyama and Tanabe 1996) and live for at least 20 years (Dunstan et al.
2011b; Landman and Cochran 2010). Nautiluses reproduce sexually and must locate and identify a mate in deep, dark ocean waters. It is not fully understood how
nautiluses locate suitable partners in the deep sea. However, laboratory studies have
shown that males are attracted to the scent of other nautiluses, both male and female,
and that females are attracted to males, while being repelled by female scent (Basil
et al. 2000; Westermann and Beuerlein 2005). Coupling this behavior with their
large olfactory organs, it is conceivable that nautiluses detect mates through the
ocean currents. It has been demonstrated that they have an acute sense of olfaction
and can track patchy, turbulent, and dilute odors from great distances (Basil et al.
2000). When male and female nautiluses are successful in contact, copulation may
occur for several hours with the male grasping the female tentacles to tentacles. Actual spermatophore transfer is not well understood, but the male sexual organ, called
the spadix, is in contact with the female buccal area during copulation (Mikami
and Okutani 1977). After copulation, the female will lay only a few eggs with its
labial tentacles (Mikami and Okutani 1977; Arnold et al. 1993). Female nautiluses
will only lay 10–20 eggs per year (Okubo et al. 1995; Uchiyama and Tanabe 1996).
Based upon captive observations, eggs are laid on a rocky substrate and attached to
the substrate with a cement-like substance. There is no information on the exact location of where females lay the eggs, though isotopic analysis suggests the eggs are
laid in warmer, shallower water (Arnold et al. 1990; Oba et al. 1992; Landman et al.
1994; Okubo et al. 1995). The eggs take approximately 11 months to develop and
hatch (Arnold et al. 1990) at which point the hatchlings have already formed seven
to eight internal chambers (Arnold et al. 1987; Oba et al. 1992; Okubo et al. 1995)
and migrate to cooler, deeper water (Landman et al. 1994; Landman et al. 2001).
10.3 Embryology
The embryos of nautiluses may provide key insights into cephalopod and molluscan evolution. Nautiluses represent the primitive externally shelled body type of
cephalopods and their eggs are ideal for developmental studies because of their
large size. The first observations of nautilus embryos occurred in 1985. Arnold and
Carlson (1986) confirmed that nautiluses, as in other extant cephalopods, do not
have larval stages and develop directly along with many other similarities with
extant coleoids. Arnold et al. (1990) described the movement of the embryo within
the egg during organogenesis and the formation of the first shell. The movements
were attributed to four possible causes: protection, respiration, rearrangement of
yolk, and extraembryonic yolk sac respiration. Carlson et al. (1992) reported on the
10 Nautilus
10.2 Reproductive Biology
Nautiluses do not fully mature until at least 12–15 years (Saunders 1983; Dunstan
et al. 2011b). They have long embryonic periods of 10–12 months (Okubo et al.
1995; Uchiyama and Tanabe 1996) and live for at least 20 years (Dunstan et al.
2011b; Landman and Cochran 2010). Nautiluses reproduce sexually and must locate and identify a mate in deep, dark ocean waters. It is not fully understood how
nautiluses locate suitable partners in the deep sea. However, laboratory studies have
shown that males are attracted to the scent of other nautiluses, both male and female,
and that females are attracted to males, while being repelled by female scent (Basil
et al. 2000; Westermann and Beuerlein 2005). Coupling this behavior with their
large olfactory organs, it is conceivable that nautiluses detect mates through the
ocean currents. It has been demonstrated that they have an acute sense of olfaction
and can track patchy, turbulent, and dilute odors from great distances (Basil et al.
2000). When male and female nautiluses are successful in contact, copulation may
occur for several hours with the male grasping the female tentacles to tentacles. Actual spermatophore transfer is not well understood, but the male sexual organ, called
the spadix, is in contact with the female buccal area during copulation (Mikami
and Okutani 1977). After copulation, the female will lay only a few eggs with its
labial tentacles (Mikami and Okutani 1977; Arnold et al. 1993). Female nautiluses
will only lay 10–20 eggs per year (Okubo et al. 1995; Uchiyama and Tanabe 1996).
Based upon captive observations, eggs are laid on a rocky substrate and attached to
the substrate with a cement-like substance. There is no information on the exact location of where females lay the eggs, though isotopic analysis suggests the eggs are
laid in warmer, shallower water (Arnold et al. 1990; Oba et al. 1992; Landman et al.
1994; Okubo et al. 1995). The eggs take approximately 11 months to develop and
hatch (Arnold et al. 1990) at which point the hatchlings have already formed seven
to eight internal chambers (Arnold et al. 1987; Oba et al. 1992; Okubo et al. 1995)
and migrate to cooler, deeper water (Landman et al. 1994; Landman et al. 2001).
10.3 Embryology
The embryos of nautiluses may provide key insights into cephalopod and molluscan evolution. Nautiluses represent the primitive externally shelled body type of
cephalopods and their eggs are ideal for developmental studies because of their
large size. The first observations of nautilus embryos occurred in 1985. Arnold and
Carlson (1986) confirmed that nautiluses, as in other extant cephalopods, do not
have larval stages and develop directly along with many other similarities with
extant coleoids. Arnold et al. (1990) described the movement of the embryo within
the egg during organogenesis and the formation of the first shell. The movements
were attributed to four possible causes: protection, respiration, rearrangement of
yolk, and extraembryonic yolk sac respiration. Carlson et al. (1992) reported on the