Nautilus belauensis
Nautilus belauensis in Palau
CITES Appendix II (CITES)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order: Nautilida
Family: Nautilidae
Genus: Nautilus
Species:
N. belauensis
Binomial name
Nautilus belauensis
Saunders, 1981

The Palau nautilus, Nautilus belauensis, is mainly found in Palau in the Western Carolines[2] as its name suggests. It can be found on fore reef slopes[3] in depths ranging from 95m to 504m but typically prefers to remain within 150-300m where water temperatures range between 16.6 and 9.4 °C.[4] N. belauensis are highly mobile epibenthic scavenging herbalist and opportunistic predators that rely mostly on scent detection.[4] They are active both diurnally and nocturnally within the preferred depth range[4] although most shallow-water-incursions are usually nocturnal events that coincide with greatly diminished fish activities.[4]

Anatomy

N. belauensis' shell is similar to that of N. pompilius, but it is distinguished by its larger mean mature shell diameter and shell weight.[5] Its shell characteristic pattern consists of bifurcating brown to red stripes that extend from the umbilicus to the venter without coalescing across the venter[5] with delicate, longitudinally crenulated ridges[2] that produce a distinctive, concentrically lirate pattern.[2] It can also be distinguished from N. pompilius by its inwardly sloping umbilical walls and evenly rounded umbilical shoulder.[6] The shell is also distinguishable by the presence of longitudinally crenulated shell sculpture, and a broadly triangular central rachidian radular tooth and a lack of umbilical callus.[5] Fresh shells were also found to implode at 680-789m depth equivalent pressures.[4]

Development

At the immature/juvenile stage, the Palau nautilus' shell is covered in colored bands.[3] Its body chamber is covered by a thick, gelatinous, and slippery periostracum.[3] As it reaches the sub mature stage, most of its body chamber is white but with thin margins.[3] However, it still lacks a black layer that develops upon maturity.[3]

Maturity in the Palau nautilus is reached when there is a rapid decrease in growth rate until there is no additional growth.[3] The body chamber shell wall thickens with deposition of a black layer along the apertural margin and the accentuation of the hyponomic and ocular sinuses.[3] The exterior body chamber lacks colour banding.[3] The last septum is thickened but has a reduced volume in the final chamber.[3] There are usually around 35 septa in the shell.[2] The maximum observed range in shell sizes extends from 180mm to 239mm in diameter[5] with the umbilical diameter taking up 16% of the shell diameter.[6] The Palau nautilus can live for 5–10 years after reaching maturity and have a life span that may range beyond 20 years.[3]

Behaviour

The Palau nautilus is able to traverse across a wide range of temperatures and great lateral distances in short periods of time.[7] It is also able to survive in warm water up to 30 °C for tens of hours up to several days.[4] It typically migrates from deeper water into shallower water following sunset and returns to the deep before sunlight.[7] It is also able to travel an average distance from 0.45 km per day over 322 days up to 0.8 km per day over 5 days.[7]

References

  1. ↑ "Appendices | CITES". cites.org. Retrieved 2022-01-14.
  2. 1 2 3 4 Saunders, W. Bruce (1981). "A New Species of Nautilus from Palau". The Veliger. 24 (1): 1–7.
  3. 1 2 3 4 5 6 7 8 9 10 Saunders, W. Bruce (1983). "Natural Rates of Growth and Longevity of Nautilus belauensis". Paleobiology. 9 (3): 280–288. doi:10.1017/s0094837300007697.
  4. 1 2 3 4 5 6 Saunders, W. Bruce (1984). "The Role and Status of Nautilus in its Natural Habitat: Evidence from Deep-Water Remote Camera Photosequences". Paleobiology. 10 (4): 469–486. doi:10.1017/s0094837300008472.
  5. 1 2 3 4 Saunders, W. Bruce; Landman, Neil (2009). The Biology and Paleobiology of a Living Fossil. Springer Science & Business Media. pp. 41–43. ISBN 978-90-481-3299-7.
  6. 1 2 Saunders, W. Bruce (1981). "The Species of Living Nautilus and Their Distribution". The Veliger. 24 (1): 41–43.
  7. 1 2 3 Carlson, Bruce A.; McKibben, James N.; DeGruy, Michael V. (1984). "Telemetric Investigation of Vertical Migration of Nautilus belauensis in Palau". Pacific Science. 38 (3): 183–188.
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