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Nautilidae 709 click for previous page Nautilidae 709 Nautilidae NAUTILIDAE Chambered nautiluses by M.C. Dunning iagnostic characters: Coiled, pearly, external shell punctuated with chambers with the animal Dliving in the outermost chamber; 2 pairs of gills; up to 47 pairs of arm-like appendages around mouth; suckers and hooks lacking; eyes simple, without lenses; funnel (or infundibulum) consisting of 2 lobes which fold together to form a tube-like structure that serves for locomotion. Chromotophores and ink sac absent. septa separating chambers umbilicus chambers dorsal region of mantle hood siphonal tube R arm-like | S stomach appendages T| ovary mouth shell obturating muscle of funnel funnel radula digestive gland (tooth-plate) ventral region of anus mantle gills schematic cross-section of a Nautilus Habitat, biology, and fisheries: The nautiloids are represented by 6 living species of Nautilus. All of these are found in the tropical Indo-West Pacific. Nautiluses live in association with the bottom, primarily coral reefs, from depths of about 50 to 500 m. They are slow foragers of the deep nektobenthos and are generally found in deeper water during the day and at shallower depths at night. Nautiluses are the longest lived of the extant cephalopods, recent mark-recapture studies indicating they may live for more than 20 years. They exhibit determinate growth, i.e. after reaching maturity they show no more somatic growth, but may live several years after reaching maturity. Egg capsules in natural habitats are unknown but in captivity are laid singly attached to hard substrates and take up to 14 months to hatch in warm water (22° to 25°C). It is hypothesized that they are laid in nature in relatively shallow water (80 to 100 m). At least 2 of these species are of commercial value as food (largely at the artisanal and subsistence levels) and in the specimen shell trade (e.g. Indonesia, Fiji, New Caledonia, and the Philippines). Nautiluses are also collected alive for public display and home aquaria, and for research. They are caught using baited fish traps. Similar families occurring in the area Argonautidae: a kind of octopus, the female argonaut produces a white calcareous “shell” in which she resides and eggs are laid and incubated. This “shell” has a single chamber only. Female argonauts have 8 true arms with biserial suckers compared to the many sucker-less arm-like appendages of nautiluses. - Argonautidae 710 Cephalopods Key to the species of Nautilidae occurring in the area 1a. Umbilicus small, up to 5% of shell diameter ............................→ 2 1b. Umbilicus larger, at least 10% of shell diameter ..........................→ 3 2a. Umbilicus covered by a calcareous deposit, the umbilical callus .................→ 4 2b. Umbilicus without umbilical callus (northeastern Australia)..........Nautilusstenomphalus 3a. Umbilicus moderate with sloping umbilical walls and an evenly rounded umbilical shoulder, approximately 16% of shell diameter (New Caledonia, Loyalty Islands) ........................................Nautilusmacromphalus 3b. Umbilicus large (approximately 20% shell diameter) with subangular shoulders and vertical walls (Solomon Islands, Papua New Guinea) .............Nautilusscrobiculatus 4a. Umbilicus approximately 5% of shell diameter, brown to reddish brown colour banding from the shell margin to the umbilicus or at least half way ....................→ 5 4b. Umbilicus small, fine yellowish brown colour banding, sometimes greatly reduced (northwestern Australia) ...............................Nautilusrepertus 5a. Fine raised longitudinal growth lines on the shell (found only around Palau, Western Caroline Islands) .................................Nautilusbelauensis 5b. Shell generally smooth, without growth lines (widespread distribution, Indo-West Pacific) ...........................................Nautiluspompilius (after Swan and Saunders, 1986) a d schematic lateral view of Nautilus shells showing the umbilicus width (a) and the shell diameter (d) List of species occurring in the area The symbol % is given when species accounts are included. Nautilus belauensis Saunders, 1981 % Nautilus macromphalus Sowerby, 1849 % Nautilus pompilius Linnaeus, 1758 Nautilus repertus Iredale, 1944 Nautilus scrobiculatus (Lightfoot, 1786) Nautilus stenomphalus Sowerby, 1849 Reference Saunders, W.B., and N.H. Landman. 1986. Nautilus, the biology and paleobiology of a living fossil. New York, Plenum Press. Nautilidae 711 Nautilus macromphalus Sowerby, 1849 Frequent synonyms / misidentifications: None / None. FAO names: En - Bellybutton nautilus; Fr - Nautile bouton; Sp - Nautilo ombligo. Diagnostic characters: Umbilicus a deep, round shouldered concavity, approximately 16% of shell diameter. Size: Maximum shell diameter about 160 mm. Habitat, biology, and fisheries: Inhabits continental shelf and slope waters associ- ated with coral reefs, from the surface to a depth of about 500 m. Consumed by arti- sanal fishers; also supports a small fishery for public and private aquarium and re- search trade. Collected alive at a depth of about 65 m on the outer slope of the barrier reef in New Caledonia; in the Coral Sea, trapped at depths between 300 and 400 m. Distribution: Restricted to New Caledonia and Loyalty Islands. Nautilus pompilius Linnaeus, 1758 Frequent synonyms / misidentifications: None / None. FAO names: En - Emperor nautilus; Fr - Nautile flammé; Sp - Nautilo común. Diagnostic characters: Umbilicus small, filled in with a concretion; brown to reddish brown striped colour pattern, extending to the umbilicus in some specimens or only half way across the shell in others. Size: Populations of this species reach shell diameters typically between 170 and 180 mm around Fiji and the Philippines. Habitat, biology, and fisheries: Inhabits deeper continental shelf and slope waters around coral reefs, from near the surface to a depth of about 750 m. Supports shell trade, mostly from beach-drift specimens, and subsistence and artisanal fisheries in the Philippines. Captured in bamboo fish traps at depths from 60 to 240 m. Distribution: Indo-West Pacific; An- daman Islands, Ambon, the Philippines, New Guinea to Fiji; northeastern Australia. Absent from around New Caledonia where it is replaced by N. macromphalus.Sympatric with N. scrobiculatus off New Guinea, N. repertus off northwestern Australia, and N. stenomphalus off northeastern Australia. Replaced by N. belauensis around Palau. 712 Cephalopods Sepiolidae SEPIOLIDAE Bobtail squids 1 or both dorsal arms by A.L. Reid and M.D. Norman hectocotylized in males iagnostic characters: Small rounded Dsquids (mantle length typically less than 80 mm) with 8 arms and 2 functional retrac- tile tentacles with well-developed clubs. Dor- sal mantle free from, or fused to, head. Ventral mantle attached to funnel by fun- nel locking apparatus, mantle edge may cover funnel base. Fins present, rounded and typically wide. Maximum fin length distinctly longer than length of attach- ment to mantle. Suckers spherical, usually larger in males than females. Internal shell chitinous, rudimentary or absent. Frequently with light organ on ink sac. One or both dorsal arms hectocotylized in males. Habitat, biology, and fisheries: Benthic or mesopelagic squids. Mesopelagic species live in midwater over or near the continental slope. Benthic species associate with soft substrates and seagrass beds, typically re- maining submerged in soft sediments during the day. Bury using fins and funnel to cover the entire animal with sand or shell, using the arms to rake grains onto the head and man- tle. Animals typically emerge at night to for- age for benthic and free-swimming crustaceans. A number of sepiolid species are of minor commercial importance throughout the area, harvested primarily as fins wide and bycatch in trawl fisheries. rounded Remarks: The taxonomy of many genera dorsal view within this family is poorly known as most species are identified solely on sexual char- both or only left ventral arms hectocotylized acters of mature males. Similar families occurring in the area Sepiadariidae (bottle squids): no internal shell; no light or- gans within the mantle cavity; dorsal mantle fused to head in all species; fins elongate, much longer than wide; ventral arms hectocotylized in males. Key to the genera of Sepiolidae occurring in the area 1a. Only third and fourth arms united by a broad web; anterior edge of ventral man- mantle tle not covering funnel base; light organ always present or absent; internal shell present fused to or absent; benthic species ............→ 2 head dorsally 1b. All arms except the fourth pair united by a broad web; anterior edge of ventral mantle extends to cover base of funnel, reaching level of eye in certain species; light organ on ventral ink sac; internal shell absent; pelagic or deeper benthic fins distinctly species ......(subfamily Heteroteuthinae) → 3 longer than dorsal view wide Sepiadariidae Sepiolidae 713 2a. Dorsal mantle fused to head; nuchal cartilage absent; left dorsal arm hectocotylized; internal shell rudimentary or absent ...................(subfamily Sepiolinae) → 4 2b. Dorsal mantle not fused to head; nuchal cartilage present; left or both dorsal arms hectocotylized; shell present ........................(subfamily Rossinae) → 6 3a. Dorsal mantle fused to head by narrow strip ........................Sepiolina (a single species, S. nipponensis, in this genus) 3b. Dorsal mantle not fused to head ............................Heteroteuthis (a single species, H. weberi, in
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