Blanket octopusKatharina M. Mangold (1922-2003), Michael Vecchione, and Richard E. Young
The Tremoctopodidae contains a single genus with the following four species:
- Tremoctopus violaceus
- Tremoctopus gelatus
- Tremoctopus gracilis
- Tremoctopus robsoni
Most species have large, muscular females, ca. 1 m or more in total length, that occupy surface waters of tropical and subtropical oceans. In females the dorsal and dorsolateral arms are distinctly longer than arms III and IV and are connected by an extensive web which is absent from the other arms.
Figure. T. violaceus swimming just above the shallow ocean floor. Note the string-like structure trailing from the broad web of arm I. This "string" is actually the slender arm I extending beyond the web. Posterolateral view of T. violaceus swimming just above the shallow ocean floor. Photographed by Rob Rush at 68 feet deep off Delray Beach Ledge, Florida, USA (near 26°N 80°W), May 12, 2001, 9:06 AM local time.
Large ocelli can be displayed on the dorsal web. This web and the slender tip of the arms can, apparently, be autotomized along visible "fracture" lines. The automized arms and membranes presumably wiggle to distract a predator while the octopod swims away.
Figure. Same individual of T. violaceus pictured above, showing web and ocelli on arm I. Photographed by Rob Rush.
The color phase most typically associated with T. violaceus is with silvery sides and a very dark purple/blue dorsal surface.
Figure. The picture of T. violaceus on the left, taken in an aquarium, shows the typical color pattern. Photograph taken by Vicente Hernandez. The photograph on the right of Tremoctopus sp. taken from a submersible shows the octopod swimming at a depth of 340 m and about 5 m above the bottom in Hawaiian waters. An AVI format video clip of this individual is available at Cephalopods in Action. Submersible photograph courtesy of the Hawaii Undersea Research Laboratory.
An argonautoid ...
- with extensive web between dorsal four arms; web virtually absent between other arms.
- Dorsal four arms much longer than ventral four arms.
- Deep web present between dorsal four arms (see title photograph).
- Hectocotylus develops in sac burried beneath right eye.
- Proximal half of hectocotylus with papillate lateral fringes.
- Swim bladder
- Hydrostatic organ (swim bladder) present dorsal to digestive system.
- Water pores
- Present at base of dorsal and ventral arms.
CommentsThe presence of a hydrostatic organ was recently reported by Bizikov (2004).
A list of all nominal genera and species in the Tremoctopodidae can be found here. The list includes the current status and type species of all genera, and the current status, type repository and type locality of all species and all pertinent references.
The systematics of the Tremoctopodidae was review by Thomas (1977). He concluded that two species existed, T. violaceus and his new species T. gelatus Thomas, 1977. The former species he divided into two subspecies, T. v. violaceus, from the Atlantic Ocean and T. v. gracilis, from the Pacific and Indian Oceans. O'Shea (1999) has resurrected a New Zealand species, T. robsoni. Since the degree of difference between the latter and T. violaceus is of the same order as that between the two subspecies of T. violaceus we here elevate the two subspecies to specific level:
- Tremoctopus violaceus violaceus Chiaie, 1830 becomes Tremoctopus violaceus Chiaie, 1830
- Tremoctopus violaceus gracilis (Eydoux and Souleyet, 1852). becomes Tremoctopus gracilis (Eydoux and Souleyet, 1852).
There is some confusion on the proper name of T. robsoni. Mike Sweeney (USNMNH) explains: "The name Tremoctopus robsonianus is in the title of the paper (an abstract from a meeting of the Wellington Philosophical Society). However the taxon is introduced in the text with the name Tremoctopus robsoni n.sp. The taxon was published in the 1883 volume (#16) of the Transactions of the New Zealand Institute, but had a publication date of May 1884." The correct name is Tremoctopus robsoni Kirk, 1884.
Of the four recognized species, T. gelatus is easily recognized by its gelatinous consistency and generally pale pigmentation, the other three species are very similar. The most useful character is the number of sucker pairs on the distal half of the hectocotylus of the male. Another character is the number of gill filaments on the outer demibranch of the gill not including the terminal filament.
|Species||Consistency||Distal hecto. suckers||Gill filaments males||Gill filaments females|
|T. violaceus||Muscular||15-19 pairs||9-11||13-16|
|T. gracilis||Muscular||19-22 pairs||9-11||13-16|
|T. robsoni||Muscular||27-28 pairs||10-13||15|
|T. gelatus||Gelatinous||- ? -||7-8||8-11|
A few additional features on the hectocotylus seem to have specific value. The proximal suckers number 22-23 pairs in T. violaceus, 27-29 pairs in T. gracilis (Thomas, 1977) and 9-15 in T. robsoni according to the figures shown here from O'Shea, 1999. Also the hectocotylus of the first two species has a fringe of fleshy papillae that extend the full length of the proximal section, while the third species, according to the illustration, has the fringe restricted to the base of the proximal section.
Young individuals carry broken tentacles of the Portuguese man-of-war (jellyfish) on the suckers of the dorsal four arms. The borrowed tentacles, which have stinging cells, presumably have a defensive and/or offensive function.
Figure. Ventral view of a young female T. gracilis, Hawaiian waters. The white arrow points to the man-of-war tentacles held by the left arm II. Similar worm-like tentacles can be seen attached to suckers of arms I and the other arm II. Note the large white balls with long streaming white tentacles. The identity of these is unknown but presumably they are larger pieces of the man-of-war or some other jellyfish.
Males are dwarfs (15 mm ML), often reaching only 5-10% of the female size. The females carry numerous (100,000 to 150,000) small eggs (0.9 X 1.5 mm in size). The eggs are attached to a sausage-shaped calcareous secretion held at the base of the dorsal arms and carried by the female until hatching. The hatchling has the arm bases in a cuff as in Argonauta. Data are from Thomas (1977) and Naef (1921/23). More information of the egg mass, embryos and hatchlings can be found here.
T. violaceus lives in the Atlantic and T. gracilis in the Indo-Pacific; T. gelatus is a deep-living, gelatinous, presumably mesopelagic, species that is cosmopolitan in tropical and temperate seas (Thomas, 1977). T. robsoni is known from waters off New Zealand (O'Shea, 1999).
Bizikov, V. A. 2004. The shell in Vampyropoda (Cephalopoda): Morphology, functional role and evolution. Ruthenica. Supplement 3: 1-88.
Naef, A. 1921-23. Cephalopoda. Fauna und Flora des Golfes von Neapel. Monograph, no. 35. English translation: A. Mercado (1972). Israel Program for Scientific Translations Ltd., Jerusalem, Israel. 863pp., IPST Cat. No. 5110/1,2.
O'Shea, Steve. 1999. The Marine Fauna of New Zealand: Octopoda (Mollusca: Cephalopoda). NIWA Biodiversity Memoir 112:280pp.
Thomas, R. F. 1977. Systematics, distribution, and biology of cephalopods of the genus Tremoctopus (Octopoda:Tremoctopodidae). Bull. Mar. Sci. 27: 353-392.
Katharina M. Mangold (1922-2003)
National Marine Fisheries Service
National Museum of Natural History
Washington, D. C. 20560
Richard E. Young
Dept of Oceanography
University of Hawaii
Honolulu, Hawaii 96822
Page copyright © 1996 Katharina M. Mangold (1922-2003), , and Richard E. Young
Citing this page:
Mangold (1922-2003), Katharina M., Vecchione, Michael, and Young, Richard E. 1996. Tremoctopodidae http://tolweb.org/Tremoctopus/20202/1996.01.01 in The Tree of Life Web Project, http://tolweb.org/. Tremoctopus . Blanket octopus. Version 01 January 1996 (complete).