Mollusca

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Expert

Identification guide

Cirrata

  • An octopod, with fins, with cirri on arms.

Unidentifiable cirrate octopod

Cirroteuthidae

A cirrate, with secondary webs between primary web and aboral surfaces of arms, with long cirri, with saddle-shaped shell, possible

Cirroteuthis sp.

possibly Cirrothauma sp.

Opisthoteuthidae

A cirrate, without secondary web, with cirri of short to moderate length, with body axis strongly compressed in anteroposterior plane, with simple U-, V- or W-shaped shell.

Grimpoteuthis sp.

Possible Grimpoteuthis sp.

Characteristics

Mollusks with well-developed heads in which the mouth is characterized by a pair of chitin-like jaws (termed beaks) and radula and is encircled by the bases of eight to ca. 60 grasping appendages; single pair of lateral, image-forming eyes; well-developed circum-oesophageal brain and peripheral nervous system. A posterior, sac-like, mantle encloses the U-shaped digestive system and other organs in a mantle cavity filled with seawater that can be expelled through the muscular funnel for respiration, pulsed-jet locomotion, and waste disposal. Although the shell is internalized and greatly modified or reduced in most living species, an important ancestral characteristic is a buoyant phragmocone, a chambered shell penetrated by a siphuncle, which is a tube of tissue that exchanges gas for fluid in shell chambers. The phragmocone is found today in the families Nautilidae, Siprulidae, and (much modified) Sepiidae.

Two very different subclasses live in modern seas: (1) the nautilids (one extant family in subclass Nautiloidea), comprised of two genera and about six species that have two pairs of gills and an external shell into which they can withdraw, and (2) the neocoleoids (a division of subclass Coleoidea), sometimes called dibranchiates because they have a single pair of gills, comprising all other living species (<1000), including the familiar squids, cuttlefishes, and octopods.

Eight distinctive groups of neocoleoids can be defined: Incirrata (common octopods), Cirrata (finned octopods), Vampyromorpha (the vampire “squid”, one species), Sepiida (cuttlefishes), Spirulida (the ramshorn squid, one species), Sepiolida (bobtail and bottle squids), Myopsida (inshore squids), and Oegopsida (oceanic squids). Consensus is lacking on the taxonomic level of these groups, and some families cannot be assigned confidently to any of these groups. The first three groups listed comprise the Octopodiformes and the remaining five are the Decapodiformes, commonly called decapods.

Cephalopods range in size from the giant squids, Architeuthis spp., which are commonly >2 m mantle length (ML) and reportedly reach 5 m ML, 18 m total length and 300 kg in weight, to tiny species which mature at a few mm ML. Several squid species and at least two species of octopods reach sizes larger than an adult human. Some cirrate octopod species are among the largest animals of the deep sea.

Basic anatomy

Three regions can easily be discerned on a cephalopod. From anterior to posterior, these regions are: (1) the arms and tentacles, or brachial crown, surrounding the mouth, (2) the head, on which the lateral eyes are prominent, and (3) the mantle, or body, to which a pair of lateral fins may be attached. Neocoleoids have a single ring of either eight or ten appendages surrounding the mouth. On those with ten, two appendages are modified into either ventrolateral tentacles (decapods) or dorsolateral velar filaments (vampires). Thus, all living cephalopods other than nautilids have eight arms and some additionally have either two tentacles or two filaments.

An ink gland and ink sac associated with the intestine is characteristic of neocoleoids. Complex, highly developed nervous and sensory systems are also typical of living cephalopods. Especially noteworthy are the image-forming eyes, with lenses in neocoleoids, and the complex brain developed from the molluscan circumoral nerve ring. Cephalopods are renowned for rapidly changing their appearance by a combination of skin texture modification with a complex system of chromatophores under direct nervous control

Ecology

Cephalopods are entirely marine and are found throughout most marine environments from lower estuaries and fjords to the deep sea and polar regions. None have yet been found in hadal enviroments. All cephalopods are mobile throughout their lives, except for the egg stages. As far as we know, all cephalopods are either carnivorous (neocoleoids, except vampires, which feed on detritus) or scavengers (nautilids) throughout their lives after hatching.

The life cycles of most neocoleoid cephalopods are (as far as we know) very different from that of nautilids. Whereas the latter are long-lived (>20 yr), the lives of other cephalopods have been characterized as "live fast and die young." Life spans seem to range from a few months for small species to a few years for larger species. However, many of the generalizations that are claimed for neocoleoid cephalopods have been based on observations of a few coastal species that are convenient to research labs. Important gaps exist in our information about life history, especially for deep-sea species.

Some cephalopod species, especially squids, can be very abundant, occasionally among the dominant organisms in their ecosystems. Because they are important food for larger animals, in addition to being voracious predators, such species are key members of some marine food webs. Cephalopods are major food items in the diets of many marine vertebrates, including toothed whales, seals, pelagic birds, and both benthic and pelagic fishes.

The range of depths extends from intertidal to over 5000 m. Different marine ecosystems have very different cephalopod faunas. Many octopod species have recently been described from Antarctic waters whereas Arctic Seas seem to be depauperate. The deep sea is home to both primitive vampires and morphologically similar finned octopods, as well as some strange oegopsid squids. Oegopsid squids tend to be dominant in epipelagic and mesopelagic oceanic waters whereas myopsid squids share the continental shelves with incirrate octopods and cuttlefishes. Some incirrate octopods are found in deep-sea benthic habitats whereas others are entirely pelagic.

Cephalopods of the CCFZ

All cephalopod images from CCFZ have been cirrate (=finned) octopods in two families, Cirroteuthidae and Opisthoteuthidae. It is possible that other deep-sea cephalopods may be encountered in the area. Incirrate octopods (both pelagic and benthic) occur to depths of about 3400 m and squids are known to 4100 m. Of these, the most likely to be encountered in the CCFZ are “bigfin” squids in the family Magnapinnidae, the deepest known squids.

For Grimpoteuthis sp., five nominal species might occur in the CCFZ. Distinguishing them requires careful examination of arm suckers and internal anatomical features. The species and web pages with information about them are:

Globally, there are few recognized species of cirroteuthid (see http://tolweb.org/Cirroteuthidae/20091). However, it is very likely that many undescribed species exist.

Limitations of photography

The major groups of cephalopods can be identified confidently from visual records of large animals, as can some families with distinctive external morphology. Identification at the genus and species levels often require examination of detailed morphological characters, which may not be visible in visual records, or internal characters. Often if a visual record can be accompanied by collection of the specimen for detailed examination, then subsequent visual records in the same geographic area may be identifiable.

References

  • Aldred, R. G., M. Nixon and J. Z. Young. 1983. Cirrothauma murrayi Chun, A finned octopod. Phil. Trans. R. Soc. Lond. B, 301:1-54.
  • Boletzky, S. v., M. Rio and M. Roux. 1992. Octopod "ballooning" response. Nature, London. 356: 199.

Collins, M. A. and R. Villanueva. 2006. Taxonomy, ecology and behaviour of the cirrate octopods. Oceanography and marine biology: An annual review 44: 277-322.

  • O'Shea, S. 1999. The Marine Fauna of New Zealand: Octopoda (Mollusca: Cephalopoda). NIWA Biodiversity Memoir 112: 280pp.

Roper, C. F. E. and W. L. Brundage, Jr. 1972. Cirrate octopods with associated deep-sea organisms: New biological data based on deep benthic photographs (Cephalopoda). Smithson. Contr. Zool., No. 121: 1-45.

  • Vecchione, M. and R. E. Young. 1997. Aspects of the functional morphology of cirrate octopods: locomotion and feeding. Vie Milieu, 47:101-110.
  • Vecchione, M., K. M. Mangold, and R. E. Young. 2008. Cirrata Grimpe, 1916. Finned octopods. Version 27 May 2008 (under construction). http://tolweb.org/Cirrata/20086/2008.05.27 in The Tree of Life Web Project, http://tolweb.org/
  • Vecchione, M., K. M. Mangold, and R. E. Young. 2008. Opisthoteuthidae Verrill 1896. Version 21 May 2008 (under construction). http://tolweb.org/Opisthoteuthidae/20089/2008.05.21 in The Tree of Life Web Project, http://tolweb.org/
  • Vecchione, M. and R. E. Young. 2013. Magnapinnidae Vecchione and Young, 1998. Magnapinna Vecchione and Young, 1998. Bigfin squid. Version 08 January 2013 (under construction). http://tolweb.org/Magnapinna/52203/2013.01.08 in The Tree of Life Web Project, http://tolweb.org/
  • Vecchione, M., R. E. Young, and K. M. Mangold. 2008. Cirroteuthidae Keferstein 1866. Version 28 April 2008 (under construction). http://tolweb.org/Cirroteuthidae/20091/2008.04.28 in The Tree of Life Web Project, http://tolweb.org/
  • Voss, G. L. 1988. Evolution and phylogenetic relationships of deep-sea octopods (Cirrata and Incirrata). P. 253-276. In: Clarke, M. R. and E. R. Trueman (Eds.). The Mollusca. Vol. 12. Paleontology and Neontology of Cephalopods. Academic Press, New York. 355pp.
  • Voss, G. L. and W. G. Pearcy. 1990. Deep-water octopods (Mollusca: Cephalopoda) of the Northeastern Pacific. Proc. Calif. Acad. Sci., 47: 47-94.