Cephalopods, as a whole, are a particularly weird group of animals.  Looking into the strangely human eyes of an octopus or squid, one is struck by the weight of what might have been, had vertebrates not been so quick to grab the aquatic niches.  On Spec, an entire world of might-have-beens, the weight of this question approaches that of a sledgehammer blow.  Spec's land is home to giant dinosaurs, saved from destruction by happy coincidence, and the oceans are, for the same reason, home to a very wide range of tentacled mollusks.

AMMONOIDEA
    Probably the most famous fossil form, the shape of ancient organism recognized by anyone in any place where such rocks occur, is the coiled ramshorn shell of an ammonoid.

    Aside from the ammonoids and nautiloids, all modern cephalopods are classified as coleoids, possessing a single pair of gills and a reduced shell.  This clade includes belemnoids (which still possess a shell), baleen-squids and their kin , true squids, octopuses, and vampire squids.  Cuttlefishes (Sepioidea) are absent from Spec.

BELEMNOIDEA
    Belemnoids are a group of cephalopods superficially similar to squids.  They possess advanced eyes and nervous systems and an ink sac, and they bear suckers and chitinous hooks on their tentacles just like true squids.  However, belemnoids have not ten tentacles, but eight, and their nether regions, which, in squids, are supported by a flimsy pen, are protected by a complex torpedo-shaped structure similar to the shell of an ammonoid.  This internal shell, the belemnoid structure, is not coiled, as in most ammonoids, but straight, composed of a bullet-shaped, calcite rostrum, a chambered phragmocone, and a pro-ostracum, which extends to protect the head.

    In our home time-line, belemnoids went extinct at the end of the Cretaceous, doomed by the same calamity that killed the dinosaurs and their cousins, the ammonoids.  Early explorers in Spec, seeing no living belemnoids, assumed something similar must have happened in this timeline, as well.  However, close inspection of the Great Gulf Reef, the coral reef that fills Spec's Gulf of Mexico and Caribbean reveals a relic taxon, a group of tiny belemnoids that cleans the skins of fishes.

    The cleaner-squids form a strange of living fossils, constituting the last living members of clade Belemnoidea.  Although these squid-like creatures made it through the K-T extinction fairly unscathed, they seem to have suffered greatly during the much more severe Eocene-Oligocene extinction, when marine equatorial communities the world over were wiped out.  If not for this extinction, the belemnoids, which combine the swim bladder of a fish with the tentacles and siphon of a squid, could well have gone on to eclipse the teleost radiation, but that path was not to be. Only one group of belemnoids made it though the extinction, the cleaner-squids, containing two genera and 12 described species. Cleaner-squid are locally common and quite diverse in the Caribbean reefs, but no trace of them or their kin has been found in any of Spec's other oceans.  Most likely, this clade represents a fraction of a much larger, now extinct, belemnoid diversity.

   Modern cleaner-squids are distinguished from their Cretaceous ancestors by several unique features.  The rostrum (covered by the muscular mantel) is short and conical, forming the tip of the rear end of the animal.  The phragmocone, which occupies the bulk of  the cleaner-squid's hind portion, carries a number of chambers and is used by the animal to regulate buoyancy to sink or float.  The pro-ostracum, on the other hand, is reduced, forming the base for a fleshy hood.  As in true squids, cleaner-squids have two "fins", flexible extensions of the mantel on either side of their bodies that allow them to maneuver with great facility.

    In some respects a cleaner-squid had certain advantages when they came to occupy that niche that, in our timeline, is occupied by the cleaner wrasse and shrimps. As a small cephalopod, the cleaner-squid was already the predators of small crustaceans, and were already capable of the complex signaling that the modern cleaner squid uses to advertise their services.

SAMPLE TAXA: The Gulf of Mexico

• Banded cleaner squid

BALAENATEUTHIA
    The balaenateuths are perhaps the most highly-derived of all mollusks.

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