Boletzkyida is a primitive

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

of teuthid coleoid

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

: the boletzkyids are thought to be the earliest forms of coleoid cephalopods, and appear to form a link between nautiloid orthocerids and more advanced coleoids. Boletzkyida was named and described by Bandel, Reitner, and Sturmer in 1983 (B.R.&S) from specimens found in the Lower Devonian black slate (" Hunsrück Slate") in Germany.

Taxonomy

Bandel, ''et al'' (1983) divided the Boletzkyida into two, not too dissimilar families, each based on a single genus. They are the Boletzkyidae based on the genus ''Boletzkya'' and the Naefiteuthidae based on the genus ''Naefiteuthis''. The main difference between ''Boletzkya'' and ''Naefiteuthis'' is the length of the phragmocone at which time the living chamber becomes gladius-like and dominates the shell.

Ontogeny

Boletzkyd shells grew to as long as 16 cm. The juvenile portion is a phragmocone that closely resembles that of Silurian orthocerid ''

Michelinoceras ''Michelinoceras'' is the oldest known genus of the Michelinocerida, more commonly known as the Orthocerida, characterized by long, slender, nearly cylindrical orthocones with a circular cross section, long camerae, very long body chambers, and a ...

'' with a spherical protoconch (first chamber) and tubular living (or body) chamber with a simple rounded aperture. In the early juvenile stage the living chamber is about as long as the chambered phragmocone. Later in the juvenile stage the living chamber grows proportionally longer and develops a median dorsal and two lateral keels and has an aperture with a receded ventral or lower lip (B.R.&S). At full maturity the narrowly expanding, keeled living chamber dominates all but the first few centimeters of shell and is reminiscent of the

gladii ''Gladius'' () is a Latin word meaning "sword" (of any type), but in its narrow sense it refers to the sword of ancient Roman foot soldiers. Early ancient Roman swords were similar to those of the Greeks, called '' xiphe'' (plural; singular ''xi ...

or pens of later squid. ''Boletzkya'' probably hatched with a shell only about 3–4 mm long and was at least in outward appearance a miniature adult. With two septa the living chamber is as long as 5 mm. Later in the juvenile stage the phragmocone increased in size relative to the living chamber until, at an overall length of about 8 mm, it reached equal length. Shortly after this the dorsal median keel first appeared and the inner (ventral) apetural lip became retarded while the outer (dorsal) lip grows into a gladius-like proostracum (B.R.&S). Once started, the "gladius" grew rapidly. At a phragmocone of slightly more than 4 mm it reached a length of more than 3 times (15 mm). A 12–13 mm phragmocone had a "gladius" of 70 mm, and with only two more mm of phragmocone (15 mm) a "gladius" of 100 mm (B.R.&S). ''Naefiteuthis'' is similar to ''Boletzkya'' and hatched at about the same size, except that it has almost no phragmocone and the keeled gladius-like living chamber developed almost immediately. Also the living chamber in ''Naefiteuthis'' expanded more rapidly than in ''Boletzkya'', with an apical angle of 20–25 degrees versus only 5–10 degrees for ''Boletzkya''. ''Naefiteuthis'' seems to have been more stout and perhaps more robust than ''Boletzkya'' which was apparently quite streamlined. Like ''Boletzkya'', the ''Naefiteuthis'' hatchling was most likely a miniature adult.

Affinity

Nothing is known directly of the boletzkyid animal but judging from its most likely michelinocerid ancestors (B.R.&S) and their obvious squid descendants that it had 10 arms. A ''Michelinoceras'' from the Silurian of Bolivia was found (Mehl 1984) with imprints showing it had 10 arms and a distantly related ''Treptoceas'' (''Orthonybyoceras'') from the Upper Ordovician near Cincinnati, Ohio were found with indications it, too, had 10 arms (Flower 1955). The 10 arms of squid (8 arms and 2 tentacles) are well known. Boletzkyida brings the origin of the eo?oleoidea near simultaneous with that of the Ammonoidea and may put their ancestry directly in the nautiloid Orthocerida. On another view... the group's taxonomic position is uncertain, with a possible affinity with the Dibranchiata Coleoidea conceivably at a stem-group level, which would place its divergence as before the ammonoids had diverged from other coleoids.

Taxonomy

Ontogeny

Affinity

References

Further reading