Boletzkyida
Encyclopedia
The Boletzkyda are perhaps the very earliest of the teuthid coleoid
Coleoidea
Subclass Coleoidea, or Dibranchiata, is the grouping of cephalopods containing all the primarily soft-bodied creatures. Unlike its sister group Nautiloidea, whose members have a rigid outer shell for protection, the coleoids have at most an internal bone or shell that is used for buoyancy or support...

 cephalopods, which seem to form a link between nautiloid orthocerids
Orthocerida
Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...

 and more advanced coleoids. The Beletzkyda was named and described by Bandel, Reitner, and Sturmer in 1983 (B,R,&S) from specimens found the Lower Devonian ("Hunrichschhiefer") black slate in Germany.

Boletzkyd shells grew to as long as 16 cm. The juvenile portion is a phragmocone that closely resembles that of Silurian orthcerid Michelinoceras
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 central or near central tubular siphuncle free of...

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 pens or gladius of later squid.

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

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 phargmocone 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 4mm 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).

Naefituethis 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 Naefituethis expanded more rapidly than in Boletzkya, with an apical angle of 20–25 deg vis only 5–10 deg for Boletzkya. (B,R,&S). Naefituethis seems to have been more stout and perhaps more robust than Boletzkya which was apparently quite streamlined. Like Boletzkya, the Naefituethis hatchling was most likely a miniature adult.

Nothing is known directly of the boletzkyd 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.

The Boletzkyda brings the origin of the Coleoidea near simultaneous with that of the Ammonoidea and may put their ancestry directly in the nautiloid Orthocerida.
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