. Cephalopoda. Cephalopoda. FIGURE 59. Embryo (a,c) and early young stage (b,d) of Pro toteuthis: a and b — lateral aspects with translucent the attachment of the muscular mantle; c and d — median sections. Compare the relation- ships shown here with those of Figure 36. co — cone; si — rudimentary siphuncle; ma — attachment of the muscular mantle. For details see Protodibranchus (p. 107). d. VARIATION OF THE TYPE OF TEUTHOIDEA To the Teuthoidea belong a number of fossil genera (see below) which closely resemble the idealized Prototeuthis. They have in common with Prototeuthis the
. Cephalopoda. Cephalopoda. FIGURE 59. Embryo (a,c) and early young stage (b,d) of Pro toteuthis: a and b — lateral aspects with translucent the attachment of the muscular mantle; c and d — median sections. Compare the relation- ships shown here with those of Figure 36. co — cone; si — rudimentary siphuncle; ma — attachment of the muscular mantle. For details see Protodibranchus (p. 107). d. VARIATION OF THE TYPE OF TEUTHOIDEA To the Teuthoidea belong a number of fossil genera (see below) which closely resemble the idealized Prototeuthis. They have in common with Prototeuthis the form of the median plate of the gladius (p. 137), which widens anteriorly into a wide, slightly variable curve. This causes the lateral position of the stellate ganglions, taken over from the typical Decapoda (Belemnoidea) but never observed in the recent Teuthoidea, and the form of the muscular mantle, which necessarily affects the manner of movement. Other anatomical differences are necessarily connected with it (see p. 146). These forms had a moderately convex, strongly calcified gladius without a sharply projecting, ventrally groove-shaped median keel. They apparently had a large, pointed cone. I have named them Prototeuthoidea because of their close relations to the Belemnoidea. Prototeuthoidea (nov.) (= Loliginites t enu ic a r ina t i Quenstedt) Diagnosis: Fossil Teuthoidea (Liassic to Cretaceous) in which the median 143 plate of the strongly calcified gladius''' is usually sharply delimited by asymptotes, and the gladius very blunt anteriorly and at least half as wide as the mantle sac; lower side of middle plate without a median keel which is gutter-shaped ventrally (Figure 62), but instead at most with solid sup- porting ridges which become reduced or disappear anteriorly. ' It is difficult to determine the degree of primary calcification of fossil shells embedded in calcareous material; the very delicate growing marginal parts are almost never preserved. A
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Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectcephalopoda
