Chiroteuthid families

Introduction

Chiroteuthid families are a group of six families that share some similar features but whose inclusion as a monophyletic clade has not been firmly established. The most distinctive feature of the group is the loss of the true tentacle club and its replacement by a variety of unusual clubs that generally have more than four series of suckers.

Diagnosis

An oegopsid ...

• without primary tentacular club (possible exception in Planctoteuthis).
• with secondary tentacular clubs.

Characteristics

1. Arms
1. Suckers generally in two series (exceptions in Joubiniteuthidae and some Promachoteuthidae and Magnapinnidae).
2. Buccal connectives attach to ventral borders of arms IV.
   
   
2. Tentacles
1. Primary club apparently lost except in Planctoteuthis; secondary clubs present and characterized by:
1. Protective membranes on club approximately bilaterally symmetrical (ie, dorsal and ventral membranes similar) when present.
2. Keel absent.
3. Carpal-locking apparatus absent.
   
4. Terminal pad absent.
5. Club not expanded.
6. Club straight.
3. Funnel
   1. Locking-apparatus oval in most taxa but often with inward protruding knobs (tragus and antitragus) or other bumps making appearance highly variable.
      
      

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      Figure. Ventral view of a funnel locking-apparatus of Chiroteuthis joubini. Drawing by A. Hart modified.

4. Fins
1. Fins usually terminal (more than 50% of fin length posterior to termination of muscular mantle).
   
   
5. Tail
1. A tail, often very long, and supported by the secondary conus of the gladius, generally present.

Comments

In the older doratopsid paralarvae of Chiroteuthis suckers develop on the tentacular stalk proximal to the tentacular club; during the transition to the juvenile/subadult stage, the doratopsid club either drops off or is resorbed leaving the distal stalk with its suckers to develop into the adult club (e.g., Naef, 1921-23). We assume that this sort of process is ancestral to the chiroteuthid families with the steps in the process still visible in the Chiroteuthidae. The fact that the doratapsid club in present in Planctoteuthis species is thought to indicate that these species are essentially mature paralarvae (Roper and Young, 1967).

A more complete description of the paralarval clubs in other chiroteuthid genera (Young, 1991) suggests that the primary doratopsid club has some of the characteristics of the basic oegopsid club. The primary doratopsid club has (1) suckers in four series (they diminish in number proximally and distally), (2) a club keel, and (3) an apparent terminal pad (distinct tip with a few suckers and a terminal cap). However, there is no clear division into manus and dactylus nor is there a carpal locking-apparatus although there is some modification of both distal (change in dentition) and proximal (change in relative diameter of acetabulum) suckers that could represent these structures. When these and other clubs are better understood, the primary doratopsid club could provide clues to the relationship of the chiroteuthid families to other oegopsids.

Discussion of Phylogenetic Relationships

The relationships among the families of this apparent clade are obscure with one exception. The Chiroteuthididae and Mastigoteuthididae have sometimes been placed within the same family due to similarities in the shape of the funnel locking-apparatus and the presence of elongate arms IV (e.g., Chun, 1910).

References

Chun, C. 1910. Die Cephalopoden. Oegopsida. Wissenschaftliche Ergebnisse der Deutschen Tiefsee-Expedition, "Valdivia" 1898-1899, 18: 1-522 + Atlas.