Myopsida Naef, 1916

Introduction

Myopsid squids are neritic, often in very shallow water, or upper slope demersal species. Many species are strong swimmers, occur in large schools and are fished commercially for food. The Loliginidae contains many species some of which reach a rather large size (at least 90 cm ML in Loligo forbesii) but those in Pickfordiateuthis, are dwarf species where males may mature at less than 14 mm ML (Brachoniecki, 1996). The Australiteuthidae contains a single species that is also a dwarf with males that mature as small as 17 mm ML (Lu, 2005).

Brief diagnosis:

A decapodiform ...

• with corneal membranes covering eye lenses.
• without secondary eyelids.
• with well-developed gladius.

Characteristics

1. Arms
1. Suckers of arms (and tentacles) with circularis muscles (unknown in Australiteuthidae).
   
   
2. Tentacles
1. Club without proximal (= carpal) locking-apparatus. More details of the typical club can be found here.
   

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Figure. Oral view of the tentacular club of Loligo plei, 105 mm ML, preserved. Photograph by R. Young.

3. Head
1. Head with tentacle pocket.
2. Eyes with corneal membranes covering lenses.
3. Eyes without secondary (= ventral) eyelid.

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Figure. Left - Dorsal view of the head of Sepioteuthis sp. (Loliginidae) showing cornea covering lens. Photograph by Mark Norman. Right - Ventrolateral view of the head of Lollicuncula diomedeae showing the absence of a ventral eyelid. Photograph by R. Young.

4. Funnel
1. Funnel without lateral adductor muscles.
   
   
5. Mantle
1. Mantle locking-apparatus extends to mantle edge (except Australiteuthidae).
   
   
6. Shell
1. Shell a gladius, extending the full length of the mantle.
   
   
7. Viscera
1. Gills with branchial canal (except Pickfordiateuthis, unknown in Australiteuthis).
2. Right oviduct absent.
3. Females with accessory nidamental glands.

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Figure. Diagramatic cross-section through gills. Drawing modified from Naef (1921-23).

8. Eggs
1. Eggs, where known, attached to substrate.
2. Embryo with large external yolk sac.

Discussion of Phylogenetic Relationships

The two families of the Myopsida appear to be closely related. The Australiteuthidae differs from the Loliginidae primarily in the structure of the funnel/mantle locking-apparatus and the position of the mantle component which does not reach the mantle margin. A number of features of phylogenetic importance in the Australiteuthidae, however, are not known: the presence or absence of a branchial canal, an anterior eye pocket, circularis muscles in the suckers, an interstellate connective; the location of spermathecae; the symmetry of the gills; the type and place (pelagic or benthic) of deposition of egg masses and the position of the intestine relative to the cephalic vein and the vena cavae.

References

Brakoniecki, T. F. 1996. A revision of the genus Pickfordiateuthis Voss, 1953 (Cephalopoda; Myopsida). Bull. Mar. Sci., 58: 9-28.

Lu, C. C. 2005. A new family of myopsid squid from Australasian waters (Cepahlopoda: Teuthida). P. 71-82. In: Chotiyaputta, C., E. M. C. Hatfield and C. C. Lu (editors). Cephalopod biology, recruitment and culture. International Cephalopod Symposium and Workshop, 17-21 Feb. 2003. Research Bulletin, Phyuket Marine Biological Center, No. 66, Published by the Center Phuket, Thailand, July 2005, 365 pp.

Naef, A. 1921-1923. Die Cephalopoden. Fauna e Flora del Golfo di Napoli, Monographie 35, Vol I, Parts I and II, Systematik, pp 1-863.