Megalocranchia Pfeffer, 1884

Megalocranchia contains four recognized species. Voss, et al. (1992), however, suggest that six species exist.

Introduction

Some species of Megalocranchia are very large and can reach 1800 mm ML, (Tsuchiya and Okutani, 1993). The vertical distribution is best known in M. fisheri. The paralarval stage, which reaches 40-50 mm ML, is spent in near-surface waters. Larger individuals occupy mesopelagic depths during the day and migrate into near-surface waters at night (Young, 1978).

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Figure. Side view of earyl juvenile M. fisheri. Photograph by R. Young.

Brief diagnosis:

A taoniin ...

• with photophores on the digestive gland.

Characteristics

1. Tentacles
   1. Tentacular clubs with suckers only.
   2. Tentacular stalk with two series of suckers and pads in mid-third, then four series to carpal group.
      
      
2. Head
   
   1. Beaks: Descriptions can be found here: Lower beaks; upper beaks.
      
      
3. Funnel
   1. Funnel valve present.
   2. Funnel organ: Dorsal pad with two triangular flaps, no papillae.
      
      
4. Mantle
   1. Tubercules absent at funnel-mantle fusion.
   2. Paralarvae (to ca. 50 mm ML) with thick gelatinous dermis on mantle.*
      
      
5. Fin
   1. Anterior 10-15% of fin inserts on mantle (in subadults).**
      
      
6. Photophores
   1. Photophores present on digestive gland.*
   2. Photophores present on tips of arms I-III or only II or only III of adult females.
      

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      Figure. Visceral photophores from a subadult, M. fisheri, off Hawaii. The visceral photophores contain four reflecting cups (green). The intestine, partially covered with red pigment, is seen here passing between photophores of either side. The barely-discernable digestive gland is the fuzzy central dark region. Photograph by R. E. Young.

*Within family, unique to this genus.
**Within family, unique degree of mantle attachment. Most genera lack a mantle attachment but two have more than 30% of fin attached to the mantle(Egea, Teuthowenia) rather than to the gladius.

Comments

Characteristics are from Voss (1980).

Life History

Paralarvae of M. fisheri from Hawaiian waters have been identified. The large posterodorsal mantle chromatophore seen in both stages is distinctive among cranchiid paralarvae from these waters. What appears to be an unusually long club may actually be a combination of the club with a large number of carpal suckers on the distal stalk.

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Figure. Paralarvae of M. fisheri, Hawaiian waters. Thumbnail (far left) - Illustration shows relative sizes of the two paralarvae. Left - Ventral and dorsal views of a 4.9 mm ML paralarva. Right - Ventral and dorsal views of a 14.5 mm ML paralarva. The scale bars are 1 mm. Drawings by R. Young.

Distribution

This genus occurs circumglobally in tropical and subtropical waters (Voss, 1992).

References

Tsuchiya, K. and T. Okutani. 1993. Rare and interesting squids in Japan -X. Recent occurrences of big squids from Okinawa. Venus 52: 299-311.

Voss, N. A. (1980). A generic revision of the Cranchiidae (Cephalopoda; Oegopsida). Bull. Mar. Sci., 30: 365-412.

Voss N. A., S. J. Stephen and Zh. Dong 1992. Family Cranchiidae Prosch, 1849. Smithson. Contr. Zool., 513: 187-210.

Young, R. E. 1978. Vertical distribution and photosensitive vesicles of pelagic cephalopods from Hawaiian waters. Fish. Bull. 76: 583-615.