Leachia Lesueur, 1821

Six of the 14 nominal species of Leachia are considered valid by Voss, et al. (1992). These authors suggest that ll species exist in the genus, 5 of which are undescribed.

Introduction

Members of this genus are easily recognized by the two straight cartinagenous, tubercular strips on the mantle that arise from each point of funnel-mantle fusion, the slender, tapering mantle and the terminal fins with a combined oval shape. The species of the genus, however, are not easily recognized. Many names exist in the literature and most have poor descriptions associated with them and are based on paralarvae. At present, geographical location is one of the most important characteristics used in identification. The type localities of the named species are:

Atlantic Ocean

• Leachia atlantica - eastern North Atlantic, 36°, 10°W.
• Leachia lemur - western North Atlantic, east of Cape Hatteras, 35°N, 73°W,.
• Leachia sp. A - western South Atlantic, 39°S, 53°W.

Indian Ocean

• Leachia cyclura - south Indian Ocean, 37°S 33°E.

Pacific Ocean

• Leachia danae - (Gulf of Panama).
• Leachia dislocata - off Southern California, eastern temperate Pacific.
• Leachia pacifica - south Pacific Ocean, 15°S, 168°W

Diagnosis

A cranchin...

• with one row of cartilagenous tubercules on the mantle originating at each funnel-mantle fusion.

Characteristics

1. Tentacles
   1. Median suckers of tentacular club greatly enlarged.**
      
      
2. Funnel
   1. Funnel valve absent.
   2. Funnel organ: dorsal pad U-shaped with 3-7 papillae.
      
      
3. Mantle
   1. Single tuberculate cartilagenous strip on mantle originates at each funnel-mantle fusion.*
      
      
4. Fins
   1. Fins barely unite posterior to gladius (transversely elliptical in combined outline).
      
      
5. Photophores
   1. Each eye with 5-21 oval photophores depending on species.
   2. Photophores on tips of arms III in mature or nearly mature females.

Comments

This is the only genus in the subfamily Cranchiinae with paralarvae that have stalked eyes. Characteristics are from Voss (1980).

Comparison of species

Figure. Comparison of the structure of the mantle tubercular strips among five of the species. A - Leachia lemur, north Sargasso Sea, 42 mm mL. B - Leachia atlantica, subtropical North Atlantic, 54 mm ML. C - Leachia dislocata, off California, 34 mm ML. D - Leachia danae, eastern tropical Pacific, 53 mm ML. E - Leachia pacifica, off Hawaii, 41 mm ML. Drawings from Voss, et al. (1992, p. 191).

Life History

The paralarvae of the genus have a very distinctive appearance. A paralarva has a very long, slender brachial pillar and a pointed tip to the gladius. Paralarvae of Leachia were originally placed in the genus Pyrgopsis and are now often referred to as pyrgopsis paralarvae.

Figure. Dorsal and ventral views of paralarval L. pacifica, 7.9 mm ML, Hawaiian waters, original.

Distribution

Vertical distribution

Off Hawaii, L. pacifica has a peculiar vertical distribution pattern which may prove to be common within the genus. Small squid are found in near-surface waters. As sexual maturity approaches, the squid undergoes an abrupt ontogenetic descent. At depths greater than 1000 m males and females become mature. Large photophores develop on the tips of the third arms of females and these are, presumably, used to attract males at great depths where the risk of predation is low.

Figure. Vertical distribution chart of L. pacifica, Hawaiian waters. Captures were made with both open and opening/closing trawls. Bars - Fishing depth-range of opening/closing trawl. Circle - Modal fishing depth for either trawl. Blue color - Night captures. Yellow color - Day captures. Chart modified from Young (1978).

References

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.