Sandalops melancholicus Chun, 1906

Sandalops contains one recognized species. Voss, et al. (1992), however, suggest that 3-4 species exist.

Introduction

Sandalops melancholicus is a small squid. Maximum known size is about 110 mm ML. It is most easily recognized by the shape and method of attachment of the short fins. It occurs circumglobally in tropical and subtropical waters and at depths within the mesopelagic zone.

Brief diagnosis:

A taoniin...

• with tubular eyes as juvenile.
• with contiguous ocular photophores.
• with short, broad vanes of gladius with matching fins.
• without tubercules at funnel-mantle fusion.

Characteristics

1. Tentacles
   1. Tentacular clubs with suckers only.
   2. Two series of suckers and pads on distal 1/2 of tentacular stalk.
      
      
2. Funnel
   1. Funnel organ: Dorsal pad with two large triangular flaps.
   2. Funnel valve absent.
      

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      Figure. View of funnel organ of mature male Sandalops sp. a, 102 mm ML. drawing from Voss (1980, p. 387, fig. 6e).

3. Mantle
   1. Tubercles absent at funnel-mantle fusion.
      
      
4. Fins
   1. Fins short, oval to round.
   2. Posterior insertion of fins does not reach end of gladius (i.e. fins subterminal).
   3. Anterior insertion at broadest point on vanes of gladius (i.e., fins attach to posterolateral margins of lanceola).
      

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      Figure. Dorsal view of the fins and gladius of Sandalops sp. a, mature male, 102 mm ML. Drawing modified from Voss (1980, p. 387, fig. 6a).

5. Photophores
   1. Two ocular photophores (one large, one small) on each eye are contiguous.*
   2. Arm tip photophores absent.
      

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      Figure. Left - Anteroventral view of the ocular photophores of Sandalops sp. a, mature male, 102 mm ML. Drawing from Voss (1980, p. 387, fig. 6d). Right - Anteroventral view of the oclar photophores of S. melancholicus, Hawaiian waters. Photograph by R. Young.

*Unusual in family; found also in Liguriella.

Comments

The eyes of juveniles are tubular, a feature shared only with Taonius. Also, the short, broad vanes of the gladius (see drawing for character no. 5 above) are distinctive and of considerable help in identifying damaged squid. Characteristics are from Voss (1980).

Nomenclature

Uranoteuthis bilucifera (Lu and Clarke, 1974) is a junior synonym (Nesis, 1982).

Life history

Paralarvae are found in the upper few hundred meters of the ocean (epipelagic zone) (see Vertical Distribution) and have eyes that are laterally compressed and possess a "rostrum" (see photograph to the right). Both features aid in concealment of the eye which, along with the digestive gland complex, are opaque structures in an otherwise transparent squid. The generic and common names of this squid are drawn from the shape of the paralarval eye as seen in illustration below of the holotype from Chun, 1910.

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Figure. Left- Side view of the paralarval head of S. melancholicus, holotype, 11.5 mm ML. Drawing modified from Chun (1910). Right - Side view of the paralarval head of S. melancholicus, Hawaiian waters. Photograph by R. Young.

The juvenile develops tubular eyes during its occupancy of the upper mesopelagic (=twilight) zone. The head is tilted with respect to the body axis and the eyes apparently, in life, are directed vertically upward toward the brightest downwelling light. Two photophores conceal the ventral silhouette of each eye.

The subadult is found in lower mesopelagic depths and has nearly hemispherical eyes (Young, 1975).

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Figure. Left - Side view of the head of a juvenile S. melancholicus, Hawaiian waters, showing tubular eyes. Right - Side view of a subadult S. melancholicus, Hawaiian waters, showing near-hemispherical eyes. Photographs by R. Young.

More information on the life history can be found here.

Distribution

Vertical distribution

This squid undergoes ontogenetic descent. As it reaches greater depths with increasing age, the morphology of the eye changes greatly (see Life History).

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Figure. Chart of the vertical distribution of S. melancholicus from Hawaiian waters, taken with both opening/closing and open trawls. Circle with black filling- Night capture. Circle with white filling- Day capture. Circles represent the modal depth of the trawl regardless of trawl type. Bars with circles- Trawl fishing-range of open/closing trawls. Bars without circles- Depth range of oblique trawl (solid bar- night capture; dashed bar- day or twilight capture). Chart modified from Young (1975).

Geographical distribution

The type locality is off Tristan da Cunha Island, South Atlantic.

Other Names for Sandalops melancholicus Chun, 1906

• The sandal-eye squid
• Sandalops Chun, 1906

References

Lu, C. C. and M. R. Clarke. 1974. Two new species of cranchiid cephalopods from the North Atlantic, Uranoteuthis bijucifera n. gen., n. sp. And Galiteuthis triluminosa n. sp. J. Mar. Biol. Ass. U.K. 54: 985-994.

Nesis, K. N. 1982/87. Abridged key to the cephalopod mollusks of the world's ocean. 385+ii pp. Light and Food Industry Publishing House, Moscow. (In Russian.). Translated into English by B. S. Levitov, ed. by L. A. Burgess (1987), Cephalopods of the world. T. F. H. Publications, Neptune City, NJ, 351pp.

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. 1975. Transitory eye shapes and the vertical distribution of two midwater squids. Pac. Sci. 29: 243-255.