Those Amazing Spider Conchs
By Bill Frank
     Some of the most interesting and distinctive-looking large marine gastropods are the members of the genus Lambis (Spider Conchs) of the family Strombidae. Found exclusively in the Indo-Pacific region, its species readily exhibit traits not so easily recognizable in other genera/families.

     One such trait is sexual dimorphism of shells. The females of some species, Lambis lambis (Linnaeus, 1758) as an example, are generally much larger, have more well developed knobs on the dorsum, and have the spines angled upward (occasionally nearly vertical). The males of the species are generally much smaller, occasionally much more colorful, less knobby, with the spines being near horizontal.

     Another very interesting, if not well understood, trait of the genus is the propensity for hybridization. While hybridization is not an uncommon phenomenon in nature, it is poorly documented for marine gastropods. The limited studies which have thus far have been conducted suggest that it does in fact occur in other families (specifically West American Haliotidae). There is even evidence that some of the hybrids were capable of producing offspring.

Lambis lambis x millepeda hybrid - Bohol, Philippines (117 mm.)

Virtually all popular shell book authors accept the existence of nine valid species, divided into three sub-genera. These include:

Subgenus Lambis:

  • Lambis crocata crocata (Link, 1807) (Orange Spider Conch) and subspecies L. crocata pilsbryi Abbott, 1961 (Pilsbry's Spider Conch)
  • Lambis truncata truncata (Humphrey, 1786) (Truncate Spider Conch) and subspecies L. truncata sebae (Kiener, 1843) (Seba's Spider Conch)
  • Lambis lambis (Linnaeus, 1758) (Common Spider Conch)

Subgenus Millepes:

  • Lambis digitata (Perry, 1811) (Elongate Spider Conch)
  • Lambis millepeda (Linnaeus, 1758) (Milleped Spider Conch)
  • Lambis robusta (Swainson, 1821) (False Scorpion Conch)
  • Lambis scorpius scorpius (Linnaeus, 1758) (Scorpion Conch) and subspecies L. scorpius indomaris Abbott, 1961 (Lesser Scorpion Conch)
  • Lambis violacea (Swainson, 1821) (Violet Spider Conch)

Subgenus Harpago:

  • Lambis chiragra chiragra (Linnaeus, 1758) (Chiragra Spider Conch) and subspecies L. chiragra arthritica (Röding, 1798) (Arthritic Spider Conch).

     A potential tenth species, in all likelihood a hybrid resulting from the mating of L. truncata sebae and L. millipeda, which has gained some acceptance as a valid species, was originally described by Shikama in 1971 as Lambis arachnoides. This same morph was named L. wheelwrighti by Joel Green in 1978. The latter binomen has gained wider acceptance due to some inconsistencies in Shikama's original description.

     In addition to the so called L. wheelwrighti, to date the following Lambis hybrids have been documented: L. lambis x L. chiragra chiragra, L. lambis x L. millipeda, L. Lambis x L. scorpius scorpius, L. scorpius scorpius x L. millepeda, and L. scorpius scorpius x L. crocata crocata; thus involving six of the nine species in the genus.

Go To Images Of The Aforementioned

     Based upon availability from retail specimen shell dealers, it would appear that so called L. wheelwrighti and the L. lambis x L. millepeda hybrids are the most common. However, in light of the fact that fairly close examination is necessary in certain instances to distinguish a hybrid from the dominant parent species, this may only reflect the energy and skill applied to the supply side of the equation.

     This extensive hybridization by the Lambis does beg one question. We have a genus containing but nine species, all large and distinctive looking, with each species being easily identifiable by any amateur, and some hybrids being rarely seen. Considering that hybridization is known to occur in other families, one might ask what is the possibility that some of the described species in other families such as Conus and Cypraea (families in which there is often little difference between species) might too in fact only be hybrid, especially when the species is known/described from only a few specimens.

     That aside, next time you find yourself in a shell store catering to tourists and have a plethora of Lambis at your disposal, you may want to invest a few moments to take a closer look. You never know what you might find; especially if they are from the Philippines, which for some reason seems to be the source of most Lambis hybrids.

References:

Abbott, R. Tucker, 1961. The Genus Lambis in the Indo-Pacific, Indo-Pacific Mollusca, 1(3):147-174, photographic plate 121.

Abbott, R. Tucker and S. Peter Dance 1986. Compendium Of Seashells, American Malacologists, Inc., Melbourne, FL, 411 pp.

Kronenberg, G. C., 1993. On the identify of Lambis wheelwrighti Green, 1978 and L. arachnoides Shikama, 1971, Vita Marina, 42(2):41-55.

Walls, Jerry G. 1980. Conchs, Tibias, and Harps, TFH Publications, Inc. Ltd., New York, NY, 191 pp.

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