Idioteuthis cordiformis (Chun 1908)

Mastigoteuthis cordiformis Chun, 1908

This species is characterized by having the surface of the mantle, head, and arms covered with minute, closely-packed, conical tubercles with blunt to sharply pointed apices (Figures 52, 53). On a specimen of 87 mm ML the tubercles are 0.2 mm in diameter and 0.2–0.3 mm high. The tubercles are covered with a fine epidermis in life, but this epidermal layer generally is rubbed off in preserved specimens, as is the case with the material figured. The internal structure consists of dense connective tissue which has staining properties and appearance reminiscent of elastic cartilage or fibrocartilage of vertebrates. The fibers are arranged in an orderly pattern (Figures 54–56).

The tubercles consist of a matrix with numerous, elongate vacuoles that are arranged in an orderly pattern; those in the basal portion (in longitudinal section) radiate diagonally in layers from the center of the tubercle to the periphery, while those nearer the tip are somewhat concave and arranged in layers parallel with the surface of the mantle (Figures 55, 56). The walls of the vacuoles are moderately thick and fibrous. A zone of nuclei of epithelial cells is conspicuous around the basal periphery of the tubercles and along the basal discs that lie against the surface of the mantle.

The tissues in histological section (longitudinal sections, Figures 54–56) from superior to inferior through the mantle consist of the following layers: a thin epidermis (frequently ribbed off in preparations); the tubercles; a thick layer of loose ordinary connective tissue, with large, elongate vacuoles, the walls of which have large, dense nuclei; a pigment/ chromatophore layer at the superior-most boundary of this vacuolated area; a thin, dense sheath of connective tissue; a thick muscular layer that consists primarily of circular muscle, interspersed with bundles of longitudinal muscle, and penetrated by radial muscle fibers from the inferior thick layer of radial muscle in which is sandwiched a narrow band of circular muscle (the radial muscle is loosely arranged with large spaces between fiber bundles); an inferior-most sub-layer of very loosely scattered circular muscle bundles and other randomly oriented muscle fibers; and the thin, dense inferior mantle epithelium. It should be noted that this tissue sample comes from a long-preserved specimen in which the initial fixation was not uniform, and the inferior tissue has deteriorated to a certain extent. Subsequent examination of well-fixed specimens shows that the inferior layer of circular muscle actually is as well developed and extensive as the superior circular muscle.

Idioteuthis cordiformis is a species of whip-lash squid found in tropical regions of the west Pacific Ocean. The species is commonly known as the 'love-heart squid' because the species name cordiformis is Latin for 'heart shaped'. Recently, this species has been found to consume small birdbeak dogfish.