Carinaria japonica Okutani 1955

Introduction

Carinaria japonica is a moderately large species, achieving a maximal body length of 105 mm. The shell is compressed laterally and, when viewed from the side, is triangular in shape with a height to basal length ratio of 0.8-1.0. The keel is low initially, but increases in height with shell growth. The tail is moderately well-developed and has a prominent dorsal crest. The geographical distribution of the species is unique among carinariids; it is limited to the cool, temperate waters of the Transition Zone in the North Pacific Ocean.

Brief Diagnosis

A species of Carinaria with:

• Maximal adult body length of 105 mm
• Viewed laterally, shell triangular in shape, with a height to basal length ratio of 0.8-1.0 
• Keel increases in height with shell growth
• Tail moderately well-developed, with a prominent dorsal crest

Characteristics

1. Body morphology
   1. Proboscis, trunk and tail regions well-developed
   2. Eye shape triangular in dorsal view
   3. Tail with a prominent dorsal crest (see title photograph)
   4. Larva with a colorless velum except for a dark brown pigment patch at the end of each of the six velar lobes. The body is an overall brown color, although the tentacles are transparent.
      
2. Shell
   1. Adult shell triangular in lateral view; ratio of height to basal length = 0.8-1.0; keel height increases with growth
      
      

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      Figure. Sketch of Carinaria japonica shell (left) and photograph of transparent shell that covers the stalked visceral nucleus (right). In the intact shell, the keel height increases ventrally (as in the sketch on the left), but the keel is often damaged and is much lower (as in the in-situ field photograph on the right). The esophagus emerges from the base of the digestive gland (brown) and leads anteriorly (see title illustration) to the buccal mass. On the surface of the cutis, the ciliated sperm groove extends ventrally from the testis (light brown) to the penial complex (consisting of the white penis and light brown penial appendage). Left © , Right © David Wrobel

   2. Larval shell transparent and globular in shape. Very small and numerous punctae are arranged in spiral rows on the shell surface. Viewed on the right side, the second whorl has a prominent spiral ridge, from which narrow, elevated striae radiate. On the left side of the shell, the umbilicus is deep and the umbilicus wall has about 18 broad, elevated spiral striae.
      
      

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      Figure. Larval shell of Carinaria japonica from the right side, left side, and aperture, respectively. Shell diameter = 0.5 mm. ©

   3. At metamorphosis the larval shell consists of 3-2/3 whorls; the adult shell (teleoconch) grows outward and downward from the larval shell aperture, and immediately includes a prominent dorsal keel
      
      

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      Figure. Right side of shell from a juvenile Carinaria japonica. Shell length = 1.0 mm. ©

Distribution

The geographic distribution of Carinaria japonica is restricted to Transition Zone Faunal Province in the North Pacific Ocean (McGowan, 1971; Seapy, 1974). This faunal province consists of a narrow band of surface water at the Subarctic Boundary (located between the Subarctic Pacific and Central Pacific water masses at about latitude 40-41°N), extending eastward from Japanese waters and broadening as it approaches the coast of North America to extend southward as the broad California Current.

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Location of the Transition Zone faunal province (shaded blue) in the North Pacific. The province is separated from the Central North Pacific province by the Subarctic Boundary and its southeasterly extension to Baja California; it merges more broadly with the Subarctic Pacific province to the north. © 2005

Feeding Habits

Among the species of Carinaria, the feeding habits and food preferences of C. japonica have been most thoroughly studied (Seapy, 1980). Thaliaceans (small doliolids and salps), chaetognaths and copepods dominated numerically in the diet. Comparisons of the proportion of each prey species in the diet and available in the plankton indicated preferential feeding on thaliaceans, chaetognaths and mollusks. In contrast crustaceans, and particularly copepods, were non-preferred prey. These prey preference patterns may reflect differences among prey species in their ability to escape capture.

References

McGowan, J. A. 1971. Oceanic biogeography of the Pacific, pp. 3-74. In: The micropaleontology off oceans, B. M. Funnell and W. R. Riedel (eds.). Cambridge: University Press.

Seapy, R. R. 1974. Distribution and abundance of the epipelagic mollusk Carinaria japonica in waters off southern California. Marine Biology 24:243-250.

Seapy, R. R. 1980. Predation by the epipelagic heteropod mollusk Carinaria cristata forma japonica. Marine Biology 60:137-146.

Seapy, R. R. and C. Thiriot-Quievreux. 1994. Veliger larvae of Carinariidae (Mollusca: Heteropoda) from Hawaiian waters. Veliger 37:336-343.