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Clio pyramidata Linnaeus, 1767 forma lanceolata (Lesueur, 1813)

Overview

This is a shelled, uncoiled, pyramidally shaped, pelagic snail, up to 1.5 cm long. The shell is transparent, broadly triangular in shape and in cross-section. The reddish or dark brown visceral mass is seen through the shell. Growth lines are prominent, the lateral sides are rounded in cross section. It is a good swimmer that feeds on phytoplankton and protozoa. It lives in the warm upper water layers of all oceans, where it can occur in mass blooms (Clio p. lanceolata swimming).

Taxonomic Description

Shell is nearly straight, pyramidally shaped, thin and transparent (Clio p. lanceolata 1, Clio p. lanceolata drawing). The lateral ribs are thickened, and extremely strongly diverging. The dorsal rib is straight and protrudes distinctly above the shell aperture. The lateral ribs are very long, but do not end in free processes, the lateral ribs are rounded posteriorly. The shell, near the posterior top, is rounded in cross-section, triangular medially and in the anterior half. Anteriorly the ventral surface is hollow and lunar-shaped in cross-section, the hollow shape of the ventral side is caused by the lateral ribs which bend ventrally in the upper part. At both latero-dorsal sides three longitudinal ribs are present and one rib ventrally. The transverse striation and growth lines are distinct but usually not as pronounced as in the forma pyramidata. The greatest width of the shell is found near the middle of the shell. The oval embryonic shell is more elongate than in the forma pyramidata. The wings are colourless. The lips are brown to reddish. The radula formula is 1-1-1 (Clio p. lanceolata radula, Clio p. lanceolata radula2) and has about 6 transverse rows. The shape of the teeth can be variable (Clio p. lanceolata lateral teeth).
The shell length is about 20 mm; the maximum width about 15 mm.

Morphology

The muscle arrangement(Clio p. lanceolata muscles) is discussed under the forma Clio p. pyramidata.

Juveniles

Protoconch I is slender oval and continues into protoconch II with only a small incision. After protoconch II the juvenile shell is triangular in cross section (Clio p. lanceolata protoconchs, Clio p. lanceolata 2). Daily growth increment is much larger in the juvenile shell than in the older parts of the teleoconch.

Reproduction

Clio pyramidata forma lanceolata is a protandric hermaphrodite. In areas with a short of phytoplankton bloom period the male phase is shortened in favour of the female phase. This can be studied by counting the male and female sex products under a matrix (Clio p. lanceolata gonad histology). The different types of gonad stadia (Clio p. lanceolata gametes) are given in the illustration as follows, from top to bottom: juvenile, male and female, can then be recognised and measured. In populations transported out of their normal range strobilation (later considered to be schizogamy) may occur (Van der Spoel, 1979, Pafort and Van der Spoel, 1986, Pokora, 1989). During strobilation the soft parts of an adult specimen abruptly split into two parts (Clio p. lanceolata aberrant 1 hatching). The upper part without gonads swims (Clio p. lanceolata swimming abb) out of the shell, the remaining part remains for a period in the shell and is completely filled with sperm and eggs except for the wings which have normal muscle tissue. A diagram for Clio p. lanceolata strobilation shows the process of the formation of the Clio p. lanceolata strobila. The strobula or aberrant stage (Clio p. lanceolata aberrant) has wings and a body. Aberrant stages (#Clio p. lanceolata aberrant 2) in shells are the most frequently found type as shown in the population in the next illustration (Clio p. lanceolata with aberrants). See also Clio p. pyramidata.
The shells grows old in a short time, as seen from the growth lines (see illustration for the forma pyramidata) and it takes about 3 weeks to reach its final size.

Ecology

The species is omni- or phytophagous, epipelagic to mesopelagic and shows strong diurnal vertical migration between 0 and 1000 m (see illustration). Young specimens are found 50-200 m below the adults. Copepod juveniles and nauplii, tintiniids, radiolarians, and centric diatoms were found in the gut. The temperature range is 7.0°-27.8° C, the salinity range is 36.1-36.5°/oo S.
Horizontal swimming speed is 40.1 mm/sec. upward swimming is 8.2 mm/sec and sinking speed is 33.5 to 40.2 mm/sec (Davenport and Bebbington, 1990).
This species is food for the squid Loligo opalescens in the Pacific (Wendt, 1990).

Practical Importance

Blooms of Clio pyramidata forma lanceolata form an important food source for fish and whales. Moreover, the size of the embryonic shell measured under the microscope (Clio p. lanceolata protoconchs) can be used as an indicator [and palaeo-indicator (Clio p. lanceolata protoconch fossil)] for water temperature (Diester-Haass and Van der Spoel, 1978).

Distribution

Clio pyramidata forma lanceolata occurs in warmer waters of the Atlantic, Indian, and Pacific Oceans. Near Iceland some records of lanceolata are known presumedly from specimens transported accidentally far north by the North Atlantic Drift. Only a large population north of Madagascar is found in the Indian Ocean. In the Pacific forma lanceolata is found in the Indonesian seas, north of New Zealand, in the eastern part of the South Equatorial Current and in the NE and NW-Pacific Area. Between 40°N and 30°S the whole population is probably composed of the formae lanceolata. From pteropod ooze the forma lanceolata is reported in NW-Atlantic, Central Indian and N-Pacific Oceans, the southern Red Sea and Arabian Sea. See the Clio p. lanceolata map.

Geological Record

This form was found in the Pleistocene and Pliocene (Plaisancien) of the Mediterranean and from the Late Quaternary of the Red Sea. It only occurs after the Pleistocene in the Adriatic succeeding forma pyramidata and the same may be true in the Mediterranean. It is found in the Late Pliocene of Italy.

Others

Neurosecretion is described for this species.

Types

Hyalaea lanceolata Lesueur, 1813: 284, pl. 5, fig. 3.
Types are not located.

Clio pyramidata lanceolata