Labidocera pseudacuta, a new pontellid copepod from the Indian Ocean, with remarks on the related species Labidocera acuta (Dana)

Abstract

In recent years, attention has been drawn to the importance of species of Pontellidae as possible biological indicators of water masses (Fleminger, 1957; Heinrich, 1960 ; Voronina, 1962 ; and Sherman, 1963). The Senior author while participating in the Vth cruise of the U.S. Research Vessel Anton Bruun in the Indian Ocean from January to May, 1964, made a series of surface plankton collections using a rectangular frame net of mouth dimension 76 cm. x45 cm. The conical bag attached to the frame was of perlon monodur No. 0.333 /^ mesh size (3 meshes to the mm.). The net was kept buoyant with floats attached lo the outer sides of the frame, allowing only part of the aperture (25 cm.) to remain below water at any time. Two bridle ropes attached to the sides of the frame and an additional guide rope tied to the lower beam of the frame helped to keep the net opening in the desired position while it was allowed to drift at each station for about thirty minutes. In the samples collected thus, pelagic copepods, especially Pontellidae is well represented. The following 13 species of Pontellidae, namely Calanopia minor A. Scott,Pontella atlantica Milne-Edwards, P. diagonalis Wilson (=P. andersoni Sewell?) P.fera Dana, P. spinipes Giesbrecht, P. princeps Dana, Pontellopsis armata (Giesbr.), P. regalis (Dana), P. villosa Brady, Pontellina plumata (Dana), Labidocera acutifrons (Dana), L. detrmcata (Dana), L. minuta Giesbrecht, and an undescribed species of Labidocera were obtained from 18 stations on two transects on 55 °E, and 75 °E longitudes, and between latitudes 15"42'N and 35^42'S. The undescribed species of Labidocera which appears to be a cognate of the neritic species Labidocera acuta (Dana) is described here as Labidocera pseudacuta sp. nov. The differential characters of L. acuta from the new species are also included in this account and the two species illustrated. Details of the temperature-salinity-pontellid relation of the new species is also dealt with here. The material of £. acuta was obtained from off the south-west coast of India during the cruises of R.V. Varuna