Planktomya henseni

Planktomya henseni Simroth, 1896


A small (0.1 cm) bivalve species, adapted to an extended period of larval pelagic life. It belongs to the mesoplankton as it is a juvenile of a benthic species. It is found in the N-Atlantic Ocean (Planktomya henseni line drawing).

Taxonomic Description

This is a teleplanic bivalve larva and not a neotenous species. The shell is a smooth except for fine growth lines. It is an equivalve bivalve, the shell is transparent golden-brown or amber. The shell is proteinaceous and completely dissolves in sodium hypochlorite (Allen and Scheltema, 1972). Prominent anteriorly directed umbos are found posteriorly to the hinge. In some specimens Allen and Scheltema (1972) found a prodissoconch capping the umbonal parts. The umbo is supported by two strong buttresses, anteriorly and posteriorly. These are hollowed out on the inward faces and contain viscera. There is a single, simple tooth immediately below the umbo anterior to the opisthodetic ligament. The ligament consists of a wedge-shaped inner layer which is internal and a much longer outer, external layer. The valves are interlocking along the anterio-dorsal, ventral and posterio-dorsal edges in a 'tongue in groove' structure.
Even in the largest specimens, a velum is present (Planktomya henseni). A foot is well developed.
The shell length is up to 1.5 mm.


This is a juvenile and the adults are not known.


This is a teleplanic microplankton feeding larva living in surface waters.


No reproductive organs developed.


This species occurs in the warmer waters of the Atlantic Ocean (Planktomya henseni map).


Planktomya henseni Simroth, 1896: 28. pl. 1, fig. 1A-C.
Types were not indicated.
Type locality: N-Atlantic Ocean 23° to 24°N.