The arctic species Heterostigma separ Ärnbäck-Christie-Linde, 1924 (Ascidiacea: Pyuridae) in the strait of Gibraltar (southern Spain)

The arctic species Heterostigma separ Arnbäck-Christie-Linde, 1924, a component of the interstitial fauna in coastal soft bottoms from Nova Zembla, was found in gravels of Algeciras Bay (Gibraltar Strait, Southern Spain). This new record constitutes the southernmost limit of the geographical range of this species. Some traits of branchial morphology of H. separ are studied, and new data are presented to establish the anatomical variability of this species. Furthermore, some aspects of reproduction, life cycle and ecological requirements are provided and discussed. The geographical distribution of european species of this genus is summarized.