TWO NEW SPECIES OF HETEROMYSINI (MYSIDA, MYSIDAE) FROM THE ISLAND OF MADEIRA (N.E. ATLANTIC), WITH NOTES ON SEA ANEMONE AND HERMIT CRAB COMMENSALISMS IN THE GENUS HETEROMYSIS S. I. SMITH, 1873

BY

KARL J. WITTMANN1) Abteilung für Ökotoxikologie, Zentrum für Public Health, Medizinische Universität Wien, Währinger Straße 10, A-1090 Vienna, Austria

ABSTRACT Faunistic studies and a survey of anemone commensals in near-shore habitats at the Island of Madeira yielded two new species belonging to the genus Heteromysis: H. dardani commensal with the diogenid hermit crab, Dardanus calidus (Risso, 1827), and H. wirtzi with the sea anemone, Telmatactis cricoides (Duchassaing, 1850). Both species differ from previously known E. Atlantic species by a flagellate, modified seta on the inner distal corner of the antennular trunk. H. wirtzi shows more spines on the second to fourth male pleopods, and four spines on the endopods of the uropods compared to three spines in H. dardani. Morphological differences suggest that commensalism of Heteromysis species with hermit crabs has independently evolved in the (sub)tropical shelf areas of the Indo-Pacific, E. Pacific, and Atlantic oceans. The W. Atlantic anemone commensals belong to two morphologically distinct lines within the subgenus Olivemysis Bacescu,˘ 1968, one of which shows close relationships to the two newly described E. Atlantic species. A key to the species of Heteromysis known from the E. Atlantic and the Mediterranean is given.

ZUSAMMENFASSUNG Faunistische Untersuchungen und eine Erfassung von Anemonen-Kommensalismen entlang der Küsten von Madeira ergaben zwei neue Arten der Gattung Heteromysis: H. dardani, ein Kommen- sal der Einsiedler-Art Dardanus calidus (Risso, 1827) und H. wirtzi, ein Kommensal der Anemone Telmatactis cricoides (Duchassaing, 1850). Beide unterscheiden sich von den bisher bekannten os- tatlantischen Arten durch eine begeißelte modifizierte Borste an der inneren endständigen Ecke des Antennulastammes. Im Vergleich zu H. dardani hat H. wirtzi vier anstelle von drei Dornen am Uropoden-Endopoditen und mehr Dornen an den zweiten bis vierten Pleopoden des Männchens. Morphologische Unterschiede legen nahe, dass Kommensalismen von Heteromysis-Arten mit Ein- siedlerkrebsen in den (sub)tropischen Schelfgebieten von Indopazifik, Ostpazifik und Atlantik un- abhängig entstanden sind. Die westatlantischen Anemonen-Kommensalen gehören zu zwei unter- schiedlichen morphologischen Linien innerhalb der Untergattung Olivemysis Bacescu,˘ 1968, wobei

1) e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2008 Crustaceana 81 (3): 351-374 Also available online: www.brill.nl/cr 352 KARL J. WITTMANN eine Linie nähere Beziehungen zu den neubeschriebenen ostatlantischen Arten zeigt. Ein Bestim- mungsschlüssel für Heteromysis aus Ostatlantik und Mittelmeer wird vorgelegt.

INTRODUCTION

The comparatively stout body proportions in most species of the genus Hetero- mysis S. I. Smith, 1873 strongly hint at a benthic mode of life. These mysids, i.e., species of the family Mysidae, prefer cryptic habitats such as dense vegetation, gravel, empty shells, and micro-caves during daytime. Benthic invertebrates can also function as cryptic habitats in a broader sense, e.g., sponges, stony corals and gorgonians, sea anemones, brittle stars, and shells inhabited by hermit crabs. As in many benthic mysids, a number of Heteromysis species emerge at night and can be sampled with epi-benthic nets only during the night. Methodological constraints mainly explain why only 17 of the currently recognized Heteromysis species were described up to the 1950s. With more specifically designed benthic sampling methods, this number has increased more than fourfold since then, arriving at 79 species with the present contribution. A systematic survey of commensals of sea anemones by Wirtz (1997) and a systematic inventory of mysids in coastal waters of the Madeira archipelago by Wittmann & Wirtz (1998) revealed two new Heteromysis species, which will be described here. They are commensals of anemones and hermit crabs, respectively. Associations between mysids and hermit crabs were previously reported only from the Red Sea and the Indian and Pacific oceans (see Discussion). All such species belong to the genus Heteromysis. Their hosts are various hermit crab species, in most cases belonging to the diogenid genus Dardanus Paulson, 1875. A number of facultative associations of mysids with sea anemones, representing only loose inter-specific relationships, have been reported. Four species of Lep- tomysis G. O. Sars, 1868 from the Mediterranean are frequently associated with the sea anemone, Anemonia viridis (Forskål, 1775). Two of these four mysids are much less frequently associated with Aiptasia mutabilis (Gravenhorst, 1831) (dur- ing daytime and to a lesser extent also at night) whereas a larger number of speci- mens of these species is found in various other types of microhabitats (Wittmann, 1978, 1986a, b): swarms or small groups may hover close to, usually not between, the tentacles of the anemones. The mysids are never observed in physical con- tact with A. viridis; when forced into contact with the anemone’s tentacles they are stung and may die. Among these species, L. truncata (Heller, 1863) shows the closest relations to A. viridis: the mysids returned to their host after having been driven away experimentally. Patzner (2004) observed that L. lingvura (G. O. Sars, 1866) from Banyuls-sur-Mer (W. Mediterranean) remained at the anemones