Arenopontia subterranea Kunz 1937

Arenopontia subterranea Kunz, 1937

Arenopontia (Arenopontia) subterranea Kunz, 1937: Wells (1967: 324)

Original description. Kunz (1937): 107–110; Abb. 8 (Figures 38–42), 9 (Figures 43–47), 10 (Figures 48–51).

Additional descriptions. Mielke (1975): 109–110; Abb. 73. Martínez Arbizu & Moura (1994): 64; Fig. 3a, c.

Type locality. Germany, Kieler Förde, Schilksee; intertidal coastal groundwater (“Küstengrundwasser”).

Body length. 380 μm (♀) [Kunz, 1937]; 300 μm (♀), up to 390 μm (♂) [Noodt, 1952]; 310–430 μm (♀), 280–400 μm (♂) [Mielke, 1975].

Remarks. Arenopontia subterranea is morphologically close to A. problematica and A. adriatica sp. nov. All three species can be differentiated from one another by morphometric differences displayed by the P1 endopod (Table 1). According to Mielke (1975: Abb. 73A), the female P5 has a minute dentiform projection at its distal margin, possibly representing a vestige of the fourth seta that is expressed in A. riedli, A. basibuyuki sp. nov. and A. syltensis sp. nov. Although this feature has not been reported in any other Arenopontia species, confirmation of its consistent presence in a larger sample is required before its significance as a diagnostic character can be corroborated.

The type material of Arenopontia subterranea no longer exists since Kunz’s pre-1940 copepod collections that were deposited at the Institut für Meereskunde in Kiel were destroyed in 1944 during World War II (Schriever 1984). Despite several sampling efforts in German waters, we have been unable to obtain topotype or other material that could be positively attributed to A. subterranea. The discovery of a closely related species, A. syltensis sp. nov., from the Isle of Sylt also casts further doubt on the validity of certain German records and indeed most northwestern European reports of the species. As pointed out by Sak et al. (2008), the problem is exacerbated by Arlt’s (1983) discovery of a female specimen from the Baltic which was identified as A. subterranea. His illustrations indicate that he was dealing with a different species (see below), raising the suspicion that not all records east of the Skagerrak can be attributed to the type species with confidence. Arenopontia subterranea has not only been reported throughout Europe from the Baltic to the Black Sea basin. Additional unverified records from Madeira, the Indian subcontinent, Mozambique and both North and South Carolina have led to the suggestion that this species is potentially cosmopolitan (Lindgren 1972, 1976; Rao 1980; Wells 1967, 1986). Lindgren (1976) claimed that it is conceivable that its geographical range will be extended even further when more sandy intertidal habitats become surveyed in the Pacific. The great majority of the published records of A. subterranea are not accompanied by illustrations that could confirm their authenticity. This unfortunate state of affairs stems from the fact that many authors have identified their material with A. subterranea, assuming that this species displays extensive intraspecific variability. Faced with this widely adopted misconception we have elected to take a critical stance in accepting records as sufficiently reliable. The true range of the species is as yet unknown but it is likely to be restricted to northwestern Europe where it occurs sympatrically with other congeners such as A. syltensis sp. nov.