First report of the order Mysida (Crustacea) in Antarctic marine ice caves, with description of a new species of Pseudomma and investigations on the taxonomy, morphology and life habits of Mysidetes species

Abstract

SCUBA diving explorations of three islands off Dumont d’Urville Station at the coast of Adélie Land, East Antarctica, enabled the observation of marine ice caves. Sampling in this unusual habitat yielded a total of three species of Mysidae, altogether previously poorly known or unknown to science. Pseudomma kryotroglodytumsp. nov. is described, based on the structure of the antennal scale, telson and on cornea-like lateral portions set off against the main body of eyeplates. Mysidetes illigi is re-established at species level after almost a century in synonymy. Re-descriptions are provided for M. illigi and M. hanseni, based on types and ice cave materials. Keys to the Southern Ocean species of Pseudomma and to the world-wide species of Mysidetes are given. Phylogenetic trees are provided for the genera Pseudomma and Mysidetes. 18S rDNA sequences of P. kryotroglodytum differ from GenBank sequences of other Pseudomma species. First sequence data are given for species of the genus Mysidetes: 18S differs between the two examined species and COI is quite diverse between and within species. We found previously unknown, probably sensorial structures in these ice cave species: in P. kryotroglodytum, the basal segment of the antennula shows a pit-like depression with striated pad on the bottom and a median cyst, connected with the bottom of the eyeplate cleft. M. illigi shows a female homologue of the appendix masculina bearing a field of modified setae. Subsequent investigations demonstrated these structures also in species from other habitats. The feeding apparatus and stomach contents of the three ice cave species point to brushing of small particles (detritus, microalgae) from available surfaces, such as sediment, rock and the ice surface. Differences in the feeding apparatus are very subtle between the two Mysidetes species. The high content of fat bodies in M. hanseni could help it to survive periods of starvation. The large storage volume of the foregut in P. kryotroglodytum points to the collection of food with low nutritional quality and could help to balance strongly fluctuating food availability. Summer specimens of M. hanseni showed a bimodal frequency of developmental stages in the marsupium and bimodal size-frequency distribution of free-living stages. The females with younger brood (embryos) were, on average, larger and carried more marsupial young than those with older brood (nauplioid larvae). All examined incubating and spent females showed (almost) empty foreguts and empty ovarian tubes, suggesting possible semelparity and death following the release of young. The absence of juveniles and immature females from summer samples suggests that growth and accumulation of fat and yolk occur outside ice caves, while such caves could be used by fattened adults as shelter for brooding. A provisional interpretation proposes a biannual life cycle for M. hanseni, superimposed with shifted breeding schedules, the latter characterised by early breeding and late breeding females, probably in response to harsh physical and trophic conditions along the continental coast of Antarctica.

Evidence and Modification of Non-Visual Eyestalk Organs in Troglobiont Mysida and Stygiomysida (Crustacea)

“…Measurements, preparation, and microscopy are as previously published [12]. BL (mm) was measured from the tip of the rostrum to the terminal margin of the telson in free-living stages or as an unspecific anteroposterior extension in marsupial larvae with the rostrum and telson not yet fully differentiated.…”

“…The terminology and distinction of stages are based on previous publications [11,12] unless explicitly addressed below. 'Neonates' are freshly molted individuals from larval to juvenile stage upon release from the brood pouch.…”

“…Trogloxene species are photo-sensory competent and are not or rarely found in these habitats. As an exception from the categorization by Pesce et al, Leptomysis buergii Băcescu, 1966, is here categorized as trogloxene rather than troglophile because it forms hyperbenthic swarms mostly above sandy bottoms and only exceptionally inhabits caves [15] [5,12,16]. Finally, Siriella gracilipes H. Nouvel, 1942, is categorized as a troglophile due to its well-known massive presence in intertidal marine caves of the Mediterranean during daytime.…”

The Petalophthalmidae (Crustacea: Mysida) of the ANDEEP I–III expeditions to the Antarctic deep sea, with description of a new species and first record of photophores in mysids

“…Materials including the here defined types were returned to the Zoological Museum of Hamburg in vials with aqueous solution of ethanol 80% with propylene glycol 10% unless explicitly stated as having been dissected and mounted on slides. Terminology, measurements, preparation, microscopy, and documentation as in Wittmann & Chevaldonné (2021). By convention the lateral portions of the carapace in front of the cervical sulcus are termed ʻhepatic regionʼ and the teeth therein ʻhepatic teethʼ, although some hepatic caeca are found more dorsally outside this area.…”

The Mysidae (Crustacea, Mysida) of the ANDEEP I–III expeditions to the Antarctic deep sea with the description of twelve new species, establishment of four new genera and with world-wide keys to the species of Erythropinae and Mysidellinae

“…The secondmost species-rich subfamily, Heteromysinae, contributes 8 Antarctic and 11 sub-Antarctic species to this inventory. Descriptions of a total of three additional species by San and Wittmann & Chevaldonné (2021), along with the descriptions below of 11 new species boost the Antarctic Erythropinae from 15 to 29 species. This almost doubling of known species numbers in only 14 years (2011-2024) indicates that the exploration of Antarctic Erythropinae is at its very beginning.…”