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New species of Mexicope, stat. nov. and Ianthopsis from Australia and a rediagnosis of Acanthaspidiidae (Isopoda : Asellota)
Abstract
Two new species, Mexicope westralia and
Ianthopsis vanhoeffeni, are described from south-western
and south-eastern Australia respectively. One species of
Mexicope was known previously from the Gulf of Mexico
and the Caribbean. New morphological evidence shows that
Mexicope, hitherto considered as family
incertae sedis, should be transferred to the
Acanthaspidiidae. New diagnoses are presented for the family Acanthaspidiidae
as well as the genera Mexicope and
Ianthopsis. The distribution of species in the
Acanthaspidiidae is summarised. The vertical distribution patterns of the
three genera in the family (Acanthaspidia,
Ianthopsis, Mexicope) are shown to
be very different. It is suggested that the family originated in cold water of
the southern hemisphere at lower shelf to upper bathyal depth
(Ianthopsis) with subsequent evolution and radiation of
Acanthaspidia in the deep sea and
Mexicope in shallow warmer to tropical waters.
... The first theory is based on the hypothesis that the asellote deep-sea fauna was populated mainly through emigration from 'centres of origin in shallow waters' (submergence), especially at high latitudes ( Wolff 1960; Kussakin 1973; Menzies et al. 1973), where the temperature difference between shallow and deep waters, a potential physiological barrier for many taxa, is small (Gage & Tyler 1991; Childress 1995). For example, most shallow-water species of the family Acanthaspidiidae are widely distributed on the Antarctic shelf, but various related species can be found in the deep sea of the Southern Ocean, a distribution that could have arisen by a southern diversification after multiple polar submergence events (Brandt 1991a; Just 2001). By contrast, other authors (Hessler & Thistle 1975; Hessler et al. 1979; Wägele 1989; Wilson 1999) argue that cold shallow waters should have been colonized from the deep sea (high-latitude emergence) for two main reasons. ...
... The Acanthaspidiidae are a good example where morphological characters failed to provide sufficient phylogenetic information for a reliable tree reconstruction (see Just 2001). The distribution of the Acanthaspidiidae is concentrated in the Southern Hemisphere , specifically in the Southern Ocean, and includes both eye-bearing shallow-water and blind deep-sea genera (Brandt 1991a,b; Just 2001). The taxonomic status of this family was unclear, because no valuable synapomorphies define either the family or the genera ( Wägele 1989; Brandt 1991a,b; Just 2001). ...
... The distribution of the Acanthaspidiidae is concentrated in the Southern Hemisphere , specifically in the Southern Ocean, and includes both eye-bearing shallow-water and blind deep-sea genera (Brandt 1991a,b; Just 2001). The taxonomic status of this family was unclear, because no valuable synapomorphies define either the family or the genera ( Wägele 1989; Brandt 1991a,b; Just 2001). By contrast, all our analyses clearly support the monophyly of the Acanthaspidiidae (1.00/100/99/12) and indicate a close relationship with other shallow-water Asellota ( Joeropsididae, Iathrippa). ...
The Asellota are a highly variable group of Isopoda with many species in freshwater and marine shallow-water environments. However, in the deep sea, they show their most impressive radiation with a broad range of astonishing morphological adaptations and bizarre body forms. Nevertheless, the evolution and phylogeny of the deep-sea Asellota are poorly known because of difficulties in scoring morphological characters. In this study, the molecular phylogeny of the Asellota is evaluated for 15 marine shallow-water species and 101 deep-sea species, using complete 18S and partial 28S rDNA gene sequences. Our molecular data support the monophyly of most deep-sea families and give evidence for a multiple colonization of the deep sea by at least four major lineages of asellote isopods. According to our molecular data, one of these lineages indicates an impressive radiation in the deep sea. Furthermore, the present study rejects the monophyly of the family Janiridae, a group of plesiomorphic shallow-water Asellota, and several shallow-water and deep-sea genera (Acanthaspidia, Ianthopsis, Haploniscus, Echinozone, Eurycope, Munnopsurus and Syneurycope).
... Exploration of the slope benthos off south-eastern Australia towards the Tasman Sea over the past two decades by Museum Victoria, Melbourne, and the Australian Museum, Sydney , has revealed a high level of diversity and novelty of Isopoda (Poore & Wilson 1993;Poore et al. 1994). Works on several families or parts of families of janiroidean Asellota have been published (Brandt 1994, Cohen 1998, Just 1990, 2001a, 2001b, 2003, Just & Wilson 2004, Merrin 2004, Merrin & Poore 2003), and several more are in progress. In this paper a new genus and species, Xenosella coxospinosa, is described from the same collections. ...
A new genus and species of janiroidean Asellota, Xenosella coxospinosa, is described from the mid-bathyal slope off the coast of south-eastern Australia. Following a comparison of the new species to several families of broadly similar body shape, with emphasis on monotypic Pleurocopidae, a new family, Xenosellidae, is proposed for the new species. In the course of comparing relevant taxa, the current placements of Prethura Kensley in the Santiidae and Salvatiella Müller in the Munnidae are rejected. The two genera are considered to be incertae sedis within the Asellota superfamily Janiroidea pending further studies.
... were collected during Museum Victoria's SLOPE expeditions of south-eastern Australia between 1979 and 1988. These expeditions yielded a high diversity of isopod species ) and many new species have been described in recent years (for example see Brandt 1994, Just 2001a, 2001b, 2009, Merrin and Poore 2003, Brix 2006. Epikopais mystax sp. ...
A new munnopsid isopod genus from the southern hemisphere, Epikopais gen. nov. is described here and includes Epikopais aries (Vanhöffen, 1914) comb. nov. from Antarctica and three new species described here from the south-west Pacific: Epikopais mystax sp. nov. from the Bounty Trough east of the South Island of New Zealand; and Epikopais poorei sp. nov. and Epikopais waringa sp. nov., both from the south-eastern Australian continental slope. Epikopais gen. nov. can be distinguished by the combination of the short laterally rounded cephalic frons; the absence of dorsal spines; the lack of a mandibular palp; the mandibular fossa, which curves along the lateral margin of the mandible; and the biramous uropods.
... Of the approximately 300 species recognised, but as yet mostly unpublished, nearly all represent new species as well as a high level of morphological novelty. Based on these collections, some families or subgroups of families have been treated in recent years, (Brandt 1994; Cohen, 1998; Just 1990 Just , 2001a Just , 2001b Just , 2003 Just , 2005 Just & Wilson 2004, 2006, 2007 Merrin 2004; Merrin & Poore 2003; Poore & Just 1990; Serov & Wilson 1994, 1999). The purpose of the present paper is to diagnose a new genus of Paramunnidae of interesting novelty and high diversity in Australasian waters. ...
A new genus, Pentaceration, in the janiroid asellote family Paramunnidae from the Bass Strait area in south-eastern Australia is diagnosed. The distinguishing characters of species in the new genus are 1 central and 2 lateral spines on the frontal margin of the head, elongate eyestalks, lateral spines of varying length on pereonites 2-7, and reduced width of pereonite 4 compared with 3 and 5. Descriptions are presented of the type species, Pentaceration bassiana, and a second new species, P. spinosissima. The new genus appears to be wide-spread around Australia and New Zealand, where several as yet undescribed species have been noted, ranging from the upper sublitoral to abyssal depth. The relationship of Pentaceration to other paramunnid genera with covered coxae on all legs is discussed.
... In Southern Ocean Acanthaspidiidae, most eye-bearing species belong to the genus Ianthopsis, which can be predominantly found on the shelf, while blind species within the genus Acanthaspidia usually inhabit greater depths (>500 m, Fig. 3). Thus, Just (2001) concluded that deep-sea Acanthaspidiidae (i.e. species within Acanthaspidia) evolved from eye-bearing ancestors (Ianthopsis) inhabiting Southern hemisphere shelf and slope habitats. ...
Isopod crustaceans (whose representatives on land are known as woodlice, pill bugs or slaters) are an order of the crustacean supraorder Peracarida. The latter represents a heterogeneous and highly diverse group, comprising more than a third (~21,000 species) of total described crustaceans (Martin & Davis
2001). Isopoda have been proved a popular and useful taxon to assess large-scale patterns in biodiversity and biogeography (e.g. Hessler & Wilson 1983, Brandt 1992, Svavarsson et al. 1993, Wilson 1998) for several reasons. Their dispersal potential is limited to adult movement (such as passive and to a lesser extent active migration). This is because, like all peracarids, isopods brood their offspring in a ventral brooding pouch (marsupium), which is formed by extensions of their thoracic limbs. Thus, isopod distributions have the potential to reflect older centres of origin and radiation and so be valuable for
biogeographic analyses.
Apart from amphipod crustaceans, Isopoda are the most diverse peracarid order occurring across all major realms including terrestrial, freshwater and marine habitats. Many isopod species inhabit groundwater and caves, and some have even been recorded from deserts. In marine habitats isopods are a rich and ubiquitous element and have been described across all oceans and depths (intertidal to hadal; Schotte
et al. 2009 onwards). Of the 10,300 isopod species described to date, more than half occur in the sea (Bruce
2001, G.C.B. Poore pers. comm.). Isopoda show a remarkable morphological diversity (relative to other peracarids). The earliest marine fossil record (a phreatoicidean) dates back to the Carboniferous (~325 Ma, Schram 1970); few more ancient isopod taxa may have even occurred in the Devonian (416 — 359.2 Ma, Schram 1974). For the Asellota, a group particularly diverse in the deep sea, it has been suggested that they have they evolved between the Carboniferous (359.2 ± 2.5 Ma) and Triassic (250–200 Ma), while the Cymothoidea, Limnoridea and Sphaeromatidea (formerly Flabellifera) are more derived and probably experienced a major radiation during the late Mesozoic (145.5–65.5 Ma, Wilson 1998 and citations therein).
Most isopod species have become well adapted to a benthic lifestyle and only few taxa have secondarily regained the ability to swim (e.g. family Munnospidae; Hessler & Strömberg 1989). The great variety of morphologies and functional traits is, for example, reflected by a wide range of feeding strategies — from detritus- and filter-feeders to ecto-parasites and active predators. A highly specialised mating system (particularly in asellotes) has probably been key to explain the ability of isopods to have colonised and
thrived even in ‘extreme’ habitats such as the deep sea and polar regions (cf. Wilson 1991).
In the Southern Ocean, the ecological and evolutionary success of isopod crustaceans has been suggested to be partly due to the Cenozoic extinction of brachyuran decapods, and the subsequent occupation of their niches by isopods and some other peracarid orders (e.g. Brandt 1992). Peracarids have some physiological and morphological adaptations to the highly seasonal and cold Antarctic environment, including the possession of a ventral marsupium. Particularly, the inability of Mg 2+ regulation in combination with general Mg 2+ sensitivity has been thought to be a reason for the near extinction of benthic decapods in the Antarctic (e.g. Thatje et al. 2005). However, recent work by Wittmann et al. (2010) revealed similarly high haemolymph magnesium levels in some Antarctic isopods compared to decapods. Thus different eco-physiological and behavioral features must be responsible for the diversification of isopods at high Southern latitudes (Wittmann et al. 2010).
... diagnosis (modified from Brandt 1991;Just 2001). Head frontally with long rostrum, often longer than lateral margins of cephalothorax, without functional eyes; with prolonged, almost always pointed lateral projections of pereonites (length ≥ 0.2 pereonite width). ...
A new acanthaspidiid species, Acanthaspidia matsi sp. nov., is described from the Powell Basin slope (Weddell Sea, Southern Ocean). Specimens of the new species were collected during the expedition ANDEEP III on board RV Polarstern in March 2005. The new species most closely resembles Acanthaspidia typhlops (G. O. Sars, 1879), Acanthaspidia na- talensis (Kensley, 1977) and Acanthaspidia bifurcatoides Kussakin & Vasina, 1982, but can be distinguished from all these species by the following characters: rostrum strongly trifid (tips 0.4 times rostrum length); pereonites 1, 3–4 and 6 with 2 mid-dorsal spines; pleotelson spinulated, with 2 robust mid-dorsal spines. Systematic difficulties to distinguish the genera Acanthaspidia Stebbing, 1898 and Ianthopsis Beddard, 1886 are discussed and a key to all species in the genus Acanthaspidia is provided.
Background
The marine isopod family Acanthaspidiidae Menzies, 1962 (Asellota, Janiroidea) has global distribution from shelf to hadal depth. The majority of species has been recorded from relatively deep waters and the Southern Hemisphere. To date, 36 species have been described in the family belonging to three genera: Ianthopsis Beddard, 1886; Iolanthe Beddard, 1886; and Mexicope Hooker, 1985.
New information
Here, a new species of Mexicope is described from Maltese waters, adding a fourth species to the genus. It is the first member of the family reported from the Mediterranean Sea. The new species can be recognised by the unique combination of the following characters: cephalothorax with pre-ocular spine large and pointed anterolaterally, rostral projection blunt, eyes reduced; pereonal sternites each with one ventral spine; pereonite two lateral margins with single projection; pleotelson posterior apex long, projecting to approximately half of the length of the uropod protopod; pleopods I distolateral lobes projecting beyond distomedial lobes, apices curved and pointed laterally; uropod exopod length approximately 0.5 endopod length. An identification key to the species of Mexicope is presented and the generic diagnoses of Ianthopsis and Mexicope are compared, discussed and revised.
Mexicope sushara sp. nov. is recorded from southeastern New Zealand coastal waters, the first record of the genus from the Pacific and the first record of the Acanthaspidiidae from New Zealand. The species is from the continental shelf, taken in association with a bryozoan colony at a depth of 80 metres on the Otago Shelf, southeastern South Island. The distinguishing characters are a rostral spine and prominent and acute pre-ocular lobes; these characters in conjunction with stalked eyes separate the species from all others in the family.
Acanthaspid isopods are well known from the deep sea regions of all oceans. Many species have been found also on the continental shelf around Antarctica. Phylogenetic relationships within the Acanthaspidiidae and the genetic differentiation of populations are poorly understood. In this study we analysed 16S rRNA gene sequences of 36 specimens of Acanthaspidiidae, including 17 specimens of Acanthaspidia
drygalskii Vanhöffen, 1914. This species is known from several locations along the Antarctic shelf, supporting the idea of a circum-Antarctic distribution of this taxon. Our molecular data support the monophyly of all six species analysed, but there is only limited evidence for the interspecific relationships between the species. However, we were able to identify three distinct groups of haplotypes within Acanthaspidia
drygaskii. Our results indicate the evidence of cryptic, reproductively isolated species. Further data are needed to understand mechanisms underlying speciation in deep sea isopods.
This paper deals with a poorly known species, Ianthopsis pulchra (Hansen, 1916), found on the Kolbeinsey Ridge, north of Iceland (North Atlantic) during the expedition M21-5 with RV Meteor. The species was thought to be a member of the family Acanthaspidiidae, however, a detailed study, including comparison with the type material of Hansen from the Ingolf expedition and redescription with complete illustration, document that this species belongs to the Janiridae.