George D. Wilson

The deep-sea isopods: A biogeographic and phylogenetic overview

Abstract Isopod crustaceans are among the most numerous and diverse macrofaunal taxa in the deep sea. In contrast to the situation in shallow water, the Asellota encompasses the majority of the deep-sea fauna. Taxa within the Asellota exhibit marked depth zonation. Its most primitive superfamily is limited to fresh water. The rest are marine, where with increasing depth the incidence of more specialized taxa increases. Within its most advanced superfamily, Janiroidea, the most primitive families are primarily restricted to shallow water, while the more specialized families dominate in the deep sea. The most notable exception is the occurrence of these specialized families in shallow water at high latitudes. On the basis of this pattern, it has been suggested that the deep-sea fauna is a result of invasion from shallow water, primarily at high latitudes. The present paper argues that, on the contrary, the specialized deep-sea families evolved in situ, and that their presence at shallow high latitudes is th...

A Revision of the Genus Eurycope (Isopoda, Asellota) With Descriptions of Three New Genera

ABSTRACT Most of the genera in the important deep-sea isopod family Eurycopidae need revision. In this paper, the type-genus Eurycope is revised, and three new genera (Disconectes, Tytthocope, and Belonectes) are proposed to contain some of the species removed from it. The new genera are based on redescribed type-species, permitting more precise generic placement of other species. New records are given for Disconectes phalangium and Belonectesparvus.

New insights into the colonization of the deep sea: Systematics and zoogeography of the Munnidae and the Pleurogoniidae comb. nov. (Isopoda; Janiroidea)

Summary The Munnidae (sensu Wolff 1962) are a heterogeneous group of tiny marine isopods (Asellota; Janiroidea) generally characterized by stalked eyes and an ambulatory epibenthic existence. They are found in shallow water in many parts of the world, especially in colder regions, and are a small component of the deep-sea fauna. This paper deals with the systematics and zoogeography of these isopods in two sections. The first section redefines the Munnidae and erects a new family with an old name, the Pleurogoniidae. The relationships of the genera in these two new taxa are discussed and the systematics of two related families, the Antiasidae and the Abyssianiridae, is clarified. The second section examines the zoogeographic data on the basis of this new systematic information. The Munnidae are found to be an essentially cosmopolitan, shallow-water family with a few species in the deep sea with very broad depth ranges, perhaps related to the apparent eurytopy of many munnid species. The evidence suggests ...

VARIATION IN THE DEEP-SEA ISOPOD EURYCOPE IPHTHIMA (ASELLOTA, EURYCOPIDAE): DEPTH RELATED CLINES IN ROSTRAL MORPHOLOGY AND IN POPULATION STRUCTURE

In an especially good sample series of the deep-sea isopod Eurycope iphthima Wilson, substantial variation occurs in the cephalic rostrum and in several aspects of its population structure: the size-frequency distribution, size of maturation of males and females, proporxad tions of female stages, proportions of juvenile stages, and maximum size of adults. Comxad parisons of samples from different depths (2,500 to 4,800 m) and different localities (northxad eastern and central Atlantic Ocean) show the variation to be distinctly depth-related: populations from similar depths are more similar than those from different depths. Because of continuity in other taxonomically important characters, the variation must be clinal and reflects adaptation to local environments, directed genetic variation, or both, The parallel clines in rostral morphology and population structure are most apparent on the continental slopes and rises off Ireland and in the Bay of Biscay. Bimodality in the population structure of the deeper populations is unusual; two hypotheses for its explanation are discussed, although evidence to support either is currently unavailable. Clinal variation in terrestrial organisms is well known (Mayr, 1970; Endler, 1977); it is little known in deep-sea animals. Clines should exist in the deep sea, especially in strong environmental gradients such as those found on the contixad nental slopes. As depth increases, so does hydrostatic pressure, whereas temxad perature and the quality and quantity of food decreases. Different levels of the slopes are subject to varying current fields and diurnal tidal rhythms. Most imxad portant, the slope faunas change greatly with depth (e.g., Hartman and Fauchald, 1971; Sanders and Hessler, 1969; Rex, 1979; Grassle et ai., 1979), both signaling this environmental change and becoming part of it. Genetic studies on deep-sea benthic megafauna (Doyle, 1972; Siebenaller, 1978) have demonstrated shifts in allozyme freq~enc. ies between depth-separated popxad ulations. However, such studies are techn~lly unfeasible on smaller deep-sea invertebrates and must give way to morphological investigations. Individual morxad phological variation may be important in deep-sea populations (e.g., Schopf, 1976; Hansen, 1967); often there are large differences between localities. For example, Rex (1979) analyzed two populations of Aivania peiagica, a shallow bathyal gasxad tropod found above and below the shelf-slope break off New England, and showed abrupt differences between the popUlations. In contrast, Gardiner (1975) noted striking vertical morphological similarity in specimens of the tanaid Neotanais americanus over a depth range of 2,800 to 5,020 m in the same area. Nevertheless, he found variation with depth in two characters. These two studies lack either verification of conspecificity of the populations or enough specimens for a popxad ulation analysis. In addition to large samples of conspecific populations, the identification of a cline further requires at least three or more popUlation samples, a rare occurrence in the vagaries of deep-sea sampling. This study uses abundant material of the dominant deep-sea eurycopid isopod EuryciJpeiphthima Wilson (1981) (Table 1), to establish the presence of, clinal variation in one morphological character and in various aspects of the population structure of this species.

The systematics and evolution of Haplomunna and its relatives (Isopoda, Haplomunnidae, New family)

Summary A re-examination of Haplomunna Richardson (1908) reveals a close relationship between this genus and Munella Bonnier (1896), Abyssaranea Wilson & Hessler (1974) and Thylakogaster ibid. As a consequence, a new family, Haplommunidae, is erected to contain these four genera. The systematic problems with this new grouping, its relation to the Dendrotionidae, and some peculiarities of its members are discussed. A key and the geographical ranges of the four genera are included. A generic diagnosis for Haplomunna is given, and H. caeca (Richardson, 1905) and H. hubbsi, sp. nov. are described.

Evolution of the female cuticular organ in the asellota crustacea isopoda

In an effort to understand the variation and probable origin of a female copulatory organ found in isopods of the asellote superfamily Janiroidea, the morphology of female reproductive structures among the Asellota was surveyed. Examples of four asellote superfamilies were studied using whole mount staining after potassium‐hydroxide maceration or clearing with lactic acid. In contradiction to previous conclusions, the cuticular organ is shown to occur in the more primitive Asellota, although the position of its opening varies considerably. In the genera Asellus, and Stenetrium, Munna, and Santia, the cuticular organ originates adjacent to the oopore, and in the remaining janiroidean isopods, it is placed dorsally and usually anteriorly. This information permits a simple hypothesis explaining the origin of the cuticular organ: it was present in the proximate ancestor of the Asellota and evolved to the janiroidean condition by anterodorsal migration.

SOME UNUSUAL PARASELLOIDEA (ISOPODA, ASELLOTA) FROM THE DEEP BENTHOS OF THE ATLANTIC

It is nearly a truism that in the deep-sea benthos supraspecific taxa tend to be cosmopolitan. As a result, additional sampling only rarely yields radically new morphological types, even in poorly studied parts of the ocean. As an unusual exception to this rule, two adjacent stations in the equatorial Atlantic, made on Atlantis II cruise no. 31, were found to be populated by two species of paraselloid isopods which are quite aberrant in their general body and limb form. The unusual morphologies exhibited by these species clearly require the definition of new genera, Abyssaranea and Thylakogaster, to contain them. These genera have restricted distributions despite the fairly extensive sampling in the Atlantic that has taken place in the past decade. Thylakogaster has appeared in only three different areas, and only once on the extensively sampled Gay HeadBermuda transect (Sanders et al., 1965; Hessler & Sanders, 1967). Abyssaranea at present is known only from the Equatorial Atlantic, and Munella was known prior to this paper, which records it from Bermuda, from the Bay of Biscay and the Mediterranean Sea (Bonnier, 1896; Lo Bianco, 1930). This patchy geographic distribution probably cannot be explained by some unusual geographic isolating factor since the stations listed in this paper yielded other Paraselloidea more comxad mon to the deep-sea fauna. One can only speculate on possible ecological factors that may be affecting the distributions of these genera. Thylakogaster tends to be badly fragmented during collection so that there may have been potential past records which were not reported due to the unrecognizable condition of the maiterial. It is probable that more careful sampling in other areas will bring to light more populations and species of the genera described herein, though they might not prove to be cosmopolitan as are many deep-sea isopod genera. These species do belong to a confusing cluster grouped within the families Munnidae and Dendrotionidae. Our inability to satisfactoril y include the genera of this paper in any of these families, as presently defined, documents the great need for a general revision. However, such an effort is beyond the scope of the present study and will be attempted in a future paper. Methods for collection and for preparing the taxonomic descriptions can be