The ingolfiellidean amphipods are not abundant in regards to the number of species. To date, some 39 species are recognized, a remarkably low number considering the wide-ranging ecological conditions in which they occur. It is also a low number when compared to other family groups of amphipods with partly overlapping habitat requirements such as bogidiellids, with 110 species (Koenemann & Holsinger, 1999) and crangonyctids (250 species, pers. comm. Koenemann).
The first specimens of Ingolfiellidea were reported by Hansen in 1903. He classified them in a new suborder, a rank they have continued to hold in most publications ( Bousfield & Shih, 1994; Ruffo & Vigna Taglianti, 1989; Martin & Davis, 2001) despite several objections over the years (Dahl, 1977; Bowman & Abele, 1982; Barnard & Karaman, 1983). It is a challenge to compare this small group of crustaceans to other larger well-defined groups and try to find comparable habitat preferences and overlapping biogeographic distribution patterns. From consideration of the literature a picture emerges of the uniqueness of ingolfiellideans within the entire crustacean world with regard to their incredibly diverse habitat tolerances. No other small taxon of crustaceans is found in the soft mud of the deep-sea floor, as well as in high mountain freshwater river beds, or in subterranean fresh, brackish and marine interstitial waters of continental ground waters and continental shelves (Fig. 1, map)
Fig. 1. World map of distribution of Ingolfiellidea. Black dots = marine localities. Open stars = brackish water conditions. Open circles = fresh water localities.
The study of the first species of Ingolfiella marked this habitat diversity. Hansen (1903) described two species, Ingolfiella abyssi, from 3521 m. deep sea bottom out of a trawl of 1 litre of mud in the Davis Strait, east of Greenland, and I. littoralis, from coral sands on the shores of Thailand. Several years later another species, I. acherontis (S. Karaman, 1933), was described from a groundwater well in Skopje, Macedonia. The material of I. acherontis has been lost and only a few incomplete drawings remain. S. Karaman apparently was not aware of the work by Hansen, 1903. Therefore he described Balcanella acherontis n. gen. n. sp. in a new family Balcanellidae.
After the Second World War expeditions focused more on environments that were difficult to access, and the majority of species of ingolfiellideans were collected in the last half of the twentieth century. A large species was found in cave waters from Congo, later ranked in a separate genus: Trogloleleupia leleupi (Ruffo, 1951). Compared to the 2.5 mm specimens for previous taxa this African cave lake species stood out at 14.5 mm maximum length.
Then more species were discovered in Macedonia: Ingolfiella petkovskii S. Karaman, 1957, and I. macedonica S. Karaman, 1959. S. Karaman characterized their rarity when he stated that he had searched through several thousand samples from ground water and wells. He concluded that Ingolfiella is either very rare or lives in inaccessible biotopes (S. Karaman, 1959).
Meanwhile, another species was found in South America in a new habitat, the coastal ground water in a coarse shingle beach. In the description of I. ruffoi Siewing, 1958, Siewing posed a dilemma particularly relevant to the work underlying this publication. He asked whether the large African cave form was ancestral to the smaller marine and freshwater forms, or if it was the other way around.
Another type of habitat was added to the list with the collection of 20 specimens of I. britannica Spooner, 1960, from the shell gravel at the sea bottom at 46 meter depth off the south coast of England. Spooner remarked on the true deep subsurface occurrence of these ingolfiellids in contrast with other small malacostracans that more typically inhabit only the first few centimeters of these gravels.
Euryhaline tolerance was revealed within one species with the discovery of I. manni Noodt, 1961, taken from both brackish and fresh ground water in Chile. In addition, I. manni was found not only at sea level, but also at 800 m. Later I. uspallatae Noodt, 1965 was described from Argentina in the riverbanks of a floodplain at 2000 m in the Andes mountains.
In Europe at this time, two freshwater species were reported from the interstices of river alluvia of southern France: I. catalanensis Coineau, 1963 and I. thibaudi Coineau, 1968. This marked the discovery of more species where special subsurface habitats were sampled in a conscious effort to uncover new taxa. A large 2.3 cm ingolfiellid was found in a well in Namibia, first described as Leleupiella eggerti, Ruffo, 1964, later renamed by Ruffo (1974) as Trogloleleupia eggerti.
From the Indian Ocean I. xarifae Ruffo, 1966 and I. kapuri Coineau & Rao, 1973 were reported from the Maldives in shallow coral sands, and from the Andaman and Nicobar Islands in intertidal muddy shell debris, respectively.
A second deep-sea species, I. atlantisi Mills, 1967, was collected at more than 4700 m depth in the North American Basin of the Atlantic Ocean. This species probably occupies the same habitat as I. abyssi and was found amidst typical abyssal fauna elements, presumably residing “...in the flocculent and relatively oxidized upper centimeters or two on the surface of the deep-sea ooze.” (Mills, 1967).
Back in Europe, an environment equally difficult to access as the deep sea was tapped, namely the ‘fossil water’ of a 50 m deep well in Italy. Here the aberrant Metaingolfiella mirabilis Ruffo, 1969 was described, for which a new family was necessary, the Metaingolfiellidae. Later efforts to recapture this rare species were never successful (pers. com. Ruffo). Not surprisingly, the area south and east of Yugoslavia has yielded more specimens of I. petkovskii and the new species I. vandeli Bou, 1970. They were reported from wells and river sediments on the Greek mainland and the large islands of the Peloponnesus and Euboea.
Another discovery occurred in the littoral sands of Table Bay, Cape Town: I. berrisfordi Ruffo, 1974. From the same environment, but a little deeper at 8 m below the surface in the Gulf of Naples, Italy, Schiecke (1976) described I. ischitana. Stock named 6 species from islands off the coast of Venezuela. These species are: I. (Gevgeliella) putealis Stock, 1976, in a slightly brackish well on Bonaire (Dutch Antilles); I. (Gevgeliella) fontinalis Stock, 1977, from a spring on Bonaire; I. (Gevgeliella) tabularis Stock, 1977, from marine sands situated below a cave entrance on Bonaire (also recorded on Curacao); I. (Hansenliella?)quadridentata Stock, 1979, from coarse coral sand of a submarine flat, Curacao; I. (Trianguliella?) grandispina Stock, 1979, pumped from brackish ground water in gravel at a cave entrance; I. (Gevgeliella) margaritae Stock, 1979, from a capped freshwater well used for drinking water on Isla de Margarita (Venezuela). These southern Caribbean species were sampled either by diving in shallow coastal water, or pumped up from beach interstitia and oligohaline water reservoirs more inland. In addition, animals occurred in wells and small cave chambers with brackish water or water with frequently and strongly fluctuating salinities.
Stock utilized subgeneric names, but the splitting of the genus Ingolfiella into smaller units had already begun with that earlier discovery of Ingolfiella (Balcanella) acherontis Karaman, 1933. Nevertheless, Karaman’s original effort did not prove very useful due to subsequent workers’ lack of male or female specimens in cases where both sexes were needed to make critical distinctions. Consequently, new species were difficult to incorporate into the existing system.
Ruffo (1985) described another large ingolfiellid from Namibia’s freshwater reservoirs, Stygobarnardia caprellinoides. The most striking aspect of this animal was the resemblance of the form of the cephalon to that of the Italian Metaingolfiella. In Metaingolfiella the fusion of the first segment (pereionite) with the cephalon was described as fully complete (although we have discovered after SEM investigation that this appears not to be the case), while in Stygobarnardia the head form with a typically small cephalon could be interpreted as in a partial stage of the fusion.
One of the larger Canary Islands facing the coast of West Africa, Fuerteventura, yielded Ingolfiella similis Rondé-Broekhuizen & Stock, 1987, from an oligohaline freshwater well. Ingolfiella fuscina Dojiri & Sieg, 1987, was found in the Gulf of Mexico and off the coast of South Carolina in box core and grab samples ranging in depth from 17 – 151 m. This was the first time a species from the bottom of the sea was reported over a large area. On Bermuda, I. longipes Stock, Sket & Iliffe, 1987 was collected in a brackish water cave pool. More large ingolfiellids came from Namibia: Trogloleleupia dracospiritus Griffiths, 1989 and T. gobabis Griffiths, 1989, were found in cave lakes, 350 km apart from each other.
The Southwest Pacific yielded no ingolfiellids until Lowry & Poore (1989) described I. australiana and I. bassiana from the Bass Strait at, respectively, 85 m depth in sandy shell, and 121 m at another locality in the strait. A cave on a small offshore island of Sardinia, Italy, brought to light I. cottarellii Ruffo & Vigna-Taglianti, 1989 from a freshwater pool. The most recent of the large, cave dwelling, African ingolfielids is Trogloleleupia nudicarpus Griffiths, 1991 from subterranean waters in western Namibia. It was found crawling on stones in shallow water in a small pool 60 m below ground surface.
I. canariensis Vonk & Sánchez, 1991, was collected with a Bou-Rouch biophreatic pump on several beaches along the north coast of Tenerife, Canary Islands, and in bottom debris of an anchialine cave on El Hierro, another island in the geologically younger part of the Canary group. From the island of Madeira, some 700 km to the north, I. unguiculata Stock, 1992 occurs in the coarse sand bottom of an anchialine lagoon. In Slovenia, I. beatricis Ruffo & Vonk, 2001 was described from a single specimen caught in a feeble flowing cave stream with a hand net.
Of course, more species will be discovered, and we must wait to see how far the ecological tolerance and biogeographical spread of this group of amphipods can be stretched. Already there are reports of discoveries in fresh- and brackish water of Japan (Shokita, 1992) and in marine sediments of the Prince William Sound, Alaska, and the Virgin Islands, Caribbean (Cadien, pers. comm.) that are yet to be confirmed.
From the above it is clear that almost all previous work on the Ingolfiellidea has concentrated on alpha-taxonomy. To remedy this situation we undertook the following:
a. Performed a cladistic analysis of phylogenetic relationships within the Ingolfiellidea based on a comprehensive character matrix.
b. Restudied type material of Metaingolfiella mirabilis, Trogloleleupia eggerti, T. leleupi, Ingolfiella abyssi, I. littoralis, I. tabularis, I. quadridentata, and I. margaritae to add more details to former descriptions.
c. Compared the cephalic lobes of Ingolfiella putealis and I. ischitana, using SEM photography, to lend insight into the anatomical and functional role this structure plays.
d. Re-examined the type material of Metaingolfiella mirabilis to determine the degree of fusion between the head and the first pereionite.
e. Performed a biogeographic analysis with the results of the cladistic analysis and explored palaeobiogeographic patterns and the timing of evolutionary events in the deep history of ingolfiellideans.