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35-461: Arcellinid testate amoebae or Arcellinida , Arcellacean or lobose testate amoebae are single-celled protists partially enclosed in a simple test (shell). Arcellinid testate amoebae are commonly found in soils, leaf litter , peat bogs and near/in fresh water. They use their pseudopodia , a temporary cell extension, for moving and taking in food. Like most amoebae, they are generally believed to reproduce asexually via binary fission. However

70-449: A cavern dive into a cave dive. Contrary to cenote cavern diving, cenote cave diving requires special equipment and training (certification for cave diving). However, both cavern and cave diving require detailed briefings, diving experience, and weight adjustment to freshwater buoyancy. The cenotes are usually filled with rather cool fresh water. Cenote divers must be wary of possible halocline ; this produces blurred vision until they reach

105-602: A collapse of limestone bedrock exposes groundwater . The term originated on the Yucatán Peninsula of Mexico, where the ancient Maya commonly used cenotes for water supplies, and occasionally for sacrificial offerings . The name derives from a word used by the lowland Yucatec Maya — tsʼonoʼot —to refer to any location with accessible groundwater. In Mexico the Yucatán Peninsula alone has an estimated 10,000 cenotes, water-filled sinkholes naturally formed by

140-450: A combination of both. Past environmental changes can be determined by analysing the composition of fossil tests, including the reconstruction of past climate change . Testate amoebae species have been used to reconstruct hydrological changes over the late Holocene , as a result of individual species possessing a narrow tolerance for ecohydrological conditions such as water-table depth or pH. Fossils of arcellinid testate amoebae date back to

175-416: A list of the longest and deepest water-filled and dry caves within the state boundaries. When cavern diving, one must be able to see natural light the entire time that one is exploring the cavern (e.g., Kukulkan cenote near Tulum , Mexico). During a cave dive, one passes the point where daylight can penetrate, and one follows a safety guideline to exit the cave. Things change quite dramatically once moving from

210-571: A recent review suggests that sexual recombination may be the rule rather than the exception in amoeboid protists in general, including the Arcellinid testate amoebae. Arcellinida always have a shell or testa. The tests lie outside the cell membrane and consist of organic or mineral materials that are either secreted or incorporate external particles. The testa has a single main opening. Simple tests are made by secretion (autogenous tests), agglutination of foreign material (xenogenous tests), or sometimes

245-470: A rock overhanging above the water. The stereotypical cenotes often resemble small circular ponds , measuring some tens of meters in diameter with sheer rock walls. Most cenotes, however, require some degree of stooping or crawling to access the water. In the north and northwest of the Yucatán Peninsula in Mexico, the cenotes generally overlie vertical voids penetrating 50 to 100 m (160 to 330 ft) below

280-436: A section of Sistema Aktun Hu (part of Sistema Sac Actun ) known as the pit Hoyo Negro . At a depth of 57 m (187 ft) the divers located the remains of a mastodon and a human skull (at 43 m [141 ft]) that might be the oldest evidence of human habitation in the region. The Yucatán Peninsula has almost no rivers and only a few lakes, and those are often marshy. The widely distributed cenotes are

315-412: A vast coastal aquifer system, which is typically density-stratified. The infiltrating meteoric water (i.e., rainwater) floats on top of higher- density saline water intruding from the coastal margins. The whole aquifer is therefore an anchialine system (one that is land-locked but connected to an ocean). Where a cenote, or the flooded cave to which it is an opening, provides deep enough access into

350-443: Is 10 to 20 m (33 to 66 ft) below the water table at the coast, and 50 to 100 m (160 to 330 ft) below the water table in the middle of the peninsula, with saline water underlying the whole of the peninsula. In 1936, a simple morphometry-based classification system for cenotes was presented. The classification scheme was based on morphometric observations above the water table, and therefore incompletely reflects

385-418: Is actually composed of several, unrelated groups of organisms. However, some features they all share that have been used to group them together include the presence of a test (regardless of its composition) and pseudopodia that do not anastomose . Testate amoebae can be found in most freshwater environments, including lakes, rivers, cenotes , as well as mires and soils. The strong and resistant nature of

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420-542: Is likely that the group has evolved minimally over the course of the Phanerozoic . Phryganellina Organoconcha Volnustoma Hyalospheniformes Excentrostoma Sphaerothecina Longithecina Phryganellina Organoconcha Volnustoma Hyalospheniformes Excentrosoma Cylindrothecina Longithecina Sphaerothecina The classification of Arcellinida, as of 2019: Arcellinida incertae sedis : Testate amoebae The test of some species

455-483: Is produced entirely by the amoeba and may be organic, siliceous or calcareous depending on the species ( autogenic tests ), whereas in other cases the test is made up of particles of sediment collected by the amoeba which are then agglutinated together by secretions from within the cell ( xenogenic tests ). A few taxa ( Hyalospheniidae ) can build either type, depending on the circumstances and availability of foreign material. The assemblage referred to as "testate amoebae"

490-696: Is therefore associated with the mass extinction of the non-avian dinosaurs and is also known as the Cretaceous–Paleogene extinction event . In 2001–2002 expeditions led by Arturo H. González and Carmen Rojas Sandoval in the Yucatán discovered three human skeletons; one of them, Eve of Naharon , was carbon-dated to be 13,600 years old. In March 2008, three members of the Proyecto Espeleológico de Tulum and Global Underwater Explorers dive team, Alex Alvarez, Franco Attolini, and Alberto Nava, explored

525-593: The Foraminifera (both in Rhizaria). The Thecamoebida (Amoebozoa), with the genus Thecamoeba , despite their name, do not have tests. Euglyphid testate amoebae are closely related to the Foraminifera . Cenote A cenote ( English: / s ɪ ˈ n oʊ t i / or / s ɛ ˈ n oʊ t eɪ / ; Latin American Spanish: [seˈnote] ) is a natural pit , or sinkhole , resulting when

560-671: The Tonian stage of the Proterozoic , around 789-759 million years ago. The fossils indicate that by 730 million years ago, arcellinids had already diversified into major lineages. Testate amoebae are theorized to be mostly polyphyletic (coming from more than one ancestral type), but testaceafilosea, one group of testate amoebae, are theorized to be monophyletic . Ancient tests of terrestrial fauna are commonly found in fossilized amber, although mid-Cretaceous testate amoeba (i.e., Diffligia , Cucurbitella ) have been found in ancient lake sediments. It

595-683: The UNESCO Convention on the Protection of the Underwater Cultural Heritage . Cenotes have attracted cavern and cave divers, and there are organized efforts to explore and map these underwater systems. They are public or private and sometimes considered "National Natural Parks". Great care should be taken to avoid spoiling this fragile ecosystem when diving. In Mexico, the Quintana Roo Speleological Survey maintains

630-505: The lobose Tubulinea , which include Arcellinida , Difflugina and Phryganellina (within the Amoebozoa ), and the filose Euglyphida (within the SAR supergroup ), although there are smaller groups that also include other testate amoebae. The following table includes a few examples of testate amoebae genera, and reflects their position within

665-647: The Sacred Cenote there in 1904. He discovered human skeletons and sacrificial objects confirming a local legend, the Cult of the Cenote , involving human sacrifice to the rain god Chaac by the ritual casting of victims and objects into the cenote. However, not all cenotes were sites of human sacrifice. The cenote at Punta Laguna has been extensively studied and none of the approximately 120 individuals show signs of sacrifice. The remains of this cultural heritage are protected by

700-466: The afterlife, and home to the rain god, Chaac . The Maya often deposited human remains as well as ceremonial artifacts in these cenotes. The discovery of golden sacrificial artifacts in some cenotes led to the archaeological exploration of most cenotes in the first part of the 20th century. Edward Herbert Thompson (1857–1935), an American diplomat who had bought the Chichen Itza site, began dredging

735-403: The aquifer, the interface between the fresh and saline water may be reached. The density interface between the fresh and saline waters is a halocline , which means a sharp change in salt concentration over a small change in depth. Mixing of the fresh and saline water results in a blurry swirling effect caused by refraction between the different densities of fresh and saline waters. The depth of

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770-490: The cave roof have collapsed revealing an underlying cave system, and the water flow rates may be much faster: up to 10 kilometers (6 mi) per day. The Yucatan cenotes attract cavern and cave divers who have documented extensive flooded cave systems, some of which have been explored for lengths of 376 km (234 mi) or more. Cenotes are formed by the dissolution of rock and the resulting subsurface void, which may or may not be linked to an active cave system , and

805-415: The cenotes Choo-Ha , Tankach-Ha, and Multum-Ha near Tulum . There are at least 6,000 cenotes in the Yucatán Peninsula of Mexico. Cenote water is often very clear, as the water comes from rain water filtering slowly through the ground, and therefore contains very little suspended particulate matter. The groundwater flow rate within a cenote may be very slow. In many cases, cenotes are areas where sections of

840-424: The classification by Adl et al. (2012), where five supergroups ( Amoebozoa , Opisthokonta , Excavata , SAR and Archaeplastida ) were proposed to classify all eukaryotes . This classification purposefully avoids the use of Linnaean higher category names (phylum, class, order, family). While it has been noted that the names that Adl et al. provide for the clades may result confusing or uninformative regarding

875-408: The collapse of limestone, and located across the peninsula. Some of these cenotes are at risk from the construction of the new tourist Maya Train . Cenotes are common geological forms in low-altitude regions, particularly on islands (such as Cefalonia, Greece), coastlines, and platforms with young post- Paleozoic limestone with little soil development. The term cenote , originally applying only to

910-795: The features in Yucatán, has since been applied by researchers to similar karst features in other places such as in Cuba , Australia , Europe , and the United States . Cenotes are surface connections to subterranean water bodies. While the best-known cenotes are large open-water pools measuring tens of meters in diameter, such as those at Chichen Itza in Mexico , the greatest number of cenotes are smaller sheltered sites and do not necessarily have any surface exposed water. Some cenotes are only found through small <1 m (3 ft) diameter holes created by tree roots, with human access through enlarged holes, such as

945-411: The halocline is a function of several factors: climate and specifically how much meteoric water recharges the aquifer, hydraulic conductivity of the host rock, distribution and connectivity of existing cave systems, and how effective these are at draining water to the coast, and the distance from the coast. In general, the halocline is deeper further from the coast, and in the Yucatán Peninsula this depth

980-511: The measured rim of the Chicxulub crater . This crater structure, identified from the alignment of cenotes, but also subsequently mapped using geophysical methods (including gravity mapping ) and also drilled into with core recovery, has been dated to the boundary between the Cretaceous and Paleogene geologic periods, 66 million years ago. This meteorite impact at the Cretaceous–Paleogene boundary

1015-591: The modern water table. However, very few of these cenotes appear to be connected with horizontally extensive underground river systems, with water flow through them being more likely dominated by aquifer matrix and fracture flows. In contrast, the cenotes along the Caribbean coast of the Yucatán Peninsula (within the state of Quintana Roo ) often provide access to extensive underwater cave systems, such as Sistema Ox Bel Ha , Sistema Sac Actun / Sistema Nohoch Nah Chich and Sistema Dos Ojos . The Yucatán Peninsula contains

1050-407: The most secluded and darker cenotes, the fauna has evolved to resemble those of many cave-dwelling species. For example, many animals don't have pigmentation and are often blind, so they are equipped with long feelers to find food and make their way around in the dark. Although cenotes are found widely throughout much of the Yucatán Peninsula, a higher-density circular alignment of cenotes overlies

1085-537: The only perennial source of potable water and have long been the principal source of water in much of the region. Major Maya settlements required access to adequate water supplies, and therefore cities, including the famous Chichen Itza , were built around these natural wells. Many cenotes like the Sacred Cenote in Chichen Itza played an important role in Maya rites. The Maya believed that cenotes were portals to Xibalba or

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1120-437: The processes by which the cenotes formed and the inherent hydrogeochemical relationship with the underlying flooded cave networks, which were only discovered in the 1980s and later with the initiation of cave diving exploration. Flora and fauna are generally scarcer than in the open ocean; however, marine animals do thrive in caves. In caverns, one can spot mojarras , mollies , guppies , catfish , small eels and frogs . In

1155-599: The relative degree of phenotypic distinctiveness amongst groups when used in isolation, this system avoids creating superfluous ranks where unnecessary and provides stable group names that can be retained even when a group is moved to a different lineage , as is often the case with protists, as their classification remains in constant review. Plagiopyxis - Quadrulella - Trigonopyxis Traditionally, those species that form large networks of anastomosing pseudopodia , despite some of them having tests, are not counted amongst testate amoebae; this comprises genus Gromia and

1190-454: The subsequent structural collapse. Rock that falls into the water below is slowly removed by further dissolution, creating space for more collapse blocks. Likely, the rate of collapse increases during periods when the water table is below the ceiling of the void since the rock ceiling is no longer buoyantly supported by the water in the void. Cenotes may be fully collapsed, creating an open water pool, or partially collapsed with some portion of

1225-400: The tests allows them to be preserved long after the amoeba has died. These characteristics, along with the sensitivity that some species display to changes in environmental conditions (such as temperature, pH, and conductivity), has sparked their use as bioindicators and paleoclimate proxies in recent years. Testate amoebae are a polyphyletic assemblage. The main testate amoebae groups are

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