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Diplostraca
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Diplostraca
Temporal range: Devonian–Present [1]
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Branchiopoda
Subclass: Phyllopoda
Superorder: Diplostraca
Latreille, 1829
Orders[2]
Synonyms[2]
  • Cladocera Latreille, 1829
  • Eucladocera (no evidence for grouping together all other cladocerans as the sister taxon to the monotypic Haplopoda (Leptodora))

The Diplostraca or Cladocera, commonly known as water fleas, is a superorder of small, mostly freshwater crustaceans, most of which feed on microscopic chunks of organic matter, though some forms are predatory.[2]

Over 1000 species have been recognised so far, with many more undescribed.[2][3][4][5][6] The oldest fossils of diplostracans date to the Jurassic, though their modern morphology suggests that they originated substantially earlier, during the Paleozoic. Some have also adapted to a life in the ocean, the only members of Branchiopoda to do so, though several anostracans live in hypersaline lakes.[7] Most are 0.2–6.0 mm (0.01–0.24 in) long, with a down-turned head with a single median compound eye, and a carapace covering the apparently unsegmented thorax and abdomen. Most species show cyclical parthenogenesis, where asexual reproduction is occasionally supplemented by sexual reproduction, which produces resting eggs that allow the species to survive harsh conditions and disperse to distant habitats.

Description

[edit]
Leptodora kindtii is an unusually large diplostracan, at up to 18 mm long.

They are mostly 0.2–6.0 mm (0.01–0.24 in) long, with the exception of Leptodora, which can be up to 18 mm (0.71 in) long.[8] The body is not obviously segmented and bears a folded carapace which covers the thorax and abdomen.[9]

The head is angled downwards, and may be separated from the rest of the body by a "cervical sinus" or notch.[9] It bears a single black compound eye, located on the animal's midline, in all but two genera, and often, a single ocellus is present.[10] The head also bears two pairs of antennae – the first antennae are small, unsegmented appendages, while the second antennae are large, segmented, and branched, with powerful muscles.[9] The first antennae bear olfactory setae, while the second are used for swimming by most species.[10] The pattern of setae on the second antennae is useful for identification.[9] The part of the head which projects in front of the first antennae is known as the rostrum or "beak".[9]

The mouthparts are small, and consist of an unpaired labrum, a pair of mandibles, a pair of maxillae, and an unpaired labium.[9] They are used to eat "organic detritus of all kinds" and bacteria.[9]

The thorax bears five or six pairs of lobed, leaf-like appendages, each with numerous hairs or setae.[9] Carbon dioxide is lost, and oxygen taken up, through the body surface.[9]

Lifecycle

[edit]
A cladocera giving birth (100x magnification)

With the exception of a few purely asexual species, the lifecycle of diplostracans is dominated by asexual reproduction, with occasional periods of sexual reproduction; this is known as cyclical parthenogenesis.[11] When conditions are favourable, reproduction occurs by parthenogenesis for several generations, producing only female clones. As the conditions deteriorate, males are produced, and sexual reproduction occurs. This results in the production of long-lasting dormant eggs. These ephippial eggs can be transported over land by wind, and hatch when they reach favourable conditions, allowing many species to have very wide – even cosmopolitan – distributions.[9] Except for the genus Leptodora, which has a metanauplius stage, a nauplius larval stage is absent in Diplostraca.[12]

Evolutionary history

[edit]

Diplostraca are nested within the clam shrimp, being most closely related to the order Cyclestherida, the only living genus of which is Cyclestheria. Though several fossils from the Paleozoic have been claimed to represent fossils of diplostracans, none of these records can be confirmed. The oldest confirmed records of diplostracans are from the Early Jurassic of Asia. Fossils from the Jurassic are assignable to modern as well as extinct groups, indicating that the initial radiation of the group occurred prior to the beginning of the Jurassic, likely during the late Paleozoic.[13] A Devonian to Carboniferous genus, Ebullitiocaris, is tentatively placed as a diplostracan, however since it is only known from carapaces this is uncertain.[1]

Ecology

[edit]
Evadne spinifera, one of very few marine diplostracan species

Most diplostracan species live in fresh water and other inland water bodies, with only eight species being truly oceanic.[10] The marine species are all in the family Podonidae, except for the genus Penilia.[10] Some diplostracans inhabit leaf litter.[14]

Taxonomy

[edit]
Daphnia magna

According to the World Registry of Marine Species, Cladocera is a synonym of the superorder Diplostraca, which is included in the class Branchiopoda. Both names are currently in use. The superorder forms a monophyletic group of 7 orders, about 24 families, and more than 11,000 species. Many more species remain undescribed.[2][8] The genus Daphnia alone contains around 150 species.[11] Many groups of the water fleas are cryptic species or species flocks.[15]


The following families are recognised:[2]

Superorder Diplostraca Gerstaecker, 1866 (=Cladocera)

Order Anomopoda G.O. Sars, 1865
Family Acantholeberidae Smirnov, 1976
Family Bosminidae Baird, 1845
Family Chydoridae Dybowski & Grochowski, 1894
Family Daphniidae Straus, 1820[16]
Family Dumontiidae Santos-Flores & Dodson, 2003
Family Eurycercidae Kurz, 1875
Family Gondwanothrichidae Van Damme, Shiel & Dumont, 2007[17][18]
Family Ilyocryptidae Smirnov, 1976
Family Macrothricidae Norman & Brady, 1867
Family Moinidae Goulden, 1968
Family Ophryoxidae Smirnov, 1976
Order Ctenopoda G.O. Sars, 1865
Family Holopediidae G.O. Sars, 1865
Family Pseudopenilidae Korovchinsky & Sergeeva, 2008
Family Sididae Baird, 1850
Order Cyclestherida Sars G.O., 1899
Family Cyclestheriidae Sars G.O., 1899
Order Haplopoda G.O. Sars, 1865
Family Leptodoridae Lilljeborg, 1861
Order Laevicaudata Linder, 1945
Family Lynceidae Stebbing, 1902
Order Onychopoda G.O. Sars, 1865
Family Cercopagididae Mordukhai-Boltovskoi, 1968
Family Podonidae Mordukhai-Boltovskoi, 1968
Family Polyphemidae Baird, 1845
Order Spinicaudata Linder, 1945
Family Cyzicidae Stebbing, 1910
Family Eocyzicidae Schwentner, et al., 2020
Family Leptestheriidae Daday, 1913: 44
Family Limnadiidae Burmeister, 1843
Ephippia (singular: ephippium) are winter or dry-season eggs of the various species of small crustacean in the order Cladocera (within the Branchiopoda); they are provided with an extra shell layer, which preserves and protects the resting stages inside from harsh environmental conditions until the more favorable times, such as spring, when the reproductive cycle is able to take place once again. Ephippia are part of the back of a mother carrying them until they are fully developed. After molting, the ephippium stays in the water, or in the soil of dried puddles, small ponds, and vernal pools. The resting stages are often called eggs, but are in fact embryos with arrested development. Ephippia can rest for many years before the embryo resumes development upon an appropriate hatching stimulus.

Etymology

[edit]

The word "Cladocera" derives via Neo-Latin from the Ancient Greek κλάδος (kládos, "branch") and κέρας (kéras, "horn").[19]

The water flea in the photo belongs to the daphnia family. In addition, the photo shows the embryo in her brood pocket

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Diplostraca

View on Grokipedia
from Grokipedia
Diplostraca is a monophyletic of small, primarily freshwater crustaceans within the class , characterized by a bivalved that encloses the body and diverse reproductive modes, including and gamogenesis. This group encompasses the order Cladocera—commonly known as water fleas—and several lineages of clam shrimps, such as Laevicaudata, Spinicaudata, and Cyclestheriida, which together form a to the tadpole shrimps () within . Diplostracans are ecologically significant as key components of planktonic and benthic communities in ephemeral and permanent inland waters, where they serve as primary consumers and prey for larger aquatic organisms, with many species adapted to harsh, temporary habitats through rapid reproduction and desiccation-resistant eggs. The evolutionary history of Diplostraca traces back to the era, with fossil records indicating their diversification alongside the radiation of continental freshwater ecosystems, supported by molecular phylogenies that confirm their based on shared morphological traits like the duplicated trunk limbs and telsonal structures. Taxonomically, the clade is often ranked as a superorder under the subclass Phyllopoda, though recent analyses emphasize its phylogenetic unity over traditional Linnaean categories, incorporating sub-clades like Onychocaudata (encompassing Spinicaudata, Cyclestheriida, and ). Notable diversity includes approximately 620 described species of , which dominate freshwater (with estimates suggesting 2-4 times more undescribed species), and around 250 species of shrimps, many of which exhibit and complex mating behaviors in temporary pools. Mitochondrial genome studies reveal higher evolutionary rates and biases in Diplostraca compared to other branchiopods, reflecting adaptations to variable environments.

Overview

Physical Description

Diplostraca are small crustaceans typically ranging in body length from 0.2 to 18 mm, with Cladocera often 0.2–6 mm and clam shrimps 2–17 mm. The body is generally enclosed within a bivalved that folds over the trunk, sometimes featuring a true dorsal as in Laevicaudata, providing and, in many species, serving as a brood pouch for developing embryos. This is often transparent and subspherical, covering the head and trunk while leaving the posterior end exposed. The head bears a single median , which develops from the fusion of paired naupliar eyes during embryogenesis. Diplostracans possess paired antennae: the antennules (first antennae) are small, one-segmented structures primarily serving sensory functions, while the second antennae are biramous and act as the main swimming organs in Cladocera, enabling propulsion through undulating movements. The trunk region contains 5–6 pairs of phyllopodous limbs in Cladocera but 10–32 pairs in clam shrimps, adapted for both feeding and locomotion in most species, with setose structures facilitating filter-feeding in many, though predatory forms like Leptodora use prehensile limbs to capture prey. The posterior terminates in a pair of caudal furcae, which provide additional propulsion and stability during swimming. Morphological variations occur across the group; for instance, Leptodora lacks a full , exposing its segmented trunk and limbs, while in many cladocerans, the doubles as a dorsal brood pouch.

General Characteristics

Locomotion in Diplostraca varies; Cladocera exhibit a distinctive jerky, intermittent swimming motion achieved through powerful thrusts of their second antennae, generating a "hop-and-sink" pattern, while clam shrimps often crawl along substrates or swim using their trunk limbs. During the power stroke in Cladocera, the antennal branches splay outward to maximize drag and , propelling the animal forward before it sinks briefly due to its relatively high . Feeding in Diplostraca varies, with filter-feeding common in Cladocera, where thoracic limbs create water currents to draw in microscopic , , and organic particles captured on filtratory setae forming a sieve-like structure, while many shrimps are detritivores or use scraping mechanisms. This allows efficient exploitation of suspended food in planktonic environments for filter-feeders. In contrast, predatory species such as Polyphemus pediculus employ modified limbs to actively seize and manipulate larger prey like smaller , diverging from the passive filtration typical of most cladocerans. Sensory capabilities in Diplostraca are adapted for their often turbid, low-visibility habitats, featuring a single sessile that detects light intensity and direction for orientation and predator avoidance. The antennules serve as primary chemosensory organs, bearing aesthetascs and other setae that detect chemical cues such as food odors or pheromones in the . Their is simple, comprising a cerebral near the eye and , connected to a ventral nerve cord with segmental ganglia that coordinate basic reflexes without complex central processing. Physiologically, Diplostraca maintain high metabolic rates that facilitate rapid growth and population expansion, enabling them to capitalize on transient resource booms in dynamic aquatic systems. Many species, including Daphnia magna, produce hemoglobin under hypoxic conditions, enhancing oxygen transport and allowing tolerance of low-oxygen environments common in stratified waters. The carapace provides additional protection for these soft-bodied organisms during locomotion and feeding.

Taxonomy and Classification

Etymology

The term Diplostraca derives from the Ancient Greek diploos (διπλός), meaning "double" or "doubled," and ostrakon (ὄστρακον), meaning "shell," referring to the bivalved carapace that encloses the body and resembles a doubled shell. The name was coined in 1866 by German zoologist Carl August Gerstaecker to group branchiopod crustaceans distinguished by this bivalved morphology from those with single-shelled (monostracan) structures. Norwegian zoologist Georg Ossian Sars advanced the classification of diplostracans in the late 19th century through detailed studies of their morphology and diversity. The common name "water fleas" for diplostracans, especially cladocerans, stems from their characteristic erratic, flea-like jumping motion during swimming, produced by rapid beats of the second antennae. In contrast, the related term Cladocera—coined by French zoologist in —originates from klados (κλάδος, "branch") and kéras (κέρας, "horn"), describing the branched structure of the antennae. Although Cladocera is technically an order within Diplostraca, the terms are occasionally used interchangeably to refer to the bivalved branchiopods.

Orders and Diversity

Diplostraca constitutes a superorder within the class (subphylum Crustacea), characterized by bivalved carapaces and comprising four orders that reflect a range of morphological adaptations from planktonic to benthic lifestyles: Cladocera (with suborders Anomopoda, Ctenopoda, Haplopoda, and Onychopoda), Laevicaudata, Spinicaudata, and Cyclestheriida. Recent phylogenetic analyses confirm the of Diplostraca and identify sub-clades such as Onychocaudata, which encompasses Cladocera, Spinicaudata, and Cyclestheriida. The superorder encompasses approximately 24 families and more than 800 described species, though this figure is conservative given ongoing taxonomic revisions and the presence of cryptic species. Diversity is heavily skewed toward the suborder Anomopoda within Cladocera, which dominates with nearly 90% of cladoceran species (around 450-500 total for Cladocera), including the ecologically significant genus with approximately 150 species widely used in research on and environmental responses. Ctenopoda represents a smaller but distinct group of about 50 , featuring filter-feeding forms like the marine planktonic Penilia avirostris, which contrasts with the predominantly freshwater habits of most diplostracans. Haplopoda includes only 1 (Leptodora kindtii), a predatory form. Onychopoda includes around 130 , with many being predators in marine and brackish environments. Among the non-Cladoceran orders, Spinicaudata (clam shrimps) accounts for roughly 215 valid across 13 genera, often inhabiting ephemeral pools and exhibiting ancient morphological traits. Laevicaudata comprises approximately 40 (as of 2016) in alkaline or temporary waters, while Cyclestheriida is highly depauperate with only 1 known , Cyclestheria hislopi, distinguished by its reduced limb count. Estimates indicate thousands of undescribed within Diplostraca, particularly in tropical freshwater ecosystems where sampling remains limited, underscoring the group's potential for further discoveries. Carapace shapes vary markedly across orders, from the enveloping bivalves of Spinicaudata to the more open or absent structures in some Onychopoda.

Reproduction and Lifecycle

Asexual Reproduction

Asexual reproduction in Diplostraca, predominantly within the order Cladocera, occurs through cyclical , a process where diploid eggs develop via without fertilization, resulting in genetically identical female clones. These eggs are produced in the ovaries and incubated in the brood pouch—a specialized chamber formed by the —until the juveniles hatch and are released. A single female typically produces 10–50 offspring per brood, though clutch sizes vary by species, ranging from 1–2 in smaller forms like Daphnia cucullata to over 100 in larger ones such as D. magna. Broods are released synchronously after each adult molt, occurring every 3–4 days under optimal conditions, allowing for continuous generations of females. This reproductive mode is favored in stable, resource-rich environments with abundant food and low population density, where parthenogenesis supports rapid clonal expansion. In such settings, all-female populations predominate due to genetic mechanisms that suppress male development, such as mutations or regulatory changes in sex-determination genes like doublesex (dsx), which prevent the production of haploid male eggs during oogenesis. For instance, obligate parthenogenetic lineages in species like Daphnia pulex maintain female-only reproduction through these genetic controls, ensuring persistent asexual cycles even without environmental shifts to sexuality. The primary advantage of lies in its facilitation of explosive population growth, enabling Daphnia species to achieve doubling times as short as 3 days at 20°C and form dense blooms in favorable habitats. This clonal strategy promotes genetic uniformity across individuals but is complemented by high adaptability through , where offspring adjust traits like body size or helmet formation in response to environmental cues, enhancing survival without . is widespread in Cladoceran orders such as Anomopoda, exemplified by genera like Daphnia and Bosmina, where many species rely on it as the dominant mode, occasionally producing parthenogenetic eggs alongside potential shifts in other phases.

Sexual Reproduction and Dormancy

Sexual reproduction in Diplostraca is typically triggered by environmental stressors such as population crowding, decreasing photoperiods, or temperature drops, which signal deteriorating conditions and prompt a shift from asexual to sexual phases. In cladocerans like Daphnia, males are produced parthenogenetically from unfertilized eggs, allowing rapid male generation without prior mating; these males then mate with females to fertilize haploid eggs, which develop into dormant resting stages. This process introduces genetic recombination, enhancing variability and adaptability in offspring compared to clonal asexual reproduction. The fertilized eggs are encased in protective structures known as ephippia, tough chitinous capsules typically containing 1–2 eggs that form from modified parts of the female's carapace, such as a dorsal shield in Daphnia species. Ephippial eggs enter diapause, a state of suspended development, enabling survival through adverse conditions including desiccation, freezing, and even passage through vertebrate digestive tracts for dispersal; viability can persist for decades in sediment egg banks. Upon return to favorable conditions like reflooding or warming, these eggs hatch primarily into amictic females and males, restarting population cycles with increased genetic diversity. In the clam shrimp lineages (Laevicaudata, Spinicaudata, and Cyclestheriida), is absent, and predominates with diverse mating systems including (separate males and females), (males and hermaphrodites), and self-fertilizing hermaphroditism. Females produce eggs continuously throughout the adult stage, releasing them with each molt onto the substrate; these eggs are highly resistant to and environmental extremes, entering a dormant state that allows viability for months to years until rehydration or other cues trigger and direct development into juveniles. This strategy supports survival and of temporary pools, paralleling the adaptive role of ephippia in Cladocera but without specialized protective cases. These dormant stages collectively facilitate survival and dispersal in ephemeral habitats, underscoring the adaptive value of sexuality in Diplostraca.

Ecology and Distribution

Habitats and Distribution

Diplostraca primarily inhabit freshwater environments worldwide, including lakes, ponds, temporary pools, and ephemeral wetlands, where they often dominate the or benthic communities. These habitats range from permanent lentic waters to highly variable systems such as vernal pools and saline lakes, with many species adapted to low-oxygen conditions among aquatic vegetation or decaying . Certain taxa, like those in the order Cyclestherida, are particularly associated with tropical and subtropical temporary waters, while Spinicaudata favor astatic pools in arid regions. The distribution of Diplostraca is cosmopolitan, spanning all continents, including polar regions for some Cladocera, though highest occurs in tropical and subtropical zones. Spinicaudata, for instance, are absent from but present on all other continents in temporary freshwater bodies. Adaptations such as via resistant eggs or ephippia enable survival in ephemeral habitats, allowing rapid recolonization after drying events; some species also tolerate hypersaline conditions, as seen in Moina salina in steppe saline waters, or acidic environments. In deeper lakes, certain Cladocera exhibit , briefly referenced as a to optimize feeding and evade visual predators. Exceptions to the freshwater dominance include approximately eight to ten marine species, primarily in the orders Ctenopoda and Onychopoda, such as Penilia avirostris, Evadne spinifera, Pseudevadne tergestina, and Pleopis polyphemoides, which form part of oceanic and neritic plankton communities. These marine forms are restricted to coastal and open waters, contrasting with the vast majority of the over 1,000 described Diplostraca species in inland systems. Diplostraca in temporary pools are particularly vulnerable to anthropogenic threats, including from agricultural runoff and , which disrupts and survival, as well as climate change-induced alterations in patterns that shorten hydroperiods and increase frequency. These impacts disproportionately affect arid-zone and Mediterranean-climate reliant on predictable wetting cycles.

Ecological Interactions

Diplostraca, particularly within the order Cladocera, serve as primary consumers in aquatic food webs by filtering phytoplankton and bacteria, thereby linking basal producers to higher trophic levels. Species such as Daphnia are keystone zooplankton that graze on algae, helping to regulate algal populations and maintain water clarity in lakes and ponds. This herbivorous role facilitates nutrient recycling within the water column, supporting overall ecosystem productivity. In addition to their consumer function, certain diplostracans act as predators; for instance, Leptodora kindtii preys on smaller cladocerans, rotifers, and , exerting top-down control on communities in eutrophic lakes. Diplostracans are also vital prey items, serving as a primary source for larval , invertebrates like copepods and insects (e.g., larvae), and vertebrates including adult , birds, and salamanders, thus transferring energy upward through the . Competitive interactions occur with copepods for shared resources like , while occasional parasitic associations, such as those involving predaceous cladocerans on smaller taxa, influence community structure. As sensitive organisms, diplostracans function as bioindicators in monitoring, with like Daphnia exhibiting rapid responses to pollutants and environmental stressors that signal . Their abundance and diversity are used in programs to assess levels, as they accumulate toxins and show altered reproduction or mortality in degraded habitats. Human activities intersect with diplostracan ecology through their use as model organisms in ecotoxicology, where species like Daphnia magna and Ceriodaphnia dubia are standard test subjects for evaluating chemical safety and pollutant effects on aquatic life. Additionally, some non-native species, such as the invasive Daphnia lumholtzi, pose risks in introduced ecosystems by altering local food webs and competing with native zooplankton in ponds and reservoirs.

Evolutionary History

Fossil Record

The fossil record of Diplostraca extends back to the period, with the earliest tentative evidence from the in , dated to approximately 410 million years ago (Ma). The Ebullitiocaris, known solely from isolated bivalved carapaces, is provisionally assigned to the total-group Diplostraca based on its overall morphology, though its precise phylogenetic position remains uncertain due to the lack of soft-tissue preservation. This suggests potential early origins for the group, but the assignment is debated as it may represent a stem-lineage branchiopod rather than a crown-group diplostracan. More definitive fossils appear in the (Emsian stage, ~400 Ma), particularly from marginal marine to brackish deposits in the of , such as the Klerf Formation at Willwerath and Waxweiler. These include genera like Estheria (e.g., E. diensti) and Pseudestheria, preserved as carapaces in deltaic sediments indicative of ephemeral freshwater habitats adjacent to marine environments. The record remains sparse overall, with limited occurrences beyond these sites and some limited evidence from the and Permian, highlighting potential preservational biases in pre-Mesozoic non-marine settings. Diplostracan fossils become far more abundant and diverse in and lacustrine sediments, reflecting adaptation to continental aquatic environments. Key sites include the Yixian Formation of the in northeastern , where spinicaudatans such as Eosestheria and Leptestheria are commonly preserved, often with exceptional detail including eggs and growth lines that reveal reproductive strategies. In the , the Eocene Green River Formation in , , yields well-preserved clam shrimps in laminated lake shales, representing some of the earliest Paleogene records for the group in and demonstrating continuity in lacustrine habitats. The bivalved structure facilitates ready fossilization in anoxic lake bottoms, preserving diagnostic features like ornamentation and radial sulci that track morphological stasis across lineages; for instance, some spinicaudatan forms from the closely resemble extant in design, underscoring limited evolutionary change over 100 million years. No major discoveries altering this timeline have been reported since 2023.

Phylogenetic Position

Diplostraca is recognized as a superorder within the class , a basal group of crustaceans, with (tadpole shrimps) typically positioned as its based on combined morphological and molecular analyses. This placement situates Diplostraca within the larger clade Phyllopoda, which excludes , and as a whole is part of the subphylum in the Arthropoda. Molecular data, including mitochondrial genomes and multi-locus sequences, strongly support the monophyly of Diplostraca, encompassing Cladocera (water fleas) and the clam shrimps (including Laevicaudata, Spinicaudata, and Cyclestheriida). Key evolutionary relationships within show variation across studies. In many phylogenies, Diplostraca is the sister group to (tadpole shrimps), forming a that excludes , though some molecular analyses suggest nests within a paraphyletic Diplostraca, potentially as sister to Spinicaudata plus Cladoceromorpha. The inclusion of Cyclestheriida within Diplostraca remains debated, with evidence supporting its close affinity to Cladocera in the monophyletic Cladoceromorpha, based on shared limb structures and reproductive traits, while other views treat it as a distinct basal lineage. The divergence of , including Diplostraca, from (the largest class) is estimated at approximately 500 million years ago during the period. Phylogenetic inferences draw from both morphological and molecular evidence. Morphological characters, such as biramous limbs and structure, support Diplostraca's but face challenges from in bivalved s across unrelated lineages. Molecular approaches, including 18S rRNA, 28S rRNA, and phylogenomic datasets with over 130 genes, provide robust support for these relationships, though early studies using fewer loci highlighted debates. Recent phylogenomic analyses up to 2025, including a comprehensive time-tree calibration, confirm the monophyly of and its subclades without major revisions since pre-2023 work, while noting potential for undescribed basal lineages in understudied tropical habitats.

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