diff --git a/Release-notes.md b/Release-notes.md
index be97334..8b9ed6a 100644
--- a/Release-notes.md
+++ b/Release-notes.md
@@ -2,6 +2,14 @@
 
 ## Latest changes
 
+### Breaking changes
+
+- In `obimultiplex`, the short version of the **--tag-list** option used to specify the list 
+  of tags and primers to be used for the demultiplexing has been changed from `-t` to `-s`.
+
+- The **--taxdump** option used to specify the path to the taxdump containing the NCBI taxonomy
+  has been renamed to **--taxonomy**.
+
 ### Bug fixes
 
 - In `obipairing`, correct the stats `seq_a_single` and `seq_b_single` when
@@ -13,6 +21,10 @@
 
 ### New features
 
+-   NCBI Taxonomy dump does not need to be uncompressed and unarchived anymore. The
+    path of the tar and gziped dump file can be directly specified using the
+    **--taxonomy** option.
+
 -   Most of the time obitools identify automatically sequence file format. But
     it fails sometimes. Two new option **--fasta** and **--fastq** are added to
     allow the processing of the rare fasta and fastq files not recognized.
diff --git a/cmd/test/main.go b/cmd/test/main.go
index 71eb38b..84ab35d 100644
--- a/cmd/test/main.go
+++ b/cmd/test/main.go
@@ -1,36 +1,12 @@
 package main
 
 import (
-	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obifp"
-	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obikmer"
-	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiseq"
+	"os"
 
-	log "github.com/sirupsen/logrus"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitaxformat"
 )
 
 func main() {
 
-	one := obifp.OneUint[obifp.Uint128]()
-	a, b := obifp.OneUint[obifp.Uint64]().LeftShift64(66, 0)
-	log.Infof("one: %v, %v", a, b)
-	shift := one.LeftShift(66)
-	log.Infof("one: %v", shift)
-
-	seq := obiseq.NewBioSequence("test", []byte("atcgggttccaacc"), "")
-
-	kmermap := obikmer.NewKmerMap[obifp.Uint128](
-		obiseq.BioSequenceSlice{
-			seq,
-		},
-		7,
-		true,
-		10,
-	)
-
-	kmers := kmermap.NormalizedKmerSlice(seq, nil)
-
-	for _, kmer := range kmers {
-		println(kmermap.KmerAsString(kmer))
-	}
-
+	obitaxformat.DetectTaxonomyFormat(os.Args[1])
 }
diff --git a/pkg/obiformats/csv_read.go b/pkg/obiformats/csv_read.go
index 8ec842d..239989c 100644
--- a/pkg/obiformats/csv_read.go
+++ b/pkg/obiformats/csv_read.go
@@ -157,9 +157,9 @@ func ReadCSV(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, err
 func ReadCSVFromFile(filename string, options ...WithOption) (obiiter.IBioSequence, error) {
 
 	options = append(options, OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))))
-	file, err := Ropen(filename)
+	file, err := obiutils.Ropen(filename)
 
-	if err == ErrNoContent {
+	if err == obiutils.ErrNoContent {
 		log.Infof("file %s is empty", filename)
 		return ReadEmptyFile(options...)
 	}
@@ -173,9 +173,9 @@ func ReadCSVFromFile(filename string, options ...WithOption) (obiiter.IBioSequen
 
 func ReadCSVFromStdin(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, error) {
 	options = append(options, OptionsSource(obiutils.RemoveAllExt("stdin")))
-	input, err := Buf(os.Stdin)
+	input, err := obiutils.Buf(os.Stdin)
 
-	if err == ErrNoContent {
+	if err == obiutils.ErrNoContent {
 		log.Infof("stdin is empty")
 		return ReadEmptyFile(options...)
 	}
diff --git a/pkg/obiformats/embl_read.go b/pkg/obiformats/embl_read.go
index 992660c..4a5ca60 100644
--- a/pkg/obiformats/embl_read.go
+++ b/pkg/obiformats/embl_read.go
@@ -227,9 +227,9 @@ func ReadEMBLFromFile(filename string, options ...WithOption) (obiiter.IBioSeque
 
 	options = append(options, OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))))
 
-	reader, err = Ropen(filename)
+	reader, err = obiutils.Ropen(filename)
 
-	if err == ErrNoContent {
+	if err == obiutils.ErrNoContent {
 		log.Infof("file %s is empty", filename)
 		return ReadEmptyFile(options...)
 	}
diff --git a/pkg/obiformats/fastaseq_read.go b/pkg/obiformats/fastaseq_read.go
index 86b5de7..a3ab5c8 100644
--- a/pkg/obiformats/fastaseq_read.go
+++ b/pkg/obiformats/fastaseq_read.go
@@ -271,9 +271,9 @@ func ReadFasta(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, e
 func ReadFastaFromFile(filename string, options ...WithOption) (obiiter.IBioSequence, error) {
 	options = append(options, OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))))
 
-	file, err := Ropen(filename)
+	file, err := obiutils.Ropen(filename)
 
-	if err == ErrNoContent {
+	if err == obiutils.ErrNoContent {
 		log.Infof("file %s is empty", filename)
 		return ReadEmptyFile(options...)
 	}
@@ -287,9 +287,9 @@ func ReadFastaFromFile(filename string, options ...WithOption) (obiiter.IBioSequ
 
 func ReadFastaFromStdin(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, error) {
 	options = append(options, OptionsSource("stdin"))
-	input, err := Buf(os.Stdin)
+	input, err := obiutils.Buf(os.Stdin)
 
-	if err == ErrNoContent {
+	if err == obiutils.ErrNoContent {
 		log.Infof("stdin is empty")
 		return ReadEmptyFile(options...)
 	}
diff --git a/pkg/obiformats/fastqseq_read.go b/pkg/obiformats/fastqseq_read.go
index f350f5a..55ba783 100644
--- a/pkg/obiformats/fastqseq_read.go
+++ b/pkg/obiformats/fastqseq_read.go
@@ -370,9 +370,9 @@ func ReadFastq(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, e
 func ReadFastqFromFile(filename string, options ...WithOption) (obiiter.IBioSequence, error) {
 	options = append(options, OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))))
 
-	file, err := Ropen(filename)
+	file, err := obiutils.Ropen(filename)
 
-	if err == ErrNoContent {
+	if err == obiutils.ErrNoContent {
 		log.Infof("file %s is empty", filename)
 		return ReadEmptyFile(options...)
 	}
@@ -386,9 +386,9 @@ func ReadFastqFromFile(filename string, options ...WithOption) (obiiter.IBioSequ
 
 func ReadFastqFromStdin(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, error) {
 	options = append(options, OptionsSource(obiutils.RemoveAllExt("stdin")))
-	input, err := Buf(os.Stdin)
+	input, err := obiutils.Buf(os.Stdin)
 
-	if err == ErrNoContent {
+	if err == obiutils.ErrNoContent {
 		log.Infof("stdin is empty")
 		return ReadEmptyFile(options...)
 	}
diff --git a/pkg/obiformats/genbank_read.go b/pkg/obiformats/genbank_read.go
index b0a0dfc..34fed24 100644
--- a/pkg/obiformats/genbank_read.go
+++ b/pkg/obiformats/genbank_read.go
@@ -266,9 +266,9 @@ func ReadGenbankFromFile(filename string, options ...WithOption) (obiiter.IBioSe
 
 	options = append(options, OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))))
 
-	reader, err = Ropen(filename)
+	reader, err = obiutils.Ropen(filename)
 
-	if err == ErrNoContent {
+	if err == obiutils.ErrNoContent {
 		log.Infof("file %s is empty", filename)
 		return ReadEmptyFile(options...)
 	}
diff --git a/pkg/obiformats/universal_read.go b/pkg/obiformats/universal_read.go
index 6ee0750..5e7d6da 100644
--- a/pkg/obiformats/universal_read.go
+++ b/pkg/obiformats/universal_read.go
@@ -172,15 +172,15 @@ func OBIMimeTypeGuesser(stream io.Reader) (*mimetype.MIME, io.Reader, error) {
 // - error: An error if any occurred during the reading process.
 func ReadSequencesFromFile(filename string,
 	options ...WithOption) (obiiter.IBioSequence, error) {
-	var file *Reader
+	var file *obiutils.Reader
 	var reader io.Reader
 	var err error
 
 	options = append(options, OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))))
 
-	file, err = Ropen(filename)
+	file, err = obiutils.Ropen(filename)
 
-	if err == ErrNoContent {
+	if err == obiutils.ErrNoContent {
 		log.Infof("file %s is empty", filename)
 		return ReadEmptyFile(options...)
 	}
diff --git a/pkg/obioptions/options.go b/pkg/obioptions/options.go
index ab72159..4951afe 100644
--- a/pkg/obioptions/options.go
+++ b/pkg/obioptions/options.go
@@ -6,8 +6,8 @@ import (
 	"os"
 	"runtime"
 
-	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiformats/ncbitaxdump"
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitax"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitaxformat"
 	log "github.com/sirupsen/logrus"
 
 	"github.com/DavidGamba/go-getoptions"
@@ -32,7 +32,7 @@ var _Quality_Shift_Input = byte(33)
 var _Quality_Shift_Output = byte(33)
 var _Read_Qualities = true
 
-var __taxdump__ = ""
+var __taxonomy__ = ""
 var __alternative_name__ = false
 
 type ArgumentParser func([]string) (*getoptions.GetOpt, []string)
@@ -131,8 +131,8 @@ func GenerateOptionParser(optionset ...func(*getoptions.GetOpt)) ArgumentParser
 			log.Info("  go tool pprof -http=127.0.0.1:8080 'http://localhost:6060/debug/pprof/block'")
 		}
 
-		if options.Called("taxdump") {
-			taxonomy, err := ncbitaxdump.LoadNCBITaxDump(CLISelectedNCBITaxDump(),
+		if options.Called("taxonomy") {
+			taxonomy, err := obitaxformat.LoadTaxonomy(CLISelectedTaxonomy(),
 				!CLIAreAlternativeNamesSelected())
 			if err != nil {
 				log.Fatalf("Loading taxonomy error: %v", err)
@@ -186,14 +186,14 @@ func GenerateOptionParser(optionset ...func(*getoptions.GetOpt)) ArgumentParser
 
 func LoadTaxonomyOptionSet(options *getoptions.GetOpt, required, alternatiive bool) {
 	if required {
-		options.StringVar(&__taxdump__, "taxdump", "",
+		options.StringVar(&__taxonomy__, "taxonomy", "",
 			options.Alias("t"),
 			options.Required(),
-			options.Description("Points to the directory containing the NCBI Taxonomy database dump."))
+			options.Description("Path to the taxonomy database."))
 	} else {
-		options.StringVar(&__taxdump__, "taxdump", "",
+		options.StringVar(&__taxonomy__, "taxonomy", "",
 			options.Alias("t"),
-			options.Description("Points to the directory containing the NCBI Taxonomy database dump."))
+			options.Description("Path to the taxonomy database."))
 	}
 	if alternatiive {
 		options.BoolVar(&__alternative_name__, "alternative-names", false,
@@ -462,12 +462,12 @@ func SetParallelFilesRead(n int) {
 	_ParallelFilesRead = n
 }
 
-func CLISelectedNCBITaxDump() string {
-	return __taxdump__
+func CLISelectedTaxonomy() string {
+	return __taxonomy__
 }
 
 func CLIHasSelectedTaxonomy() bool {
-	return __taxdump__ != ""
+	return __taxonomy__ != ""
 }
 
 func CLIAreAlternativeNamesSelected() bool {
@@ -479,8 +479,8 @@ func CLILoadSelectedTaxonomy() (*obitax.Taxonomy, error) {
 		return obitax.DefaultTaxonomy(), nil
 	}
 
-	if CLISelectedNCBITaxDump() != "" {
-		taxonomy, err := ncbitaxdump.LoadNCBITaxDump(CLISelectedNCBITaxDump(),
+	if CLISelectedTaxonomy() != "" {
+		taxonomy, err := obitaxformat.LoadTaxonomy(CLISelectedTaxonomy(),
 			!CLIAreAlternativeNamesSelected())
 		if err != nil {
 			return nil, err
@@ -489,5 +489,5 @@ func CLILoadSelectedTaxonomy() (*obitax.Taxonomy, error) {
 		return taxonomy, nil
 	}
 
-	return nil, errors.New("no NCBI taxdump selected using option -t|--taxdump")
+	return nil, errors.New("no taxonomy selected using option -t|--taxonomy")
 }
diff --git a/pkg/obioptions/version.go b/pkg/obioptions/version.go
index 45175d7..72251f0 100644
--- a/pkg/obioptions/version.go
+++ b/pkg/obioptions/version.go
@@ -8,7 +8,7 @@ import (
 // corresponds to the last commit, and not the one when the file will be
 // commited
 
-var _Commit = "757448c"
+var _Commit = "ffd6725"
 var _Version = "Release 4.2.0"
 
 // Version returns the version of the obitools package.
diff --git a/pkg/obiformats/ncbitaxdump/read.go b/pkg/obitaxformat/ncbitaxdump/read.go
similarity index 100%
rename from pkg/obiformats/ncbitaxdump/read.go
rename to pkg/obitaxformat/ncbitaxdump/read.go
diff --git a/pkg/obitaxformat/ncbitaxdump/readtar.go b/pkg/obitaxformat/ncbitaxdump/readtar.go
new file mode 100644
index 0000000..92d112b
--- /dev/null
+++ b/pkg/obitaxformat/ncbitaxdump/readtar.go
@@ -0,0 +1,142 @@
+package ncbitaxdump
+
+import (
+	"archive/tar"
+	"bufio"
+	"fmt"
+
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitax"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiutils"
+
+	log "github.com/sirupsen/logrus"
+)
+
+func IsNCBITarTaxDump(path string) bool {
+
+	file, err := obiutils.Ropen(path)
+
+	if err != nil {
+		return false
+	}
+
+	defer file.Close()
+
+	citations := false
+	division := false
+	gencode := false
+	names := false
+	delnodes := false
+	gc := false
+	merged := false
+	nodes := false
+
+	tarfile := tar.NewReader(file)
+
+	header, err := tarfile.Next()
+
+	for err == nil {
+		name := header.Name
+
+		if header.Typeflag == tar.TypeReg {
+			switch name {
+			case "citations.dmp":
+				citations = true
+			case "division.dmp":
+				division = true
+			case "gencode.dmp":
+				gencode = true
+			case "names.dmp":
+				names = true
+			case "delnodes.dmp":
+				delnodes = true
+			case "gc.prt":
+				gc = true
+			case "merged.dmp":
+				merged = true
+			case "nodes.dmp":
+				nodes = true
+			}
+		}
+		header, err = tarfile.Next()
+	}
+
+	return citations && division && gencode && names && delnodes && gc && merged && nodes
+}
+
+func LoadNCBITarTaxDump(path string, onlysn bool) (*obitax.Taxonomy, error) {
+
+	taxonomy := obitax.NewTaxonomy("NCBI Taxonomy", "taxon", obiutils.AsciiDigitSet)
+
+	//
+	// Load the Taxonomy nodes
+	//
+
+	log.Printf("Loading Taxonomy nodes\n")
+
+	file, err := obiutils.Ropen(path)
+	if err != nil {
+		return nil, fmt.Errorf("cannot open taxonomy file from '%s'",
+			path)
+	}
+
+	nodefile, err := obiutils.TarFileReader(file, "nodes.dmp")
+	if err != nil {
+		file.Close()
+		return nil, fmt.Errorf("cannot open nodes file from '%s'",
+			path)
+	}
+
+	buffered := bufio.NewReader(nodefile)
+	loadNodeTable(buffered, taxonomy)
+	log.Printf("%d Taxonomy nodes read\n", taxonomy.Len())
+	file.Close()
+
+	//
+	// Load the Taxonomy nodes
+	//
+
+	log.Printf("Loading Taxon names\n")
+
+	file, err = obiutils.Ropen(path)
+	if err != nil {
+		return nil, fmt.Errorf("cannot open taxonomy file from '%s'",
+			path)
+	}
+
+	namefile, nerr := obiutils.TarFileReader(file, "names.dmp")
+	if nerr != nil {
+		file.Close()
+		return nil, fmt.Errorf("cannot open names file from '%s'",
+			path)
+	}
+	n := loadNameTable(namefile, taxonomy, onlysn)
+	log.Printf("%d taxon names read\n", n)
+	file.Close()
+
+	//
+	// Load the merged taxa
+	//
+
+	log.Printf("Loading Merged taxa\n")
+	file, err = obiutils.Ropen(path)
+	if err != nil {
+		return nil, fmt.Errorf("cannot open taxonomy file from '%s'",
+			path)
+	}
+
+	aliasfile, aerr := obiutils.TarFileReader(file, "merged.dmp")
+	if aerr != nil {
+		file.Close()
+		return nil, fmt.Errorf("cannot open merged file from '%s'",
+			path)
+	}
+
+	buffered = bufio.NewReader(aliasfile)
+	n = loadMergedTable(buffered, taxonomy)
+	log.Printf("%d merged taxa read\n", n)
+
+	root := taxonomy.Taxon("1")
+	taxonomy.SetRoot(root)
+
+	return taxonomy, nil
+}
diff --git a/pkg/obitaxformat/taxonomy_read.go b/pkg/obitaxformat/taxonomy_read.go
new file mode 100644
index 0000000..58c26ef
--- /dev/null
+++ b/pkg/obitaxformat/taxonomy_read.go
@@ -0,0 +1,91 @@
+package obitaxformat
+
+import (
+	"fmt"
+	"os"
+
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitax"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitaxformat/ncbitaxdump"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiutils"
+	"github.com/gabriel-vasile/mimetype"
+
+	log "github.com/sirupsen/logrus"
+)
+
+type TaxonomyLoader func(path string, onlysn bool) (*obitax.Taxonomy, error)
+
+func DetectTaxonomyTarFormat(path string) (TaxonomyLoader, error) {
+
+	switch {
+	case ncbitaxdump.IsNCBITarTaxDump(path):
+		log.Infof("NCBI Taxdump Tar Archive detected: %s", path)
+		return ncbitaxdump.LoadNCBITarTaxDump, nil
+	}
+
+	return nil, fmt.Errorf("unknown taxonomy format: %s", path)
+}
+
+func DetectTaxonomyFormat(path string) (TaxonomyLoader, error) {
+
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+
+	fileInfo, err := file.Stat()
+	if err != nil {
+		file.Close()
+		return nil, err
+	}
+
+	file.Close()
+
+	if fileInfo.IsDir() {
+		// For the moment, we only support NCBI Taxdump directory format
+		log.Infof("NCBI Taxdump detected: %s", path)
+		return ncbitaxdump.LoadNCBITaxDump, nil
+	} else {
+		file, err := obiutils.Ropen(path)
+
+		if err != nil {
+			return nil, err
+		}
+
+		mimetype, err := mimetype.DetectReader(file)
+
+		if err != nil {
+			file.Close()
+			return nil, err
+		}
+
+		file.Close()
+
+		switch mimetype.String() {
+		case "text/csv":
+			return LoadCSVTaxonomy, nil
+		case "application/x-tar":
+			return DetectTaxonomyTarFormat(path)
+		}
+
+		log.Fatalf("Detected file format: %s", mimetype.String())
+	}
+
+	return nil, nil
+}
+
+func LoadCSVTaxonomy(path string, onlysn bool) (*obitax.Taxonomy, error) {
+
+	return nil, nil
+}
+
+func LoadTaxonomy(path string, onlysn bool) (*obitax.Taxonomy, error) {
+	loader, err := DetectTaxonomyFormat(path)
+
+	if err != nil {
+		return nil, err
+	}
+
+	taxonomy, err := loader(path, onlysn)
+
+	return taxonomy, err
+}
diff --git a/pkg/obitools/obifind/obifind.go b/pkg/obitools/obifind/obifind.go
index 6534a0c..f1df393 100644
--- a/pkg/obitools/obifind/obifind.go
+++ b/pkg/obitools/obifind/obifind.go
@@ -53,7 +53,7 @@ func CLICSVTaxaIterator(iterator *obitax.ITaxon) *obicsv.ICSVRecord {
 		OptionsWithScientificName(CLIWithScientificName()),
 		OptionsWithPath(CLIWithPath()),
 		OptionsRawTaxid(CLIRawTaxid()),
-		OptionsSource(obioptions.CLISelectedNCBITaxDump()),
+		OptionsSource(obioptions.CLISelectedTaxonomy()),
 	)
 
 	return NewCSVTaxaIterator(iterator, options...)
diff --git a/pkg/obiutils/tar.go b/pkg/obiutils/tar.go
new file mode 100644
index 0000000..3731439
--- /dev/null
+++ b/pkg/obiutils/tar.go
@@ -0,0 +1,20 @@
+package obiutils
+
+import (
+	"archive/tar"
+	"fmt"
+)
+
+func TarFileReader(file *Reader, path string) (*tar.Reader, error) {
+	tarfile := tar.NewReader(file)
+	header, err := tarfile.Next()
+
+	for err == nil {
+		if header.Name == path {
+			return tarfile, nil
+		}
+		header, err = tarfile.Next()
+	}
+
+	return nil, fmt.Errorf("file not found: %s", path)
+}
diff --git a/pkg/obiformats/xopen.go b/pkg/obiutils/xopen.go
similarity index 99%
rename from pkg/obiformats/xopen.go
rename to pkg/obiutils/xopen.go
index 8a0c093..7231b2c 100644
--- a/pkg/obiformats/xopen.go
+++ b/pkg/obiutils/xopen.go
@@ -9,7 +9,7 @@
 // Ropen opens a (possibly gzipped) file/process/http site for buffered reading.
 // Wopen opens a (possibly gzipped) file for buffered writing.
 // Both will use gzip when appropriate and will user buffered IO.
-package obiformats
+package obiutils
 
 import (
 	"bufio"
diff --git a/pkg/obiformats/xopen_test.go b/pkg/obiutils/xopen_test.go
similarity index 99%
rename from pkg/obiformats/xopen_test.go
rename to pkg/obiutils/xopen_test.go
index 45b2b92..b99cae7 100644
--- a/pkg/obiformats/xopen_test.go
+++ b/pkg/obiutils/xopen_test.go
@@ -1,4 +1,4 @@
-package obiformats
+package obiutils
 
 import (
 	"bufio"