Tracheloraphis apoligostriata, Ma & Xu & Yan & Li & Warren & Song, 2021

Ma, Mingzhen, Xu, Yuan, Yan, Ying, Li, Yuqing, Warren, Alan & Song, Weibo, 2021, Taxonomy and molecular phylogeny of four karyorelictid species belonging to the genera Apotrachelocerca and Tracheloraphis (Protozoa: Ciliophora), with descriptions of two new species, Zoological Journal of the Linnean Society 192 : -

COMMENTS ON TRACHELORAPHIS PRENANTI

Taxonomically, this taxon is uncertain, although there have been several redescriptions of Tracheloraphis prenanti since it was first reported by Dragesco (1960) ( Raikov & Kovaleva, 1968; Dragesco & Dragesco-Kernéis, 1986; Foissner & Dragesco, 1996b). Furthermore, Raikov & Kovaleva (1968) and Wright (1983) reported two subspecies in this taxon.

Borror (1973) suggested that this species should be a member of the ‘ T. phoenicopteruscomplex’. Details of the infraciliature of the T. phoenicopterus-complex were supplied by Dragesco & Dragesco-Kernéis (1986) and Foissner & Dragesco (1996b) who noted that ‘whether the phoenicopterus- complex consists of a single, highly variable species, of several distinct, still insufficiently characterized morphospecies or, as we believe, of a set of sibling species, needs further investigation’. More recently, Xu et al. (2011c) reported a Chinese population of T. phoenicopterus from the Yellow Sea coastal waters of Qingdao.

The population described in the present study is consistent with the original description regarding all main morphological and ecological characters, i.e. body shape and size, general features of the ciliature, appearance of the nuclear apparatus and habitat. Hence, we do not think that its identity is in doubt. Including the present study, only four isolates of the Tracheloraphis phoenicopterus- complex species have been described in sufficient detail using modern methods, that is, including details of the infraciliature and the cortical features, i.e. two populations of T. phoenicopterus ( Foissner & Dragesco, 1996b; Xu et al., 2011c), one of T. prenanti oligocineta ( Raikov & Kovaleva, 1968) and one of T. prenanti (present work). Based on their living morphology, Tracheloraphis prenanti and T. phoenicopterus can be separated by the appearance of their cortical granules: in T. phoenicopterus they are ellipsoidal, yellowish and 0.6 × 1.2 Μm, whereas in T. prenanti they are colourless, globular and about 0.5 Μm in diameter ( Foissner & Dragesco, 1996b; Table 5).

Xu et al. (2011c) described a population under the name T. phoenicopterus that has cortical granules with the same appearance as those of T. prenanti , but differs from the latter in the number of somatic kineties (23–32 vs. 14–26) ( Table 5). In addition, the present study shows that the SSU rDNA sequence of T. phoenicopterus sensu Xu et al., 2011 differs from that of T. prenanti by 30 bp, indicating that they are not conspecific ( Table 4). Based on differences in their cortical granules, T. phoenicopterus sensu Xu et al., 2011 is not identical to the population reported by Foissner & Dragesco (1996b) and likely represents an undescribed species of the T. phoenicopterus- complex.

In Table 5, we list ten isolates that were believe to be members of the T. phoenicopterus- complex. Most of them lack some critical information, for example, details of the cortical granules and molecular data, therefore, their identity remains unresolved. Nevertheless, we tentatively suggest that the ten isolates listed in Table 5 could belong to five species: the form described in the present study and two populations described by Dragesco (1960) and Dragesco & Dragesco-Kernéis (1986) are T. prenanti ; the subspecies T. prenanti oligocineta Raikov &

DESCRIPTION

OF

FOUR

TRACHELOCERCIDS

703

Figure

10

.

Photomicrographs

of

Tracheloraphis

apoligostriata

sp

.

nov

.

from

life

(

A

–

F

)

and

after

protargol

staining

(

G

–

J

)

from

present

study

.

Photomicrographs

of

T

.

apoligostriata

sp

.

nov

.

from

life

(

K

–

P

)

,

after

protargol

staining

(

Q

–

S

)

according

to

Xu

et

al

.

(

2011

c

)

.

A

–

C

,

views

of

different

individuals

.

D

,

E

,

cortical

granules

(

arrows

)

in

the

glabrous

stripe

.

F

,

detail

of

macronuclei

(

arrow

)

.

G

,

H

,

anterior

end

,

noting

the

circumoral

kinety

,

brosse

and

bristle

kinety

.

I

,

J

,

general

infraciliature

of

the

holotype

specimen

,

showing

nuclear

apparatus

,

somatic

kineties

(

arrow

)

and

bristle

kinety

(

arrowhead

)

.

K

–

N

,

views

of

different

individuals

.

O

,

P

,

cortical

granules

(

arrows

)

in

the

glabrous

stripe

of

a

contracted

(

O

)

and

extended

(

P

)

cell

.

Q

,

mid-body

,

showing

the

glabrous

stripe

,

bristle

kinety

,

macronuclei

and

micronuclei

(

arrowheads

)

.

R

,

S

,

anterior

end

,

noting

the

circumoral

kinety

(

arrows

)

,

brosse

and

bristle

kinety

.

Abbreviations

:

B

,

brosse

;

BK

,

bristle

kinety

;

CK

,

circumoral

kinety

;

GS

,

glabrous

stripe

;

Ma

,

macronuclei

;

Mi

,

micronuclei

.

Scale

bars

:

200

Μm

(

A

–

C

,

K

–

L

)

;

70

Μm

(

I

,

J

)

.

Kovaleva

,

1968

with

14

–

18

somatic

kineties

could

separate

species

.

Further

evidence

is

needed

to

test

be

a

distinct

species

,

i

.

e

.

T

.

oligocineta

stat

.

this

hypothesis

.

nov

.

;

T

.

prenanti

multicineta

Raikov

&

Kovaleva

,

1968

,

which

has

20

–

26

kineties

,

might

also

be

a

distinct

species

,

i

.

e

.

T

.

multicineta

stat

.

nov

.

;

the

C

OMMENTS

ON

T

RACHELORAPHIS

OLIGOSTRIATA

population

of

T

.

phoenicopterus

described

by

Foissner

There

have

been

several

redescriptions

of

this

species

&

Dragesco

(

1996

b

)

and

that

of

T

.

cf

.

phoenicopterus

since

it

was

first

reported

(

Dragesco

,

1960

;

Raikov

,

1962

;

described

by

Xu

et

al

.

(

2011

c

)

could

each

represent

a

Kattar

,

1970

;

Borror

,

1972

;

Czapik

&

Jordan

,

1976

;

©

2020

The

Linnean

Society

of

London

,

Zoological

Journal

of

the

Linnean

Society

,

2021

,

192

,

690

–

709

Notes: Values below the diagonal are numbers of unmatched sites, while those above the diagonal are sequences similarity in percentage (%).

Wright, 1983). Foissner & Dragesco (1996b) provided a redescription with details of both living morphology and infraciliature, based on which they transferred this species from Trachelonema to Tracheloraphis . Xu et al. (2011c) described a Qingdao population under the name Tracheloraphis oligostriata ( Raikov, 1962) Foissner & Dragesco, 1996 . However, the morphology, infraciliature and molecular information of this population suggest that it is a separate species (see below).

COMMENTS ON TRACHELORAPHIS APOLIGOSTRIATA SP. NOV.

Tracheloraphis apoligostriata sp. nov. most closely resembles T. oligostriata , which was originally described by Raikov (1962) and redescribed in detail by Foissner & Dragesco (1996b). However, the former can be separated from the latter by the colour and distribution pattern of cortical granules (brownish and densely distributed vs. colourless and sparsely distributed). Furthermore, their SSU rDNA sequences differ by 105 nucleotides, indicating that these two species are not conspecific ( Table 4).

Xu et al. (2011c) reported an isolate from Qingdao, which they identified as T. oligostriata . This isolate possesses the same morphological features and shares the same nuclear structure and infraciliature as T. apoligostriata sp. nov.. Given these similarities and their localities, we conclude that both are populations of T. apoligostriata sp. nov. (Fig. 10)

PHYLOGENETIC ANALYSES

Six genera were represented in the current phylogeny among which about 40–200 bp differences were detected ( Fig. 11). However, two species within a single genus can differ by as much as 125 bp ( Table 4). Few reasonable explanations are available that can account for the high sequence divergence level within congeners of Tracheloraphis : first, it could be that the oral ciliature, which has been used as the main character to define trachelocercid genera and to unite Tracheloraphis species morphologically, is a plesiomorphy or homoplasy. Thus, the information provided by SSU rDNA sequences might not support the monophyly of Tracheloraphis since, as suggested by Vďacný (2017), only apomorphies can be well represented and supported by the phylogenetic analysis. Second, misidentification of related material cannot be completely excluded because species identification for this genus is difficult and some data in the GenBank might be supplied by non-taxonomists as revealed recently for other taxa ( Lian et al., 2019; Lu et al., 2019; Wang et al., 2019a; Zhang et al., 2019; Xu et al., 2020). Finally, it is also possible that the genus Tracheloraphis is indeed a more divergent assemblage than related groups, which is undergoing a process of rapid evolution, while the 18S gene does not yet completely reflect this change.

In addition, among Tracheloraphis species that have available SSU rDNA sequences ( Fig. 2) and detailed morphological descriptions, T. apoligostriata sp. nov. and T. oligostriata , both of which lack anterior and posterior secant systems and have only one brosse kinety, are grouped together and basal within the assemblage that includes all other Tracheloraphis species. The latter assemblage (including a non- Tracheloraphis , that is, Prototrachelocerca fasciolata ) possesses both anterior and posterior secant systems and two or three brosse kineties ( Table 6). It is not completely clear if these features represent generic characters at intra- or interspecific level or even indicate that the genus Tracheloraphis is a multiphyletic complex. Nevertheless, we expect that combined data of molecular information and the evidence in structure of infraciliature will facilitate better understanding of evolutionary relationships among karyorelictid ciliates. Further information with more diversely sampled trachelocercids is urgently needed.

Bold indicates our own results.

* See text, could be a valid and distinct species, T. oligocineta .

** Could be a second valid species, T. multicineta .

*** Could be an undefined but non- phoenicopterus species, namely T. cf. phoenicopterus . -, Not applicable.