ILLUSTRATED KEY FOR THE IDENTIFICATION OF NEMATODES
IN THE SUBORDER CEPHALOBINA

 Khuong B. Nguyen
Entomology & Nematology Department
University of Florida

.
 The illustrations (collected from different sources mentioned in the text), the key and
     the diagnoses in this document were prepared for students in the course Nematode
             Taxonomy and Systematics. Other users are welcome.
 
 

1- Stoma narrow; esophagus without median bulb; head with separate lips, labial edges
    strongly cuticularized or head with cirrated appendages anteriorly.................................2
    Soma narrow; esophagus without median bulb; but head not as above, female gonad
    always  monodelphic...................................................................................................3

2- Head with separated lips, their edges strongly cuticularized; cheilorhabdion not
    cuticularized (Fig. 1-4) ........................................ TERATOCEPHALOIDEA ........40
    Head and lips not as above but with 6 simple or cirrated bristles (Fig. 5-11);
    cheilorhabdion prominent ..................................... CHAMBERSIELLOIDEA.........43

3- Esophagus cylindrical, not divided into different parts... DRILONEMATOIDEA. ......7
     Esophagus divided into three parts: corpus, isthmus and basal bulb .............................. 4

4- Stoma narrow, structural parts equally cuticularized; gonad, posterior to vulva,
     reflexed twice........................................................CEPHALOBOIDEA....................8
             Two families:
       - Vulva near anus ............................................................ family Metacrobelidae
            Only one subfamily ...............................................................Metacrobelinae
            Only one genus  (Fig. 1) .............................................................Metacrobeles
      - Vulva far from anus................................................family Cephalobidae...........8
   Stoma not evenly cuticularized; gonad posterior to vulva not reflexed twice ...................5

5- Mouth ventrally directed and bordered laterally by membranous
    fins, dorsally by truncate appendage ............................ELAPHONEMATOIDEA
         One family ..........................................................................Elaphonamatidae
         One subfamily.......................................................................Elaphonematinae
         One genus  (Fig.2).......................................................................Elaphonema
    Mouth not as above ..................................................................................................6

6- Bursa present with very large ribs; spicules absent (Fig. 3)......MYOLAIMOIDEA
         One family ...............................................................................Myolaimidae
         One subfamily ..........................................................................Myolaiminae
         One genus  (Fig.3).........................................................................Myolaimus
     Bursa absent, sexual papillae small; spicules present.. PANAGROLAIMOIDEA....28

DRILONEMATOIDEA

FamilyOsstellidae or Drilonematidae

7- Stoma with rhabdions fused to form a tube projected beyond
    labial level; lips transformed into 4 hooks (Fig. 4 ).....................................Osstellinae
         One genus  (Fig.4).............................................................................Osstella
    Stoma absent; head region rounded, smooth; lip normal  (Fig. 5).......Drilocephalobinae
        One genus  (Fig.5)..................................................................Drilocephalobus

CEPHALOBOIDEA

Family Cephalobidae

8- Head with probolae.............................................................................................9
    Head without probolae.......................................................................................10

9- Cephalic probolae large, longer than labial probolae
     (Fig. 7)............................................................................Kirjanoviinae..................11
     Cephalic probolae small, always shorter than labial probolae (Fig.10 )..Acrobelinae..12

10- Cheilostom and prostom wider and rhabdions more heavily cuticularized than following
      parts of stoma (Fig.6 )...........................................................Panagrocephalinae
      Only one genus (Fig.6)............................................................Panagrocephalus
      Only cheilostom wider than other parts of stoma (Fig. ).............Cephalobinae.........25

11- (9) Six paddle-like (or ear-like) cephalic probolae; post vulval sac absent
        (Fig.7).........................................................................................Kirjanovia
            Three paddle-like cephalic probolae; post vulval present
        (Fig.8)................................................................................Acromoldavicus

Subfamily Acrobelinae

12)- Labial probolae furcate (Fig.10 )......................................................................13
      Labial probolae not furcate (Fig.17 )..................................................................20

13)- Labial probolae well cirrated (Fig.10 )..............................................................14
        Labial probolae not cirrated (Fig.11 )...............................................................15

14 (13)- Pointed flap-like cephalic probolae absent; basal portion of labial probolae wollen,
              projecting toward cephalic probolae  (Fig.9)..............................Nothacrobeles


Nothacrobeles anterior region
(All SEM pictures in this key are from Sauer, 1985)

              Pointed flap-like cephalic probolae present; basal portion of labial probolae not
              swollen  (Fig.10)......................................................................Acrobeles


Acrobeles face view

15 (13)- Annules and longitudinal ridges forming blocks all over the body
             (Fig. )...............................................................................................16
               Body without longitudinal ridges, or at most, only in neck region
               ......................................................................................................17

16 (15)- Labial probolae with T- or Y-shaped terminus; female tail
             conical  (Fig.11)....................................................................Stegelletina
              Labial probolae with arcuate, fork-like terminus; female tail broadly rounded
             (Fig.12)................................................................................Stegelleta


Stegelleta labial region
17 (15)- Posterior end of corpus swollen to form median bulb, its lumen forming a
               large chamber; labial probolae divided at or close to its bottom
            (Fig.13).......................................................................................Paracrobellus
                Posterior end of corpus not swollen, its lumen normal;
                labial probolae divided at about their middle..............................................18

18 (17)- Cephalic probolae with serrate cuticularized borders  (Fig.14) ...........Cervidellus
              Cephalic probolae without serrate borders..................................................19

19 (18)- Labial probolae very thin, hair-like, Y- or T-shaped; head edges cuticularized as in
              Teratocephalus  (Fig.15).......................................................Ypsilonellus
              Labial probolae fork-like; head edges not as above  (Fig.16)........Acrobelophis

20 (12)- Body with plate-like segments (at least in anterior part) (Fig. )........................21
              Body without plate-like segments...................................................................22

21 (20)- Cephalic probolae long pointed; labial probolae low  (Fig.17)..............Scottnema
              Cephalic probolae short, semicircular, lobe-like  (Fig.18)...................Placodira

22 (20)- Cephalic probolae flap-like with dentate projection at
              base; notches between cephalic probolae deep; post vulvar sac absent
           (Fig.19)...................................................................................................Zeldia


Zeldia face view

              Cephalic probolae without dentate projection at base; notches between cephalic
               probolae shallow; postvulvar sac usually present (Fig. ).............................23

23 (22)- Female tail usually long, pointed; cephalic probolae 3, setae-like; labial probolae low,
              rounded  (Fig.20)....... ......................................................Pseudacrobeles
             Tail short, bluntly rounded; cephalic probolae always lower than labial
             probolae....................................................................................................24

24 (23)- Labial probolae, at least the dorsal one, furcate; esophageal corpus almost cylindrical
          (Fig.21)..............................................................................Chiloplacus

              Labial probolae low, rounded or conical, but never furcate; esophageal corpus with
              elongate, spindle-like swelling  (Fig.22).....................................Acrobeloides

25 (10)- Head offset, notched; labial edges cuticularized (as in Teratocephalus)
        (Fig.23)................................................................................Teratolobus
            Head not offset and labial edges not as above.............................................26

26 (25)- Six lips sharply pointed and equal in size  (Fig.24).......................Eucephalobus
              Three lips, never sharply pointed, asymmetrical........................................27

27 (26)- Tail bluntly rounded, sometimes with mucron  (Fig.25)....................Cephalobus
              Tail slender, conoid, pointed  (Fig.26) ...............................Heterocephalobus

PANAGROLAIMOIDEA

Keys to Families, Subfamilies and Genera:

28 (6)- Stoma tubular, its cuticularized portion at least twice as long as wide
            (Fig. 27)...............................................................................................29
             Stoma not tubular, its cuticularized portion about as long as wide
             (Fig. 28, 29)......................................................Panagrolaimidae..... 30

29 (28)- Stoma very long and narrow; vulva at mid body; postvulvar sac
              present.......................................................................... Alirhabditidae
                    Only one subfamily.....................................................Alirhabditinae
                    Only one genus  (Fig.27)..................................................Alirhabditis
              Stoma not very long, relatively wide; vulva near anus; postvulvar sac
              absent.............................................................................Brevibuccidae
                    Only one subfamily ...........................................Brevibuccinae......38

Family Panagrolaimidae:

30 (28)- Esophagus with bulb-like median swelling (Fig.29 )....Tricephalobinae....33
             Esophagus without bulb-like median swelling.............................................31

31 (30)- Promesostom short, metarhabdion with several denticles; anterior end of spicula
              usually hooked  ventrally..............................................Panagrellinae......34
              Promesostom well developed; anterior end of spicula not hooked..............32

32 (31)- Spicula S-shaped, slender (Fig. 28 ) ........................................Turbatricinae
              Only one genus  (Fig.28)........................................ .................Turbatrix
              Spicula not S-shaped, stouter ................................Panagrolaiminae .....35

33 (30)- Distal end of ovary reflexed; postvulvar sac absent; very
              small nematodes (0.25-0.50 mm)  (Fig.29)...........................Halicephalobus
              Distal end of ovary usually passing anus, not reflexed; postvulvar sac present; body
              longer than 0.50 mm  (Fig.30)............................................Tricephalobus

34 (31)- Spicules with bifid tips, proximally knobbed often hooked
              ventrally; postvulvar sac present  (Fig.31) ................................Panagrellus
              Spicules with non-bifid tips, proximal end not hooked; postvulvar sac absent
          (Fig.32).......................................................................Anguilluloides

35 (32)- Six lips divided by deep grooves, their edges cuticularized.........................36
              Labial region without deep grooves, their edges not cuticularized................37

36 (35)- Tail long, 7-8 times as long as anal body widths; postvulvar sac absent
          (Fig.33).....................................................................Panagrobelium
              Tail shorter, 3 times as long as anal body widths; postvulvar sac present
          (Fig.34).......................................................................Panagrobelus

37 (35)- Posterior end of corpus swollen as a median bulb; pro- and mesorhabdions separated
          (Fig.35).....................................................................Procephalobus
              Posterior end of corpus not swollen; pro- and mesostom fused to form a chamber
          (Fig.36)....................................................................Panagrolaimus

Family Previbuccidae:

38 (29)- Body with sheath; inner cuticle with longitudinal rows of pores; six lips separated by
              deep grooves  (Fig.37).......................................................Cuticonema
              Not as above..............................................................................................39

39 (38)- Spicules unequal; female tail long, hair-like (Fig.38)...................Brevibucca
              Spicules equal; female tail shorter, not hair-like (conoid) ( Fig.39)
              ...................................................................................Plectonchus

TERATOCEPHALOIDEA

One family: Teratocephalidae

40 (1)- Gonad single; amphids small, at beginning of stoma: Teratocephalinae........41
            Gonads paired; amphids large, behind stoma: Metateratocephalinae...........42

41 (40)- Cuticle with punctation; vulva at about 40% of body
          (Fig.40).................................................................Steratocephalus
              Cuticle without punctation; vulva at about 65% of body
          (Fig.41)................................................................ Teratocephalus

42 (40)- Head not offset with four fine setae; esophagus, anterior to esophageal bulb,
              with isthmus  (Fig.42)............................................ Euteratocephalus
              Head well offset without setae; esophagus, anterior to esophageal bulb,
              cylindrical  (Fig.43) ............................................ Metateratocephalus

CHAMBERSIELLOIDEA

One family: Chambersiellidae

43 (1)- Cephalic setae with cirri (Fig. 44-46): ..............Chambersiellinae.........44
            Cephalic setae without cirri: ........................Macrolaiminae.................46

44 (43)- Head with two lateral setae (Fig.44)  ...................................Bicirronema
              Head with 6 setae ...............................................................................45

45 (44)- Gonad single  (Fig.45)...................................................Chambersiella
              Gonads paired  (Fig.46). ..................................................Geraldius

46 (43)- Gonad single ......................................................................................47
              Gonads paired ....................................................................................48

47 (46)- Tail long, filiform  (Fig.47)...........................................Macrolaimellus
              Tail short, conical  (Fig.48)...........................................Macrolaimus

48 (46)- Head with 6 cephalic setae and 6 smaller subcephalic setae
          (Fig.49).. ..................................................................Cornilaimus
              Head with 6 cephalic setae only  (Fig.50)..........................Diastolaimus



Updated October 2009