Leptostracan character list.

The following is a list of features that are among those for which we record morphological data. The list includes characters previously observed by other authors (e.g., Walker-Smith and Poore) and features noted for the first time through our own research.

All Leptostraca possess a hinged rostrum.  This feature has received attention from nearly all authors of descriptive work on the group.  Tattersall (1905) referred to the rostrum as the 'frontal plate.'

1. Rostrum: length to width ratio.

Johnson (1970: 51) noted the variability of this character for his specimens of Nebalia longicornis, where the ratio ranged from approximately 1.7 to 1.3.  However, for the lectotype of N. longicornis examined by Dahl (1990) the length of the rostrum was 2.6 times its width.

2. Rostrum distal margin: bearing seta(e) (0) vs. unornamented (1).

3. Rostral keel: absent (0) vs. present, shorter than rostrum vs. (1) present, longer than rostrum.

In many species, a keel is present basally on the ventral surface of the rostrum.  The keel probably confers some stability to the rostrum; it is a medial extension of the rostrum that rests between the eyestalks.  It can be quite short, as in Nebalia, or extend beyond the distal margin of the rostrum as in Nebaliella.  In most genera (Dahlella, Levinebalia, Paranebalia, Saronebalia, and Speonebalia), the keel is altogether lacking.

4. Eye: eyestalk elliptical, shorter than rostrum (0) vs. elliptical, subequal in length to rostrum (1) vs. tubular, much longer than rostrum (2) sickle-shaped, elongate.

5. Eyestalk ommatidia: unpigmented (0) vs. with pigment more than half of eye (1).

6. Eye cuticle: unornamented, lacking protuberances (0) vs. bearing multiple projections, or denticles (1).

7. Eye distal margin: evenly rounded, lacking protuberances (0) vs. flattened, bearing protuberances (1) vs. medially invaginated, producing dorsal and ventral lobe (2).           

8. Eye supraocular plate: subequal in length or longer than eye, and tapering distally to acute apex (0) vs. shorter than eyestalk, tapering distally to rounded apex (1).

9. Carapace: extending beyond pleonite three (0) vs. extending beyond pleonite 4 (1) vs. extending beyond pleonite 5 (2).

10. Carapace surface: smooth, ornamented (0) vs. bearing series of subtriangular cuticular scales (1).

11. Carapace posterodorsal margin: non-emarginate (0) vs. emarginate (1).

12. Carapace posterodorsal notch: U-shaped, minute (0) vs. U-shaped, large (1) vs. Y-shaped.

13. Carapace ventral margin: even, lacking folds or other indentations (0) vs. characteristically bearing one or more small folds (1).

14. Antennule peduncular article 3: lacking robust, spine-like setae (0) vs. bearing multiple robust, spine-like setae (1).

15. Antennule peduncular article 3 relative sizes of peduncular articles

16. Antennule peduncular article 4: lacking robust, spine-like setae (0) vs. bearing single spine-like seta (1) vs. bearing two robust, spine-like setae (2) vs. bearing three robust, spine-like setae (3) vs. bearing four robust, spine-like setae (4).

Some authors have observed variation in the number of robust setae present on the distal surface of the fourth peduncular article, and there has been considerable controversy regarding the usefulness of this character.  Dahl (1985) noted variation among different size classes of Nebalia pugettensis for this and other setal characters.  Johnson (1970), for instance, stated '...about half of the specimens have a single short and stout spine. The remainder have 2 or rarely 3 such spines.'

17. Antennule peduncular article 4 length to width ratio: 2.0 or greater (0) vs. less than 2.0 (1).

18. Antennule peduncular article 4: lacking distal extension, or process (0) vs. bearing denticulate process distally (1).

19. Antennular scale: absent (0) vs. present, broad and ovate (1) vs. present, narrow and elliptical (2).

Sexual dimorphism of the antennular flagella has been described in the literature (Tattersall, 1905).

20. Antennular flagellum of female: composed of 20 or fewer articles (0) vs. composed of 30 or more articles (1).

The antennules and antennae of the benthic Nebalia bipes are used for digging through sediment (Vannier et al., 1997); one might suspect then that the flagella of these appendages would be shorter and more robust than those of the non-burrowing, pelagic species.

21. Antennular flagellum of male: with articles distinct, similar in form to that of female (0) vs. with articles fused and expanded, forming callynophore (1).

22. Antennular flagellum of male: bearing few aesthetascs (0) vs. bearing multiple dense rows of aesthetascs (1).

23. Antenna peduncular article 2: lacking acute anterodistal process (0) vs. bearing acute anterodistal process (1).

24. Antenna peduncular article 3: lacking acute anterodistal process (0) vs. bearing acute anterodistal process (1).

25. Antenna peduncular article 3: bearing only simple and plumose setae along anterior margin (0) vs. bearing robust, conical setae along anterior margin (1).

26. Antenna peduncular article 4: present, separate from article 3 (0) vs. fused to article 3 (1).

27. Antenna peduncular articles: smooth, lacking cuticular denticles (0) vs. ornamented, bearing minute denticles (1).

28. Antennal flagellum: composed of less than 20 articles (0) vs. elongate, composed of more than 25 articles (1).

29. Mandibular molar: well developed (0) vs. reduced (1).

30. Mandibular molar apex:: smooth, unornamented (0) vs. bearing setal brush (1).

31. Mandibular molar accessory spine: absent (0) vs. present (1).

32. Mandibular molar subterminal accessory process: absent (0) vs. present (1).

33. Mandibule: lacking incisor (0) vs. bearing single-toothed incisor (1) vs. with double-toother incisor (2).

34. Mandibular palp: two-articulate (0) vs. three-articulate (1) vs. four-articulate (2).

35. Mandibular palp article 2: with evenly rounded proximal margin, lacking tubercle (0) vs. bearing proximal tubercle on superior [dorsal] margin (1).

36. Mandibular palp article 2: with unornamented subterminal surface (0) vs. with elongate subterminal seta (1).

37. Mandibular palp article 2: ventromedially unornamented (0) vs. with ventromedial seta (1).

38. Mandibular palp article 3 [terminal article]: tapering distally (0) vs. margins parallel, rounded distally (1) vs. expanded distally (2).

39. Mandibular palp article 3 [terminal article]: with setal row occupying less than half length of inferior [ventral] margin (0) vs. with setal row occupying two-thirds or more of length of inferior [ventral] margin (1).

40. Mandibular palp article 3 [terminal article]: lacking terminally directed, submarginal setae at mid-length (0) vs. bearing terminally directed, submarginal setae at mid-length (1).

41. Mandibular palp article 3 [terminal article] secondary row of spine-like setae: absent (0) vs. present (1).

42. Maxillule: with two distinct endites (0) vs. with three distinct endites (1) vs. with four distinct endites (2).

43. Maxillule distalmost endite: bearing plumose and serrate setae (0) vs. bearing plumose setae, as well as serrate setae with subterminal, spatulate flange (1) vs. bearing plumose setae and conical, spine-like setae (2).

44. Maxillulary palp: shorter than maxilla (0) vs. elongate, several times length of maxilla (1).

45. Maxillulary palp: lacking proximal cluster of plumose setae (0) vs. with proximal cluster of plumose setae (1).

46. Maxillary endite 1 [proximalmost]: nearly square, with length subequal to width (0) vs. broad, ovate, larger than other endites (1).

47. Maxillary endite 4 [distalmost]: minute (0) vs. well-developed (1).

48. Maxillary endopod [distalmost]: uniarticulate (0) vs. two-articulate (1).

49. Thoracopod 1-8 endopod: composed of multiple articles (0) vs. with distinctly separate terminal article (1) vs. with all articles fused (2).

50. Thoracopod 1 exopod: much broader than endopod (0) vs. narrow, subequal in width to endopod (1).

51. Thoracopod 2-7 exopod: absent (0) vs. shorter than endopod (1) vs. longer than endopod (2).

52. Thoracopod 1 exopod: much broader than endopod (0) vs. narrow, subequal in width to endopod (1).

53. Thoracopod 8 length: subequal to thoracopods 1-7 (0) vs. much greater than thoracopods 1-7 (1).

54. Pleonite 4 posterolateral corner: forming acute point, even with posterior margin (0) vs. extended beyond posterior margin, tapering to acute point (1) vs. extending beyond posterior margin, well rounded (2).

55. Pleonite 4 posterodorsal margin: smooth, lacking dentition (0) vs. bearing blunt, well rounded teeth (1) vs. bearing teeth, each with parallel margins proximally and tapering to acute point distally (2) vs. bearing sharply tapering teeth (3).

56. Pleonite 5-7 length: subequal to pleonite 4 (0) vs. greater than pleonite 4 (1).

57. Pleonite 6-7: smooth, lacking dentition (0) vs. bearing blunt, well rounded teeth (1) vs. bearing teeth, each with parallel margins proximally and tapering to acute point distally (2) vs. bearing sharply tapering teeth (3).

58. Pleonite 5: basal triangular processes between pleopods lacking (0) vs. with acute triangular process between pleopods (1).

59. Pleonite 6: basal triangular processes between pleopods lacking (0) vs. with acute triangular process between pleopods (1).

60. Pleopod 1-4 protopod: posterior margin smooth (0) vs. posterior margin bearing multiple serrations (1).

61. Pleopod 1-4 protopod: lacking acute, laterally directed conical process at point of insertion (0) vs. bearing acute, laterally directed conical process at point of insertion (1).

62. Pleopod 1-4 protopod: posterior margin smooth (0) vs. posterior margin bearing multiple serrations (1).

63. Pleopod 1 protopod: with triangular process at base of endopod (0) vs. lacking triangular process at base of endopod (1).

64. Pleopod 1 protopod medial margin: lacking elongate, simple seta (0) vs. bearing elongate, simple seta (1).

65. Pleopod 1 protopod distolateral margin: lacking elongate, simple seta (0) vs. bearing elongate, simple seta (1).

66. Pleopod 1 exopod: lacking setal row (0) vs. bearing row of 15 or less trident-like setae (1) vs. bearing row of 30 or more trident-like setae (2).

67. Pleopod 1-4 appendix interna: absent (0) vs. with two coupling hooks (0) vs. with three coupling hooks (1) vs. with four coupling hooks (2).

68. Pleopods 2-4 appendix interna: absent (0) vs. rectangular (1) vs. tapering distally, apex subacute (2).

69. Pleopods 2-4 exopod length: subequal to endopod (0) vs. shorter than endopod (1).

70. Pleopods 2-4 endopod distal margin: bearing single, robust seta (0) vs. bearing two, robust setae (1).

71. Pleopods 2-4 exopod lateral margin: bearing row or unpaired smooth setae (0) vs. bearing row of paired smooth setae (1).

72. Pleopod 5 article 2 length to width ratio: less than 1.5 (0) vs. greater than 2.0 (1).

73. Pleopod 5 lateral margin: bearing three robust, spine-like setae (0) vs. bearing four to six robust, spine-like setae (1) vs. bearing seven or more robust, spine-like setae (2).

74. Pleopod 6: two-articulate (0) vs. uniarticulate (1).

75. Pleopod 6 distal margin: smooth (0) vs. bearing circlet of fine teeth (1).

76. Pleopod 6 lateral margin: bearing three robust, spine-like setae (0) vs. bearing four to six robust, spine-like setae (1) vs. bearing seven or more robust, spine-like setae (2).

77. Pleopod 6 lateral margin robust, spine-like setae: lacking subterminal seta (0) vs. with subterminal sensory seta (1).

78. Telson length to width ratio [dorsal aspect]: less than 1.5 (0) vs. greater than 2.0 (1).

79. Telson anal plates: distally acute, forming V-shaped invagination (0) vs. distally acute, forming Y-shaped invagination (1).

80. Caudal furca length: shorter than telson (0) vs. longer than telson (1).

81. Caudal furca medial margin: lacking setae (0) vs. densely setose (1).

82. Caudal furca lateral margin: bearing only smooth, spine-like setae (0) vs. bearing smooth, spine-like setae and fine, plumose setae (1).

83. Total body length: less than 20 mm (0) vs. greater than 20 mm (1).