Laevocnus O’Loughlin, 2014

O’Loughlin, P. Mark, Mackenzie, Melanie, Paulay, Gustav & VandenSpiegel, Didier, 2014, Four new species and a new genus of Antarctic sea cucumbers with taxonomic reviews of Cladodactyla, Pseudocnus, Paracucumidae and Parathyonidium (Echinodermata: Holothuroidea: Dendrochirotida), Memoirs of Museum Victoria 72, pp. 31-61 : 46-48

Laevocnus O’Loughlin gen. nov.

Zoobank LSID. http://zoobank.org:act:6A6572E8-B33F-4200-

80F8-5963E557DE65

Key 1; figure 9

Diagnosis. Ten equal dendritic tentacles; tube feet on radii only, radial series cross introvert to base of tentacles; ‘calcareous’ ring lacking posterior prolongations; ring sometimes not calcified in larger specimens; gonad tubules not branched; body wall ossicles single-layered perforated knobbed plates with one end tapered and distally spinous; lacking fourholed knobbed buttons; tentacles ossicles perforated plates, rarely rods, never rosettes.

Type species. Pentactella laevigata Verrill, 1876a , b (type locality Kerguelen Islands )

Assigned species and occurrence. Laevocnus cornutus ( Cherbonnier, 1941) (Patagonia) ; L. intermedius ( Théel, 1886) ( Heard and Kerguelen Islands); L. katrinae O’Loughlin sp. nov. (Shag Rock); L. laevigatus ( Verrill, 1876a, b) (Kerguelen Is); L. leachmani Davey and O’Loughlin sp. nov. (Ross Sea); L. leoninoides ( Mortensen, 1925a) ( New Zealand sub-antarctic islands); L. leoninus (Semper, 1867) (Falkland Is); L. marionensis ( Théel, 1886) (Marion I.) ; L. perrieri ( Ekman, 1927) (Falkland Is, South Georgia); L. serratus ( Théel, 1886) ( Heard I.).

Etymology. Formed from a combination of “ laev ” from laevigata (the species name of the type for the new genus), with the established and related generic name Ocnus (masculine).

Remarks. We judge that having 10 equal tentacles or eight large and 2 small ventral ones is a significant distinguishing generic character. Cherbonnier 1941 reported that his species P. cornutus had two slightly small ventral tentacles. No other Laevocnus species has other than 10 equal tentacles. Laevocnus species are distinguished from Pseudocnus species (sensu stricto) by: lacking inter-radial tube feet; having ossicles in the body wall limited to single-layered knobbed plates with spines at one end; rarely having rods and never rosettes in the tentacles.

As noted above in the previous Remarks Laevocnus leoninus is an anomalous inclusion in Laevocnus , having: a uniform cover of tube feet; numerous buttons in the body wall; and tentacle rods. It does have 10 equal tentacles. Laevocnus leoninus is sympatric with Laevocnus perrieri as a cold temperate species of the new genus. Also noted above is the provisional inclusion of Laevocnus cornutus that has two smaller tentacles and rod-plates in the tentacles.

Laevocnus marionensis is also a somewhat anomalous inclusion as it has body wall ossicles with slightly developed tapered spinous ends inter-grading with knobbed buttons that usually show some distal development.

O’Loughlin (2009) assigned Cucumaria serrata var. intermedia Théel, 1886 ( Heard and Kerguelen Islands) and Cucumaria serrata var. marionensis Théel, 1886 (Marion Island) to Pseudocnus and raised them to species status. We now reassign these species to Laevocnus .

O’Loughlin (1994) reported that Laevocnus laevigatus exhibited brood-protection in “two ventral invaginated marsupia that opened through a common mid-body vestibule”. In some female specimens (NMV F165742 (6)) of Laevocnus serratus we observed two ventral brood pouches invaginated into the coelom, with one or two ventral inter-radial external openings. There were up to 40 brood juveniles in one individual, each up to 3 mm long, sub-equal in size, and with their tentacle crowns developed. Two ventral openings but no internal pouches were observed (specimen NMV F84982) for Laevocnus intermedius and it is assumed that this species also has this brood-protecting adaptation.

COI sequence data from several hundred dendrochirotids (Michonneau et al. in prep) recovers Laevocnus as a single clade, albeit poorly supported, that includes L. katrinae sp. nov., L. laevigatus , L. leachmani sp. nov., L. leoninus , L. perrieri and L. serratus ( Fig. 9 ).

Key (1) to the species of Laevocnus O’Loughlin gen. nov.

1. Tube feet cover the body uniformly Laevocnus leoninus (Falkland Is)

— Tube feet restricted to the radii 2

2. Tube feet in single well-spaced series in mid-body on all radii 3

— Close zig-zag or paired series of tube feet on all radii, may be more scattered on dorso-lateral radii 5

3.

Body up to 40 mm long; tube feet in paired series anteriorly; body wall ossicles with long, narrow “goose neck”, ending in a sparsely perforated and spinous taper

Laevocnus serratus ( Heard I.)

— Body up to 15 mm long; single series of tube feet anteriorly; body wall ossicles with short tapered spinous end 4

4.

Calcareous ring thin and indistinct; two polian vesicles; body wall ossicles smaller, up to 208 µm long

Laevocnus katrinae sp. nov. (western Antarctica, Shag Rock , 206 m)

— Calcareous ring distinct; single polian vesicle; body wall ossicles larger, up to 280 µm long

Laevocnus leachmani sp. nov. (eastern Antarctica, Ross Sea and off King George V Land, 299–1645 m)

5. Body wall ossicles with spinous end predominantly rounded or not significantly elongate and tapered; body wall ossicles small, up to 160 µm long 6

— Body wall ossicles with distal spinous end typically elongate and tapered; largest body wall ossicles longer than 180 µm long 7

6. Body wall ossicles irregularly oval, predominantly with one end rounded and closely spinous, up to 140 µm long; tentacles ossicles large smooth perforated plates; preserved specimens smaller, up to 35 mm long

Laevocnus leoninoides ( New Zealand sub-antarctic Is)

— Body wall ossicles with slightly developed tapered spinous ends, inter-grading with knobbed buttons usually showing some distal development, up to 160 µm long;

tentacles ossicles perforated plates with surface spines;

preserved specimens larger, up to 55 mm long

Laevocnus marionensis (Marion I.)

7.

Two smaller tentacles; rod-plate ossicles in the tentacles Laevocnus cornutus (Patagonia, Falkland Is)

— Equal tentacles; plate ossicles in the tentacles 8

8.

Preserved specimens small, up to 40 mm long; tentacle plates with some surface spines; lacking ventral coelomic brood sacs and openings

Laevocnus perrieri (Falkland Is, South Georgia)

— Largest preserved specimens up to at least 60 mm long; tentacle plates with knobs or smooth, not with surface spines; females with ventral coelomic brood sacs and openings 9

9. Preserved body up to 115 mm long; body wall ossicles up to 220 µm long; tentacles ossicles smooth plates Laevocnus laevigatus (Kerguelen Is)

— Preserved body up to 65 mm long; body wall ossicles up to 185 µm long; tentacle ossicles plates with surface knobs Laevocnus intermedius ( Heard I.)

Figures

Figure 9. Maximum likelihood tree for Laevocnus clade, based on COI sequences, GTR+I model, 100 bootstrap replicates, Cladodactyla sicinski as outgroup. Filled circles>0.95 bootstrap support.