Plesiocolochirus minaeus O’Loughlin, 2016

O’Loughlin, P. Mark, Harding 1, Caroline & Paulay, Gustav, 2016, The sea cucumbers of Camden Sound in northwest Australia, including four new species (Echinodermata: Holothuroidea), Memoirs of Museum Victoria 75, pp. 7-52 : 27-30

Plesiocolochirus minaeus O’Loughlin sp. nov.

Zoobank LSID. http://zoobank.org/ urn:lsid:zoobank.org:act:

189703BE-67E5-4212-B337-8C5B2F39D1E8

Table 1 ; appendices 1, 2; figures 1, 13, 14;

Material examined. Holotype. Northwest Western Australia, Kimberley Region, Camden Sound , WAMSI 1.1 .1, RV Solander, sled, site no SOL 117, WAM station no 31, barcode 10002268, from -15.674833 124.279779 39 m to -15.674794 124.279012 39 m, 22 Mar 2015, WAM Z89026 .

Description (preserved in 95% ethanol). Body hard, packed with calcareous ossicles, elongate, square in transverse section, 70 mm long, 10 mm high and wide; surface of body wall creased, imbricating scales around tips of papillae only; five anterior oral valves, lobed terminal papillae on each valve; each dorso-lateral margin with about 15 spaced, zig-zag, pyramidal, hard papillae, up to 2 mm high; ventro-lateral margin lacking papillae, except for 2–3 smaller papillae on each of the three ventral oral radii, and one on each of the three ventral anal radii; five tongue-like, radial anal scales/teeth; five pyramidal, radial, anal papillae, not as high as dorso-lateral papillae; dorsal and lateral inter-radii with scales evident, irregular form and size, up to about 1.5 mm long. Ventral surface flat with three broad, raised radii with lace-like network of oblong scales each about 1 mm long, tube feet mostly deeply retracted, ventro-lateral radial tube feet band about four wide, mid-ventral band about five wide. Typical cucumariid calcareous ring, undulating posteriorly, lacking posterior prolongations. Ten dendritic tentacles, two ventral smaller. Single polian vesicle, gonad tubules not branched.

Dorsal body wall and dorso-lateral papillae ossicles of six intergrading types:

1. surface layer of deep bowls with tapering rounded base and bluntly to sharply spinous or knobbed marginal rim, some bridged internally, bowls typically about 55 µm wide 48 µm deep;

2. thick and thin walled shallow bowls, irregularly rectangular, many with smooth rims, many with indented lateral rims, variably bridged to create irregular hollow ellipsoids, frequently 55 µm long, up to 144 µm long;

3. smooth, irregularly round to oval, hollow ellipsoids, up to 64 µm across;

4. some regular, four-holed, thickened, flat buttons, up to 72 µm long;

5. abundant knobbed and thickened irregular flat buttons, many with incipient secondary layering, inter-grading with small multi-layered scales, up to about 176 µm long;

6. multi-layered ossicles/scales, irregularly oval, up to at least 1.00 mm long.

Dorso-lateral papillae lacking apical tube feet and endplates.

Ventral tube feet ossicles of four forms (lacking multi-layered ossicles and buttons):

1. endplates with fairly uniform perforations, smallest centrally, endplates up to at least 280 µm diameter;

2. straight and curved, smooth, tube foot support rod-plates, typically widened and perforated mid-rod and distally, some marginally denticulate, rod-plates up to 200 µm long;

3. knobbed oval to rectangular shallow bowls, margins knobbed to bluntly spinous, variably bridged to create irregular hollow ellipsoids, bowls up to 55 µm long;

4. shallow bowls of variable size, not bridged, some with marginal and surface knobs, bowls up to 128 µm long.

Tentacle ossicles of four inter-grading forms:

1. thick, smooth, perforated rod-plates up to 440 µm long;

2. smooth rods, variably perforated and branched

3. fine thin rods with distal perforations, typically about 60 µm long;

4. knobbed, branched rod rosettes, some perforated plates with knobbed margin, up to 50 µm long.

Live body colour very pale yellow to off-white, dorso-lateral papillae and oral valves reddish-orange, ventral radii greenish yellow; preserved colour off-white.

Distribution. Northwest Western Australia, Kimberley Region, Camden Sound, 39 m.

Etymology. From the Latin minae (“parapets”), with reference to the parapet-like hard papillae on the dorso-lateral margins of the body in lateral view.

Remarks. The phylogenetic tree ( Figure 1 ) includes a CO1 sequence for the new species, Plesiocolochirus minaeus O’Loughlin , within the congeneric clade of Plesiocolochirus species. This sequence is understandably remote from the Plesiocolochirus challengeri clade that we anticipate on morphological grounds will be a clade close to Plesiocolochirus spinosus .

The morphological characters that distinguish Plesiocolochirus minaeus O’Loughlin sp. nov. from other Plesiocolochirus species are the:

1. pyramidal, firm, dorso-lateral papillae;

2. complete absence of a ventro-lateral raised firm papillae;

3. absence of inter-radial tube feet;

4. presence of imbricating scales at tips of dorso-lateral papillae only;

5. abundance of knobbed and thickened irregular buttons in the body wall, many with incipient secondary layering, inter-grading with small multi-layered scales;

6. ventral tube feet surrounded by a ring of about four ellipsoidal scales, not penetrating scales;

7. live colour of red dorso-lateral papillae on off-white body.

We note the presence of tentacle rosettes in the new species. This indicates that the presence or absence of tentacle rosettes is not a sound generic diagnostic character for genera Colochirus and Plesiocolochirus .

We also note the presence of two Pilumnidae crabs in the coelom of the holotype of the new species.

Figures

Figure 1. Maximum likelihood tree of Colochirus–Plesiocolochirus COI data, with mid-point rooting. Bootstrap support (100 replicates) indicated by circles (100%) and rectangles (>95%).