Laubieriellus cacatua, Erickson & Wilson, 2018

Erickson, Ricky-Lee & Wilson, Robin S., 2018, A new Laubieriellus species (Annelida, Spionidae) from Western Australia, Zootaxa 4461 (2), pp. 261-268 : 262-268

Laubieriellus cacatua sp. nov.

Figures A–L.

Material examined. Australia. Northwestern Western Australia. Holotype: Stn SS07/2005 76, Indian Ocean, Carnarvon region, L5, 24° 35.18’S 112° 15.23’E, 405 m, 27 Jul 2005, 1 (complete, NMV F242821). Paratypes: Stn SS05/2007 191, Northwestern Australia, Ashmore L30 transect, 12° 30.93’S 123° 25.33’E, 407 m, 6 Jul 2007, paratypes: 2 (af, NMV F 110695).—Stn SS05/2007 0 74, Northwestern Australia, Mermaid L24 transect, 16° 43.88’S 119° 15.36’E, 696 m, 17 Jun 2007, paratype: 1 (af, NMV F167451).—Stn SS07/2005 76, Indian Ocean, Carnarvon region, L5, 24° 35.18’S 112° 15.23’E, 405 m, 27 Jul 2005, paratypes: 4 (4 af, 1 pf, NMV F 160691); paratypes: 1 (1 af, NMV F245555); paratypes: 1 (1 complete, NMV F245554).—Stn SS07/2005 173, Indian Ocean, Albany region, T6 100, 35° 20.37’S 118° 16.91’E, 101 m, 8 Aug 2005, paratype: 1 (complete, NMV F158729).—Stn SS07/2005 182, Indian Ocean, Albany region, T6 150, 35° 21.32’S 118° 17.40’E, 153 m, 9 Aug 2005, paratypes: 2 (2 af, NMV F 110702); paratypes: (1 complete, NMV F245553); paratypes: 1 (1 af, NMV F167427); paratypes: 1 (1 complete, NMV F245556).—Stn SS07/2005 183, Indian Ocean, Albany region, T6 200, 35° 21.50’S 118° 17.40’E, 193 m, 9 Aug 2005, paratypes: 3 (af, NMV F158701).

Description. Holotype. 0.3 mm wide at chaetiger 5, 6.9 mm long for 43 chaetigers. Yellow-white colour in alcohol, unpigmented. Prostomium broadly rounded with anterior margin slightly indented, extending as caruncle to the base of chaetiger 2 (Figure A, C, E). Peristomium fused with, and surrounding prostomium. Eyes absent. Occipital tentacle absent. Palps missing. Nuchal organs not observed. Notopodial lamellae elongated over dorsum; connected in dorsal crests on chaetigers 6–11, low crests on chaetigers 6 and 11 (Figure A, C, D). Neuropodial lamellae connected in ventral crests on chaetigers 2–11, crests largest on chaetigers 5–7 and low on chaetigers 10– 11. Ventral crests incomplete with a small median gap, more so anteriorly, gap reducing posteriorly (Figure B). Branchiae numbering 4 pairs, on chaetigers 2–5 (1 branchia on chaetiger 4 is missing). Branchiae simple, unciliated and slightly longer than notopodial lamellae (Figure C, D, H). The first pair of branchiae are shorter than the following 3 pairs.

Chaetiger 1 with notochaetae and neurochaetae, shorter and thinner than those on following chaetigers. Anterior chaetae all capillaries, notochaetae and neurochaetae arranged in 2–3 rows, with longest chaetae in posterior row (Figure F). From chaetiger 10, neurochaete are reduced to one row, with sabre chaetae in ventralmost position, followed by hooded hooks and finally several capillary chaetae in dorsal-most position (Figure I). Ventral sabre chaetae usually 1 per fascicle, 2 at most (Figure I). Neuropodial multidentate hooded hooks numbering up to 8 per fascicle; hooks with 2 pairs of apical teeth above main tooth (Figures K, L). Hood opening with serrated edges and almost completely encloses the chaeta (Figure J). Notopodial hooks absent. Chaetal arrangement is otherwise unchanged on posterior chaetigers. Pygidium a short, circular ring, not divided into lobes (Figure G). Pygidial cirrus absent or perhaps lost from all specimens (see Remarks below).

FIGURES A–B. Scanning electron micrographs of Laubieriellus cacatua sp. nov. A. Anterior end, dorsolateral view, scale: 500µm (NMV F245553) B. Anterior end, ventrolateral view, scale: 200µm (NMV F245554).

FIGURE C. Laubieriellus cacatua sp. nov., left branchiae missing from chaetigers 2 and 4, right branchiae missing from chaetiger 5. Branchial scars and other damaged or obscured structures are denoted by dashed lines. Some chaetae are shown to demonstrate their placement, but are not to scale. Scale: 250µm (NMV F245553).

FIGURE D. Laubieriellus cacatua sp. nov., scale: 200µm (holotype, NMV F242821).

FIGURES E–G. Laubieriellus cacatua sp. nov. E. Anterior end, dorsal view, pigmented eye-spots visible, scale: 500 µm (NMV F245555) F. Anterior end, dorsolateral view, scale: 200µm (NMV F167451) G. Terminal view, pygidium, scale: 200µm (NMV F245556).

Paratypes. 0.2–0.4 mm wide, 2.9–6.9 mm long with 43 chaetigers. Eyes absent from most specimens, but a pair of lightly pigmented eye-spots can be seen in some specimens (Figure E). Dorsal crests commence on chaetigers 6–7 and end on chaetigers 9–11. Ventral crests start on chaetiger 2 and continue to chaetigers 6–12. Branchiae are present from chaetigers 2–4 to chaetigers 4–5. No specimen possesses a full set of branchiae, but we infer that the branchial distribution is from chaetigers 2–5. Neuropodial multidentate hooded hooks from chaetiger 10 and ventral sabre chaetae from chaetigers 10–11. No ontogenetic variability in taxonomically significant characters was observed within the size range of specimens studied.

Remarks. Laubieriellus cacatua sp. nov. can be distinguished from the other two species in this genus, Laubieriellus grasslei and Laubieriellus salzi as follows (Table A). The caruncle of L. cacatua sp. nov. is shorter and wider than that of the other species, extending to the anterior end of chaetiger 2. Laubieriellus grasslei and L. salzi have a longer, narrow caruncle extending to chaetiger 3. Laubieriellus cacatua sp. nov. possess simple, cirriform branchiae, lacking cilia and longest on chaetiger 5, but branchiae are heavily ciliated in L. salzi and L. grasslei . Branchiae are longest on chaetiger 2 in L. salzi , decreasing in size posteriorly. In L. grasslei , branchiae are equal in size or the anterior pair is slightly longer than posterior pairs. Dorsal crests are first present on chaetiger 6 in L. cacatua sp. nov., but on chaetiger 7 in L. grasslei and L. salzi .

The three species may also differ by the number of teeth present on the neuropodial hooded hooks. It seems that L. cacatua sp. nov. has two rows of accessory teeth on neuropodial hooded hooks, as is the case in many species in the Prionospio -complex ( Blake and Kudenov 1978). Scanning electron microscopy failed to reveal the arrangement and number of accessory teeth, since they are always concealed under the hood, which is opaque under SEM. Despite many light microscopy preparations, we were unable to observe any views of the hooded hook other than the lateral view. The hood itself, even though slightly translucent under the light microscope, still obscures some detail of the apical accessory teeth. Figure K shows all the detail that is visible under light microscope. We were unable to observe the hood in frontal view, but we assume that the apical teeth are in pairs, as present in the other species, so we have drawn what is visible in lateral view. We observed at least two apical teeth above the main tooth, but it is plausible that there is a third, even smaller pair of teeth at the apex of the hook. The number of rows of accessory teeth is also unclear in L. salzi : the text and figures of Laubier (1970) and Dagli (2013) contradict one another. According to the original description by Laubier (1970), L. salzi has 2 pairs of accessory teeth, although on some chaetae a third pair of minute teeth are visible dorsally. Dagli (2013) states that L. salzi has 4 pairs of accessory teeth. It is not surprising that these details of hooded hooks are ambiguously described, the structures are extremely small and difficult to observe. We were unwilling to continue experiments with destructive observation methods since the species can be distinguished using the easily observed characters listed above. In Australian samples, Laubieriellus cacatua sp. nov. is immediately recognisable as the only known Australian spionid with prominent ventral crests.

FIGURES H–I. Laubieriellus cacatua sp. nov. H. Scanning electron micrograph of simple branchiae, chaetigers 2–3. Chaetiger 2 missing 1 branchiae, scale: 50µm (NMV F245553) I. Scanning electron micrograph of chaetiger 11 neurochaetae; capillary chaetae, hooded hooks and sabre chaeta, scale: 20µm (NMV F245554).

TABLE A. Selected characters of Laubieriellus species

*2–3 pairs according to Laubier 1970 and 4 pairs according to Dagli 2013. FIGURES J–L. Laubieriellus cacatua sp. nov. J. Scanning electron micrograph of hooded hook sheath. Hooded hooks obscured by sheath, scale: 5µm (NMV F245554) K. Light microscope image of hooded hooks, scale: 25 µm (NMV F167451) L. Lateral view, multidentate hooded hook with 2 pairs of apical teeth above main tooth, one apical tooth of each pair shown, scale: 10µm (NMV F167451).

Laubieriellus cacatua sp. nov. has a simple pygidium without appendages, made of a continuous circular ring. It is possible that the pygidial cirrus is fragile and easily damaged, although some doubt remains (we have 29 specimens and 6 are complete posteriorly). In the original description of L. salzi, Laubier (1970) described a pygidium consisting of a short circle, without a medial cirrus. However in the Dagli (2013) description of the same species, he adds that the species does possess a medial cirrus. Similarly, the pygidium of L. grasslei is formed by 2 short, rounded ventrolateral lobes and one slightly longer, thinner dorsomedial cirrus, or 3 subequal lobes.

Laubieriellus cacatua sp. nov. also differs from L. salzi by the presence of notopodial lamellae on chaetiger 1, which are absent from L. salzi . In addition, L. cacatua sp. nov. differs from L. grasslei by the number of sabre chaetae present per neuropodium. Laubieriellus cacatua sp. nov. usually possess 1 sabre chaeta per neuropodium, where L. grasslei usually possess 2.

Prionospio rugosa ( Sigvaldadóttir 1997) also has ventral crests, but on chaetiger 9 (ventral crests commence on chaetiger 2 in Laubieriellus ). Prionospio rugosa also has pinnate branchiae on chaetigers 2 and 5, and notopodial hooded hooks, neither of which are present in Laubieriellus species. Sigvaldadóttir (1997) conducted a phylogenetic analysis based on morphological characters to address the question of a possible close relationship between her new species and Laubieriellus ; she found instead that P. rugosa is more closely related to other species of Prionospio than it is to Laubieriellus . To this result we would add our view that a ventral crest on chaetiger 2 cannot be homologous with a ventral crest on chaetiger 9. Sigvaldadóttir (1997) simply coded ventral crests as a single character (present/absent); treating the ventral crests of P. rugosa and Laubieriellus as different characters would remove an inferred parallelism between the two taxa and further distance P. rugosa from Laubieriellus .

Distribution. Laubieriellus cacatua sp. nov. occurs off the West Australian coast in the Indian Ocean (101– 696 m).

Etymology. Cacatua is a genus of cockatoos, containing birds known for their expressive, feathered crests. The epithet ‘cacatua’ refers to the spionid’s ventral crests, a character that places this species in the genus Laubieriellus .