Mesomyzostoma leukos Rouse, Lanterbecq, Summers and Eeckhaut

Greg W. Rousea, Deborah Lanterbecq, Mindi M. Summersa & Igor Eeckhaut, 2016, Four new species of Mesomyzostoma (Myzostomida: Annelida), Journal of Natural History 50 (1), pp. 1-23 : 18-19

Mesomyzostoma leukos Rouse, Lanterbecq, Summers and Eeckhaut sp. nov.

( Figure 7 )

Mesomyzostoma n. sp. 4a in Lanterbecq et al. (2006, 2009) Mesomyzostoma n. sp. 4b in Lanterbecq et al. (2006, 2009) Mesomyzostoma n. sp. 4 in Summers and Rouse (2014)

Material examined

North Point, Lizard Island Great Barrier Reef (Australia), 14°38.655' S, 145°27.267ʹ E; 10 – 15 m depth. Collector: Greg Rouse, 20 November 2001. One specimen each from two hosts that cannot be reliably identified at present. Each was parasitic inside a species of the Dichrometra , Lamprometra or Liparometra complex ( Mariametridae ) pending revision by Taylor et al. (in prep.; see Summers, Messing, et al. (2014). Holotype (SAM- E3408) (host = Dichro- /Lampro- / Liparometra sp. 1) incomplete, in two fragments; one piece in 70% ethanol following formalin fixation; the other fixed and preserved in 95% ethanol. A fragment of the holotype was dissolved in bleach for observation of the parapodial hook apparatus. A piece of the holotype and the whole of the other individual (host = Dichro- /Lampro- / Liparometra sp. 4) were digested for DNA extraction and molecular phylogenetic analyses.

Etymology

Named for the white colour of the body, from leukos, Greek for white.

Diagnosis

As the holotype is incomplete, in two fragments, a complete morphological diagnosis is not possible, though its separation from other species is clearly supported based on DNA data ( Figure 8 ). Lanterbecq et al. (2006: table 3) published the GenBank accession numbers for the COI, 16S and 18S DNA sequences for two individuals of this species (as Mesomyzostoma n. sp. 4a and Mesomyzostoma n. sp. 4b), all of which are unique among available sequences for species of Mesomyzostoma , but mere reference to accession numbers does not fulfil the conditions for availability of M. leukos sp. nov. under Article 13.1.2 of the International Code of Zoological Nomenclature. Therefore, as a diagnostic feature of this new species fulfilling Article 13.1.1 of the Code, we here provide the COI gene ’ s DNA sequence in full (Appendix 1). This sequence differs from those of all previously sequenced Mesomyzostoma ( Table 1 ) by an uncorrected pairwise distance of at least 5.5%.

Description

Holotype ( Figure 7 A), a 2-mm anterior or posterior fragment, thickest part about 1 mm across; two chaetigers present. Other fragment from an undetermined body region. No pharynx visible. No lateral organs visible. Chaetae from one side of a chaetiger removed for microscopy. Emergent hook inconspicuous, very thin shaft, tip curving to 90° with respect to shaft ( Figure 7 B, C). No replacement hooks. Aciculae 0.1 mm long and 5 μm wide along most length except at tip, as long but thicker than emergent hooks. Manubrium small ( Figure 7 C). Colour of individuals in life white.

Remarks

Mesomyzostoma leukos sp. nov. is clearly a new species based on DNA data ( Figure 8 ), but the limited amount of material for morphological study means only a cursory description can be made at this time. The two specimens of M. leukos sp. nov. sequenced for DNA showed no differences for any gene.

Figures

Figure 7. Mesomyzostoma leukos sp. nov. (A) Remaining fragment of holotype fi xed in formalin (SAM-E 3408). (B) Micrograph of a parapodium from the holotype digested in bleach showing acicula and emergent hook. (C) Di ff erent view of same chaetal bundle showing acicula, hook and manubrium. Abbreviations: ac, acicula; h, hook; ma, manubrium.

Figure 8. Phylogenetic relationships of the new Mesomyzostoma species: single most parsimonious tree resulting from the combined dataset alignment. Numbers above and below branches indicate support values> 50 % obtained in the maximum likelihood (100 bootstrap pseudoreplicates) and maximum parsimony analyses (1000 jackknife replicates), respectively. An asterisk (*) indicates> 95 % support for both analyses. There was low support for the relationships among the various Mesomyzostoma species and the maximum likelihood and maximum parsimony results showed some topological di ff erences. Uncorrected pairwise distance percentage values for COI sequences for Mesomyzostoma species from di ff erent localities or with obvious divergences are given. These are specimens of M. botulus sp. nov. from Papua New Guinea and Australia, M. cf. reichenspergeri from Papua New Guinea (PNG) and Australia, M. lanterbecqae from PNG. Unfortunately COI comparisons were not possible between M. katoi (Japan) and M. cf. katoi (PNG) and between Mesomyzostoma B and M. lobus sp. nov. Hypomyzostoma fasciatum was used as outgroup in the analyses, but excluded from the fi gure.