Saturday, January 19, 2019

[Invertebrate • 2019] Polychaete meets Octopus: Symbiotic Relationship Between Spathochaeta octopodis gen. et sp. nov. (Annelida: Chrysopetalidae) and Octopus sp. (Mollusca: Octopodidae)

Spathochaeta octopodis
Jimi, Moritaki & Kajihara, 2019

Marine annelids in the subfamily Calamyzinae (family Chrysopetalidae) are either symbiotic or free-living forms that have been mainly reported from deep-sea chemosynthetic systems. Symbiotic calamyzines mainly live in the mantle cavity of bivalves in hydrothermal vents or cold seeps, but one species is also found to be inserted into the epidermis of polychaetes. We found a single specimen of calamyzine polychaete on the body surface of Octopus sp. collected in the Sea of Kumano (Japan), which represents the first known record of symbiotic association between polychaetes and octopuses. We described the specimen as Spathochaeta octopodis gen. et sp. nov. Spathochaeta gen. nov. can be discriminated from other genera in Calamyzinae by the presence of spatula-shaped notochaetae and dorsal chaetal lobes. We also provided the phylogenetic position of S. octopodis gen. et sp. nov. within Chrysopetalidae based on four gene markers (COI, 16S, 18S, H3). 

Key words: marine invertebrates; Pacific; parasite; phylogeny; Polychaeta; taxonomy

Fig. 1. Live specimen of  Spathochaeta octopodis gen. et sp. nov. on Octopus sp.
A, full view of the octopus: white arrow indicates the worm.
B, enlarged view of the worm on the octopus web. Scale bar: A, 1 cm.

Chrysopetalidae Ehlers, 1864 
Calamyzinae Hartmann-Schröder, 1971 

Spathochaeta gen. nov. 
[New Japanese name: tako-yadori-gokai-zoku]

 Type species: Spathochaeta octopodis gen. et sp. nov.

 Etymology: The new genus name, feminine in gender, derives from the Latin spatha (spatula) and chaeta (mane, hair), referring to the spatula-shaped notopodial chaetae, which are characteristic for the new genus. 

Remarks: Within Calamyzinae, notopodia having notochaetae are found not only in Spathochaeta but also in Boundemos Watson et al., 2016; Microspina Watson et al., 2016; and Vigtorniella Kiseleva, 1992 (Aguado et al., 2013; Kiseleva, 1992; Watson et al., 2016). Spathochaeta differs from these three genera in having dorsal chaetal lobes and simple spatular chaetae on notopodia. The molecular analysis indicated the new genus is sister to Calamyzas Arwidsson, 1932 (see 'Molecular analysis' sectionbelow). The new genus can be discriminated from Calamyzas by the following features: (i) absence of dorsal lobe; (ii) absence of notochaeta; (iii) having only one type of chaeta (compound chaeta) (Aguado et al., 2013).

 Spathochaeta octopodis gen. et sp. nov. 
[New Japanese name: tako-yadori-gokai]

Etymology: The new specific name is a noun in the genitive case of the Latin octopus, indicating the host organism of the new species. 

Habitat: Spathochaeta octopodis gen. et sp. nov. was collected from the external body surface of Octopus sp. (Fig. 1). Our observation that the living specimen of S. octopodis kept attaching on the octopus’ body surface for three days strongly supports a symbiotic relation between the species and the octopus, instead of an accidental attachment. When alive, the worm was observed to move around from the mantle to web of the host octopus. However, further findings and observations on the behaviour of the species are required to confirm the postulated symbiotic association. The octopus was collected from off Owase, the Kumano Sea, off central Japan, eastern North Pacific, 150 m depth.

Naoto Jimi, Takeya Moritaki and Hiroshi Kajihara. 2019.  Polychaete meets Octopus: Symbiotic Relationship Between Spathochaeta octopodis gen. et sp. nov. (Annelida: Chrysopetalidae) and Octopus sp. (Mollusca: Octopodidae).  Systematics and Biodiversity. DOI:  10.1080/14772000.2018.1520753  

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