Robsonella huttoni

Brief diagnosis: A small, coastal octopus species with biserial arm suckers, branching papillae above the eyes, and 69-74 suckers on the male's modified right third arm (hectocotylus).

Key morphological features:  

Head:

• The head is well developed and has one or two multi-branched ocular cirri. The surface is papillose, with each papilla being low and rounded (O’Shea, 1999).

Gill lamellae:

• There are 6-8 gill lamellae, but usually it is 7 (O’Shea, 1999).

Arms:

• The surface of the arms are papillose, with each papilla being low and rounded. All arms have enlarged 10th-13th suckers in adults. These enlarged suckers are not greatly raised from the arm surface.
• In males, the 3rd right arm is hectocotylised. On this modified arm, there are 69-74 suckers, of which the distal 6-11 pairs are enlarged (O’Shea 1999; O’Shea & Jackson, 2009).

This species is widespread throughout New Zealand’s shorelines between 0 and 386m in depth (O’Shea, 1999). It typically occurs in intertidal and subtidal reefs (O’Shea & Jackson, 2009). It is known to occur around all of New Zealand’s islands, including the sub-Antarctic islands, except for Campbell Island. Only larval specimens have been collected from Macquarie Island. It is also known from south Australia (O’Shea, 1999).

Colouration:

• Live specimens are highly variable in colouration and have been seen in red, orange and green. There are two iridescent patches behind the eyes. The arms are without bluish patches (O’Shea & Jackson, 2009).

Size:

• Small bodied, reaching an average overall length of 24cm and mantle length of 57mm (O’Shea, 1999).

Eggs:

• The eggs are 2.5mm in length and 1mm wide. They are entwined with each other to form string structures that range in length from 11mm to 25.8mm (Carrasco, 2013).

Hatchlings:

• Hatchlings have been measured at roughly 3mm in length and 1.55mm in width. The body is semitransparent and covered in small iridescent dots (Carrasco, 2013).

This species has been reported to lay 50-125 eggs per festoon with a total of 3800-6500 eggs total. Although reproduction may occur at any time throughout the year, it peaks during spring and summer. Embryo development length is temperature dependent, with a 44 day duration being reported at 17.3°C whereas at 12.7°C it was 158 days (Donlon et al, 2021).

One study reported that this species can live up to 250 days, but considered this to be an underestimation (Donlon et al, 2019).

Genetic evidence indicates that this species is most closely related to the Australian Octopus pallidus, and that it forms a clade with several New Zealand and southern hemisphere species. The genetic evidence also supported its transfer to the Robsonella genus (Ibáñez et al, 2020).  

So far, specimens from New Zealand that have been DNA barcoded (COI) form a single BIN (BOLD:AED8990) on the Barcode of Life Data System.  

Taxonomy and etymology

This species was first described as Octopus huttoni by William Benham in 1943 from specimens primarily caught in Otago, New Zealand. The species is named after notable zoologist Frederick Wollaston Hutton, who was the first to describe a species of octopus (Macroctopus maorum) from New Zealand (Benham, 1943). The most recent taxonomic redescription was in O’Shea (1999). It was transferred to the Robsonella genus in 2020 on the basis of genetic data (Ibáñez et al, 2020).

Conservation status and threats

Under the IUCN Red List, R. huttoni is listed as “Data Deficient” due to insufficient information about the general biology of this species (Allcock & Headlam, 2018). Due to the vulnerability of larval stages to high seawater temperatures, it has been suggested that the distribution of this species will shift southwards due to global warming (Higgins et al, 2012).

Synonyms

• Octopus adamsi Benham, 1944
• Octopus huttoni (Benham, 1943)

Common names

• Midget Octopus
• Club Pygmy Octopus

• Article about research cited here: https://www.orc.govt.nz/your-council/latest-news/news/2018/march/studying-midget-octopus/
• WoRMS species entry: https://www.marinespecies.org/aphia.php?p=taxdetails&id=342385