Octophialucium irregularis, Peter, 2021

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 310

Octophialucium irregularis n.spec.

Fig. 45 A-G

Holotype: BFLA4290 ; observed and collected 19-DEC-2019; size 12 mm, with incipient gonads; part preserved in formalin and deposited as UF-013843 , part preserved in alcohol for DNA extraction (MHNG- INVE-0137379); 16S sequence MW528701 .

Other material: BFLA3829 ; 1 specimen; 15-NOV- 2018; size 4 mm, juvenile; preserved in alcohol for DNA extraction; 16S sequence identical to MW528701 . – BFLA3838 ; 1 specimen; 19-NOV-2018; size 7 mm, without gonads; preserved in alcohol for DNA extraction; 16S sequence identical to MW528701 . – BFLA4131 ; 1 specimen; 11-JUN-2019; size 12 mm, without gonads; part preserved in formalin and deposited as UF-013807 , part preserved in alcohol for DNA extraction; 16S sequence identical to MW528701 . – BFLA4259 ; 1 specimen; 30-NOV-2019; size 8 mm, incipient gonads; part preserved in formalin and deposited as UF-013838 , much damaged, part preserved in alcohol for DNA extraction; 16S sequence identical to MW528701 . – BFLA4311 ; 1 specimen; 15-JAN- 2020; size 5 mm, no gonads; preserved in alcohol for DNA extraction; 16S sequence identical to MW528701 . – BFLA4377 ; 1 specimen; 18-MAR-2020; size 6 mm, no gonads; preserved in alcohol for DNA extraction; 16S sequence identical to MW528701 .

Description: Bell diameter 8-12 mm for animals with gonads, bell rather shallow, apical jelly about half of height and subumbrella relatively shallow, soft walls and rim deformed easily. Velum narrow. Manubrium cross-section like a multi-rayed star ( Fig. 45 A-C, G), as many rays as radial canals, multirayed outline present from base to mouth, diameter narrowing towards mouth, mouth with about eight lips. Occasionally a secondary manubrium may be present. Radial canals 7-9, originating from manubrium rays, initially broad and then tapering, sometimes also one incomplete centrifugal canal present that does not reach circular canal. Arrangement of radial canals irregular, some irregularly curved, branching once, sometimes coalescing again or fusing with other radial canals, general appearance very variable, irregular, and disordered ( Fig. 45A, D, G, F ). Gonads arise in middle region of complete radial canals, oblong, slightly pendant ( Fig. 45C ), fully developed state unknown. Circular canal thin, in larger animals with incomplete centripetal canals arising from non-perradial bulbs, reaching about to mid-subumbrella height ( Fig. 45D ). Tentacles 27 to 30, on ovoid marginal bulbs which taper rapidly into thin tentacles, these often neatly coiled when contracted ( Fig. 45E ); bulbs with adaxial excretory papilla pointing into subumbrella, size variable, sometimes relatively large ( Fig. 45C ). Between tentaculate bulbs 1 to 3 smaller bulbs with very short tentacle ( Fig. 45E ) or without tentacle. Between successive marginal bulbs 1 to 3 closed statocysts with 2 statoliths ( Fig. 45 D-E). Colours: orange gastrodermis of tentaculate marginal bulbs, gonads orange; manubrium in younger stages transparent green ( Fig. 45G ), later whitish, sometimes at base in interradial position orange ( Fig. 45A ) or a weak interradial, brown pigment band from base to mouth ( Fig. 45C ).

16S Data: The seven specimens gave all an identical 16S sequence. The single haplotype ( MW528701 ) was used in a blastn search in GenBank and gave as best match with 93% identity an Octophialucium indicum from New Zealand ( AY787897 ). The pairwise identities with the 16S of O. aphrodite were lower, about 88%. A maximum likelihood tree using a wide selection of leptomedusae did not yield any well supported relationship (tree not shown).

Remarks: There are currently 11 accepted species of Octophialucium ( Schuchert, 2020) . In terms of size and tentacle numbers, the new species resembles only Octophialucium mollis Bouillon, 1984b , a species known from the tropical Western Pacific Ocean. Octophialucium mollis is also the only Octophialucium species that has centripetal canals. Octophialucium irregularis differs from O. mollis in the following aspects: it lacks the interradial rows of black spots on the manubrium wall (although in some there is a faint brown band, see Fig. 45C ), the centripetal canals are longer, and the radial canals are very irregular in appearance and number. The latter feature is the most characteristic trait of this species and its specific epithet irregularis is intended to reflect this. This irregular organisation is likely not only due to genetic factors, but – as irregularities of the bell margin suggest ( Fig. 45A, G ) – also due to repeated damage and subsequent regeneration.

Figures

Fig. 45. Octophialucium irregularis n. spec. (A) Holotype, BFLA4290, aboral view, 12 mm diam. (B) BFLA4290, lateral view of manubrium. (C) BFLA4259, 8 mm, partial lateral view, arrow points to excretory papilla. (D) BFLA4259, oral view, arrow points to centripetal canal. (E) BFLA4259, bell margin, lateral view. (F) BFLA4131, 12 mm diameter, aboral view, arrow points to secondary manubrium. (G) BFLA3838, 7 mm oral view, arrow points to incomplete centrifugal canal.