Octopus rapanui, new species, is described from Easter Island. It is distinguished from other Indo-Pacific species by a combination

of characters including the shape of the lower mandibular rostrum, long rachidian radular teeth, large secondary diverticulum of the penis and long, slender posterior salivary glands

Voss, Gilbert L.

OceanRep

PROC. BIOL. SOC. WASH.92(2), 1979, pp. 360-367OCTOPUS RAPANUI, NEW SPECIES, FROM EASTERISLAND (CEPHALOPODA: OCTOPODA)Gilbert L. VossAbstract.—Octopus rapanui, new species, is described from Easter Is-land. It is distinguished from other Indo-Pacific species by a combinationof characters including the shape of the lower mandibular rostrum, longrachidian radular teeth, large secondary diverticulum of the penis and long,slender posterior salivary glands.In 1977 I received a small octopus for identification, collected at EasterIsland by B. Alarcon and sent to me by Harald A. Rehder, SmithsonianInstitution. The specimen was immature and in poor condition, but thebeaks and radula were different from others I have examined from the Pa-cific. A search through the collections at the Rosenstiel School of Marineand Atmospheric Science, University of Miami, brought to light eight morespecimens, some sexually mature but all in poor condition. These specimenswere collected by Ian E. Efford and Jack Mathias, University of BritishColumbia, on the Medical Expedition to Easter Island. Examination of allof the specimens convinced me that they represent a new and undescribedspecies. A survey of the cephalopod literature has revealed no record of anoctopod from Easter Island although the islands were visited by several ofthe major expeditions of the 18th and 19th centuries. Thus this speciesrepresents the first octopod to be included in the faunal reports of EasterIsland.Octopus rapanui, new speciesFigs. 1,2Holotype.—Male, mantle length 115 mm, F82, rotenone at Hanga Piko,Easter Island, Efford and Mathias, leg., 14 January 1965, USNM 729860.Paratypes.—2 males, mantle lengths 97-113 mm, 1 female, mantle length69 mm, F82, rotenone at Hanga Piko, Easter Island, Efford and Mathias,leg., 14 January 1965, USNM 729990.— 1 female, mantle length 90 mm,M12, Apina Iti, Easter Island, Efford and Mathias, leg., 18 January 1965,UMML 1746.— 1 male, mantle length 70 mm, 1 female, mantle length 107mm, "collected in about 12 feet of water. Bottom rocky; in a sheltered cove.Caught at about 4:30 p.m." Vinapu, Easter Island, Efford and Mathias, leg.,25 January 1965, UMML 1742.— 1 male, mantle length 88 mm, rotenone insubtidal pool near camp at Hanga Roa, Easter Island, Efford and MathiasJVOLUME 92, NUMBER 2 361leg., 5 February 1965, UMML 1743.— 1 female (?), mantle length 27 mm,Sta. E-37, in tide pool, B. Alarcon leg., Hanga Piko, Easter Island, 2 No-vember 1974, USNM 751587.Description.—The mantle is somewhat cyHndrical and rather narrow ex-cept in one specimen (MWI males 41^9.5-74; females 51-56.<^-63); thehead is set off from the mantle by a slight constriction. The head is narrow(HWI males 29-J7.6-49; females 3^-^4.8-52) and bears small eyes. Themantle aperture is wide.The funnel is large, free for about half of its length. The funnel organ isindistinct but appears to be W shaped with the outer limbs a little longerthan the median ones.The arms are long (MAI males 13-25.^-27; females 22-24.0-2^: ALImales 75-80.6-96; females 76-75.5-80), stout basally but tapering to longslender tips. The arm order is usually I. II. III.IV, but is somewhat variable,although I is almost always the longest and IV the shortest. In the femalesI is always the longest but in the males I was longest in two, II longest inthree. The suckers are biserial and moderately large (Sin males 9-10.2-11;females 9-77.5-15). There are no specially enlarged suckers in the males.The third right arm of the male is hectocotylized. It is shorter than thethird left arm (HAI 12-84-95) and has a conspicuous spermatophoralgroove. The ligula is small (LLI 1.4-2.5-4.0), medially excavated with thick-ened margins. The calamus is small but distinct (CLI 28.5-52.7-33.3). Aninteresting and possibly distinctive feature is best shown in the holotype.The spermatophoral groove at the base of the calamus widens and deepensinto a pocket-like depression. It is visible but less distinct in other males ofthe species. The male with a mantle length of 88 mm had lost the major partof its hectocotylized arm but a new ligula had been produced that measured1.8 mm complete with a calamus.The web order cannot be ascertained if there is one, for it is extremelyvariable. The web is rather low but it extends up the ventral side of thearms to near the distal third or further (WDI males 19-27.2-22; females 18-19.8-22).The gills bear 11 to 12 lamellae on the outer demibranch.The digestive tract was dissected out. It shows many unusual features.The buccal mass is more elongate than in the typical Octopus. The upperbeaks are normal but the lower beaks have a nearly straight rostrum thatprojects forward Hke a spine. The radula is normal except for the very longand slender rachidian teeth. The rachidian shows a 64.7 asymmetry. In thesmallest specimen of 27 mm mantle length the rachidians are very long andslender with a possibility of three cusps on one side and two on the other.In the male of 88 mm mantle length the rachidians are somewhat shorterand broader with two to three cusps on one side with a B7 order, while362 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTONFig. L Octopus rapanui: a, Lateral view of male, mantle length 88 mm; b, Radula of female,mantle length 107 mm; c, Radula ofjuvenile female (?), mantle length 27 mm; d, Digestive tractfrom female, mantle length 90 mm; e, Genitalia from male, holotype; f, Genitalia from female,mantle length 90 mm.VOLUME 92, NUMBER 2 363Fig. 2. Octopus rapanui: a-b, Upper and lower mandibles of female, mantle length 107mm; c-d, Upper and lower mandibles of male, mantle length 70 mm; e, Hectocotylus ofholotype.there are only two cusps on the other side with a 64.5 order. In bothspecimens the third laterals are hooked at the tip. Both have marginal plates,those of the smaller poorly formed and indistinct.The anterior salivary glands are large, somewhat free from the buccal massand closely embrace the esophagus. In the 88 mm length male these glandsare darkened, leaflike, and curled away from the esophagus. The second orposterior salivary glands have exceptionally long and stout ducts. Theglands themselves are long, stout anteriorly and taper posteriorly. They arevery large. The esophagus is long and in its posterior third enters the cropwhich is composed almost in its entirety of an exceptionally large caecumfree for about "^/s of its length.The short posterior esophagus leads into the typical bipartite stomach.The spiral caecum is large and strongly coiled. The digestive ducts lie sin-gularly close together and lead into the strongly bilobed digestive gland nearthe midline. The digestive gland is long and tubular. There are no surfaceindications of the digestive duct appendages which may, however, be bur-ied.The intestine is exceptionally long and tripartite. The anus bears twoslender anal flaps. The ink sac is long, runs the length of the digestive gland364 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTONTable 1. Measurements (in mm) and counts of 5 males of Octopus rapanui.Paratypes HolotypeMantle length 70 88 97 113 115Mantle width 32 65 45 47 47Head width 27 43 32 43 33Arm length L R L R L R L R L RI 262 235 379 71 + 296 301 360 156 275 354II 246 206 370 359 290 368 353 373 418 272III 218 208 328 75+ 322 231 278 240 210 279IV 170 186 332 303 281 276 217 313 209 374Total length 336 393 475 500 550Arm width 11 22 12 14 14Hect. Arm length 208 75+ 231 240 279Ligula length 3 1.8»> 9 7 9Calmus length 1 0.45 3 2 3Sucker diameter 7 9 11 12 10Web depth 43 48.5i 40 71 8330 50 61 58 58 78 84 61 77 7351 49 82 48 80 58 70 58 80 6631 41 76 53 38 62 50 60 78 3223 51 78 60 72Gill lamellae 11 12 12 12 12and is deeply set into it. The free duct is very long, strongly convoluted atthe proximal end, then straight, but looped several times at the distal end.It enters the intestine just proximal to the anus.The female genitalia consist of a large round posterior ovary with pairedoviducts and glands. The proximal oviducts are short and narrow. Theoviducal glands are spherical with a dark band around the middle. The distaloviducts are long and a Httle stouter than the proximal ones. No matureeggs were seen.The male genitalia were dissected out of two specimens. The penis isstout with a long penial diverticulum and a short stout supplementary di-verticulum at the midpoint at the juncture with the duct from Needham'ssac (PL! 20-29). Needham's sac is rather small but with a long accessorygland.Two of the males had spermatophores. These were long (SpLI 66-75),slender, with large sperm reservoirs (SpRI 42.3-43.4). There were no un-usual morphological features.The specimens were all in a poor state of preservation and little can betold concerning their original coloration. They appear to be somewhat flesh-colored ventrally with a darker purpHsh cast dorsally. The dorsal and lateralsurfaces of the mantle, head and arms are covered with scattered but prom-VOLUME 92, NUMBER 2 365Table 2. Measurements (in mm) and counts of 4 females of Octopus rapanui.ParatypesMantle length 27 69 90 107Mantle width 17 35 54 57Head width 14 28 43 41Arm length L R L R L R L RI 115 86 310 156 394 364 387 383II 104 111 291 296 389 321 321 370III 99 86 264 271 380 271 193 381IV 93 97 226 234 336 349 335 331Total length 144 387 500 508Arm width 6 9 14 16Sucker diameter 4 7 10 10Web depthsector A 17 49 69 68B 23 21 57 47 68 69 38 29C 19 25 53 34 55 57 67 64D 16 22 51 34 81 40 60 58E 19 34 33 68Gill lamellae 11 11 11 12inent tubercles. Some of the tubercles over the eyes are somwhat largerthan the others but not sufficiently so as to be called cirri.Type Locality.—Hanga Piko, Easter Island.Etymology.—This octopus is named for Easter Island which in the nativelanguage is called Rapa Nui. The specific name is, therefore, a noun inapposition.Discussion.—Octopus rapanui is unusual in a number of aspects andshows no close relationship with any of the other species of the genus inthe Indo-Pacific. While it might be grouped with those species having longfirst arms such as Octopus macropus and O. ornatus, it differs in so manyother features that this relationship cannot be seriously considered. One ofthe distinctive features is the secondary diverticulum of the penis. This isunusual in the octopods and is not known in other species of Octopus sensustricto. Most of the other distinguishing characters are associated with thedigestive tract. The straight spine-like rostrum of the lower beak is knownso far only in Pareledone polymorpha (Robson, 1930) in which this featureis even more accentuated. Associated with this is the very long rachidianteeth of the radula which are longer (in the young specimen) than in anyother known octopod. These two features suggest a specialized diet, perhapsbarnacles or some type of bivalve. There are no indications of food in anyof the stomachs or crops investigated. Other speciaHzed features are thevery long, slender but large second salivary glands, the comparatively enor-mous crop, elongate digestive gland, and the long tripartite intestine.366 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON5(/3So(/)<->coc(/)e,0(/3cOOouo0)O'•BGO m>o '—( On 00 \0 (N-^-^ (N CN r-- —^VO Tt<7s^^f*^rnt-^\Or4m'I>en (N "sOQPQ <NON 10m tN 00 m lo <N m^-" Tf m '^ r^ —H f\i -H 00^ <l-H PQt- \o m vo t^ rj (NON -^ m rvi t^ ^H r^ r4om ONen CN<QPQUrsi00Tta\m>oio(NO0Or~~^(NON<N<N^^ PQQUI—I no <NO^0Nr^0N^0\O>O'^rnO <QPQUo X X^3 T3X! -s .s^.-2.S CSocj^ ^ 36-S.5 Xa.S_aj ^ -^ (u <u ^ -5*-' +3 n-l T3 '^T3-tiD TO(U6 6< < > OD ffiX(UX 73(U c•£ :S*-' G60 (UC '~—' 3JS s3 cdJ U^ XT3 .5 C— £ j=C (U <uPL, C/2 00Xcc/3 3 3 ^Se e 6 13u, u ecJ? < ^ OIIVOLUME 92. NUMBER 2 367Table 4. Indices of bodily proportions, formulas and counts of 4 females of Octopus ra-panui.Mantle length 27 69 90 107Mantle width index 63 51 60 53Head width index 52 41 48 38Mantle arm index 23 22 23 28Arm length index 80 80 78 76Arm width index 22 13 15 15Web depth index 22 18 21 18Sucker index normal 15 10 11 9Arm formula I. II. III.IV I.II.III.IV I.II.III.IV I.II.III.IVWeb formula BCDEA BCDAE DA = BCE A = BCDEGill lamellae 11 11 11 12Easter Island is a high island with steep-to shores where competition forfood is probably intense; hence an adaptation to a favorable food nichewould be more valuable and perhaps reinforced than in the more widespreadcoral reef habitats of the other areas of the tropical Pacific.While this species appears to be distinct, the description of any newspecies of Octopus from the Pacific must be approached with caution. Ex-ternal characters would not have sufficed to distinguish this species fromothers, but it should also be noted that we know little of the internal anatomyof Pacific octopods in general, and it is possible that future work may showthis combination of characters in another named species. Until then it seemsbest to regard O. rapanui as a new and distinctive member of the Indo-Pacific octopod fauna.AcknowledgmentsI with to thank Dr. Harald A. Rehder of the Smithsonian Institution andDrs. Ian E. Efford and Jack Mathias of the University of British Columbiafor the opportunity to study the material described above. The illustrationof the whole animal is by Charles Messing; the remainder by Banjong Mian-manus and the writer.This work was supported by National Science Foundation grant DEB 76-03456 which is gratefully acknowledged. This paper constitutes a scientificcontribution from the Rosenstiel School of Marine and Atmospheric Scienceof the University of Miami.Literature CitedRobson, G. C. 1932. A monograph of the recent Cephalopoda based on the Collections in theBritish Museum (Natural History), Part II The Octopoda (excluding the Octopodinae).—The British Museum, London, pp. 1-359, 79 figs., 6 pis.Rosenstiel School of Marine and Atmospheric Science, University ofMiami, 4600 Rickenbacker Causeway, Miami, Florida 33149.

Octopus rapanui, new species, from Easter Island (Cephalopoda: Octopoda)

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