Choneteuthis tongaensis, Lu, C. C. & Boucher-Rodoni, R., 2006

Lu, C. C. & Boucher-Rodoni, R., 2006, A new genus and species of sepiolid squid from the waters around Tonga in the central South Pacific (Mollusca: Cephalopoda: Sepiolidae), Zootaxa 1310, pp. 37-51 : 39-50

Choneteuthis tongaensis sp. nov.

( Figs. 1–4 )

Type material: HOLOTYPE: MNHN 3820, Tonga Islands: N Ha’apai group, 19°42’S, 174°26’W, depth 332m, N/O Alis, Cruise Bordau 2, stn. CH 1579, 11 June 2000, 1M, 33.8mm, mature; Coll. Bouchet, Warén & Richer. (Tentacles missing).

PARATYPES: MNHN 3821, Same station as Holotype. 1M, head only. (Paratype 1) MNHN 3822, Tonga Islands: Seamount, 22°11’S, 175°27’W, depth 385–405m, N/O Alis, Cruise Bordau 2, stn. CH 1609, 16 June 2000, 1F, 24.3mm, subadult; Coll. Bouchet, Warén & Richer. (Tentacles missing). (Paratype 2)

Diagnosis: Animal reaches large size to at least 33.8 mm ML. Nuchal cartilage well developed, not fused to mantle. Web formula D.A.E.C.B. in male, deepest web 27–29% of longest arm; D.C.B.A.E. in female, deepest web 38% of longest arm; web joining dorsal arm pair shallow, about 10% of longest arm length in male, 14% in female. Eye orbit well developed. Aqueous pore absent. Club suckers in 6 series. Several enlarged suckers present on ventral series of arm II in males. Funnel long, tubular, not covered by mantle. Round photophore on ink sac.

Description: Measurements, indices and counts for specimens are presented in Table 1 .

Mantle ( Fig. 1 A,B) ovoid, longer than wide. Mantle not fused to nuchal cartilage by a broad muscle band. Ventral mantle wall not extended anteriorly to cover funnel ( Fig. 1 B). Head ( Figs. 1 A,B) wide, slightly narrower than mantle. Head length about 53% ML. Eyes large, elliptical, located dorsolaterally on head. Cornea membrane ( Fig. 1 C) attached to head along dorsal margin to lower posterior corner of eye orbit, leaving eye orbit unattached to eyeball from lower posterior corner along ventral margin to upper anterior corner. Olfactory papilla and ventral photosensitive vesicle not found. Nuchal fixing apparatus cartilaginous, mantle member long ridge with wider anterior end ( Fig. 2 A), head member with long groove surrounded by thin edge, groove matches mantle ridge ( Figs. 2 A,B). Funnel ( Figs. 1 B,D) large, elongate and tubular for majority of its length; length over 60% ML and free from head for about 75% of funnel length. Funnel connects to head by oblique muscle band that extends from beneath anterior end of funnel locking cartilage to ventral side of head. Funnel organ ( Figs. 2 C,D) large; ventral elements long, slender, close to each other, located forward to dorsal element; dorsal element long triangular shaped with slightly convex shoulders and concave bottom, with a thick ridge that runs along anterior half of midline, terminates as a slender, long papilla at apex. Funnel valve well developed on dorsal roof, triangular with pointed anterior tip situated close to funnel aperture ( Fig. 1 D).

Diameter of photophore 9.5(l)x7.3(w) 28.11x 8.4(l)x6.6(w) 34.57x (mm) 21.6 27.16 Mantle locking cartilage ( Figs. 3 A,B) simple, curved, raised ridge with well­defined edges and tips; anterior tip arises from mantle aperture, rapidly increases in height to about two thirds of ridge length, then gradually decreases in height posteriorly. Funnel locking cartilage ( Figs. 3 A,B) shoe­shaped with wider anterior end, depression curved, matching mantle locking cartilage.

Fins ( Figs. 1 A,B), large, ear­shaped with rounded posterior end, attached obliquely along dorso­lateral mantle; anterior fin insertion at level about 10% mantle depth (from dorsal surface); posterior fin insertion at level of dorsal mantle surface. Anterior edge of fins curved, free from mantle for 16% of fin length; fin attachment length about 40% ML. Anterior point of fin attachment about 34–42% ML from anterior mantle margin; anterior tip of fins 26–27% ML from anterior margin of mantle. Posterior point of fin attachment about 24–32% ML from posterior margin of mantle; posterior tip of fins 9–23% ML from posterior mantle margin.

Arms short with attenuated tips, flange­like ridges present along aboral midline of arms I, III and IV, indistinct on arm II in both sexes. All arm suckers globular, attached to arms by pedicels of variable development, chitinous ring with smooth edge present on all suckers.

Male arm formula 2=3.1.4. Suckers in two series on all arms to arm tip. Suckers on arms I and IV diminish in size gradually from base distally; suckers on dorsal row of arms II increase in size from base distally to about middle of arm then decrease in size distally to tip, suckers on ventral row of arms II increase in size from base distally to about middle of arm, followed by 3 or 4 abruptly enlarged enormous and somewhat flat suckers, then decrease in size distally to tip; suckers on dorsal row of arms III increase in size from base distally for 3 or 4 suckers, followed by 2 or 3 abruptly enlarged suckers to about middle of arm, then decrease in size distally to tip, suckers on ventral row of arm III decrease in size distally to tip, no abruptly enlarged suckers on ventral row.

Female arm formula 2.3.4.1. Suckers in two series on all arms to arm tip. Suckers on arms increase in size from base distally to about middle of arm, then decrease in size distally to tip. No enlargement of any suckers.

Club only known for male (Paratype 1) ( Fig. 3 C), slender, slightly expanded, and curled, pointed at distal tip; covered with many small stalked suckers in about 6 longitudinal series. Protective membranes well­developed. Proximal to club, tentacular stalk nearly round in cross section. Swimming keel lines close to dorsal protective membrane, from tip of club to just beyond carpal region, keel widest along manus of club. Tentacular stalk slenderer than arms. Club sucker rings with fine triangular teeth around entire edge.

Webs between all arms shallow, web formula in male D.E.A.C.B., web D about 30% of longest arm, web E and A subequal, about 10%, webs C equal to or slightly deeper than B, slightly shallower than E or A, about 8 to 5 %; web formula in female D.C.B.A.E., web D deepest, about 39% of longest arm, web C about 26%, webs B and A subequal, about 14%, web E shallowest, about 7%. Web D half encloses base of tentacles in both sexes.

Gills with 25–26 lamellae per demibranch, plus a terminal lamella.

Photophore present on ventral side of ink sac ( Figs. 3 A,D). Photophore embedded but distinct externally, cream­coloured, round. Orifices of photophore distinct. Membranous extension of mantle adductor muscle connects midline of photophore and mantle adductor muscle, bisects visceral mass along ventral midline, mantle cavity divided into right and left halves. Anterior end of mantle adductor muscle expanded and incorporates rectum at a point just beyond photophore orifices, posterior to dorsal element of funnel organ. Anal flaps ( Figs. 3 A,D) large, distinct. Ink sac functional. Gladius rudimentary. Only the anterior half of mantle with thin, narrow gladius. Alcohol­preserved specimen brown in color: dark chocolate brown chromatophores scattered over brown colored background; dorsal mantle surface lighter than ventral surface.

Upper beak ( Fig. 4 A) with pointed, slightly curved rostrum. Lateral wall edge damaged, presence of depression unknown. Jaw angle nearly 90°. Cutting edge of shoulder irregular. Crest wide, slightly curved. Entire beak, except the margin, brown; rostrum and upper part of shoulder black; margin clear.

Lower beak ( Figs. 4 B,C) with slightly curved, irregular, sharp, thick edge. Jaw angle distinct. Shoulder tooth distinct, large. Anterior edge of shoulder irregular. Wings widely spread. Hood notch absent. Crest slightly curved. Indentation at posterior edge of lateral wall shallow. Entire beak, except the margin, brown; rostrum and anterior part of shoulder blackish brown, rostral tip black; margin clear.

Radula ( Fig. 4 D) with seven transverse rows of teeth of about equal length. Rhachidian teeth triangular, broad­based, without cusps, tapering to a fine point. First lateral teeth, narrow triangular, with wide heel, asymmetrical with tooth displaced toward the midline of radula, median side straight, outer side slightly curved. Second and third lateral teeth sickle­shaped with short base, second lateral teeth with pointed tip; third lateral teeth shorter than second lateral teeth, with blunt tip. Marginal plates absent.

Anteroventral surface (= ventral shield of Naef 1923) iridescent blue to violet; posterior and lateral aspects of ventral surface lighter brown. Whitish cover on ventral surface, gives posterolateral aspect of ventral surface creamy white appearance. Ventral surface of funnel brown from funnel aperture to the level of anterior margin of funnel locking cartilages, dorsal surface of funnel tube and ventral surface of base of funnel without chromatophores. Ventral surface of ventral arms creamy gold colored with welldeveloped skin ridge that runs from ventral side of eyeball, along both side of funnel to about mid­portion of ventral arms. Surfaces of fins devoid of color, except for a small, dark brown patch along dorsal surface of fin attachment. Skin smooth, papillae absent.

Etymology: The species epithet refers to Tonga, where these specimens were captured.

Distribution: Known only from the waters off Tonga, Pacific Ocean.

Discussion: Prior to the discovery of this new genus, 14 genera are recognized in the family Sepiolidae . Key characters of all the 15 genera are listed in Table 2 . The new genus differs from all other sepiolid genera in the following combination of characters: the unique long, tubular funnel not covered by the mantle; the shallow web uniting arms; the large, round photophore on the ink sac; the colored ventral shield; anterodorsal margin of mantle free from head; well developed nuchal cartilage; rudimentary gladius, and the absence of hectocotylized arms.

Appellöf (1898) erected three subfamilies for the family Sepiolidae , namely Sepiolinae , Rossiinae , and Heteroteuthinae . Nesis (1987) provided the following diagnoses for these subfamilies:

Sepiolinae Appellöf 1898 :

Anterior edge of mantle dorsally fused with head; anterior edge of mantle not extended forward ventrally, not covering funnel; 1st and 2nd arms not connected or connected only by shallow web; no nuchal cartilage; fins of moderate size, much shorter than mantle; left dorsal arms hectocotylized; gladius rudimentary or absent; a saddleshaped, 2­ears­shaped, or round luminous organ on ventral side of ink sac of some members of the subfamily; benthic animals, though some species ascend to surface during reproduction.

Choneteuthis gen. Sepiola Inioteuthis Euprymna nov.

Rondeletiola Sepietta Rossia Semirossia

Current subfamilial placement Sepiolinae Sepiolinae Rossiinae Rossiinae Nuchal cartilage developed + + + (only anterior ­ part of nuchal cartilage developed) or ­ Arms 1 & 2 connected by shallow web + (Arms I­III + (Arms I­III con­ + (Arms I­III connected by nected by deep connected by deep web) web) deep web) Photophore on ink sac + + + Functional ink sac + + + Gladius present ­ ­ ­ Mature male with enlarged arm suckers + + + Hectocotylized arm Both arms 1 Both arms 1 Both arms 1

Rossiinae Appellöf 1898 :

Anterior edge of mantle not fused with head on the back; anterior edge of mantle not extended forward ventrally, not covering funnel; 1st and 2nd arms not connected or connected only by shallow web; nuchal cartilage developed; fins of moderate size, much shorter than mantle; left or both dorsal arms hectocotylized; gladius present; a pair of luminous organs on ventral side of ink sac; benthic animals, though some species ascend to surface during reproduction.

Heteroteuthinae Appellöf 1898 :

Anterior edge of mantle dorsally fused with head; anterior ventral edge of mantle extended into extensive projecting ventral shield covering funnel from below and sometimes reaching level of eyes or farther forward; an incision for funnel mouth in center of ventral shield; first 3 pairs of arms joined by deep web; no nuchal cartilage; fins large, their length 60–100% of mantle length; usually both dorsal arms hectocotylized; gladius absent; a luminous organ on ventral side of ink sac; benthic (mainly bathyal) or pelagic animals.

The presence or absence of the morphological characters of Choneteuthis tongaensis among the various sepiolid genera are discussed below.

1. Web depth: The shallow web uniting the arms occurs in all genera except members of the subfamily Heteroteuthinae , which all possess deep webs connecting the dorsal 3 pairs of arms. The shallow web of Choneteuthis excludes it from Heteroteuthinae .

2. Photophore shape: The presence of a large, round photophore is also found in all members of the subfamily Heteroteuthinae . Photophores of different shapes are also found in Sepiola , Euprymna (both are Sepiolinae ) and Semirossia (Rossiinae) . A photophore is absent in the remaining genera of the family. The large round photophore in Choneteuthis it is most similar to that found in Heteroteuthinae .

3. Ventral shield: The presence of the colored ventral shield is only found in the members of the subfamily Heteroteuthinae except Sepiolina . However, the ventral shield of Choneteuthis does not extend forward to cover most of the funnel length.

4. Mantle­Head fusion: The non­fused condition of the anterodorsal margin of the mantle and the head is also found in all members of the Rossiinae and Heteroteuthis (Heteroteuthinae) . The presence of a free nuchal cartilage is only found in Rossiinae , and a partially developed nuchal cartilage is found only in Heteroteuthis dispar (but not in H. weberi ). The presence of a free nuchal cartilage in Choneteuthis places it in Rossiinae , and to a lesser degree in Heteroteuthinae .

5. Gladius: The presence of a gladius is found in all members of Rossiinae . A rudimentary shell is also present in Sepiola and Sepietta (Sepiolinae) . The presence of a rudimentary shell in Choneteuthis excludes it from Heteroteuthinae .

6. Hectocotylized arms: The absence of hectocotylized dorsal arms of the new genus is unique among all members of the family Sepiolidae . However, the presence of some enlarged suckers on certain lateral arms of mature males is found in all members of the family.

The above analysis indicates the new genus clearly does not belong to any of the presently recognized subfamilies of the family Sepiolidae . In some respects the new genus resembles the members of the Rossinae, i.e., the shallow web uniting the arms, the presence of a photophore, the presence of a free nuchal cartilage, and the presence of a gladius. The shape of the photophore of the new genus differs from that of Semirossia , the only genus in Rossinae with photophores. The presence of a colored ventral shield, the rudimentary nature of the gladius, and the absence of a hectocotylus also exclude Choneteuthis from Rossinae. Naef (1923) in discussing the position of Sepiolina , stated that “ Sepiolina is a transitional stage to the Heteroteuthinae before the other Sepiolinae , and the precise boundary between the two subfamilies is a matter of a feeling of form”. In Naef’s opinion, the boundary between the Heteroteuthinae and Sepiolinae is not clear­cut. The discovery of the new genus indicates the subfamilial divisions of the family Sepiolidae require further detailed analyses.

Figures

FIGURE 1. Choneteuthis tongaensis gen. et sp. nov. Photographs of holotype. A: dorsal view of whole animal; B: ventral view of whole animal; C: left lateral view of whole animal; D: ventral view of arm region.

FIGURE 2. Choneteuthis tongaensis gen. et sp. nov. A: Mantle and head members of nuchal cartilage. Photograph of paratype 1. (HNCart: head member of nuchal cartilage. MNCart: mantle member of nuchal cartilage. B: Head member of nuchal cartilage. Photograph of paratype 2. C: Funnel organs. Photograph of paratype 2. (DFO: dorsal member of funnel organ. VFO: ventral members of funnel organ). D: Drawings to illustrate relative positions of dorsal (DFO) and ventral (VFO) members of funnel organs with the funnel cut opened along the ventral mid­line.

FIGURE 3. Choneteuthis tongaensis gen. et sp. nov. (FLCart: funnel locking cartilage. MLCart: mantle locking cartilage. DFO: dorsal member of funnel organ. P: photophore.). A: Photograph of paratype 1, showing photophore, dorsal funnel organ, funnel and mantle locking cartilages. B: Photograph of paratype 2, showing funnel and funnel member of funnel­mantle locking apparatus. C: Photograph of tentacular club of paratype 2. D: Photograph of holotype, showing photophore, dorsal funnel organ, mantle member of funnel­mantle locking apparatus.

FIGURE 4. Choneteuthis tongaensis gen. et sp. nov. Paratype 2. A: Side view of upper beak. B: Side view of lower beak. C: Top view of lower beak. D. Radula.

Tables

TABLE 1. Measurements, counts and indices of Choneteuthis tongaensis gen. et sp. nov. from Tongan waters.

Specimen	Holotype	Index	Paratype 1	Index	Paratype 2	Index
Sex	M		M		F
Maturity	mature		probably mature		subadult
DML(mm)	33.8		head only		24.3
VML(mm) HL(mm)	29 18	85.8 53.3	­ 17.2		24 13.1	98.8 53.9
HW(mm)	17.5	51.8	20.1		14.2	58.4
NuCommW(mm) MW1(mm)	13.7 22.7	40.3 67.2	13 ­		10.7 17.4	44 71.6
MWmax(mm)	22.7	67.2	­		17.4	71.6

TABLE 2. Comparison of the genera in the family Sepiolidae.

Current subfamilial placement	?	Sepiolinae	Sepiolinae	Sepiolinae
Anterior ventral edge of mantle extended forward to cover fun­ nel	­	­	­	­
Colored ventral shield	+	­	­	­
Anterior dorsal edge of mantle fused with mantle	­	+	+	+
Nuchal cartilage developed	+	­	­	­
Arms 1 & 2 connected by shal­ low web	+	+ or ­	+ or ­	+ or ­
Photophore on ink sac	+	+	­	+
Functional ink sac	+	+	+	+
Gladius	+ (Rudimentary, only anterior half of man­ tle with gladius)	+ (Rudimentary)	­	­
Mature male with enlarged arm suckers	+	+ or ­	+	+ or ­
Hectocotylized arm	­	Left arm 1	Left arm 1	Left arm 1
continued.