Archeterokrohnia docrickettsae, Thuesen, Erik V. & Haddock, Steven H. D., 2013

Thuesen, Erik V. & Haddock, Steven H. D., 2013, Archeterokrohnia docrickettsae (Chaetognatha: Phragmophora: Heterokrohniidae), a new species of deep-sea arrow worm from the Gulf of California, Zootaxa 3717 (3), pp. 320-328 : 321-322

Archeterokrohnia docrickettsae n. sp.

( Figs 1–4 )

Etymology. Named for the Monterey Bay Aquarium Research Institute’s ROV Doc Ricketts, in turn named in honor of marine biologist Ed Ricketts, co-author of Sea of Cortez (Steinbeck & Ricketts 1941) and inspiration for the character “Doc” in the novel Cannery Row (Steinbeck 1945).

Material examined. Holotype: The single specimen of this species is deposited in the Santa Barbara Museum of Natural History (SBMNH)—a mature individual, 28.5 mm total length captured at 3245 m depth, at the north end of Pescadero Basin in the Gulf of California, Mexico (24°22’2.47” N, 109°12’29.44” W), 24 February 2012 (SBMNH No. 235523).

Description. Total body length excluding tail fin (TL) 28.5 mm. Tail section 55.2% of TL. Head blunt when hooded, triangular after preservation, head width 3.5 mm. Hooks 15/15, slender brown, dorsalmost three hooks on each side smaller. Anterior teeth 11/10, with wide bases of uneven sizes. Posterior teeth 4/4, small, about 25% length of anterior teeth, clustered together in front of a plate at posteriormost part of vestibular organ. Vestibular organ located laterally on both sides of anterior teeth, joining together in an extension below posterior teeth and ending in a plate with small denticles. No vestibular papillae observed. Apical organ triangular, protruding from hood while alive. Eyes absent. Corona ciliata horseshoe-shaped. Trunk section of fairly uniform width (4.0 mm); body begins to taper posteriorly at tail/trunk junction. Body with slight ventral bend at tail/trunk junction; trunk section bright orange throughout in life. Anterior part of gut forms red esophagus once preserved; gut ivorycoloured and opaque. Transverse musculature 80% of trunk, 17% of tail. Ventral ganglion beginning at midpoint of trunk section, embedded within alveolar tissue on posterior half of trunk section, robust and elongated. One pair of lateral fins, rayed, starting just anterior of tail/trunk junction extending to the seminal vesicles. Small extension of each lateral fin ending in a ciliary fence, slightly posterior of anus. Ovaries cob-like, with many ova of different sizes. Annex gland present; annex gland diverticulum not observed. The specimen had mated, and each seminal receptacle contained a sperm packet. Seminal vesicles with inner core clearly differentiated from outer section; both parts ‘hooked’ anteriorly. Tail fin reaching posterior part of seminal vesicles, its form spathulate with 6 prominent ciliary fence organs on both ventral and dorsal sides. Further diagnostic information is given in Table 1 .

Remarks. This species is placed in the genus Archeterokrohnia on the basis of its extensive transverse musculature (~80% or more of the trunk section), a tail section that is 50% or more of the total body length, transverse musculature present in the tail section, a single lateral fin, and apical head organs. At 28.5 mm in length, A. docrickettsae is the largest species in the genus. Comparisons with the other three species of Archeterokrohnia are given in Table 1 based on the information summarized in Kapp (1991), following her format. A short artificial key is presented below to readily distinguish the four species of Archeterokrohnia .

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Figures

FIGURE 1. Archeterokrohnia docrickettsae n. sp., holotype. A, lateral view, shortly after recovery aboard ship. B, dorsal view, shortly after recovery aboard ship. C, dorsal view, after 4 months preservation in 5 % formalin / seawater. Total length (not including tail fin) 28.5 mm. Scale bar: 2 mm.

FIGURE 2. Archeterokrohnia docrickettsae n. sp., holotype. A, ventral view. B, ventral ganglion, preserved specimen. Scale bars: 1 mm. Abbreviations: vg, ventral ganglion; ov, ovary; ag, accessory gland.

FIGURE 3. Head of Archeterokrohnia docrickettsae n. sp., holotype. A, ventral view of living specimen with apical gland protruding from beneath the hood. B, ventral view of preserved specimen with teeth / hooks. Scale bars: 0.5 mm. Abbreviations: at, anterior teeth; h, edge of hood; pt, posterior teeth; vp, vestibular plate.

FIGURE 4. Archeterokrohnia docrickettsae n. sp., holotype. A, trace of corona ciliata. B, lateral fins. C, seminal vesicles and tail fin. Scale bars: 1 mm.

Tables

TABLE 1. Morphological characteristics and distribution information for Archeterokrohnia docrickettsae sp. nov. and the three other species belonging to the genus Archeterokrohnia modified from the summary of Kapp (1991) with additional information from Casanova (1991).

Characteristic A. docrickettsae	A. longicaudata A. palpifera	A. rubra
sp. nov.	(Hagen & Kapp, 1986) Casanova, 1986	Casanova, 1986
Total length (TL) 28.5 mm	12.9 mm 7.1 mm	27.0 mm
Tail length 55.2% of TL	56% of TL 54.8% of TL	50–52% of TL