Crossota millsae, Thuesen, Erik V., 2003

Thuesen, Erik V., 2003, Crossota millsae (Cnidaria: Trachymedusae: Rhopalonematidae), a new species of viviparous hydromedusa from the deep sea off California and Hawaii, Zootaxa 309, pp. 1-12 : 3-4

Crossota millsae , new species

( Figs. 1­3 )

Synonymy. Crossota sp. A in Thuesen (1992) and Thuesen & Childress (1994).

Type material. All specimens are deposited in the Santa Barbara Museum of Natural History ( SBMNH). Holotype: a female specimen of 17 mm height with developing juveniles captured at 2540 m off Monterey, California, on dive 366 of the ROV Tiburon on October 4, 2001 ( SBMNH No. 349314). Paratype A: a male specimen of 12.5 mm height captured at 3244 m off Monterey, California, on dive 364 of the ROV Tiburon on October 2, 2001 ( SBMNH No. 349315). Paratype B: six juveniles captured in San Clemente Basin off Southern California using the Mother Tucker Trawl in March, 1995 ( SBMNH No. 349316).

Description. Bell reaching 28 mm diameter and 18 mm height. Inner bell pigment is burnt­tangerine; ring canal, 8 radial canals, manubrium and gonads are bright pink to lavender; mesoglea is colorless; peduncle is absent. Outer bell almost hemispherical to slightly cone­shaped with numerous exumbrellar furrows. Statocysts on short stalks (n =16, 2 per octant); velum thin reaching 35–55% of bell radius. Body more fragile than other species of Crossota . Up to 220 tentacles all in one row with rings of nematocysts; abscission zone ( Fig. 3 c) near base of each tentacle; remaining tentacle stubs usually display characteristic undulating fringe around bell; 11–13 stubs per undulation and two undulations per octant. Sexually dimorphic gonads attached ~ 4 mm from the manubrium.

Testes are pendant sausages ( Fig. 1 b) (can shrink to cones in preserved specimens); ovaries globular with eggs developing into juveniles while attached to the mother ( Figs. 1 c, d, 2). Juveniles (5 mm diameter) pink with orange tentacles, clear radial canals ( Fig 3 b). Juveniles (5 mm) with tentacles in groups (3–4 each), groups alternately per­ and interradial ( Fig 3 b).

Taxonomy. This species belongs to the genus Crossota due to its pendant gonads, exumbrellar furrows, lack of a peduncle, and absence of centripetal expansions into the ring canal ( Kramp 1968). These characteristics distinguish it from the closely related genera Vampyrocrossota Thuesen, 1993 , Benthocodon Larson & Harbison, 1990 and Vo ragonema Naumov, 1971 . This species is distinguished from other species of Crossota by its pigmentation, location of gonads and arrangement of the tentacle abscission zone that leaves a characteristic undulating fringe of tentacular bases following abscission. In previous keys to the genus Crossota ( Kramp 1959; 1968), Crossota millsae fails at the second couplet and falls intermediate between the two lugs. The gonads of C. alba are located slightly nearer to the ring canal than to the base of the manubrium. Crossota brunnea , C. rufobrunnea and C. norvegica all have gonads that cluster near the base of the manubrium. Below is a key to the four species of Crossota found in the Pacific Ocean based on Kramp (1968).

Figures

FIGURE 1. Crossota millsae, sp. nov. a) Lateral view of female specimen. Scale bar = 9 mm. b) Lateral view of male paratype specimen. Note the exumbrellar furrows. Scale bar = 5 mm. c) Oral view of female shown in Fig 1 a with developing juveniles. Scale bar = 9 mm. d) Aboral view of female with developing juveniles. Scale bar = 10 mm.

FIGURE 2. In situ video frame of Crossota millsae sp. nov. taken off California from the Monterey Bay Aquarium Research Institute’s ROV Tiburon. This is a female specimen with developing juveniles.

FIGURE 3. Crossota millsae, sp. nov. a) Two of the juvenile paratype specimens representing different stages of early development, scale bar = 2.5 mm. b) Two of the juvenile paratype specimens representing later stages of development, same scale bar as in Fig 3 a. c) Abscission zone at base of tentacles. ABS = abscission point, RC = ring canal, YIP = yellow iridescent pigment. d) Scanning electron micrograph of spermatids from testes of the male specimen shown in Fig. 1 b. Three size classes of spermatids are noted, A ~ 10 µm, B ~ 5 µm and C ~ 2 µm. The smallest spermatids have developing flagella. Scale bar = 10 µm.