Freyella benthophila Sladen, 1889

Freyella benthophila Sladen, 1889 View in CoL

Fig. 11 View Figure 11

Freyella benthophila View in CoL : Sladen 1889: 641; Wood-Mason and Alcock 1891: 440; Alcock 1893: 121; Fisher 1928: 24; Madsen 1951: 84; Cherbonnier and Sibuet 1972: 1356; Sibuet 1975: 292; Korovchinsky and Galkin 1984: 1215 (in key); Galkin and Korovchinsky 1984: 165; Zhang et al. 2024: 17.

Freyellidea benthophila View in CoL : Fisher 1917: 429.

Freyastera benthophila View in CoL : Downey 1986: 36; McKnight 1993: 173; Mah 1998: 78; Mah in Clark and Mah 2001: 318; Dilman 2014: 38; Moreau et al. 2015: 16; Moreau et al. 2018: 147; Zhang et al. 2019: 7 (in key).

Belgicella racowitzana View in CoL : Ludwig 1903: 59; Koehler 1907: 141; Koehler 1908: 245; Döderlein 1928: 293; Fisher 1928: 6; Fisher 1940: 75; A. M. Clark 1962: 68; Jangoux and Massin 1986: 91; Mah 1998: 78; Mah in Clark and Mah 2001: 317; Moreau et al. 2015: 5; Moreau et al. 2018: 147.

Material examined.

NHMUK 1890.5.7.1078 (holotype) (Fig. 11 A, B, E, G View Figure 11 ) .

Other material.

IA 3-2168; MNHN -IE-2008-1057 ; MNHN -IE-2008-1073 ; MNHN -IE-2008-1081 ; MNHN -IE-2017-1829 ; MNHN -IE-2017-1948 ; MNHN -IE-2019-5752 ; MNHN -IE-2022-2192 (Fig. 11 D View Figure 11 ); MNHN -IE-2022-2193 ; MNHN -IE-2022-2194 ; MNHN -IE-2022-2195 ; MNHN -IE-2022-2196 ; NHMUK 9237 (Fig. 11 C, F, H, I View Figure 11 ); NOC 11908 # 44; NOC 12930 # 64; NOC 12930 # 78; NOC 13200 # 27; NOC 13200 # 60; NOC 52701 # 42; NOC 54901 # 7; NOC 54902 # 1; NOC 54903 # 1; SO 268-1_29_014 ; SO 268-2_109_189 ; SO 268-02 _ 99 _ 04. (Suppl. material 1).

Diagnosis.

Arms six. Abactinal armature of disk with one primary central plate at center of the disk and a primary interradial plate at each interradius (Fig. 11 A – D View Figure 11 ). Central and interradial primary plates shield-like, much larger than the rest of abactinal disk plates (primary plates present in most specimens examined, but indistinguishable in some individuals). Abactinal disk and arm plates evenly covered with numerous short spinelets and small pedicellariae (Fig. 11 G View Figure 11 ). Beyond genital area, abactinal arm with bands of small pedicellariae. Adambulacral plate with one subambulacral spine. Proximal subambulacral spines with modified tips (truncated or flattened bifurcated) (Fig. 11 E, H View Figure 11 ). Furrow spine absent. Oral plate with 2–3 actinostomal spines and one suboral spine, each covered with membranous sheath, but the tips are bare (Fig. 11 E, F View Figure 11 ). Spines covered with small pedicellariae. Large pedicellariae absent. Inferomarginal plates and lateral spines occur at alternate adambulacral plates beyond genital area (Fig. 11 I View Figure 11 ).

Distribution.

North Atlantic, Southern Pacific, Eastern Pacific, Southern Ocean. 2450–5000 m. Type locality: Southern Pacific, 4663 m.

Remarks on F. benthophila and other six-armed Freyella .

F. benthophila stands in a peculiar position by having shared morphological characters with both Freyastera and Freyella . As a species with six arms, it is readily distinguished from other Freyella species with more than six arms. Compared with other Freyastera , it is differentiated from most species by having many small spinelets on its abactinal disk and arms and distinguished from Freyastera mortenseni , F. delicata , and F. mexicana , which also bears multiple spines on abactinal plates, by the absence of furrow spines and more distantly located inferomarginal plates. Phylogenetic analysis put it within the Freyella clade (Fig. 12 View Figure 12 ; Zhang et al. 2024), indicating that having six arms is not an autapomorphy of the Freyastera clade.

There are three other six-armed Freyella species whose taxonomic position needs to be re-evaluated, including F. oligobrachia H. L. Clark, 1920 ; F. hexactis Baranova, 1957 ; and F. vitjazi Korovchinsky & Galkin, 1984 . F. oligobrachia and F. vitjazi have inferomarginals corresponding to alternate adambulacral plates according to their original descriptions; thus, they should be retained within Freyella . F. hexactis was described to have inferomarginal plates to every third adambulacrals, then to alternate adambulacrals, then at the end of the arm, to each adambulacral plate ( Baranova 1957). It is difficult to justify it as either Freyella or Freyastera simply by this description. However, this species closely resembles F. oligobrachia and F. benthophila , as was shown in the key in Zhang et al. (2019). It is necessary to examine the types of F. oligobrachia and F. hexactis to be certain of their generic affinities and their relationship with F. benthophila . F. vitjazi , on the other hand, could be differentiated from the other six-armed Freyella species by having a diagonal line of three spines on each adambulacral plate. These three species are retained as Freyella for the time being, but they should be compared with in any future descriptions of six-armed freyellids.