Freyastera mexicana (A. H. Clark, 1939 )

Freyastera mexicana (A. H. Clark, 1939) View in CoL

Freyella mexicana View in CoL : A. H. Clark 1939: 442; Korovchinsky and Galkin 1984: 1213 (in key).

Freyastera mexicana View in CoL : Downey 1986: 38; Clark and Downey 1992: 481; Mah 1998: 87; Mah in Clark and Mah 2001: 318; Pawson et al. 2009: 1191; Zhang et al. 2019 (in key).

Diagnosis

(revised from A. H. Clark 1939). Arms six. Abactinal disk plate, each with a single spinelet. Genital region uniformly covered with larger plates, each with usually 2–4 similar spinelets, more or less in a transverse series. Pedicellariae numerous on disk and arms. Each mouth plate with 9–12 spines. First two adambulacral plates united by syzygy. Proximal adambulacrals with a diagonal row of 4 or 5 spines.

Distribution.

Only known at type locality: Gulf of Mexico, 2683 m.

Remarks.

No specimens of Freyastera mexicana were examined in the present study. However, the high-resolution photos of the holotype ( USNM E 5602) are available on the collection website of the National Museum of Natural History, US (https://collections.nmnh.si.edu/), allowing for a rough observation of some important characters. The species has a few peculiar characters as described by A. H. Clark (1939), including having a “ small unpaired interradial plate between the upper ends of the mouth plates of each pair, ” the first two adambulacral plates united by syzygy, and a high number of oral spines (9–12). These characters are not common in Freyastera or even Freyellidae . Judging from the photos of the holotype, the specimen is generally Freyastera - like. Although A. H. Clark noted that the species resembles Colpaster scutigerula Sladen, 1889 , the most, it does not have the same “ interradial plate ” (actually inferomarginal plate; see Zhang et al. 2024) inserting in between the mouth plates as in C. scutigerula . The oral spines do not seem to be as numerous as described, but this could be owing to damages during examination and long-time preservation. This species resembles F. delicata the most but differs from the latter by having numerous small pedicellariae on abactinal disk and arms, as well as having more spines on oral and adambulacral plates. Furthermore, the “ syzygy ” between the first and second adambulacral plates seems to be obvious from the photos. This structure, redefined as a “ partial fusion ” by Zhang et al. (2024), was thought to be a character only present in Brisingidae and Brisingasteridae . The nature of such a structure observed in F. mexicana needs to be further evaluated to be compared with the partial fusion found in Brisingidae and Brisingasteridae .