Tetragramma, L. Agassiz, 1838

Schlüter, Nils, Taherpour-Khalil-Abad, Morteza, Majidifard, Mahmoudreza, Hassanzadeh, Zinat & Taheri, Jafar, 2019, Two echinoid species from the early Aptian (Early Cretaceous) of the Kopet-Dagh Basin, NE Iran, Zootaxa 4656 (1), pp. 121-132 : 125

Tetragramma sp.

( Fig. 5 )

Material. A single worn and incomplete specimen from the vicinity of the village Gelian, NE Iran, (Sarcheshmeh Formation, early Aptian) was available for study ( GSINET 97FE248).

Description. The slightly distorted individual shows a complete test only above the ambitus without apical disc; most of the oral side is not preserved. The specimen is medium-sized (approximately 52 mm in diameter) and flattened (approximately 22 mm in height). The ambitus is at mid-height. The tubercles are perforate and crenulate.

The peristome is deeply invaginated as it can be seen by the remaining perioral test. The perioral plates are highly abraded; however, distinct buccal notches can be observed. The diameter is approximately 31% of the test diameter.

The apical opening is large (the longest axis spans c. 38% of the length of the test diameter). Based on the somewhat elongated pentagonal outline, a monocyclic structure of the apical disc can be inferred.

The ambulacra taper towards the apical opening and short phyllodes can be observed near the peristome. Adorally, pore pairs run uniserial towards the ambitus, from which they are biserially arranged to the apex. Ambulacral plates carry five pore pairs per plate ambitally and each ambital plate has a single large primary tubercle. Details in plate compounding are not visible due to poor preservation.

The interambulacral plates are much wider than they are tall. Ambitally, four subequal primary tubercles per plate are present. Adapically, a naked V-shaped and slightly depressed zone is present at the interradius, reaching the ambitus. Adapically from the ambitus, the primary tubercles at the adradius are replaced by smaller, vertically aligned secondary tubercles. There are more than 15 interambulacral plates in a single row, estimated by the imprints of the plates on the mould.

Discussion. Features of this specimen (e.g. four subequal primary tubercles, shape of interambulacral plates, pore pairs arrangement: biserial adapically, short phyllodes) are characteristic of the genus Tetragramma . However, due to the lack of better preserved material, the nomenclature of the here described specimen must remain open. This specimen resembles, in the number and size of primary tubercles in the ambital interambulacra and the invagination of the peristome, the Aptian species Tetragramma malbosi Agassiz & Desor, 1846 . Tetragramma tetratuberculatus Vaziri & Arab, 2013 has been described from Aptian strata from the Kerman province, Southern Iran, it was distinguished from T. malbosi in its more inflated test and the presence of phyllodes and biserial arranged pore pairs adapically. However, the statement of Vaziri & Arab (2013) on pore pairs development in T. malbosi was erroneous, T. malbosi clearly has biserial running pore pairs adapically and phyllodes as it is a diagnostic feature of the genus Tetragramma ( Smith & Wright, 1993) . Also, the name Tetragramma tetratuberculatus Vaziri & Arab, 2013 must be treated as a nomen nudum ( Kroh & Mooi 2019a), because no type specimen was designated; which fails to meet the criteria of the ICZN Article 16.4.1. Vaziri & Arab (2013) erected two further Aptian species of Tetragramma from the Kerman province: Tetragramma basabensis Vaziri & Arab, 2013 has a larger peristome than estimated for the specimen describe here; Tetragramma depressum Vaziri & Arab, 2013 was differentiated by Vaziri & Arab (2013) by the increasing numbers of secondary tubercles adorally. However, both species, T. basabensis and T. depressum , are treated as nomina nuda ( Kroh & Mooi 2019b; 2019c) as no types were designated for each name. Other Ap- tian species, Tetragramma almerai ( Lambert, 1902) from Casa-alta-Castellet (Catalonia, Spain) and Tetragramma dumasi (Lambert in Lambert & Thiéry, 1910) from Montaren (Languedoc-Roussillon, France) are very similar to T. malbosi . However, further investigations are needed to conclude whether T. almerai , T. dumasi and T. malbosi should be treated as synonyms or not.

Figures

FIGURE 5. Tetragramma sp., GSINET97FE248, from the vicinity of the village Gelian, NE Iran, (Sarcheshmeh Formation, early Aptian), in apical (A) and oral (B) view, C: detail of the aboral interambulacral plates, D: detail of the perperistomal am- bulacra, E: detail of the adapical ambulacra.